WO2017019163A1 - Multi-phase electrolyte lithium batteries - Google Patents

Abstract

A battery is constructed with a cathode that includes a non-polarizing, fluorinated liquid electrolyte which does not penetrate into the solid-state polymer electrolyte separator between it and the lithium-based anode. This assembly improves ionic conduction and avoids detrimental ionic concentration gradients in the cathode without compromising the strength and durability of the separator.

Description

MULTI-PHASE ELECTROLYTE LITHIUM BATTERIES

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Patent Application 14/811,664, filed July 28, 2015 which is incorporated by reference herein.

BACKGROUND OF THE INVENTION

Field of the Invention

[0002] This invention relates generally to lithium batteries, and, more specifically, to the use of a variety of electrolytes in the same lithium battery to optimize its performance.

[0003] In order to be useful in a cell, an electrolyte is chemically compatible/stable with both the anode material and the cathode material. In addition, the electrolyte is electrochemically stable, that is, stable against reduction at the anode and oxidation at the cathode when the cell is at potential. These requirements are especially difficult to meet in lithium batteries because of the extreme reactivity of the lithium itself. When a standard liquid electrolyte is used, it permeates both the anode and the cathode, as well as the separator, so the one electrolyte must meet all criteria. Thus some compromises must be made in choice of electrolyte, as the electrolyte that is best for the anode and the electrolyte that is best for the cathode may not be the same.

[0004] Thus there is a clear need for a battery cell design in which different portions of the cell can contain different electrolytes, each optimized for its particular function, but all functioning together without compromising the overall operation of the cell.

[0005] In one embodiment of the invention, an electrochemical cell is disclosed. The electrochemical cell has a negative electrode configured to absorb and release alkali metal ions. There is an electrolyte layer in contact with the negative electrode. The electrolyte layer includes a first block copolymer electrolyte and a first salt comprising the alkali metal. The electrochemical cell also has a positive electrode comprising positive electrode active material, binder and a liquid electrolyte comprising a fluorinated liquid and a second salt comprising the alkali metal. The liquid electrolyte is immiscible with the first block copolymer electrolyte.

SUMMARY

[0006] In one embodiment of the invention, the negative electrode is a metal foil comprising the alkali metal. The alkali metal may be any of lithium, sodium, and magnesium. In one arrangement, the negative electrode includes any of Li, Li-Al, Li-Si, Li-Sn, and Li-Mg.

[0007] In arrangements where the negative electrode contains lithium, such as in a lithium or lithium-containing foil, the first salt and the second salt are each selected independently from the group consisting of LiTFSI, LiPF₆, LiBF₄, LiC10₄, LiOTf, LiC(Tf)₃, LiBOB, and LiDFOB. In one arrangement, the first salt and the second salt are the same.

[0008] In another embodiment of the invention, the negative electrode comprises negative electrode active material particles, a negative electrode electrolyte, and optional binder. The negative electrode active material may be any of silicon, silicon alloys of tin (Sn), nickel (Ni), copper (Cu), iron (Fe), cobalt (Co), manganese (Mn), zinc (Zn), indium (In), silver (Ag), titanium (Ti), germanium (Ge), bismuth (Bi), antimony (Sb), and chromium (Cr); silicon oxides; silicon carbides; graphite; and mixtures thereof.

[0009] In one arrangement, the negative electrode electrolyte includes a liquid electrolyte that is immiscible with the first block copolymer electrolyte. The liquid electrolyte may be any of ethers, alkyl carbonates, ionic liquids, and mixtures thereof. In another arrangement, the negative electrode electrolyte includes a second block copolymer electrolyte that is immiscible with the first block copolymer electrolyte.

[0010] The positive electrode may also include electronically conducting carbon such as acetylene black, vapor-grown carbon fiber, and graphite powder.

[0011] In one arrangement, the positive electrode active material includes lithium metal oxides or lithium metal phosphates. In another arrangement, the positive electrode active material includes elemental sulfur, or sulfur composites with carbon or pyrolyzed polymer.

[0012] In one arrangement, the first block copolymer electrolyte layer in contact with the negative electrode is either a diblock copolymer or a triblock copolymer. The first block of the block copolymer may be ionically conductive and may be any of polyethers, polyamines, polyimides, polyamides, poly alkyl carbonates, polynitriles, polysiloxanes, polyphosphazines, poly olefins, polydienes, and combinations thereof. In one arrangement, the first block of the block copolymer includes an ionically-conductive comb polymer that has a backbone and pendant groups. The backbone may be any of polysiloxanes, polyphosphazines, polyethers, polydienes, polyolefins, polyacrylates, polymethacrylates, and combinations thereof. The pendants may be any of oligoethers, substituted oligoethers, nitrile groups, sulfones, thiols, polyethers, polyamines, polyimides, polyamides, alkyl carbonates, polynitriles, other polar groups, and combinations thereof.

[0013] In one arrangement, the first block copolymer electrolyte layer in contact with the negative electrode has a second block that may be any of polystyrene, hydrogenated polystyrene, polymethacrylate, poly(methyl methacrylate), polyvinylpyridine, polyvinylcyclohexane, polyimide, polyamide, polypropylene, polyolefins, poly(t-butyl vinyl ether), poly(cyclohexyl methacrylate), poly(cyclohexyl vinyl ether), poly(t-butyl vinyl ether), polyethylene,

polyfluorocarbons, polyvinylidene fluoride, and copolymers that contain styrene, methacrylate, and/or vinylpyridine.

[0014] The optional binder in the positive electrode may be any of PVDF, P(HFP-VDF), P(CTFE-VDF), carboxymethylcellulose, and styrene-butadiene rubber.

[0015] The fluorinated liquid in the positive electrode may be any of perfluoropoly ethers, mono- or diol-terminated perfluoropolyethers, alkylcarbonate-terminated perfluoropoly ethers, alkylcarbamate-terminated perfluoropolyethers, poly(perfluoropolyether)acrylates,

poly(perfluoropolyether)methacrylates, polysiloxanes with pendant fluorinated groups, and poly(perfluoropolyether)glycidyl ethers.

[0016] In one arrangement, the fluorinated liquid may include first polymers selected from the group consisting of polymerized versions of perfluoropolyether-acrylates, -methacrylates, and - glycidyl ethers and second polymers selected from the group consisting of polymerized versions of acrylates, methacrylates, or glycidyl ethers. The first polymers are copolymerized with the second polymers and the second polymers make up less than 10 wt% of the fluorinated liquid. In one arrangement, the fluorinated liquid has a molecular weight between 200 Da and 10,000 Da. In one arrangement, the fluorinated liquid is crosslinked. In one arrangement, the fluorinated liquid also includes one or more additives selected from the group consisting of cyclic organic carbonates, cyclic acetals, organic phosphates, cyclic organic sulfates, and cyclic organic sulfonates.

[0017] In one arrangement, the positive electrode also includes a polymer matrix into which the fluorinated liquid is absorbed to form a polymer gel electrolyte.

[0018] The electrochemical cell may also include a separator electrolyte layer between the electrolyte layer and the positive electrode. The separator electrolyte layer may include an electrolyte different the first block copolymer electrolyte. In one arrangement, the separator electrolyte may be any of ceramic electrolytes, polymer electrolytes, and block copolymer electrolytes. The separator electrolyte may be a solid electrolyte.

[0019] In another embodiment of the invention, an electrochemical cell is disclosed. The electrochemical cell has a negative electrode that includes an alkali metal film. There is a separator layer in contact with the negative electrode, and the separator layer includes a block copolymer electrolyte and a first salt comprising the alkali metal. The electrochemical cell also has a positive electrode that includes positive electrode active material, binder and a liquid electrolyte. The liquid electrolyte includes a fluorinated liquid and a second salt comprising the alkali metal. The liquid electrolyte is immiscible with the block copolymer electrolyte.

[0020] In yet another embodiment of the invention, an electrochemical cell is disclosed. The electrochemical cell has a negative electrode that includes a lithium metal film. There is a separator layer in contact with the negative electrode, and the separator layer includes a block copolymer electrolyte and a first lithium salt. The electrochemical cell also has a positive electrode that includes nickel cobalt aluminum oxide particles, binder, a second lithium salt, and a liquid electrolyte comprising a fluorinated liquid. The liquid electrolyte is immiscible with the block copolymer electrolyte.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The foregoing aspects and others will be readily appreciated by the skilled artisan from the following description of illustrative embodiments when read in conjunction with the accompanying drawings.

[0022] Figure 1 is a schematic illustration of various negative electrode assemblies, according to embodiments of the invention.

[0023] Figure 2 is a schematic illustration of various positive electrode assemblies, according to embodiments of the invention.

[0024] Figure 3 is a schematic illustration of an electrochemical cell, according to an embodiment of the invention.

