GB2634261A - Electrode precursor composition, electrode, cell, device, and methods - Google Patents

Abstract

An electrode precursor composition comprising: a polymer-electrolyte gel matrix phase comprising a blend of at least a first polymer, a second polymer a liquid electrolyte; and a dispersed phase comprising an electrochemically active material. The first polymer is poly(methyl methacrylate), PMMA, with a weight average molecular weight of at least 1 x 105 Da and is present between 0.1 and 10 vol % of the total volume of the blend. The second polymer comprises at least 75 mol % of vinylidene fluoride (VDF) as a constituent. The liquid electrolyte comprises an organic solvent and an alkali metal salt. The dispersed phase comprises an electrochemically active material. Also described are an electrode comprising or produced from the electrode precursor composition, an electrochemical secondary cell comprising the electrode, and an electrochemical energy storage device comprising the electrochemical secondary cell.

Description

ELECTRODE PRECURSOR COMPOSITION. ELECTRODE. CELL, DEVICE, AND METHODS

CKGROUND

Lithium-ion secondary batteries are used in a variety of applications from small personal devices to electric vehicles. Lithium-ion batteries can have high energy density and long cycle life, among other properties. They can contain a plurality of lithium-ion secondary cells, which is one example of an alkali metal ion secondary cell Lithium-ion battery components such as electrodes can be.made from solvent cast process that uses sacrificial solvent. A liquid electrolyte may be used within the lithium-ion cells of the battery, to provide conductivity of lithium ions within the cell between the solid, solvent cast anode and cathode.

different approach involves use of gel electrodes_ These electrodes can he formed from a composition prepared by mixing the necessary components such as electrochemically active material, polymer, and a liquid electrolyte, and subsequently subjecting the composition to a treatment; such as thermal treatment. Some gel electrode compositions contain a small amount of liquid electrolyte to aid gelation of the polymer.

SUMMARY

Provided herein is an electrode precursor composition for an alkali metal ion secondary cell. The composition comprises a polymer-electrolyte gel matrix phase comp:-polymer blend and a liquid electrolyte. The polymer blend is made up of a blend of polymers, the polymer blend comprising a first polymer which is polymethylmethacrylate (PMMA") having a weight average molecular weight of at least lxl 05 Da. The polymer blend also comprises a second polymer which comprises at least 75 mol% vinylidene fluoride (VD19 as constituent monomer. The liquid electrolyte comprises an organic solvent and an alkali metal salt. The polymer-electrolyte gel matrix phase includes the first polymer in an amount of between 0.1 and 10 volume% (vol.%) of the total volume of the polymer blend i.e. the total volume of the first polymer, the second polymer, and ally n L) optional further polyme sj. In addition to the polymer-electrolyte gel matrix phase, the composition comprises a dispersed phase comprising an electrochemically active material.

In solvent cast processes for producing component such as electrodes, the use of a sacrificial solvent such as N-methylpyrrolidone (NMP) is an energetically expensive step. Gel electrodes of the kind that can be produced using the compositions described herein can avoid such additional cost, thereby significantly reducing the cost of cell production.

The use of a small amount of liquid electrolyte means a gel may easily form and the processability of the gel electrodes is improved, reducing the cost of manufacture, However, in prior art compositions, taxis in turn can make the finished gel electrode more prone to dissolution in the electrolyte which is inesent between the electrodes within the finished cell, reducing the operable lifetime of the cell. By contrast, polymers haying poor solubility in electrolyte may ensure that, once assembled, the gel electrodes are not degraded by the electrolyte present in the cell_ However such electrodes can be difficult to manufacture due to the poor gelation between the polymer and the electrolyte. To balance factors such as electrode processability, cell performance, and longevity, the present gel precursor compositions employ a first polymer that acts as a processing aid. The first polymer typically has a relatively high solubility in the electrolyte chosen and can. assist in the formation of a. more easily processible gel during manufacture of the gel electrode, without compromising the cell performance or cell lifetime, In some embodiments, the first polymer may not form a gel. In some embodiments, the first polymer may form a liquid in the electrolyte chosen at the amount chosen, or in some embodiments it may dissolve from the gel in sitar.

