HK1181922A - Electrode for a secondary lithium ion battery - Google Patents

Description

Electrode for secondary lithium ion battery

The present invention relates to an electrode for a secondary lithium ion battery, which does not contain an added conductive agent and uses a lithium-metal-oxygen compound as an active material, and a secondary lithium ion battery containing the electrode of the present invention.

The field of rechargeable lithium ion batteries (secondary lithium ion batteries) has been the subject of extremely intensive research for some time, in particular in the replacement of conventional drive types (spark ignition and diesel engines) by electric motors and by the use of lithium ion batteries in computers, mobile telephones and electric tools.

In addition to new electrolyte materials, interest has focused particularly on new materials for the cathode and anode of such lithium ion batteries.

Thus, for some time it has been proposed to use lithium titanate Li in rechargeable lithium ion batteries₄Ti₅O₁₂Or lithium titanium spinel for short, as a substitute for graphite used as an anode material.

A current overview of anode materials in such cells can be found, for example, in Bruce et al, angelw.chem.int.ed.2008, 47, 2930-.

In particular, Li₄Ti₅O₁₂The advantages compared to graphite are better cycle stability, better heat load capacity and higher operational reliability. Li₄Ti₅O₁₂Has a relatively constant potential difference of 1.55V compared with lithium and can be applied only<The 20% capacitance shows thousands of charge-discharge cycles.

Thus, lithium titanate exhibits a significantly more positive potential than graphite that has been conventionally used as the anode in rechargeable lithium ion batteries.

However, a higher potential also causes a smaller voltage difference. At the same time, it has a lower capacitance of 175mAh/g compared to the 372mAh/g capacitance (theoretical value) of graphite, which together leads to a significantly lower energy density compared to lithium ion batteries with graphite anodes.

Furthermore, Li₄Ti₅O₁₂Have a long life and are non-toxic and therefore are not classified as posing a threat to the environment.

Material density of lithium titanium spinel (3.5 g/cm)³) With, for example, lithium manganese spinel or lithium cobalt oxide (4 and 5g/cm, respectively) as cathode material³) In contrast, relatively low.

However, lithium titanium spinel (containing only Ti)⁴⁺) Is an electrical insulator, which is why it is always necessary to add conductive additives (conductive agents) such as acetylene black, carbon black, ketjen black, etc. to the electrode composition of the state of the art in order to ensure the necessary electronic conductivity of the electrode. Thus, the energy density of the battery having the lithium titanium spinel anode is reduced. However, it is also known to be in the reduced state (in its "charged" form, containing Ti)³⁺And Ti⁴⁺) The lithium titanium spinel becomes almost a metal conductor, and therefore the electron conductivity of the entire electrode must be significantly increased.

Doped or undoped LiFePO in the field of cathode materials₄Recently preferred in lithium ion batteriesIs used as cathode material, with the result that, for example, Li is used₄Ti₅O₁₂And LiFePO₄A voltage difference of 2V can be obtained.

Undoped or doped mixed lithium transition metal phosphates, such as LiFePO, having an ordered or modified olivine structure or another NASICON structure₄、LiMnPO₄、LiCoPO₄、LiMn_1-xFe_xPO₄、Li₃Fe₂(PO₄)₃It was first proposed by Goodenough et al (US 5,910,382, US 6,514,640) as a cathode material in electrodes for secondary lithium ion batteries. These materials, in particular LiFePO₄And in fact, is a poorly conducting to completely non-conducting material. In addition, the corresponding vanadates have also been investigated.

It is therefore always necessary to add to the doped or undoped lithium transition metal phosphate or vanadate an additional conductive agent which has already been described in more detail above and, in the case of the above-mentioned lithium titanate, also before the lithium titanate can be processed into a cathode preparation. Alternatively, lithium transition metal phosphates or vanadates and lithium titanium spinel carbon composites have been proposed, however, they also always require the addition of a conductive agent due to the low carbon content. Thus, EP 1193784, EP 1193785 and EP 1193786 describe LiFePO₄So-called carbon composites with amorphous carbon, which, when iron phosphate is produced from iron sulfate, sodium hydrogen phosphate also plays the role of residual Fe in the iron sulfate³⁺Reducing agent of the radicals and preventing Fe²⁺Is oxidized into Fe³⁺. Carbon is also added to increase the conductivity of the lithium iron phosphate active material in the cathode. Thus, in particular EP 1193786 states that in lithium iron phosphate carbon composites, in order to obtain the necessary capacitance and the corresponding cycling characteristics necessary for a well-functioning electrode, it is necessary to contain not less than 3wt. -% of carbon in the material.