[0025] Figure 4 is a schematic illustration of an electrochemical cell, according to another embodiment of the invention.

[0026] Figures 5A, 5B, and 5C are schematic drawings of a diblock copolymer and domain structures it can form, according to an embodiment of the invention. [0027] Figures 6A, 6B, and 6C are schematic drawings of a triblock copolymer and domain structures it can form, according to an embodiment of the invention.

[0028] Figures 7A, 7B, and 7C are schematic drawings of a triblock copolymer and domain structures it can form, according to another embodiment of the invention.

[0029] Figure 8 shows a complex impedance plot for a single electrolyte system (x) and for a two electrolyte system (o).

[0030] Figure 9A and Figure 9B show specific capacity data over 500 cycles for a cell that contains one dry polymer electrolyte and specific capacity data over 100 cycles for a two- electrolyte cell, respectively.

DETAILED DESCRIPTION

[0031] The preferred embodiments are illustrated in the context of electrolytes in an electrochemical cell. The skilled artisan will readily appreciate, however, that the materials and methods disclosed herein will have application in a number of other contexts where optimizing electrochemical interactions between electrolytes and electrochemically active materials are important. These electrolytes can be useful in electrochemical devices such as capacitors, electrochemical/capacitive memory, electrochemical (e.g. , dye sensitized) solar cells, and electrochromic devices.

[0032] These and other objects and advantages of the present invention will become more fully apparent from the following description taken in conjunction with the accompanying drawings.

[0033] In this disclosure, the terms "negative electrode" and "anode" are both used to mean "negative electrode." Likewise, the terms "positive electrode" and "cathode" are both used to mean "positive electrode."

[0034] In this disclosure, the term "dry polymer" is used to mean a polymer with long chains that has not been plasticized by small molecules. Organic solvents or plasticizers are not added to such dry polymers.

[0035] Although not always mentioned explicitly, it should be understood that electrolytes, as described herein, include metal salt(s), such as lithium salt(s), to ensure that they are ionically conductive. Non-lithium salts such as other alkali metal salts or salts of aluminum, sodium, or magnesium can also be used. [0036] An electrochemical cell has a negative electrode assembly and a positive electrode assembly with an ionically conductive separator in between. In one embodiment of the invention, the negative electrode assembly contains at least negative electrode active material and an electrolyte that has been chosen specifically for use with the negative electrode active material, referred to herein as the NE (negative electrode) electrolyte.

[0037] Figure 1 illustrates various exemplary arrangements for negative electrode active material (black regions) and NE electrolyte or anolyte (grey regions). The negative electrode active material can be arranged as particles (Figures la- Id, If) or as a thin film or foil (Figure le). The negative electrode assembly can be formed by combining the negative electrode material particles with the NE electrolyte to form a composite layer (Figures la- Id). In some arrangements, other materials (not shown) can be added to the composite layer to enhance, for example, electronic or ionic conduction. In some arrangements, the composite is porous, i.e., contains voids which are shown as white spaces in Figures lb, Id; in other arrangements, the composite is pore-free (Figures la, lc). In yet other arrangements, the NE dry polymer electrolyte of Figures le and If may also contain pores (not shown). In a negative electrode assembly that has a composite layer, the NE dry polymer electrolyte may be contained entirely within the composite layer (Figures la, lb). In another arrangement, there can be a thin layer of additional NE dry polymer electrolyte adjacent the composite layer (Figures lc, Id). In some arrangements, a current collector (shown as a white layer defined by dashed lines) is also part of the negative electrode assembly.

[0038] In arrangements where the negative electrode active material is a thin film or foil, the negative electrode assembly contains at least the thin film or foil and a layer of the NE electrolyte adjacent and in ionic contact with the thin film or foil, as shown in Figure le. In some arrangements, the negative electrode material is not a solid thin film, but instead is arranged as an aggregation of negative electrode active material particles in close contact with one another to ensure ionic and electronic communication among the particles (Figure If). Such a structure can be made, for example, by pressing and/or by sintering the negative electrode active material particles. In some arrangements, other materials can be added to the layer of negative electrode material particles, for example, to enhance electronic or ionic conductivity. In one arrangement carbon particles can be added to enhance electronic conductivity. The negative electrode assembly contains at least the NE electrolyte layer in ionic communication with the layer of negative electrode active material particles. In some arrangements there is also a current collector (shown as a white layer defined by dashed lines) in electronic contact with the negative electrode assembly.

[0039] The NE electrolyte is chosen specifically for use with the negative electrode active material. In one embodiment of the invention, the NE electrolyte is a dry polymer (a polymer with long chains that has not been plasticized by any small molecules) electrolyte. The NE electrolyte is electrochemically stable against the negative electrode active material. That is to say that the NE electrolyte is reductively stable and resistant to continuous chemical and electrochemical reactions which would cause the NE electrolyte to be reduced at its interface with the negative electrode material. The NE electrolyte is resistant to reduction reactions over the range of potentials that the electrochemical cell experiences under conditions of storage and cycling. Such reduction reactions at the negative electrode would increase cell impedance, thus adversely affecting the performance of the cell and/or the capacity of the cell. In addition, the NE electrolyte is chemically stable against the negative electrode active material.

[0040] In one embodiment of the invention, the negative electrode assembly has a thin film or foil as the negative electrode active material (as shown in Figure le), and the NE dry polymer electrolyte has a high modulus in order to prevent dendrite growth from the film during cell cycling. The thin film or foil may be lithium or lithium alloy, though other metal chemistries are possible, such as sodium, magnesium, or zinc. Non-lithium metals and non-lithium metal alloys would be used with corresponding electrolyte salts that include the same metal as the electrochemically active metal in the negative electrode and with appropriate active materials in the cathode that can absorb and release the same metal ions. Graphite may also be used in combination with lithium salts and lithium-based active materials in the cathode for secondary cells. The NE dry polymer electrolyte also has good adhesion to the film or foil to ensure easy charge transfer and low interfacial impedance between the layers. In one arrangement, the NE dry polymer electrolyte is void free. The NE dry polymer electrolyte is electrochemically stable down to the lowest operating potential of the electrode. For example, with Li-Al planar electrodes, the NE dry polymer electrolyte is stable down to 0.3 V vs Li/Li⁺. See Table 1 for other NE active materials and their associated potentials. In one arrangement, the NE dry polymer electrolyte is mechanically rigid enough to prevent continuous reactivity of active material particles that undergo large volume changes during cell cycling by keeping them in electrical contact with the matrix of the composite electrode. When negative electrode active materials that undergo large volume expansion upon absorption of lithium are used as thin film electrodes, it is useful if the NE dry polymer electrolyte has high yield strain to prevent electrode fatigue. [0041] In another embodiment of the invention, the negative electrode active material is an alloy (examples of which are shown in Table 1) and has the form of particles. In order to prevent continuous reactivity, it is useful if the NE electrolyte is electrochemically stable down to the reduction potentials shown. Additionally it is useful if the NE electrolyte has high impact toughness in order to maintain mechanical integrity and high yield strain in order to

accommodate the volume change of the NE active material particles as they absorb and release lithium. It is also useful if the NE electrolyte contains voids that can shrink to accommodate expansion. Good compatibility between the electrolyte and the particle surfaces helps to ensure good adhesion and homogeneous dispersion. Finally, if a current collector is used, it is useful if the NE electrolyte can adhere to the current collector.

Table 1

Negative Electrode Active Material Characteristics

[0042] The negative electrode active material can be any of a variety of materials depending on the type of chemistry for which the cell is designed. In one embodiment of the invention, the cell is a lithium or lithium ion cell. The negative electrode material can be any material that can serve as a host material (i.e. , can absorb and release) lithium ions. Examples of such materials include, but are not limited to graphite, hard carbons, lithium titanate, lithium metal, and lithium alloys such as Li-AI, Li-Si, Li-Sn, and Li-Mg. In one embodiment of the invention, a lithium alloy that contains no more than about 0.5 weight % aluminum is used. Silicon and silicon alloys are known to be useful as negative electrode materials in lithium cells. Examples include silicon alloys of tin (Sn), nickel (Ni), copper (Cu), iron (Fe), cobalt (Co), manganese (Mn), zinc (Zn), indium (In), silver (Ag), titanium (Ti), germanium (Ge), bismuth (Bi), antimony (Sb), and chromium (Cr) and mixtures thereof. In some arrangements, graphite, metal oxides, silicon oxides or silicon carbides can also be used as negative electrode materials.