Further, the presentinventors find that use of an additive amount of a very highly soluble (first) polymer can reduce or eliminate the risk of introducing cell instability that could occur for example if a larger fraction of the first polymer was used. Even so, the addition of such small amounts of first polymer to an electrode composition can improve the processahihty, without detrimental impact on electrochemistry. That is, the present electrode precursor compositions contain only a relatively small amount of the first polymer, which means that there can be little change in structural stability and cell n L) performance which are imparted by the second polymer and an chile.

still manifesting large improvements in processability.

further benefit of the present electrode precursor c -.ins is that ie concentration le alkali metal salt in the overall composition is higher than would otherwise be possible without the presence of the first polymer in the polymer blend. A higher salt concentration increases the conductivity of the gel electrode, improving electrochemical performance of the cell. Due to the presence of the first (more soluble) polymer in the blend, a greater quantity of the liquid electrolyte can be incorporated into the electrode precursor composition. The greater quantity of liquid electrolyte means a higher salt concentration and consequently improved electrode performance, without any noticeable electrode structural stability.

The first polymer is polvmethylmethacrylate (PrvIMA). Thus, the first polymer is a I5 homopolymer having only methyl methacrylate (MMA) as constituent monomers The first polymer has a weight average molecular weight of at least 1x105 Da. Such polymers are considered to have particularly high solubility in typical liquid electrolytes used in the preparation of gel electrodes, thereby readily achieving the effects described above of improved processability, cell performance, and longevity. n L)

In some embodiments, the first polymer makes up at least 0.5 vol%, at least 1.0 vol% or at least 2.0 vol% of the total volume of the polymer blend i.e. the total volume of the first, second and optional further polymers. In sonic embodiments, the first polymer is present in an amount of up to 9.8 vol%, up to 9.5 vol% or up to 9.0 vol% of the total volume of the polymer blend. These are considered particularly useful amounts of the first polymer for which the effects described above can he observed.

In some embodiments first polymer makes up from volG% to 9.8 vol14), for example from 1.,3 voi% to 9.5 vol% or from 2.0 v6194) to 9.0 vol% of the total volume of the polymer blend i.e the total volume of the first, second and optional further polymers.

In some embodiments, the first polymer has a weight average molecular weight of at least xlf)° Da. Such polymers are considered to have particularly high solubility in typical liquid electrolytes used in the preparation of gel electrodes, thereby readily achieving the effects described above of improved processability, cell performance, and longevity.

The second polymer contpris c 0 /DP as constituer T10110111ef. In some embodiments, the second polymer has a weight average molecular weight of at least 1x105 Da. Such polymers are considered to have lower solubility in typical liquid electrolytes used in the preparation of gel electrodes, thereby imparting good structural performance to the electrodes.

In some embodiments, the polymer blend comprises at least one further polymer polymer. Any third or further polymer which is present is different to the first and second polymers. in some embodiments, the third polymer comprises at least 75 mol% VIIF as constituent monomer. The judicious choice of second and third polymers, in combination with the first polymer, can provide exemplary balance between processability and durability of the cell during use. This is particularly notable in embodiments where the second polymer has a particularly low solubility in the liquid electrolyte chosen. For example, in some embodiments the second polymer may have a higher weight average molecular weight than the third polymer.

In some embodiments, the second polymer is present in an amount e 10 vol% of the total volume of the polymer blend. This is considered a particularly useful range amount of the second polymer for which noticeable gelling effects can he observed.

In some embodiments.: the second polymer is a poiyvinylidene fluoride (PVT> homopolymer, or a copolymer. In some embodiments, a further polymer is a polyvinylidene fluoride (PVDF) homopolymer, a polytetrafluoroethylene (PT111:1.) homopol yin er, a polychforotri fluoroethylene homopolymer, polymethylmethacryl ate (PMMA) homopolymer, a PVDF copolymer, a PILE copolymer, a PC IFE copolymer, or a PIMA. copolymer. In some embodiments, a fifrther polymer is a poly vinylidene fluoride (PVDF) homopolymer, or a PVDF copolymer. In some embodiments, the second and/or a further polymer comprises hexafluoropropylene as a constituent monomer. In some embodiments, the second and/or a. further polymer comprises up to 2 mol% of one or more constituent monomers other than VDT; and HFP. Such polymers are considered to have exemplary solubilities as well as achieving gelling benefits described herein.

In some embodiments, the electrochemically active material is present in an amount of between 50 and 75 such as at least 60 vol%, of the total volume of the electrode precursor composition. Such a volume amount of electrochemically active material can achieve useful performance electrodes.

In some embodiments, the dispersed Anise further comprises a conductive adi hive. The presence of a conductive additive can m prove the performance of the electrodes.