In order to produce the above-mentioned anode and cathode materials, in particular lithium titanium spinel and lithium transition metal phosphates, solid state synthesis and so-called hydrothermal synthesis from aqueous solutions are proposed. At the same time, it is known from the state of the art that almost all metal and transition metal cations can be used as doping cations.

It is therefore an object of the present invention to provide further electrodes for rechargeable lithium-ion batteries, which have an increased specific energy density (Wh/kg or Wh/l) and a higher load capacitance.

This object is achieved by an electrode which contains no added conductive agent and uses a lithium-metal-oxygen compound as an active material.

It has surprisingly been found that the addition of conductive agents such as carbon black, acetylene black, ketjen black, graphite, etc. to the electrode formulations of the present invention can be dispensed with without adversely affecting the operation thereof. This is particularly surprising because, as mentioned above, both lithium titanium spinel and lithium transition metal phosphates or vanadates are typically very poor insulators or electrical conductivities.

However, "without added conductive agent" here also means that small amounts of carbon may be present in the electrode formulation, for example, but not limited to, by a carbonaceous coating or in the form of a lithium titanium carbon composite within the meaning of EP 1193784 a1, or as carbon particles, but that they do not exceed a proportion of carbon of at most 1.5wt. -%, preferably at most 1wt. -%, more preferably at most 0.5wt. -% relative to the active material of the electrode.

Electrode density (in g/cm) was obtained using the electrode of the present invention without added conductive agent compared to the state of the art electrode typically having 3-20% added conductive agent³Metric) increase. Thus, for example, an increase in electrode density of typically more than 10%, preferably more than 15%, more preferably more than 25% is measured compared to an electrode with added conductive agent.

This increase in electrode density results in the electrodes of the present invention having a higher volumetric capacitance even when a low charge/discharge rate is used.

Thus, by a higher density of the active material, an electrode without added conductive agent is further obtained having a higher specific power (W/kg or W/l) and specific energy density (Wh/kg or Wh/l) than an electrode with added conductive agent.

The electrode of the present invention also contains a binder. Any binder known per se to the person skilled in the art can be used as binder, for example Polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyvinylidene fluoride hexafluoropropylene copolymer (PVDF-HFP), ethylene-propylene-diene terpolymer (EPDM), tetrafluoroethylene hexafluoropropylene copolymer, polypropylene oxide (PEO), Polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), carboxymethylcellulose (CMC) and derivatives and mixtures thereof.

The electrode preferably has an active material proportion of > 94wt. -%, more preferably > 96wt. -%. In the electrode of the present invention, despite the use of these high active material levels, its operation is not limited.

The active material is preferably selected from doped or undoped lithium titanate (having a spinel structure), lithium metal phosphate and lithium metal vanadate (both latter two compound types have an ordered and modified olivine structure and NASICON structure).

In an advantageous further development of the invention, the particles of the active material have a carbon coating. This is applied as described in EP 1049182B 1. Other coating methods are known to those skilled in the art. In this particular embodiment, the proportion of carbon in the entire electrode is ≦ 1.5wt. -% and is therefore significantly lower than the values mentioned in the above-cited state of the art and previously considered necessary.

Thus, in a preferred embodiment, the active material is a doped or undoped lithium titanate, wherein the electrode functions as an anode.

The terms "lithium titanate" or "lithium titanium spinel" herein generally refer to both undoped and doped forms. It includes Li of space group Fd3m_1+xTi_2-xO₄All of typesLithium titanium spinel with 0. ltoreq. x. ltoreq. 1/3, and overall all mixed formulae Li_xTi_yO（0<y，y<1) The lithium titanium oxide of (1).

Very particularly preferably, the lithium titanate used according to the invention is phase-pure. According to the invention, "phase-pure" or "phase-pure lithium titanate" means that in the end product, no rutile phase is detectable by XRD measurement within the limits of usual measurement accuracy. In other words, in this preferred embodiment, the lithium titanate of the present invention is free of rutile.