[0043] In one embodiment of the invention, a positive electrode assembly contains at least positive electrode active material and an electrolyte that has been chosen specifically for use with the positive electrode active material, referred to herein as a PE (positive electrode) electrolyte. Figure 2 illustrates various exemplary arrangements for the positive electrode active material (light grey regions) and the PE electrolyte or catholyte (dark grey regions). The positive electrode active material can be arranged as particles (Figures 2a-2d) or as a thin film or foil (Figure 2e). The positive electrode assembly can be formed by combining the positive electrode material particles with the PE electrolyte to form a composite layer (Figures 2a-2d). In some arrangements, other materials (not shown) can be added to the composite layer to enhance, for example, electronic or ionic conduction. In some arrangements, the composite is porous, i.e., contains voids, which are shown as white spaces in Figures 2b, 2d; in other arrangements, it is pore-free (Figures 2a, 2c). In yet other arrangements (not shown), the PE electrolyte of Figures 2e and 2f can also contain pores (not shown). In a positive electrode assembly that has a composite layer, the PE electrolyte may be contained entirely within the composite layer (Figures 2a, 2b). In another arrangement, there can be a thin layer of additional PE electrolyte adjacent the composite layer (Figures 2c, 2d). In some arrangements, a current collector (shown as a white layer defined by dashed lines) is also part of the positive electrode assembly.

[0044] In arrangements where the positive electrode active material is a thin film or foil, the positive electrode assembly contains at least the thin film or foil and a layer of the PE electrolyte adjacent and in ionic contact with the thin film or foil as shown in Figure 2e. In some arrangements, the positive electrode material is not a solid thin film, but instead is arranged as an aggregation of positive electrode active material particles close together to ensure ionic and electronic communication among the particles (Figure 2f). Such a structure can be made, for example, by pressing and/or by sintering the positive electrode active material particles. In some arrangements, other materials such as carbon particles can be added to the layer of positive electrode material particles, for example, to enhance electronic or ionic conductivity. The positive electrode assembly contains at least the PE electrolyte layer in ionic communication with the layer of positive electrode active material particles. In some arrangements there is also a current collector (shown as a white layer defined by dashed lines) in electronic contact with the positive electrode.

[0045] The PE electrolyte is chosen specifically for use with the positive electrode active material. In one embodiment of the invention, the PE electrolyte is a dry polymer (a polymer with long chains that has not been plasticized by any small molecules) electrolyte. The PE electrolyte is chosen to be oxidatively stable against the positive electrode active material. That is to say that the PE electrolyte is resistant to continuous chemical and electrochemical reactions which would cause the PE electrolyte to be oxidized at its interface with the positive electrode material. The PE electrolyte is resistant to oxidation reactions over the range of potentials that the electrochemical cell experiences under conditions of storage and cycling. Such oxidation reactions at the positive electrode would increase cell impedance, thus adversely affecting the performance of the cell and/or the capacity of the cell. In addition, the PE electrolyte is chemically stable against the positive electrode active material.

[0046] The positive electrode active material can be any of a variety of materials depending on the type of chemistry for which the cell is designed. In one embodiment of the invention, the cell is a lithium or lithium ion cell. The positive electrode active material can be any material that can serve as a host material for lithium ions. Examples of such materials include, but are not limited to materials described by the general formula Li_xAi-_yM_y02, wherein A comprises at least one transition metal selected from the group consisting of Mn, Co, and Ni; M comprises at least one element selected from the group consisting of B, Mg, Ca, Sr, Ba, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Al, In, Nb, Mo, W, Y, and Rh; x is described by 0.05 < x < 1.1; and y is described by 0 < y < 0.5. In one arrangement, the positive electrode material is LiNio.5Mno_.5O₂.

[0047] In one arrangement, the positive electrode active material is described by the general formula: Li_xMn₂-_yM_y0₂, where M is chosen from Mn, Ni, Co, and/or Cr; x is described by 005 < x < 1.1 ; and y is described by 0 < y < 2. In another arrangement, the positive electrode active material is described by the general formula: Li_xM_yMn_4-y0₈, where M is chosen from Fe and/or Co; x is described by 005 < x < 2; and y is described by 0 < y < 4. In another arrangement, the positive electrode active material is given by the formula Li_x(Fe_yMi_-y)P0₄, where M is chosen from transition metals such as Mn, Co and/or Ni; x is described by 0.9 < x < 1.1; and y is described by 0 < y < 1. In yet another arrangement, the positive electrode active material is given by the general formula: Li(Nio.5-_xCoo.5-_xM_2x)0₂, where M is chosen from Al, Mg, Mn, and/or Ti; and x is described by 0 < x < 0.2. In some arrangements, the positive electrode material includes LiNiVC^. In some arrangements, the positive electrode material includes

[0048] Most electrolytes exhibit electrochemical stability over a limited window of about 4 Volts. Thus a single electrolyte cannot by itself support an electrochemical couple that has a voltage between electrodes higher than 4 Volts. Yet such high voltage electrochemical cells can be made to be stable and robust using the structures and materials described herein. Two different electrolytes - a NE electrolyte that is reductively stable at the anode (but may or may not be oxidatively stable at the cathode) and a PE electrolyte that is oxidatively stable at the cathode (but may or may not be reductively stable at the anode) can now be used in the same electrochemical cell. In one embodiment of the invention, the NE electrolyte is optimized for reductive stability and the PE electrolyte is optimized for oxidative stability. In one embodiment one or both of the NE electrolyte and PE electrolyte are dry polymers. By allowing different electrolytes to be used at the negative electrode and at the positive electrode, each electrode can be designed for optimum performance without compromise. Such an arrangement is especially useful and for high voltage applications.

[0049] There have been efforts in recent years to develop high voltage (i.e., greater than -4.2V) electrochemical cells by using "high voltage cathode materials" such as those listed in Table 2. Unfortunately, electrolytes that are stable to oxidation at the high potentials at the cathode/electrolyte interface are not generally stable to reduction at the lower potentials at the anode/electrolyte interface for standard anode materials. Now an electrochemical cell that uses different, specifically chosen electrolytes, such as dry polymer electrolytes, at the cathode and at the anode sides of the cell, as described herein, can overcome this problem and make it possible to design and build high voltage cells.

Table 2

Positive Electrode Active Material Characterist

[0050] Lithium metal and alloy negative electrode active materials are particularly prone to ongoing reduction reactions with many conventional lithium-ion electrolytes, as these negative electrode active materials tend not to form stable passivation layers. Although some electrolytes may be able to form stable interfaces with such anode materials, such electrolytes may not work well in the rest of the cell or in the positive electrode assembly due to limitations in conductivity and/or oxidative stability. Electrochemical cells that can use different electrolytes specifically chosen for their compatibility with each electrode, as described in the embodiments herein, can overcome these limitations.

[0051] The embodiments of the invention, as described above, can result in an electrochemical cell with very good performance. In one embodiment of the invention, such a cell has a Li cycling efficiency greater than 99.7%, over 500 cycles. In another embodiment of the invention, such a cell has a Li cycling efficiency of greater than 99.9%, over 500 cycles. In another embodiment of the invention, there is very little impedance increase at the negative electrode, the positive electrode, or at both electrodes as the cell is cycled. In one arrangement, the impedance value at 500 cycles increases by no more than 40% from the impedance value at 10 cycles. In another arrangement, the impedance value at 500 cycles increases by no more than 20% from the impedance value at 10 cycles. In yet another arrangement, the impedance value at 500 cycles increases by no more than 10% from the impedance value at 10 cycles. In one embodiment of the invention, the capacity of the electrolyte cell at 500 cycles decreases by no more than 40% from the capacity at 10 cycles. In another embodiment of the invention, the capacity of the electrolyte cell at 500 cycles decreases by no more than 20% from the capacity at 10 cycles. In yet another embodiment of the invention, the capacity of the electrolyte cell at 500 cycles decreases by no more than 10% from the capacity at 10 cycles. In yet another embodiment of the invention, the capacity of the electrolyte cell at 500 cycles decreases by no more than 5% from the capacity at 10 cycles.

[0052] When negative and positive electrode assemblies are each optimized independently, not only is it possible to optimize electrochemical stability, but it also presents the opportunity to overcome other key limitations that may be specific to individual electrode active materials.

[0053] For example, some negative electrode active materials undergo a large volume increase, as much as 300% or more, upon lithiation. Some examples are shown above in Table 1. For composite negative electrode assemblies that contain voids such as the electrode assemblies in Figures lb, Id, it is possible to accommodate volumetric expansion and contraction of the negative electrode active material upon cycling. It is useful if the NE electrolyte is a dry polymer electrolyte that has a yield strain greater than or equal to the maximum volume expansion of the negative electrode material. In this way, the NE electrolyte is elastic enough to move into the void space as the negative electrode active material expands. It is also useful if the total void space is at least as large as the maximum total volume expansion of the negative electrode active material. In other arrangements, the negative electrode material particles are shaped into a porous layer adjacent the NE electrolyte layer to form the negative electrode assembly as shown in Figure If. The pores in the layer can accommodate expansion of the negative electrode active material. Further details about porous electrodes can be found in U.S. Patent Application Publication Number 20110136017, published June 9, 2011, which is included by reference herein.