In some embodiments, the liquid electrolyte is present in an amount of at least 25 vol% of the total volume of tare electrode precursor composition. This amount can achieve particularly good electrode processability.

In some embodiments, the organic solvent comprises one or more cyclic or linear carbonate compounds. In some embodiments, the organic solvent comprises one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl-methyl carbonate, butylene carbonate, vinylene carbonate, fiuoroethylene carbonate, fluoropropylene carbonate and y-butyrolactone. Such organic solvents can be particularly suitable for balancing the solubility profile of the above-mentioned polymer blend, and safety.

In some embodiments, kali metal salt comprises one or more of LiPF6, Lififi, lithium bis(fluorosulfonyi) imide (LiliSI); lithium bisttrilluoromethanesulfonypitnide (MESH and lithium 2-trifluoromethy1-4,5-dicyanoimidazole (LiTDi). Such alkali metal salts are suitable for providing electrodes for lithium-ion secondary batteries.

In some embodiments, the electrode precursor composition comprises between 20 and 50 vol% of the polymer-electrolyte gel matrix phase, based on the total composition volume. This proportion of polymer-electrolyte gel matrix phase is considered to provide exemplary performance properties.

In sonic embodiments, the po ectrolyre gel matrix phase comprises 3 to ol °Ali of polymer blend, based on the total volume of polymer-electrolyte gel matrix phase. Such range is considered to provide compositions having exemplary processability properties without significantly affecting structural or cell performance and longevity properties.

In some embodiments, the electrode precursor composition is for a lithium-ion secondary electrochemical cell. It is considered that the present compositions are particularly suitable for providing electrodes that can be used in a lithium-ion secondary electrochemical cell.

Also provided herein is a method of preparing an electrode precursor composition as described herein. The method can comprise mixing the electrochemically active materiar with the first, second and any optional further polymen(s) and the electrolyte.

Also provided herein is the use of between 0.1 and 10 yr of a first poly 21.1 polymer-electrolyte gel matrix phase of a composition for an alkali metal ion secondary cell, the composition comprising the polymer-electrolyte gel matrix phase and a dispersed phase, wherein the polymer-electrolyte gel matrix phase comprises a polymer blend and a liquid electrolyte, the polymer blend comprising the first polymer which is polymethylmethacrylate (PMMA) having a weight average molecular weight of at least xi0' Da, and a second polymer which comprises at least 75 mol% vinylidene fluoride (VDU} as constituent monomer, and wherein the liquid electrolyte comprises an organic solvent and an alkali metal salt; and wherein the dispersed phase comprises an electrochemically active material.

hi some embodiments, the use results in an electrode precursor composition as described herein. The use of an additive amount of the first polymer in a composition for an alkali metal ion secondary cell, to form a composition as d hereic, advantages explained above.

Also provided herein is an electrode for use in an alkali metal ion secondary cell. The electrode comprises a polymer-electrolyte gel matrix phase and a dispersed phase, wherein the polymer-electrolyte gel matrix phase comprises a polymer blend and a liquid electrolyte, the polymer blend comprising a first polymer which is polymethyimethacrylate (purvIA.) having a weight average molecular weight of at least l xl.05 Da" and a second polymer which comprises at least 75 raol'A vinylidene fluoride (VDF) as constituent monomer, and wherein the liquid electrolyte comprises an organic solvent and an alkali metal salt; wherein the dispersed phase comprises an electrochemically active material; and wherein the first polymer makes up between 0. t and 10 vol% of the total volume of the polymer blend.

In some embodiments, the electrode comprises or is produced from an electrode precursor composition as provided herein. The relevant above-mentioned effects described for the gel electrode precursor composition described herein also apply to the electrode described herein.

n L) Also provided herein is a method of producing an electrode. The method comprises processing an electrode precursor composition described herein to form a film or coating.

In sonic embodiments, the processing comprises thermal processing or extrusion. Thermal processing or extrusion is found to provide electrodes, such as electrodes described herein, in a straightforward and relatively low-cost manner.

Also provided herein is an electrochemical secondary cell comprising an electrode described herein, or as produced by a method described herein. Also provided herein is an electrochemical energy storage device comprising an electrochemical secondary cell described herein. Since the electrochemical secondary cell and the electrochemical energy storage device each comprise an electrode as described herein, the relevant above-n L) mentioned effects described for the electrode precursor composition described her also apply.