In a preferred development of the invention, as already stated, the lithium titanate of the invention is doped with at least one further metal, which leads to a further increase in stability and cycling stability when the doped lithium titanate is used as an anode. In particular, this is achieved by incorporating other metal ions, preferably Al, Mg, Ga, Fe, Co, Sc, Y, Mn, Ni, Cr, V or several of these ions, in the lattice structure. Aluminium is very particularly preferred. In a particularly preferred embodiment, the doped lithium titanium spinel is also free of rutile.

The doping metal ions, which may be located on the lattice sites of titanium or lithium, are preferably present in an amount of 0.05 to 10wt. -%, preferably 1 to 3wt. -%, relative to the total spinel.

In other preferred embodiments of the invention, the active material of the electrode is a doped or undoped lithium metal phosphate or vanadate having an ordered or modified olivine structure or NASICON structure, and the electrode functions as a cathode.

Undoped therefore means that pure, in particular phase-pure lithium metal phosphate is used. The term "pure phase" is also understood in the case of lithium metal phosphate as defined above.

The lithium transition metal phosphate or vanadate corresponds to the formula:

Li_xN_yM_1-yZO₄，

wherein N is a metal selected from Mg, Zn, Cu, Ti, Zr, Al, Ga, V, Sn, B, Nb, Ca or mixtures thereof;

m is a metal selected from Fe, Mn, Co, Ni, Cr, Cu, Ti, Ru or mixtures thereof;

z is a group selected from the group consisting of P and V,

and wherein 0< x <1, 0< y < 1.

The metal M is preferably selected from Fe, Co, Mn or Ni, thus, when y =0, the lithium transition metal phosphate has the formula LiFePO₄、LiCoPO₄、LiMnPO₄Or LiNiPO₄。

Doped lithium transition metal phosphates or vanadates refer to compounds having the above mentioned formula, wherein y >0 and N represents a metal cation from the group as defined above.

Very particularly preferably, N is selected from Nb, Ti, Zr, B, Mg, Ca, Zn or combinations thereof, but preferably represents Ti, B, Mg, Zn and Nb. Typical preferred compounds are, for example, LiNb_yFe_xPO₄、LiMg_yFe_xPO₄、LiMg_yFe_xMn_1-x-yPO₄、LiZn_yFe_xMn_1-x-yPO₄、LiFe_xMn_1-xPO₄、LiCo_yFe_xMn_1-x-yPO₄Wherein x and y<1 and x + y<1。

Thus, as already stated above, it is very particularly preferred if the doped or undoped lithium metal phosphate or vanadate has an ordered or modified olivine structure.

The lithium metal phosphate or vanadate in an ordered olivine structure can be structurally described as the orthorhombic space group Pnma (No. 62 of the International Tables), where here the crystallographic index of the orthorhombic unit cell can be chosen such that the a-axis is the longest axis and the c-axis is the shortest axis of the unit cell Pnma, resulting in the mirror plane m of the olivine structure being brought perpendicular to the b-axis. The lithium ions of the lithium metal phosphate then align themselves in the olivine structure either parallel to the crystal axis [010] or perpendicular to the crystal plane {010}, and are therefore also the preferred direction of one-dimensional lithium ion conduction.

Modified olivine structure means that the modification takes place at anionic (e.g. phosphate is substituted by vanadate) and/or cationic sites in the crystal lattice, wherein the substitution takes place by aliovalent or identical charge carriers in order to enable better diffusion of lithium ions and to increase the electron conductivity.

In other embodiments of the invention, the electrode further comprises a second lithium-metal-oxygen compound different from the first compound, said second compound being selected from the group consisting of doped or undoped lithium metal oxides, lithium metal phosphates, lithium metal vanadates, and mixtures thereof. Naturally, two, three or even more other different lithium-metal-oxygen compounds may also be included. It is self-evident to the person skilled in the art that naturally only lithium-metal-oxygen compounds having the same functionality (and thus functioning as anode material or cathode material) can be included in the electrode formulation.

The second lithium-metal-oxygen compound is preferably selected from the group consisting of doped or undoped lithium manganese oxides, lithium cobalt oxides, lithium iron manganese phosphates, lithium manganese phosphates. The second lithium-metal-oxygen compound is particularly advantageous in certain cathode formulations, and is typically present in an amount of about 3-50wt. -% relative to the first lithium-metal-oxygen compound.