[0054] In general, cathode active materials expand and contract much less during cell cycling than do anode active materials. Thus there are different mechanical considerations when choosing an electrolyte for a cathode rather than for an anode, and it may be desirable to choose different electrolytes for these two regions of an electrochemical cell. For example, if the positive electrode active material expands and contracts much less than the negative electrode active material, it may be optimal to employ an electrolyte that is less elastic for the cathode region of the cell or to create an electrode assembly for the cathode that does not include voids, thereby optimizing other key parameters in the cathode assembly such as mechanical robustness or energy density. One key factor in determining a good PE dry polymer electrolyte is whether the electrolyte can bind and keep the positive active material particles and any electronically conductive additives (e.g. , carbon particles) intermixed and randomly dispersed through the manufacturing (e.g. , casting, extrusion, or calendering) process despite significant difference in the densities of the particles.

[0055] For positive electrode active materials that contain transition metals, dissolution of these metals into a standard liquid electrolyte upon cycling can be a serious problem, especially in high voltage cells and at high temperatures. The dissolution can cause accelerated cell degradation or premature failure. Examples of possible failure mechanisms include:

a) the composition of the positive electrode active materials changes as the metals dissolve, adversely impacting the ability of the active material to absorb and release lithium,

b) the dissolved metals can diffuse to the negative electrode and degrade the

capacity of the negative electrode active material,

c) the dissolved metals can diffuse to the negative electrode and degrade any

passivation layer on the negative electrode active material, resulting in continual electrolyte reaction with the negative electrode active material, and

d) the dissolved metals can create internal shorts or other defects within the cell. [0056] For example, in the case of Mn₂0₄ positive electrode active material, it is useful if the electrolyte does not dissolve the electrochemically active manganese. In the case of a sulfur cathode, it is useful if the electrolyte does not dissolve the electrochemically active sulfur or polysulfide. In one arrangement, less than 10% of the electrochemically active ion dissolves from the positive electrode active material after 500 cycles in the temperature range 45-80°C. In another arrangement, less than 5% of the electrochemically active ion dissolves from the positive electrode active material after 500 cycles in the temperature range 45-80°C. In yet another arrangement, less than 1% of the electrochemically active ion dissolves from the positive electrode active material after 500 cycles in the temperature range 45-80°C. This allows for selection of a separate non-dissolving electrolyte on the cathode side and can prevent diffusion of metal or other active material to the anode. A positive electrode assembly can be optimized to prevent dissolution, for example, employing a ceramic or solid polymer electrolyte as the PE electrolyte. Although dissolution of electrochemically active ions may not be an issue for the negative electrode assembly, other considerations may be important, such as high ionic conductivity or reductive stability, and it may be possible that a different electrolyte would be preferred.

[0057] In one embodiment of the invention, the NE electrolyte and/or the PE electrolyte is a solid electrolyte. In one arrangement, the NE electrolyte and/or the PE electrolyte is a ceramic electrolyte. In another arrangement, the NE electrolyte and/or the PE electrolyte is a dry polymer electrolyte. In yet another arrangement, the NE electrolyte and/or the PE electrolyte is a dry block copolymer electrolyte.

[0058] In one embodiment of the invention, the NE electrolyte and/or the PE electrolyte is a liquid electrolyte or a gel containing a liquid electrolyte. When a liquid electrolyte is used, it is most useful if the liquid electrolyte is immiscible with electrolytes in adjacent regions of the cell or if a selectively permeable membrane is positioned to prevent mixing of the liquid electrolyte with adjacent electrolytes. Such a membrane allows electrochemical cations to move through, but not the liquid itself. In some arrangements, the membrane is polymeric; in other arrangements, the membrane is a ceramic. In the absence of containment by such a membrane, miscible liquids can diffuse easily throughout the cell. If such diffusion were to occur, the benefits provided by using different electrolytes in different regions of the cell may be diminished or negated. In the worst case, active materials in the electrodes could be oxidized or reduced, seriously compromising the performance and/or the life of the cell.

[0059] In one embodiment of the invention, a separator electrolyte is used between the negative electrode assembly and the positive electrode assembly. In one embodiment of the invention, the separator electrolyte can be the same as either the NE electrolyte or as the PE electrolyte. In another embodiment, the separator electrolyte is different from both the NE electrolyte and the PE electrolyte. The separator electrolyte can be any of liquid electrolytes, solid electrolytes, ceramic electrolytes, polymer electrolytes, dry polymer electrolytes, and block copolymer electrolytes, independent of the NE electrolyte and the PE electrolyte. In some arrangements, the electrolytes are chosen so that no two liquid electrolytes are adjacent one another. When a liquid electrolyte is used, it is most useful if the liquid electrolyte is immiscible with electrolytes in adjacent regions of the cell or if a selective membrane is positioned at each interface to prevent mixing of the liquid electrolyte with adjacent electrolytes. Such a membrane allows electrochemical cations to move through but not the liquid itself. In the absence of containment, miscible liquids can diffuse easily throughout the cell. If such diffusion were to occur, the benefits provided by using different electrolytes in different regions of the cell may be diminished or negated. In the worst case, such diffusion could cause reduction at the negative electrode assembly and/or oxidation at the positive electrode assembly, causing premature failure of the cell.

[0060] In general, it is useful if the separator electrolyte has enough mechanical integrity to ensure that the negative electrode assembly and the positive electrode assembly do not come into physical contact with one another. In some arrangements, when a liquid, gel, or soft polymer is used as the separator electrolyte, a separator membrane is used with it.

[0061] It is useful if any two electrolytes meeting at an interface are immiscible in each other and chemically compatible with each other. It is also useful if there is little or no impedance or concentration overpotential across the interface.

[0062] In one arrangement, all electrolytes are stable over the range of storage and operating temperatures and the range of operating potentials for the electrochemical cell. Using the embodiments described here, this condition can be met for electrode couples that are otherwise unstable with conventional electrolytes or in conventional single-electrolyte architectures.

[0063] Figure 3 is a schematic cross section that shows an electrochemical cell in an exemplary embodiment of the invention. The cell 300 has a negative electrode assembly 310, a positive electrode assembly 320, with an intervening separator 330. The exemplary negative electrode assembly 310 is the same as the one shown in Figure l a. The negative electrode assembly 310 is an aggregation of negative electrode active material particles 314 dispersed within a NE dry polymer electrolyte 318. There can also be electronically-conducting particles such as carbon particles (not shown) in the negative electrode assembly 310. The exemplary positive electrode assembly 320 is the same as the one shown in Figure 2a. The positive electrode assembly 320 is an aggregation of positive electrode active material particles 324 dispersed within a PE dry polymer electrolyte 328. There can also be electronically-conducting particles such as carbon particles (not shown) in the positive electrode assembly 320. In other exemplary embodiments, other electrode assembly configurations, such as those shown in Figures 1 and 2, can be substituted in the electrochemical cell shown in Figure 3.

[0064] The NE electrolyte 318 and the PE electrolyte 328 are each optimized for their respective electrodes as has been discussed above. In one arrangement, the NE electrolyte 318 and the PE electrolyte 328 are different. In another arrangement, the NE electrolyte 318 and the PE electrolyte 328 are the same. The separator 330 contains a separator electrolyte 338, which is also optimized for its role in the cell 300. In one arrangement, the separator electrolyte 338 is immiscible with both the NE electrolyte 318 and the PE electrolyte 328. In another

arrangement, the separator electrolyte 338 is miscible with either or both of the NE electrolyte 318 and the PE electrolyte 328, and selectively permeable membranes (not shown) are positioned at interfaces between the miscible electrolytes. In one arrangement, the separator electrolyte 338 is the same as either the NE electrolyte 318 or the PE electrolyte 328. In another arrangement, the separator electrolyte 338 is different from both the NE electrolyte 318 and the PE electrolyte 328.

[0065] In one arrangement, the NE electrolyte 318, the PE electrolyte 328, and the separator electrolyte 338 are all solid electrolytes. In some arrangements, solid electrolytes can be made of ceramic materials or polymer materials. In one arrangement, solid electrolytes can be made of dry polymer materials. In one arrangement, the solid electrolytes are block copolymer electrolytes. In some arrangements, one or more of the NE electrolyte 318, the PE electrolyte 328, and the separator electrolyte 338 is a liquid. When a liquid electrolyte is used, care must be taken to ensure that the liquid cannot diffuse out of its own functional region (i.e. , negative electrode assembly, positive electrode assembly, or separator) into other functional regions of the cell. In some arrangements, a selectively permeable membrane is used at any interface where at least one electrolyte is liquid. In other arrangements, the liquid electrolytes that are used are immiscible with any adjacent electrolyte.