BRIEF DESCRIPTION OF DRAWINGS

Figure 1 shows photographic images of gel electrodes. Figure 1(a) shows an image of a gel electrode prepared from an electrode precursor composition not containing any first polymer (PINIMA) as described herein. Figure 1(b) shows an image of a gel electrode prepared from an electrode precursor composition as described herein. The circle of Figure 1(a) indicates an exemplary area of the electrode having electrolyte loss.

DETAILED DESCRIPTION

Electrode Precursor Corn position The electrode precursor composition for an alkali metal on secondary cell described herein comprises a polymerr-electrolyte gel matrix phase, and a dispersed phase. The electrode precursor composition may find use as a precursor material the preparation of a gel electrode.

The polymer-electrolyte gel matrix phase comprises a polymer blend comprising a first polymer, a second polymer and optionally at least one further polymer. 'The first polymer is PMMA. The second polymer is different from the first polymer and comprises VDF as constituent monomer. Any optional further polymer is different from the first and second polymers. In some embodiments, an optional further polymer may differ from the first and second polymers in type of constituent monomer(s), amount of constituent monomer(s), and/or in weight average molecular weight.

The polymer-electrolyte gel matrix phase also comprises a liquidelectrolyte.

In some embodiments, the polymer-electrolyte gel matrix phase consists of the polymer blend and the liquid electrolyte.

In general, the first(Trost soluble) polymer is present primarily to improve the processabilily of the electrode precursor composition. On the other hand, the second and any optional further (less soluble) polymer(s) are typically chosen for their ability to form a gel capable of use as a gel electrode. That is, the first polymer is used to improve the processability of a polymer (e.g. in embodiments containing only a second polymer) or polymer combination (e.g. in embodiments containing a second polymer and at least one further polymer, such as a second and third polymer') that can form gel suitable for use as a gel electrode. Thus, the second and any optional further polymers perform a more structural function in the finished gel electrode than the first polymer.

The first polymer, which is PIVIMA having; weight e e molecular weight of at least l x105 Da, has a solubility in the liquid electrolyte which is higher than the solubility of the second polymer, which comprises at least 75 mol% VDF as constituent monomer, in the liquid electrolyte. Thus, the first polymer has the highest solubility in the liquid electrolyte f any of the polymers of the polymer blend.

The first polymer makes up at least 0.1 voi l4), and t most 10 vol%, of the total volume the first, second and any optional further polymers i.e. of the total volume of the polymers of the polymer blend. Put differently, the first polymer is present in an additive amount.

In some embodiments, the first polymer-makes rp at least 0.1 vol%, at least 0.2 vol')/0" at least 0.5 vote/o, at least 1.0 vol%, or at least 2.0 vol% of the total volume of the first second and any further polymers. In some embodiments, the first polymer makes up at most 9.8 vol%, at most 9.5 vol%, or at most 9.0 vol% of the total volume of the first second and any further polymers. Any combination of the above-listed values may be combined to form a suitable range, such as between 0.1 and 9.5 vol%, between 0.5 and 9.0 vol%, or between 25.0 and 9.0 vol%.

It is noted that the sum of the volumes of the first, second and any further polymers is the total volume of the polymer blend, and the sum is 100 voi%.

Put differently, the volume ratio of the first polymer to the second polymer and any further polymer is from 0.001 to 0.1. Within this range a good balance of processability and durability can be obtained by the polymer blend. In some embodiments, the volume ratio of the first polymer to the second polymer and any further polymer is at least 0.002, at least 0.005, at least 0.01 or at least 0.02. In some embodiments, the volume ratio of the first polymer to the second polymer and any further polymer is at most 0.098, at most 0.095, or at most 0.090. Any combination of the above-listed values may be combined to form a suitable range, such as between 0.001 and 0.095, between 0.005 and 0.090, or between 0.01 and 0.090.

In sortie sxnboditnents, the first 1 an unt of atleast 0.01)1% of the total volume of the electrode precursor composition, such as at least 0.02 vol%, or at least 0.05 vol%. In some embodiments, the first polymer is present in an amount of up to 1.0 such as up to 0.8 vol% or up to 0.5 voi% based on the total volume of the electrode precursor composition. Any combination of the above-listed values may be combined to form a suitable range, such as between 0.01 and 1.0 vol%, between 0.02 and 1.0 v01%, or between 0.02 and 0.8 voill/ii; based on the total volume of the electrode precursor 15 composition.

n L) he first polymer has a weight average molecular weight of at least lx 0- In some embodiments, the first polymer is a high molecular weight polymer. In some embodiments, the first polymer is an ultra-high molecular weight polymer. In some embodiments, the first polymer has a weight average molecular weight of at least lx106 Da, at least 2x10-Da, or at least 3x106 Da. An upper limit is not particularly specified.