Further, the object of the present invention is achieved by a secondary lithium ion battery having an anode, a cathode and an electrolyte and containing the electrode of the present invention.

In the secondary lithium ion battery of the present invention, the active material of the anode is preferably doped or undoped lithium titanate in the electrode formulation of the present invention that is free of added conductive agent. In this embodiment, the cathode can be freely selected.

In other preferred secondary lithium ion batteries, the active material of the cathode is the doped or undoped lithium metal phosphate in the electrode formulation of the present invention, with and without the presence of a second lithium-metal-oxygen compound, without added conductive agent. In this embodiment, the anode can be freely selected.

Very particularly preferably, in the secondary lithium ion battery according to the invention, the active material of the anode is the doped or undoped lithium titanate in the electrode preparation according to the invention which is free of added electrical conductor, and the active material of the cathode is the doped or undoped lithium metal phosphate in the electrode preparation according to the invention which is free of added electrical conductor.

It was therefore surprisingly found in the context of the present invention that electrodes using lithium-metal-oxygen compounds as active material and without added conductive agent can be cycled at up to very high rates (20C) and at different layer thicknesses (loading) both during charging and during discharging. Only a small difference was found compared to the electrode with the added conductive agent. This was found both in the case of pure lithium-metal-oxygen compounds (produced by hydrothermal process and by solid state synthesis) and carbon-coated lithium-metal-oxygen compounds.

Without wishing to be bound by a particular theory, it is possible that the starting state of non-conductivity is never completely reached even in the presence of a long discharge (delithiation), as explained by the surprising finding that lithium-metal-oxygen compounds can also be used as electrodes without conductive additives. This is particularly the case for compounds of the lithium titanate class.

When lithium titanate is used, obviously, traces of Ti³⁺Remain in the crystal lattice and thus the material and the electrode always maintain sufficient electronic conductivity as long as the particle-particle contact remains good. Thus, electron conductivity is not a limiting factor when cycling lithium titanate.

The invention will be described in more detail below with reference to the figures and examples, which should not be considered limiting.

In the figure is shown:

FIG. 1 cycle life of a conventional lithium titanate electrode with added conductive carbon black;

fig. 2a to 2b show the polarization of an electrode with active material according to the state of the art, i.e. with conductive carbon black added, as a function of the loading;

FIG. 3a is the specific capacitance of the lithium titanate electrode of the invention, FIG. 3b is the specific capacitance of the state of the art electrode;

FIGS. 4a and 4b discharge (4 a) and charge (4 b) capacitances of the lithium titanate electrode of the present invention, wherein there is no drop during discharge;

FIGS. 5a and 5b are the discharge (5 a) and charge (5 b) capacitances, respectively, of a lithium titanate electrode of the present invention, wherein there is a dip during discharge;

fig. 6a and 6b specific capacitance of the electrode of the invention, fig. 6 a: there is a drop during discharge, fig. 6 b: no drop during discharge;

FIGS. 7a to 7b effect of active material loading on the capacitance of the electrode of the present invention;

FIG. 8a is the discharge capacitance of an electrode of the present invention containing carbon-coated lithium titanate particles as the active material, and FIG. 8b is the discharge capacitance of a state-of-the-art electrode containing carbon-coated lithium titanate as the active material;

fig. 9a to 9b (comparison of charging capacitances) of the electrode of the invention (9 a) containing carbon-coated lithium titanate as active material and the electrode of the state of the art (9 b);

FIGS. 10a to 10b comparison of the specific capacitance of an electrode of the invention (10 a) containing carbon-coated lithium titanate as the active material with that of a state of the art electrode (10 b);

FIG. 11 uses LiFePO₄Comparison of the charge/discharge capacitance at different rates of the electrode of the present invention as an active material with the state of the art electrode;

FIG. 12a Using LiFePO₄As the specific discharge capacity at 1C of the state of the art electrode and the electrode of the invention of the active material, fig. 12b using LiFePO₄The state of the art electrodes as active materials and the electrode of the invention have a volumetric discharge capacitance at 1C;

FIG. 13 use LiMn_0.56Fe_0.33Zn_0.10PO₄Comparison of the charge/discharge capacitance at different rates of the electrode of the present invention as an active material with the state of the art electrode;

FIG. 14a each using LiMn_0.56Fe_0.33Zn_0.10PO₄The specific discharge capacity at 1C of the state of the art electrode and the electrode of the invention as active materials; FIG. 14b Using LiMn_0.56Fe_0.33Zn_0.10PO₄The state of the art electrodes as active materials and the electrode of the invention have a volumetric discharge capacitance at 1C.