Optimizing Energy Density and Specific Energy

[0066] To achieve high specific energy in lithium (or other alkali metal) batteries, the proportion of active components (anode and cathode) is maximized and optimally balanced, while the proportion of the auxiliary components (separator, electrolyte and current collectors) that cannot store energy is minimized. An optimized anode may be a thin foil of lithium metal, as discussed above, which serves as both the anode and the current collector, and requires no additional ionic conduction within the foil as the lithium ions exchange at its surface with lithium metal. A lithium foil thick enough to be physically strong and manufacturable typically provides a large excess of lithium compared to the capacity of the cathode. Thus, taking full advantage of the capacity of the overly thick anode foil would require thicker, higher-capaicty cathodes as well. However, the actual thickness of the cathode is limited in practice by the depth to which both electrons and lithium ions can reach. Unlike with the lithium foil planar anode, ions and electrons in the cathode must traverse the entire thickness of the cathode. Very thick cathodes may contain regions of active material to which lithium ions cannot diffuse on relevant time scales dictated by the cell cycling rate, rendering such regions dead weight and reducing useable specific capacity of the cathode and therefore specific energy and energy density of the cell.

[0067] One approach to overcome these difficulties is to increase the ionic conductivity in the PE electrolyte of the cathode by using a liquid electrolyte. Liquid electrolytes based on mixtures of organic carbonate solvents with lithium salts and traces of performance enhancers are the industry standard in commodity-type lithium ion batteries. But the long-term stability of such batteries is limited, with shelf lifetimes of two years or less; the lifetimes are further shortened if the batteries are cycled aggressively.

[0068] As discussed above, block copolymer electrolytes can act as effective, durable separators between the anode and cathode, providing sufficient ionic conductivity for rapid charging and discharging while maintaining a physically robust barrier to prevent growth of dendrites from the anode or other detrimental breakdown. Such block copolymer electrolytes can also act as a separator between a PE electrolyte and the anode, eliminating detrimental interactions. In order to prevent any PE electrolyte from absorbing into the block copolymer electrolyte and traveling to the anode, it would be useful if the PE electrolyte and the block copolymer electrolyte were immiscible.

[0069] Another problem in electrochemical cells such as batteries is polarization (low transference number) of ionic and electronic species, which can result in suboptimal capacity even at low charge/discharge rates or high IR losses at high charge/discharge rates. A high lithium transference number (near 1, on a scale of 0 to 1) indicates that movement of lithium ions is predominantly responsible for the observed ionic conductivity, with little contribution from the counterion. In the context of battery operation, a high lithium transference number indicates that very little polarization occurs, as the counterions do not move and accumulate into concentration gradients.

[0070] Through careful choice of liquid PE electrolytes in the cathode and immiscible block copolymer separator electrolytes, high ionic conductivity in the cathode, little or no polarization (lithium transference number near 1) can be achieved resulting in high specific energy lithium (or other alkali metal) battery cells.

[0071] The block copolymer electrolytes discussed above have separated microphases of ion- conducting segments and non-conducting, structural segments often possessing polar and non- polar natures, respectively. With both polar and non-polar components, many organic solvents would be likely to swell one or both of the phases, either of which would lead to structural weakening. For example, some organic carbonate electrolyte formulations are compatible with cathode active materials and could be candidates for PE electrolytes. However, such formulations tend to be absorbed by portions of block copolymer electrolytes, leading to plasticization (softening), weakening, reaction with the lithium anode, and failure.

[0072] As an alternative, heavily fluorinated molecules are known to be immiscible with both polar and non-polar organic phases, and would not cause swelling in the block copolymer electrolyte disclosed herein. It has been reported that lithium electrolytes based on fluorinated poly ethers have very high lithium transference numbers when formulated with a lithium salt (e.g., Li TF SI). See, for example, Wong et al, "Nonflammable perfluoropoly ether-based electrolytes for lithium batteries," PNAS March 5, 2014 vol. 111 no. 4 3327-3331. Such a fluorinated liquid electrolyte, and derivations thereof, are excellent catholytes for pairing with a block copolymer separator; the catholyte has sufficient ionic conductivity, causes no

polarization and does not swell or weaken the separator. Fluorinated liquids of sufficient molecular weight can also be reliably non-volatile and non-flammable.

[0073] Figure 4 is a schematic cross section that shows an electrochemical cell in an exemplary embodiment of the invention. The cell 400 has a negative electrode 410, a positive electrode assembly 420, with an intervening separator 430. The exemplary negative electrode 410 is a lithium metal or lithium metal alloy foil. The exemplary positive electrode assembly 420 is an aggregation of positive electrode active material particles 424 held together by a binder (not shown) such as one or more of PVDF, P(HFP-VDF), P(CTFE-VDF),

carboxymethylcellulose, and styrene-butadiene rubber, and surrounded by a fluorinated liquid electrolyte 428. There can also be electronically-conducting particles such as carbon particles (not shown) in the positive electrode assembly 420. The electronically-conducting particles may be acetylene black, vapor-grown carbon fiber, or graphite powder, and are present in sufficient quantity to allow electronic conduction throughout the cathode.

[0074] The separator 430 contains a separator electrolyte 438, which is immiscible with the PE electrolyte 428. In another arrangement, the separator electrolyte 438 is miscible with the PE electrolyte 428, and a selectively permeable membrane (not shown) is positioned at the interface between the miscible electrolytes. In one arrangement, the separator electrolyte 438 is a block copolymer electrolyte as discussed above. In one arrangement, the separator electrolyte 438 is a diblock or triblock copolymer wherein one block is poly(ethylene oxide) to provide ionic conduction and the other block is poly(styrene) or other physically robust polymer providing structural support. In some arrangements, the separator electrolyte 438 is made of ceramic materials or polymer materials. In one arrangement, the separator electrolyte 438 can be made of dry polymer materials. In one arrangement, the solid electrolytes are block copolymer electrolytes. In some arrangements, the separator electrolyte 438 is a liquid. When a liquid electrolyte is used, care must be taken to ensure that the liquid cannot diffuse out of the separator region into other functional regions of the cell. In some arrangements, a selectively permeable membrane is used at any interface where at least one electrolyte is liquid. In other arrangements, the liquid electrolytes that are used are immiscible with any adjacent electrolyte.

[0075] The metal salt in the separator is typically a lithium salt with a weakly coordinating anion, such as LiTFSI, LiPF6, LiBF4, LiC104, LiOTf, LiC(Tf)3, LiBOB, LiDFOB, among others.

[0076] The active material in the cathode is selected from the lithium metal oxides or lithium metal phosphates typically used for lithium batteries. It may be possible to use elemental sulfur, or sulfur composites with carbon or pyrolyzed polymer.

[0077] The metal salt in the cathode is typically identical to one or more of the salts present in the block copolymer separator. A fluorinated counterion is more likely to be soluble at useful levels in the fluorinated liquid such as many of the salts listed above.

[0078] In one embodiment of the invention, fluorinated liquid electrolytes in the cathode contain one or more of perfluoropoly ethers, mono- or diol-terminated perfluoropoly ethers,

alkylcarbonate-terminated perfluoropolyethers, poly(perfluoropolyether)acrylates or poly(perfluoropolyether)methacrylates, or poly(perfluoropolyether)glycidyl ethers. In one arrangement, the molecular weights of the fluorinated liquids range from 200 Da to 10,000 Da. In one arrangement, the liquids based on polymerized perfluoropolyether-acrylates, - methacrylates, and -glycidyl ethers are polymerized or copolymerized with each other or with small amounts (<10 wt%) of other acrylates, methacrylates, or glycidyl ether monomers. Such copolymerization can change material properties, such as surface tension, viscosity, and adhesion. Polymers formed from these fluorinated monomers would also be immiscible with the block copolymers mentioned above.

[0079] Fluorinated liquids can have very low surface tensions, which would lead to leaching and spreading of the liquid out of the cathode if the cathode is not properly sealed. In some arrangements, the fluorinated liquid electrolyte in the cathode is gelled. The fluorinated liquid is absorbed into a polymer matrix to form such a polymer gel electrolyte. The polymer matrix may also be fluorinated to ensure compatibility with the fluorinated liquid. Possible examples include high molecular weight (>10,000 Dalton) perfluoropoly ethers,

poly(perfluoropolyether)acrylates, poly(perfluoropolyether)methacrylates, or

poly(perfluoropolyether)glycidyl ethers, as well as copolymers and block copolymers of these with non-fluorinated polymers.

[0080] In one arrangement, the fluorinated liquid electrolyte is crosslinked. Depending on whether the mechanism of ionic conduction is or is not dependent on long range motion of the electrolyte molecules, crosslinking may have very little effect on the overall ionic conductivity of the electrolyte. Crosslinking past a certain threshold may cause the liquid electrolyte to become an immobile gel. Multifunctional or telechelic variants of the fluorinated polymers listed above are examples of crosslinkable electrolytes.