Herein, the weight average molecular weight uan be measured using a gel permeation chromatography (GPC) method. Universal calibration according to a standard method, e.g. ASTM-D6474-99, may be used. UV-vis spectra and absorbances may be recorded on a spectrophotometer. Calculation of the molecular weight can be canied out by appropriate analytical software, such as CIRRUS® GPC software. GPC measurements can be carried out on a suitable HPLC system. For example, PINIMA standards and ornanic solvent eluents are appropriate for measuring polymers containing MMA or VIM By way of further example, the,eight average molecular weight of a VDF-containing polymer can be measured according to the method described in "Polyvinylidene Fluoride Analysis on Aglient PLgel 10 tun MIXED-B and CPC/SEC" Application Note (Graham Cleaver,ern Technologies, Inc. 2015). Here, PAIMA standards are used and IlATAISO is eluent. The weight average molecular weight of PA _MA can be measured according to the method described in "Synthesis of ultra-high molecular weight poly methyl methamdate) with hydrosilane as initiator" (Yuan et al.; Materials Today Communications, 2022). Here, PMMA standards are used and THE is eluent.

In some embodiments, the first polymer can;spontaneous dissolution electrolyte at room temperature. This may, depending on the polymer, be a very slow process, but in some embodiments exposing the liquid electrolyte to the first polymer at room temperature without any specific mixing leads to the formation of a gel.

In addition to the above-described first polymer, the polymer blend also comprises a second polymer which comprises at least 75 mol% vinylidene fluoride (VDF) as constituent monomer, such as at least 78 mol% VDF as constituent monomer, at least 80 mol% VDF as constituent monomer; or at least 85 mol% VDF as constituent monomer. In embodiments where the second polymer has 100 mol% VDF as constituent monomer, it is PVDF homopolymer.

n L) As used herein, "mol%" refers to the molar proportion of monomers present in the polymer, where the total moles contained in the polymer is 100%.

In some embodiments, the second polyme * has a weight average molecular is lower than that of the first polymer. In some embodiments, the second polymer has a weight average molecular weight of at least Ix105 Da, such as at least 2x105 Da or at least 5x105 Da. An upper limit is not particularly specified.

In some embodiments, the second polymer may be poly(vuiylidene difluoride) (PVDF) homopolymer or a copolymer thereof In some embodiments, the second polymer may be a copolymer comprising VDE, such as poly(vinylidene fluoride-co-hexatiubropropylene) (rVIDI2-11111?).

As used herein, "copolymer" refers to a polymer containing more than one kind of monomer. Thus, for example, a PAN' copolymer contains one or more kinds of monomer in addition to VDF monomer units, and a PMNIA-PEO copolymer contains at least MMA and ED monomers. The copolymer may be any suitable kind of copolymer, such as a random copolymer, an alternating copolymer, or a block copolymer etc. The one or more kinds of monomer in addition to the monomer mentioned may be of any suitable kind as long as the effects described herein are achieved. Suitably, a copolymer may contain the mentioned monomers in an amount of at least 20 weight% (wt%) such as at least 30 wtn, at least 50 wt%, at least 70 wt% or at least 90 wt% based on the weight of the copolymer.

In some embodiments, the second polymer has the lowest solubility in the liquid electrolyte of the polymers making up the polymer blend e.g. the lowest solubitay in the liquid electrolyte of the first, second and any optional thither polymer.

In some embodiments, in which the polymer blend consists of first and second the proportion (vol%) of second polymer is determined by the amount of first polymer.

In some embodiments, in which the polymer blend includes optional further polymer(s), the second polymer is present in an amount of at least 5.0 voluir, of the total volume of the polymer blend, such as at least 8.0 vol% or at least 10.0 vol% The upper limit of the amount of second polymer is determined by the amount(s) of other polymer(s) in the polymer blend.