Fig. 15 volumetric capacitance of the electrode of the present invention and the state of the art electrode using lithium titanate (both coated and uncoated with carbon) as the active material.

Examples

The compound lithium titanate with and without a carbon coating and the lithium iron phosphate with and without a carbon coating are commercially available from Sud-Chemie AG, Germany and Phostehlithium, Canada, respectively. LiMn with and without carbon coating_0.56Fe_0.33Zn_0.10PO₄Can be used for producing LiFePO according to the literature₄The method of (3) is similarly produced.

1.Production of electrodes

1.1 State of the art electrodes

The state of the art standard electrode contains 85% active material, 10% Super P carbon black as an added conductive agent and 5wt. -% polyvinylidene fluoride (PVdF) as a binder (Solvay 21216).

2.1 electrodes of the invention

2.1.1. Lithium titanate anode

The standard electrode formulations for the electrodes of the invention are:

a) 95wt. -% of active material and 5wt. -% of PVdF binder, and

b) 98wt. -% active material and 2wt. -% PVdF binder.

The active material is mixed with a binder (or, in the case of the state of the art electrodes, with an added conductive agent) in N-methylpyrrolidone, applied with a doctor blade onto the previously treated (base coat) aluminum foil, and the N-methylpyrrolidone is evaporated at 105 ℃ under vacuum. The electrode was then cut (diameter 13 mm) and used 5 tons (3.9 tons/cm) in an IR press at room temperature³) Is compressed for 20 seconds. The primer layer on the aluminum foil consists of a thin carbon coating, which improves the adhesion of the active material, especially when the active material content of the electrode exceeds 85wt. -%.

The electrodes were then dried at 120 ℃ under vacuum overnight and, if used as an anode, assembled and electrochemically measured for lithium metal in half cells in an argon-filled glove box.

LP30 (Merck, Darmstadt) was used as electrolyte (EC (ethylene carbonate) = DMC (dimethyl carbonate) =1:1, 1M LiPF₆) Electrochemical measurements were performed on lithium metal. The test procedure was performed in CCCV mode, i.e. in constant current cycles, the first cycle was performed at C/10 rate and the subsequent cycles were performed at C rate. In some cases, then at the limiting voltage (for Li/Li)⁺1.0 and 2.0 volts) is performed until the current is reduced to about C/50 rate to complete the charge/discharge cycle.

Fig. 1 shows the specific capacitance, i.e. the cycle life, of an electrode (anode) of the state of the art, i.e. containing lithium titanate as active material with an added conductive agent. They exhibit high cycling stability with respect to lithium metal. After 1000 cycles, only 2% of the total discharge capacitance (delithiation) and 3.5% of the charge capacitance (intercalation) were lost. The capacitance obtained at 2C shows a slightly higher loss, but still only < 6%.

Fig. 2a and 2b show the discharge and charge capacitances, respectively, of a state of the art lithium titanate electrode. It can be seen from the figure that the polarization of the electrodes is relatively small for discharge, but somewhat higher for charge. Active material loading was 2.54mg/cm². With higher loading (C-rate), the polarization increases and thus the capacitance decreases, since the voltage limit is reached at an earlier stage.

Figures 3a and 3b show the specific capacitance of lithium titanate electrodes (95 wt. -% active +5% binder) in a 3.4mg loading (3 a) and a 4.07mg loading (3 b) of the present invention, respectively. Fig. 3a shows the specific capacitance of the electrode of the invention and fig. 3b shows the specific capacitance of the electrode of the state of the art containing conductive carbon black.

As a result, the absence of added conductive agent produces a slightly lower specific capacitance during the discharge and charge cycles. However, the specific capacitance is still very high.