[0081] Certain organic molecule additives may be added to the fluorinated electrolyte to improve electrochemical stability of the cathode active material. Such molecules may be added in small enough amounts that they would not adversely affect other parts of the cell if they were to diffuse out of the cathode. Compound classes commonly used as additives include cyclic organic carbonates, cyclic acetals, organic phosphates, cyclic organic sulfates, and cyclic organic sulfonates.

Electrolytes

[0082] Examples of ceramic electrolytes that can be used in the embodiments of the invention include lithium silicate, lithium borate, lithium aluminate, lithium phosphate, lithium

phosphorus oxynitride, lithium silicosulfide, lithium borosulfide, lithium aluminosulfide, and lithium phosphosulfide, lithium lanthanum titanium oxide, lithium lanthanum zirconium oxide, LiPON, LiSICON, Lii₀SnP₂Si₂, LinSi₂PSi₂, Lii₀GeP₂Si₂, Li₂S-SiS₂-Li₃P0₄, Lii₄Zn(Ge0₄)4, Li₂S-P₂S5, Lao.₅Lio.5Ti0₃, combinations thereof, and others known in the field.

[0083] There are a variety of polymer electrolytes that are appropriate for use in the inventive structures described herein. In one embodiment of the invention, an electrolyte contains one or more of the following optionally cross-linked polymers: polyethylene oxide, polysulfone, polyacrylonitrile, polysiloxane, polyether, polyamine, linear copolymers containing ethers or amines, ethylene carbonate, Nafion®, and polysiloxane grafted with small molecules or oligomers that include poly ethers and/or alkylcarbonates.

[0084] In one embodiment of the invention, the solid polymer electrolyte, when combined with an appropriate salt, is chemically and thermally stable and has an ionic conductivity of at least 10^"5 Scm^"1 at battery cell operating temperature. In one arrangement, the polymer electrolyte has an ionic conductivity of at least 10^"3 Scm^"1 at battery cell operating temperature. Examples of useful battery cell operating temperatures include room temperature (25°C), 40°C and 80°C. Examples of appropriate salts include, but are not limited to metal salts selected from the group consisting of chlorides, bromides, sulfates, nitrates, sulfides, hydrides, nitrides, phosphides, sulfonamides, triflates, thiocynates, perchlorates, borates, or selenides of lithium, sodium, potassium, silver, barium, lead, calcium, ruthenium, tantalum, rhodium, iridium, cobalt, nickel, molybdenum, tungsten or vanadium. Examples of specific lithium salts include LiSCN, LiN(CN)₂, LiC10₄, L1BF₄, LiAsF₆, LiPF₆, LiCF₃S0₃, Li(CF₃S0₂)₂N, Li(CF₃S0₂)₃C,

LiN(S0₂C₂F₅)₂, lithium alkyl fluorophosphates, lithium oxalatoborate, as well as other lithium bis(chelato)borates having five to seven membered rings, lithium bis(trifluoromethane sulfone imide) (LiTFSI), LiPF₃(C₂F₅)₃, LiPF₃(CF₃)₃, LiB(C₂0₄)₂, LiDFOB, and mixtures thereof. In other embodiments of the invention, for other electrochemistries, electrolytes are made by combining the polymers with various kinds of salts. Examples include, but are not limited to AgS0₃CF₃, NaSCN, NaS0₃CF₃, KTFSI, NaTFSI, Ba(TFSI)₂, Pb(TFSI)₂, and Ca(TFSI)₂. As described in detail above, a block copolymer electrolyte can be used in the embodiments of the invention.

[0085] Figure 5A is a simplified illustration of an exemplary diblock polymer molecule 500 that has a first polymer block 510 and a second polymer block 520 covalently bonded together. In one arrangement both the first polymer block 510 and the second polymer block 520 are linear polymer blocks. In another arrangement, either one or both polymer blocks 510, 520 has a comb structure. In one arrangement, neither polymer block is cross-linked. In another arrangement, one polymer block is cross-linked. In yet another arrangement, both polymer blocks are cross- linked.

[0086] Multiple diblock polymer molecules 500 can arrange themselves to form a first domain 515 of a first phase made of the first polymer blocks 510 and a second domain 525 of a second phase made of the second polymer blocks 520, as shown in Figure 5B. Diblock polymer molecules 500 can arrange themselves to form multiple repeat domains, thereby forming a continuous nanostructured block copolymer material 540, as shown in Figure 5C. The sizes or widths of the domains can be adjusted by adjusting the molecular weights of each of the polymer blocks. In various embodiments, the domains can be lamellar, cylindrical, spherical, or gyroidal depending on the nature of the two polymer blocks and their ratios in the block copolymer. In one arrangement the first polymer domain 515 is ionically conductive, and the second polymer domain 525 provides mechanical strength to the nanostructured block copolymer.

[0087] Figure 6A is a simplified illustration of an exemplary triblock polymer molecule 600 that has a first polymer block 610a, a second polymer block 620, and a third polymer block 610b that is the same as the first polymer block 610a, all covalently bonded together. In one arrangement the first polymer block 610a, the second polymer block 620, and the third copolymer block 610b are linear polymer blocks. In another arrangement, either some or all polymer blocks 610a, 620, 610b have a comb structure. In one arrangement, no polymer block is cross-linked. In another arrangement, one polymer block is cross-linked. In yet another arrangement, two polymer blocks are cross-linked. In yet another arrangement, all polymer blocks are cross-linked.

[0088] Multiple triblock polymer molecules 600 can arrange themselves to form a first domain 615 of a first phase made of the first polymer blocks 610a, a second domain 625 of a second phase made of the second polymer blocks 620, and a third domain 615 of a first phase made of the third polymer blocks 610b as shown in Figure 6B. Triblock polymer molecules 600 can arrange themselves to form multiple repeat domains 625, 615 (containing both 615a and 615b), thereby forming a continuous nanostructured block copolymer material 640, as shown in Figure 6C. The sizes of the domains can be adjusted by adjusting the molecular weights of each of the polymer blocks. In various arrangements, the domains can be lamellar, cylindrical, spherical, gyroidal, or any of the other well-documented triblock copolymer morphologies depending on the nature of the polymer blocks and their ratios in the block copolymer.

[0089] In one arrangement the first and third polymer domains 615 are ionically conductive, and the second polymer domain 625 provides mechanical strength to the nanostructured block copolymer. In another arrangement, the second polymer domain 625 is ionically conductive, and the first and third polymer domains 615 provide a structural framework.

[0090] Figure 7A is a simplified illustration of another exemplary triblock polymer molecule 700 that has a first polymer block 710, a second polymer block 720, and a third polymer block 730, different from either of the other two polymer blocks, all covalently bonded together. In one arrangement the first polymer block 710, the second polymer block 720, and the third copolymer block 730 are linear polymer blocks. In another arrangement, either some or all polymer blocks 710, 720, 730 have a comb structure. In one arrangement, no polymer block is cross-linked. In another arrangement, one polymer block is cross-linked. In yet another arrangement, two polymer blocks are cross-linked. In yet another arrangement, all polymer blocks are cross-linked.

[0091] Multiple triblock polymer molecules 700 can arrange themselves to form a first domain 715 of a first phase made of the first polymer blocks 710a, a second domain 725 of a second phase made of the second polymer blocks 720, and a third domain 735 of a third phase made of the third polymer blocks 730 as shown in Figure 7B. Triblock polymer molecules 700 can arrange themselves to form multiple repeat domains, thereby forming a continuous

nanostructured block copolymer material 740, as shown in Figure 7C. The sizes of the domains can be adjusted by adjusting the molecular weights of each of the polymer blocks. In various arrangements, the domains can be lamellar, cylindrical, spherical, gyroidal, or any of the other well-documented triblock copolymer morphologies depending on the nature of the polymer blocks and their ratios in the block copolymer.

[0092] In one arrangement the first polymer domains 715 are ionically conductive, and the second polymer domains 725 provide mechanical strength to the nanostructured block copolymer. The third polymer domains 735 provides an additional functionality that may improve mechanical strength, ionic conductivity, electrical conductivity, chemical or electrochemical stability, may make the material easier to process, or may provide some other desirable property to the block copolymer. In other arrangements, the individual domains can exchange roles.