In some embodiments, the second polymer is present in an amount of at Least 0.1 vol% of the total volume of the electrode precursor composition, such as at least o vol%, or at least 0.3 vol%. In some embodiments, the second polymer is present in an amount of up to 5.0 vol%, such as tip to 1.0 vol%, up to 3.0 vol% or up to 1.0 vol%. Any combination of the above-listed values may be combined to form a suitable range, such as between 0.1 and 5.0 vo1°,4, between 0.1 and 4.0 vol%, or between 0.3 and 3.0 v01%. n L)

In some embodiments, the polymer blend comprises a further (third) polymer. In some embodiments, the polymer blend comprises more than one further polymer, such as a third polymer and a fourth polymer. Each of the one or more further polymer(s) are from the first and second polymers. So long as the difference does not impact the effects described herein, the optional one or more further polymers may differ from the first and second polymers in any respect. In some embodiments, optional further polyiner(s) may have the same constituent monomers as the first or second polymers but differ in some other property e.g. molecular weight. In some embodiments, optional further polymer(s) may differ from the first or second polymer in their constituent monomer units, for example they may comprise monomers having different fimctional s to those of the first or second polymer. In some embodiments, in which there are two or more further polymer(s), the way in which the further polymers differ from the first and second polymers may be the same or different.

hi some embodiments in which the polymer blend comprises a first, second and third polymer, the third polymer has a solubility in the liquid electrolyte which is intermediate between that of the first and second polymers. In this way, the electrode precursor composition can provide a particularly good balance between processability, through the presence of the more soluble polymers, and durability during use of the cell, through the presence of the less soluble polymer. In such embodiments, the second polymer is less prone to dissolution into the cell electrolyte during use of the cell than the first or third polymers, and therefore contributes to good cell lifetime.

In some embodiments, any further polymer, such as a third polymer, may independently be selected from poly(ethyleneglycol thmedmerylanA poly(ethyleneglycol crOikA PoWcorileneSttol dimettlaciAite), PolY0roPYIellethcol thaelYiat4 Pc4(110110 methacrylate) (PNIN1A), poly(acrylonitrile) (PAN), polyurethane (PU), poly(yinylidene difluoride) (PVD1'), poly(vinylidene fluoride-co-hexalmoropropylene) (PVDF-LIFP), polyethylene oxide) (PEG), poly(ethyleneglycol dimethylether), poly(ethyleneglycol diethylether), polychlorotrilluoroethylene (PCTFE), polytetraituoroethylene (pTFIE), poi y [b s( methoxy ethoxyethoxide)-phospnazene], poly(di methyl si oxane) (PDMS), poi pot y di SU fi de, polystyrene, polystyrene sul fon ate, poly py tro e, poiyaniline.

polythiophene, polythione, polyvinyl pyridine (PVP), polyvinyl chloride (PVC), polyaniline, poly(3,4-ethyl en edi oxythiophene) (PEDOT), poly(p-phenylenc), poly(trip nylene), polyazulene, polyfluorene, polynaphthalene, polyanthracene, polyfuran, polycarbazole, retrial aiene-substituted polystyrene, ferrocene-substituted polyethylene, carbazole-substituted polyethylene, polyoxyphenazine, poly(heteroacene), poly[(4-styrenesulfonyl)(trifluoromethanesulfonyl) imide-co-methoxy-polyethyleneglycolaerylatel ([PSITSI-co-NWEGA1), sulfonated poly(phenyiene (PPO), N,N-dimethylacryl amide (DMAArn), lithium 2-a.crylamide-2-methyl-t-propane sulfonate (Li AMPS), Poly(l ithium 2-Acrylamido-2-Methylpropanesulfoni c Acid-Co-Vinyl Triethoxysilane), poly ethyleneoxi de(PE(3)/poly(I ithi um sorb ate), PEO/poly(lith i um muconate), PEO4poly(lithium sorbate)+BF3], PEO copolymer, PEO terpolymer, and NIPPON 5,FIOKUBAI® polymer. hi some embodiments, any further polymer, such as a third polymer, is not PMIPv1A. in some embodiments, any further polymer, such as a third polymer, is independently selected from polyurethane (Pr), poly(vinylidene diftuoride) (PVDF), poly(vinylidene flood de-cio-nexafluoropropyl ene) (PVDF-FIEP), poiychlorotrifuoroethylene (PCTFE), polytetrafl uoroethy ene (PTFE), poly(dimethylsiloxane) (PDNIS), polyacene, polydisulfide, polystyrene, polystyrene sulfonate, petypyrrole, pohyanifine, polythiophene, polythione, polyvinyl pyridine (PVT), polyvinyl chloride (PVC), polyarniine, poly(3,4-ethylene.dioxythiophene) (PEDOT), polyp-phenylene), poly(triphenylene), polyazulene, polyfluorene, polynaphthalene, polyanthracene, polyfuran, potycarbazole, and [PSIFSI-co-MPEGA]. In some embodiments, any further polymer, such as a third polymer, is independently selected from poly(vinylidene difluoride) (PVDF), poly(vinylidene Cluoride-co-hexafluoropropylene) (PVDF-IfFP) poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-LIFP), polychlorotrifluoroethylene (PCTFE), polytetratitioreethylene (PTFE), polyfluorene, and WSTFSI-co-MPECiAj. In some embodiments, any further polymer, such as a third polymer, is independently selected from poly(vinylidene difluoride) (PVDF) or a copolymer comprising VDF, such as polytvinylidene fluoride-co-hexafluoropropylene) (TN/DE-REP).