Fig. 4a and 4b show the voltage dependent discharge (4 a) and charge (4 b) capacitances, respectively, of the electrode of the invention, and it can be seen that the polarization is only slightly increased (m) compared to the electrode with the added conductive agent (fig. 2)_act=2.54mg/cm²). This means that the lithium insertion/delithiation reaction is only slightly influenced by the insulating chemical behavior of the lithium titanate in its fully delithiated state. Since a completely electronically insulating material cannot function as an electrode, this result surprisingly means that sufficient electronic conductivity must be present during the charge/discharge reaction. The measurement results showed that no electron insulating region was formed in the electrode.

At the end of the measurement, the run is continued for a while at constant voltage (CV step, "down"); this is shown in fig. 5, and the results are compared with those in fig. 4. Figure 6 compares the electrodes of the invention in the presence and absence of a dip.

In fig. 5a and 6a, the CV step is performed at the end of the discharge reaction (delithiation) until the current reaches about C/50. A small effect of increased polarization was seen on charging (lithium insertion) at rates above 10C, but the effect was relatively small, about 50mV at 20C. The active material loading is comparable to the measurement without CV step during discharge (m)_act=2.55mg/cm²). This means that even after the electrode is fully delithiated, sufficient electron conductivity remains in the material, which can allow the material to continue to function as an electrode. These measurements were made for lithium metal, which means that there is no limitation on the electrodes. These measurements demonstrate that the lithium titanate anode of the invention without added electrical conductor performs its function not only in half-cells, but also in full cells.

It was furthermore found that the electrodes still show good cycling stability under both conditions, i.e. in the presence and absence of the CV step at the end of the discharge, with only a negligible reduction in capacitance even after a few hundred cycles. Therefore, in other words, omitting the addition of the conductive agent does not adversely affect the cycle stability of the lithium titanate electrode.

FIGS. 7a and 7b show active material content of 95% with different loadings (in mg/cm)²) The discharge rate (delithiation) (7 a) and the charge rate (intercalation) (7 b) of the electrode of the present invention. In addition, two different loadings were measured during discharge using an additional CV step for electrodes containing 98% active material and electrodes containing 95% active material.

The rate performance is only slightly reduced compared to the case of using an added conductive agent. This is particularly pronounced at rates > 10C. The delithiation reaction (discharge) is generally faster than the intercalation reaction (charge). Increasing the active material level from 95% to 98% did not appear to have an effect on rate performance. The CV step at the end of the charge also does not affect the rate performance.

Fig. 8a and 8b show the discharge capacitance of the electrode of the present invention containing carbon-coated lithium titanate particles (fig. 8 a) compared to the conventional formulation containing an added conductive agent (8 b), respectively. Figure 8a shows that there is no significant difference in polarization between the electrode of the present invention and the state of the art electrode (figure 8 b). However, it can be seen that the end of charge is reached earlier with the electrode of the invention than with the state of the art electrodes.

Fig. 9a shows the voltage versus charge capacitance for the electrode of the present invention and the state of the art electrode (9 b), each using carbon-coated lithium titanate as the active material. No significant difference in polarization could be determined.

The rate capability of the formulation of the invention is still very high and in fact better than that of the material not coated with carbon. The rate capability of the electrode of the present invention containing carbon-coated lithium titanate (fig. 10 a) and the state of the art electrode containing carbon-coated lithium titanate and added conductive agent (fig. 10 b) are compared in fig. 10.

Fig. 15 shows the volumetric capacitance during discharge for the electrode of the present invention and the state of the art electrode using lithium titanate as the active material. Electrode 2 contained carbon-coated lithium titanate as the active material and electrode 1 contained uncoated lithium titanate as the active material. As can be seen from the figure, the electrodes of the present invention sometimes show significantly better values than the corresponding state of the art electrodes.

2.1.2. Cathode of the invention

The standard electrode formulations used for the cathodes of the invention were:

a) 95wt. -% active material and 5wt. -% PVdF binder (LiFePO)₄Cathode)

b) 93wt. -% active material and 7wt. -% PVdF binder (LiMn)_0.56Fe_0.33Zn_0.10PO₄Cathode)

The active material is mixed with a binder (or, in the case of the state of the art electrodes, with an added conductive agent) in N-methylpyrrolidone, applied with a doctor blade onto the previously treated (base coat) aluminum foil, and the N-methylpyrrolidone is evaporated at 105 ℃ under vacuum. The electrode was then cut (diameter 13 mm) and roll coated at room temperature. The starting nip width is, for example, 0.1mm and the desired thickness is produced gradually in steps of 5-10 μm. 4 roll coats were applied in each step and the aluminum foil was rotated 180 °. After this treatment, the thickness of the coating should be between 20 and 25 μm. The primer layer on the aluminum foil consists of a thin carbon coating, which improves the adhesion of the active material, especially when the active material content of the electrode exceeds 85wt. -%.