[0093] Choosing appropriate polymers for the block copolymers described above is important in order to achieve desired electrolyte properties. In one embodiment, the conductive polymer (1) exhibits ionic conductivity of at least 10^"5 Scm^"1 at electrochemical cell operating temperatures when combined with an appropriate salt(s), such as lithium salt(s); (2) is chemically stable against such salt(s); and (3) is thermally stable at electrochemical cell operating temperatures. In another embodiment the conductive polymer exhibits ionic conductivity of at least 10^"3 Scm^"1 at electrochemical cell operating temperatures, such as at 25°C or at 80°C when combined with an appropriate salt(s). In one embodiment, the structural material has a modulus in excess of lxlO⁵ Pa at electrochemical cell operating temperatures. In one embodiment, the structural material has a modulus in excess of lxlO⁷ Pa at electrochemical cell operating temperatures. In one embodiment, the structural material has a modulus in excess of lxl 0⁹ Pa at electrochemical cell operating temperatures. In one embodiment, the third polymer (1) is rubbery; and (2) has a glass transition temperature lower than operating and processing temperatures. It is useful if all materials are mutually immiscible. In one embodiment the block copolymer exhibits ionic conductivity of at least 10^"4 Scm^"1 and has a modulus in excess of 1 x 10⁷ Pa or lxlO⁸ Pa at electrochemical cell operating temperatures. Examples of cell operating temperatures are 25°C and 80°C.

[0094] In one embodiment of the invention, the conductive phase can be made of a linear polymer. Conductive linear polymers that can be used in the conductive phase include, but are not limited to, polyethers, polyamines, polyimides, polyamides, poly alkyl carbonates, polynitriles, and combinations thereof. The conductive linear polymers can also be used in combination with polysiloxanes, polyphosphazines, poly olefins, and/or polydienes to form the conductive phase.

[0095] In another exemplary embodiment, the conductive phase is made of comb polymers that have a backbone and pendant groups. Backbones that can be used in these polymers include, but are not limited to, polysiloxanes, polyphosphazines, polyethers, polydienes, poly olefins, polyacrylates, polymethacrylates, and combinations thereof. Pendants that can be used include, but are not limited to, oligoethers, substituted oligoethers, nitrile groups, sulfones, thiols, polyethers, polyamines, polyimides, polyamides, alkyl carbonates, polynitriles, other polar groups, single ion conducting groups, and combinations thereof.

[0096] Further details about polymers that can be used in the conductive phase can be found in International Patent Application Number PCT/US09/045356, filed May 27, 2009, U.S. Patent Number 8,691,928, issued April 8, 2014, International Patent Application Number

PCT/US 10/21065, filed January 14, 2010, International Patent Application Number

PCT/US 10/21070, filed January 14, 2010, U.S. Patent Application Number 13/255,092, filed September 6, 2011, and U.S. Patent Number 8,598,273, issued December 3, 2013, all of which are included by reference herein.

[0097] There are no particular restrictions on the electrolyte salt that can be used in the block copolymer electrolytes. Any electrolyte salt that includes the ion identified as the most desirable charge carrier for the application can be used. It is especially useful to use electrolyte salts that have a large dissociation constant within the polymer electrolyte.

[0098] Suitable examples include alkali metal salts, such as Li salts. Examples of useful Li salts include, but are not limited to, LiPF₆, LiN(CF₃S0₂)₂, Li(CF₃S0₂)₃C, LiN(S0₂CF₂CF₃)₂, LiB(C₂C>4)₂, Bi₂F_xHi_2-x, Bi₂Fi₂, and mixtures thereof. Non-lithium salts such as salts of aluminum, sodium, and magnesium are examples of other salts that can be used.

[0099] In one embodiment of the invention, single ion conductors can be used with electrolyte salts or instead of electrolyte salts. Examples of single ion conductors include, but are not limited to sulfonamide salts, boron based salts, and sulfates groups.

[00100] In one embodiment of the invention, the structural phase can be made of polymers such as polystyrene, hydrogenated polystyrene ,polymethacrylate, poly(methyl methacrylate), polyvinylpyridine, polyvinylcyclohexane, polyimide, polyamide, polypropylene, polyolefins, poly(t-butyl vinyl ether), poly(cyclohexyl methacrylate), poly(cyclohexyl vinyl ether), poly(t- butyl vinyl ether), polyethylene, fluorocarbons, such as polyvinylidene fluoride, or copolymers that contain styrene, methacrylate, or vinylpyridine. It is especially useful if the structural phase is rigid and is in a glassy or crystalline state.

[00101] Additional species can be added to nanostructured block copolymer electrolytes to enhance the ionic conductivity, to enhance the mechanical properties, or to enhance any other properties that may be desirable.

[00102] The ionic conductivity of nanostructured block copolymer electrolyte materials can be improved by including one or more additives in the ionically conductive phase. An additive can improve ionic conductivity by lowering the degree of crystallinity, lowering the melting temperature, lowering the glass transition temperature, increasing chain mobility, or any combination of these. A high dielectric additive can aid dissociation of the salt, increasing the number of Li+ ions available for ion transport, and reducing the bulky Li+[salt] complexes. Additives that weaken the interaction between Li+ and PEO chains/anions, thereby making it easier for Li+ ions to diffuse, may be included in the conductive phase. The additives that enhance ionic conductivity can be broadly classified in the following categories: low molecular weight conductive polymers, ceramic particles, room temp ionic liquids (RTILs), high dielectric organic plasticizers, and Lewis acids.

[00103] Other additives can be used in the polymer electrolytes described herein. For example, additives that help with overcharge protection, provide stable SEI (solid electrolyte interface) layers, and/or improve electrochemical stability can be used. Such additives are well known to people with ordinary skill in the art. Additives that make the polymers easier to process, such as plasticizers, can also be used.

[00104] In one embodiment of the invention, neither small molecules nor plasticizers are added to the block copolymer electrolyte and the block copolymer electrolyte is a dry polymer.

[00105] Further details about block copolymer electrolytes are described in U. S. Patent Number 8,563, 168, issued October 22, 2013, U.S. Patent Number 8,268, 197, issued September 18, 2012, and U. S. Patent Number 8,889,301, issued November 18, 2014, all of which are included by reference herein.

Examples

[00106] The ionic conductance of each component of the cell can be determined. In general, conductance, G is given by:

where σ is ionic conductivity, A is cross-sectional area, and / is length. Two conductances in series, Gj, G2 have a total conductance G_M given by:

^G1^G2

G_{1 +} G₂

[00107] When the electrode assembly has a composite configuration, the ionic conductance can be calculated easily from equation (1). When the electrode assembly has a multiple layer configuration, the conductance of each layer is found, and the total conductance is given by equation (2). In one embodiment of the invention, the conductance of the negative electrode assembly and the conductance of the positive electrode assembly have a difference of no more than 25%. In another embodiment of the invention, the conductance of the NE electrode assembly, the conductance of the PE electrode assembly, and the conductance of the separator electrolyte are all within 25% of one another. Matching conductance in this way can result in a cell with an optimized, minimal impedance profile. [00108] Figure 8 shows a complex impedance plot for a single electrolyte system (x) and for a two electrolyte system (o). The two electrolyte cell has a first dry polymer electrolyte optimized for stability against the lithium metal anode film and a second dry polymer electrolyte optimized for low interfacial impedance against the composite cathode. The single electrolyte cell contains only the first dry polymer electrolyte. As is well known to a person having ordinary skill in the art, the size of the kinetic arc in the plot reflects the total resistance of the system. One might anticipate that adding an additional interface (first polymer electrolyte / second polymer electrolyte interface) could add additional resistance to the system. But, surprisingly, the two electrolyte system has lower total resistance, as indicated by the smaller kinetic arc (o), than the single electrolyte system. There is a clear advantage in using multiple electrolytes optimized for their functions in the cell.

[00109] Figure 9A shows specific capacity data over 500 cycles for a cell that contains one dry polymer electrolyte, a lithium metal anode and a lithium iron phosphate composite cathode. There is no measurable capacity fade over the first 100 cycles. After 500 cycles the capacity fade is estimated to be about 5%. Figure 9B shows specific capacity data over 100 cycles for a two-electrolyte cell. There is a first dry polymer electrolyte optimized for stability against the lithium metal anode film and a second dry polymer electrolyte optimized for conductivity in and over the composite cathode. Again, there is no measurable capacity fade over the first 100 cycles, indicating that there are no adverse effects from using the multi-layered electrolyte.

[00110] Several useful fluorinated liquids may be used as PE electrolytes in the embodiments of the invention. The following examples are meant to be illustrative and not restrictive.

[00111] In one exemplary embodiment, a perfluoropolyether is terminated with

trifluoromethoxy groups. Note that m, \-m = mole fractions of repeat units (0 <= m <= 1), n = number of repeat units (2 <= n <= 100). This structure is used to define the RF abbreviated structure referenced in the subsequent structures.