In some embodiments, the polymer blend comprises or consists of a first polymer, a second polymer and a third polymer. In some such embodiments, the second polymer and/or third polymer are each independently selected from a PVDF homopolymer or copolymer containing VDF monomers, In some such embodiments, the second polymer and a third n L) polymer are each a PVDF copolymer or are each a PVDF homopolymer. ht sonic such embodiments, the PVDF copolymer is a copolymer comprising hexalluoropropylene (REP) monomers as well as VH1) monomers. In sonic such embodiments, the second polymer is selected from PVDF, or a copolymer thereof, and the third polymer is selected from a PVDF homopolymer, or a copolymer thereof In some such embodiments, the second polymer is a PVDF copolymer, and the third polymer is selected from PVDF homopolymer or a PVDF copolymer. In some such embodiments, the second polymer is selected from a PVDF homopolymer or a PVDF copolymer, and the third polymer is PVDF copolymer. In some such embodiments, the second polymer comprises VDF and FIFP monomer as constituent monomers and the third polymer is a PVDF copolymer.

In some embodiments, in wh polymer ich the polym blend comprises a third polymer the third polymer has a weight average molecular weight which is lower than that of the second polymer. That is, in some embodiments, the third polymer has a lower weight average molecular weight than the second or third polymer. In some embodiments" the third polymer has a weight average molecular weight of at least lx101 Da, at least 5x104 Da or at least x l 0' Da. An upper limit is not particularly specified.

n L) In some embodiments, in which the polymer blend comprises a third polymer, the third polymer is present in an amount of at least 50 vol%, such as at least 60 vol°/0 or at least 70 vol%, of the total volume of the polymer blend. The upper limit of the amount of third polymer will be determined by the amounts of the first, second and any further polymers in the polymer blend.

In some embodiments, in which e polymer blend comprises a third polymer, the third polymer is present in an amount of at least 2 6 vol% of the total volume of the electrode precursor composition, such as at least 2.8 vol%, at least 3.0 vol%, or at least 3.2 vol%. in some embodiments, the third polymer is present in an amount of up to 10 voi%, such as up to 9.5 vol%, up to 9.0 vol% or up to 8.5 \Toro. Any combination of the above-listed values may be combined to form a. suitable range, such as between 2.6 and 10 vol%" between 2.8 and 9.0 vol%, or between 3.2 and 8.5 vol%.

TO

In some embodiments in which the polymer blend comprises first, second and third polymers, and in which the first polymer has the highest solubility in the liquid electrolyte and the second polymer has the lowest solubility in the liquid electrolyte so that the third polymer has a solubility in the liquid electrolyte which is intermediate between the first and third polymers, the volume ratio of the second polymer to the third polymer is from 1:4 to 1:10, such as from 115 to 1:9 or fro. 1:6 to 1:8. Such ratios provide particularly stable and processible compositions.

Accordlim some embodiments, the electrode precursor composition for an alkali metal ion secondary cell comprises a polymer-electrolyte gel matrix phase and a dispersed phase, wherein the polymer-electrolyte gel matrix phase comprises a polymer blend and a liquid electrolyte, the polymer blend comprising a first polymer which is PNI1vIA having a weight average molecular weight of at least I x10" Da, a second polymer which comprises at least 75 moi% vinylidene fluoride (VDF) as constituent monomer and having a weight average molecular weight of at least 1x105 Da, and a third polymer which comprises VDF as constituent monomer and having a weight average molecular weight lower than that of the second polymer, the liquid electrolyte comprising an organic solvent and an alkali metal salt; wherein the dispersed phase comprises an electrochemically active material; and wherein the first polymer makes up between 0.1 and 10 vol% of the total volume of the polymer blend.