Electrochemical cells were then produced as described for lithium titanate.

FIG. 11 shows a state of the art LiFePO₄The charge and discharge capacitance of the electrode and the electrode of the invention, i.e. the electrode without added conductive agent.

Unlike the lithium titanate anode, the electrode was pressed 4 times for 30 seconds at a pressure of 10 tons after the application of the active material. The electrode density of the electrode was 2.08g/cm for the state of the art electrode and the electrode of the invention, respectively³And 2.27g/cm³。

In the half cell for lithium, the rate performance during charge and discharge reactions was measured in the range of 2.0 to 4.1 volts. For these electrodes, the specific capacitance of the two electrodes is very similar at all charge/discharge rates.

Furthermore, cyclability experiments were performed in half cells at room temperature, in the range of 2.0 volts to 4.0 volts. LiFePO of the invention₄The electrode showed specific capacitance at 1C rate. There is no difference in the stability of the specific capacitance compared to the state of the art electrodes.

In contrast, the electrodes of the present invention have an improvement in volumetric capacitance (fig. 12a and 12 b).

In addition, to makeUsing LiMn_0.56Fe_0.33Zn_0.10PO₄The state of the art electrodes and the electrodes of the invention as active materials were also compared with each other:

fig. 13 shows the rate performance of the electrode of the prior art and the electrode of the present invention, and for the electrode of the present invention, an excellent relative discharge rate was found.

LiMn of the invention_0.56Fe_0.33Zn_0.10PO₄The electrode showed excellent cycling stability at 1C/1D. No difference in stability was observed compared to the electrode of the present invention containing the same active material. However, the electrode of the present invention has an improved volumetric capacitance (fig. 14a and 14 b).

Claims (14)

1. An electrode, which does not contain an added conductive agent, uses a lithium-metal-oxygen compound as an active material.

2. The electrode of claim 1, further comprising a binder.

3. The electrode of claim 2, having a proportion of active material of > 94wt. -%.

4. The electrode of claim 3, wherein the active material is selected from doped or undoped lithium titanate, lithium metal phosphate, lithium metal vanadate.

5. The electrode of claim 4, wherein the particles of active material have a carbon coating.

6. The electrode of claim 4 or 5, wherein the active material is a doped or undoped lithium titanate.

7. The electrode of claim 4 or 5, wherein the active material is a doped or undoped lithium metal phosphate.

8. The electrode of claim 7, wherein the doped or undoped lithium metal phosphate has an ordered or modified olivine structure.

9. The electrode of claim 8, having a doped or undoped lithium metal phosphate of the formula:

Li_xN_yM_1-yPO₄,

wherein N is a metal selected from Mg, Zn, Cu, Ti, Zr, Al, Ga, V, Sn, B or mixtures thereof;

m is a metal selected from the group consisting of Fe, Mn, Co, Ni, Cr, Cu, Ti, Ru;

and wherein 0< x <1 and 0< y < 1.

10. The electrode of any one of claims 7 to 9, further comprising a second lithium-metal-oxygen compound different from the first, said second lithium-metal-oxygen compound being selected from the group consisting of doped or undoped lithium metal oxides, lithium metal phosphates, lithium metal vanadates, and mixtures thereof.

11. The electrode of claim 10, wherein the second lithium-metal-oxygen compound is selected from the group consisting of doped or undoped lithium manganese oxides, lithium cobalt oxides, lithium iron manganese phosphates, lithium manganese phosphates.

12. A secondary lithium ion battery having an anode, a cathode and an electrolyte and comprising an electrode according to any one of the preceding claims.

13. The secondary lithium ion battery of claim 12, which uses doped or undoped lithium titanate as the active material of the anode.

14. The secondary lithium ion battery of claim 12 or 13 which uses doped or undoped lithium metal phosphate as the active material of the cathode.