[00112] In another exemplary embodiment, mono- and diol-terminated perfluoropoly ethers can be used as PE electrolytes:

F₃CO-R_F-0-CF₂CH₂O H ^ HOH2CF₂CO -R_F-0-CF2CH₂O H [00113] In another exemplary embodiment, alkylcarbonate-terminated peril uoropoly ether; R = C1 -C8 alkyl, C1 -C8 branched alkyl, or C5-C8 cyclic alkyl can be used as PE electrolytes:

F₃CO-R_F-0-CF₂CH₂0 1 R

O"

R R O X OCH₂CF20-R_F-0-CF₂CH20 θ'

[00114] In other exemplary embodiments, poly(perfluoropolyether)acrylate (R' = H) or poly(perfluoropolyether)methacrylate (R' = Me); k = number of repeat units (5 <= k <= 50) can be used as PE electrolytes:

[00115] In another exemplary embodiment, poly(perfluoropolyether)glycidyl ether; k - number of repeat units (5 <= k <= 50) can be used as PE electrolytes:

[00116] This invention has been described herein in considerable detail to provide those skilled in the art with information relevant to apply the novel principles and to construct and use such specialized components as are required. However, it is to be understood that the invention can be carried out by different equipment, materials and devices, and that various modifications, both as to the equipment and operating procedures, can be accomplished without departing from the scope of the invention itself.

Claims

WE CLAIM:

1. An electrochemical cell, comprising:

a negative electrode configured to absorb and release alkali metal ions;

an electrolyte layer in contact with the negative electrode, the electrolyte layer comprising a first block copolymer electrolyte and a first salt comprising the alkali metal; and

a positive electrode comprising positive electrode active material, binder and a liquid electrolyte comprising a fluorinated liquid and a second salt comprising the alkali metal, the liquid electrolyte immiscible with the first block copolymer electrolyte.

2. The electrochemical cell of Claim 1 wherein the negative electrode is a metal foil comprising the alkali metal.

3. The electrochemical cell of Claim 2 wherein the alkali metal is selected from the group consisting of lithium, sodium, and magnesium.

4. The electrochemical cell of Claim 2 wherein the negative electrode comprises a material selected from the group consisting of Li, Li-Al, Li-Si, Li-Sn, and Li-Mg.

5. The electrochemical cell of Claim 3 wherein the alkali metal comprises lithium.

6. The electrochemical cell of Claim 5 wherein the first salt and the second salt are each selected independently from the group consisting of LiTFSI, LiPF₆, LiBF₄, L1CIO4, LiOTf, LiC(Tf)₃, LiBOB, and LiDFOB.

7. The electrochemical cell of Claim 6 wherein the first salt and the second salt are the same.

8. The electrochemical cell of Claim 1 wherein the negative electrode comprises negative electrode active material particles, a negative electrode electrolyte, and optional binder.

9. The electrochemical cell of Claim 8 wherein the negative electrode active material comprises a material selected from the group consisting of silicon, silicon alloys of tin (Sn), nickel (Ni), copper (Cu), iron (Fe), cobalt (Co), manganese (Mn), zinc (Zn), indium (In), silver (Ag), titanium (Ti), germanium (Ge), bismuth (Bi), antimony (Sb), and chromium (Cr); silicon oxides; silicon carbides; graphite; and mixtures thereof.

10. The electrochemical cell of Claim 8 wherein the negative electrode electrolyte comprises a liquid electrolyte that is immiscible with the first block copolymer electrolyte.

11. The electrochemical cell of Claim 10 wherein the liquid electrolyte is selected from the group consisting of ethers, alkyl carbonates, ionic liquids, and mixtures thereof.

12. The electrochemical cell of Claim 8 wherein the negative electrode electrolyte comprises a second block copolymer electrolyte wherein the second block copolymer electrolyte is immiscible with the first block copolymer electrolyte.

13. The electrochemical cell of Claim 1 wherein the positive electrode further comprises electronically conducting carbon selected from the group consisting of acetylene black, vapor-grown carbon fiber, and graphite powder.

14. The electrochemical cell of Claim 1 wherein the positive electrode active material comprises lithium metal oxides or lithium metal phosphates.

15. The electrochemical cell of Claim 1 wherein the positive electrode active material comprises elemental sulfur, or sulfur composites with carbon or pyrolyzed polymer.

16. The electrochemical cell of Claim 1 wherein the first block copolymer electrolyte is either a diblock copolymer or a triblock copolymer.

17. The electrochemical cell of Claim 16 wherein a first block of the first block copolymer is ionically conductive and is selected from the group consisting of polyethers, polyamines, polyimides, polyamides, poly alkyl carbonates, polynitriles, polysiloxanes, polyphosphazines, polyolefins, polydienes, and combinations thereof.

18. The electrochemical cell of Claim 16 wherein a first block of the first block copolymer comprises an ionically-conductive comb polymer, which comb polymer comprises a backbone and pendant groups.

19. The electrochemical cell of Claim 18 wherein the backbone comprises one or more selected from the group consisting of polysiloxanes, polyphosphazines, polyethers, polydienes, polyolefins, polyacrylates, polymethacrylates, and combinations thereof.

20. The electrochemical cell of Claim 18 wherein the pendants comprise one or more selected from the group consisting of oligoethers, substituted oligoethers, nitrile groups, sulfones, thiols, polyethers, polyamines, polyimides, polyamides, alkyl carbonates, polynitriles, other polar groups, and combinations thereof.

21. The electrochemical cell of Claim 16 wherein a second block of the first block copolymer is selected from the group consisting of polystyrene, hydrogenated polystyrene, polymethacrylate, poly(methyl methacrylate), polyvinylpyridine, polyvinylcyclohexane, polyimide, polyamide, polypropylene, polyolefins, poly(t-butyl vinyl ether), poly(cyclohexyl methacrylate), poly(cyclohexyl vinyl ether), poly(t-butyl vinyl ether), polyethylene, polyfluorocarbons, polyvinylidene fluoride, and copolymers that contain styrene, methacrylate, and/or vinylpyridine.

22. The electrochemical cell of Claim 1 wherein the binder comprises one or more selected from the group consisting of PVDF, P(HFP-VDF), P(CTFE-VDF), carboxymethylcellulose, and styrene-butadiene rubber.

23. The electrochemical cell of Claim 1 wherein the fluorinated liquid comprises one or more selected from the group consisting of perfluoropolyethers, mono- or diol-terminated perfluoropolyethers, alkylcarbonate-terminated perfluoropolyethers, alkylcarbamate-terminated perfluoropolyethers, poly(perfluoropolyether)acrylates, poly(perfluoropolyether)methacrylates, polysiloxanes with pendant fluorinated groups, and poly(perfluoropolyether)glycidyl ethers.

24. The electrochemical cell of Claim 1 wherein the fluorinated liquid comprises: first polymers selected from the group consisting of polymerized versions of perfluoropolyether-acrylates, -methacrylates, and -glycidyl ethers; and

second polymers selected from the group consisting of polymerized versions of acrylates, methacrylates, or glycidyl ethers;

wherein the first polymers are copolymerized with the second polymers; and wherein the second polymers comprise less than 10 wt% of the fluorinated liquid.

25. The electrochemical cell of Claim 1 wherein the fluorinated liquid has a molecular weight between 200 Da and 10,000 Da.

26. The electrochemical cell of Claim 1 wherein the fluorinated liquid is crosslinked.

27. The electrochemical cell of Claim 1 wherein the fluorinated liquid further comprises one or more additives selected from the group consisting of cyclic organic carbonates, cyclic acetals, organic phosphates, cyclic organic sulfates, and cyclic organic sulfonates.

28. The electrochemical cell of Claim 1 wherein the positive electrode further comprises a polymer matrix into which the fluorinated liquid is absorbed to form a polymer gel electrolyte.

29. The electrochemical cell of Claim 1, further comprising a separator electrolyte layer between the electrolyte layer and the positive electrode, the separator electrolyte layer comprising an electrolyte different the first block copolymer electrolyte.

30. The electrochemical cell of Claim 29 wherein the separator electrolyte is selected from the group consisting of ceramic electrolytes, polymer electrolytes, and block copolymer electrolytes.

31. The electrochemical cell of Claim 29 wherein the separator electrolyte comprises a solid electrolyte.

32. An electrochemical cell, comprising:

a negative electrode comprising an alkali metal film; a separator layer in contact with the negative electrode, the separator layer comprising a block copolymer electrolyte and a first salt comprising the alkali metal; and a positive electrode comprising positive electrode active material, binder and a liquid electrolyte comprising a fluorinated liquid and a second salt comprising the alkali metal;

wherein the liquid electrolyte immiscible with the block copolymer electrolyte.

33. An electrochemical cell, comprising:

a negative electrode comprising a film of lithium metal;

a separator layer in contact with the negative electrode, the separator layer comprising a block copolymer electrolyte and a first lithium salt; and

a positive electrode comprising nickel cobalt aluminum oxide particles, binder, a second lithium salt, and a liquid electrolyte comprising a fluorinated liquid;

wherein the liquid electrolyte is immiscible with the block copolymer electrolyte..