In some embodiments, an additional energy input can be applied to initiate dissolution of the second and/or optional further polymers. In some embodiments, dissolution of the second and/or third polymer in the liquid electrolyte may be carried out at elevated temperature (for example, at or greater than 30 °C, at or greater than 50 oC. or at or greater than 80 °C) Stability of the gel can be evaluated using a number of methods: 0 A visual assessment would indicate a single phase of material for a stable gel, with no evident liquid-rich phases on the surface; An optical assessment via microscopy or similar would not show any evidence of phase separation;

IS n L)

Further analytical assessment, for example by DSC,spectroscopy methods including rim, RAMAN, or EDX, or x-ray diffra4 tion, would indicate homogenous, single phase mixtures.

In some embodiments second polymer and/or any further polymer exhibits no tendency to swell or dissolve in the liquid le olyte at elevated temperatures.

In some embodiments the second polymer and/or any h polymer shows no obvious change of physical state when exposed to the liquid electrolyte at high temperatures, even when utilising high shear mixing techniques. This can be confirmed by a. visual assessment which would indicate unchanged polymer when exposed to the liquid electrolyte In addition, DSC of this mixture would likely show an endothermic melting peak at the same temperature as the raw polymer, indicative that the crystalline polymer phase is unchanged in the material after exposure to the liquid electrolyte.

In some embodiments the second polymer and/or any further polymer shows partial tendency to swell or dissolve in the liquid electrolyte at elevated temperatures. Slight swelling; of the second polymer in the liquid electrolyte in this way may occur but may be difficult to visually observe. In this case DSC measurements of the mixture may indicate that an endothermic melting peak of the polymer in the mixture is different to that of the raw polymer, indicative of change in crystallinity on exposure to liquid electrolyte.

In some embodiments, the second polymer and/or any further polymer may show significant swelling and plasticise within the liquid electrolyte but may be unable to take up all of the liquid electrolyte at the desired quantity. A visual assessment would indicate free liquid around the gel revealing this behaviour.

In some embodiments, the second polymer and/cll any further polymer may swell and plasticise with the whole quantity of liquid electrolyte at elevated temperatures, but evaluation of this gel in this state at this temperature might suggest a non-homogenous mixture. For example, theological assessment of this mixture may be difficult to measure, or noisy, suggestive of inhomogeneous composition or phase separation.

In some embodiments, the second polymer anany further polymer may show the ability to swell or dissolve in the liquid electrolyte at elevated temperatures, but the mixture may not be stable at room temperature. A polymer such as this might swell and plasticise completely with the liquid electrolyte at elevated temperature, but when returned to room temperature it would exhibit behaviour that suggests rt is inhomogeneous or unstable. For example, visual assessment of this material may indicate liquid being rejected from as gel mass, as droplets forming on the surface, or pooling around the bulk material.

In some embodiments, the electrode precursor composition comprises the polymer blend in an amount of from 2 to 10 vol V3, based on the total volume of electrode precursor composition for example from 2 to 9 voi%, from 2 to 8 vol°,4, from 3 to 8 vol% or from 3 to 5 vol% In some embodiments, the polymer-electrolyte gel matrix phase comprises the polymer blend in an amount of from 3 to 30 vol%, based on the total volume of polymer-electrolyte gel matrix phase, for example from 3 to 25 vol%, from 3 to 24 vol%, from 5 to 24 vol%, from 10 to 23 yore', from 10 to 22 vol%, or fumn about 10 to 15 vol%.

In some embodiments, the polymer-electrolyte gel matrix phase comprises the liquid electrolyte in an amount of from 70 to 97 von"), based on the total volume of polymer-electrolyte gel matrix phase, for example from 75 to 90 vol%, or from 85 to 90 vol%.

In some embodiments, the electrode precursor composition comprises the polymer-electrolyte gel matrix phase in an amount of from 20 to 50 vol%, based on the total volume of electrode precursor composition, for example from 25 to 45 vol%, from 25 to 40 vol or from 30 to 40 vor/o. n L)

In some embodiments, the electrode precursor composition comprises the liquid electrolyte in an amount of at least 2.5 vol%, such as from 25 to 45 vol%, based on the total volume of electrode precursor composition, for example from 26 to 44. 7 to 43 vol%, from 28 to 42 vol% or from 29 to 42 voM) As explained above, the present compositions allow the amount of liquid electrolyte present to be increased while maintaining good structural stability of the gel electrode. So, in some embodiments, the liquid electrolyte makes up at least 31 vol% of the electrode precursor composition, for example greater than 31 vol%, for example greater than 31.00 vol%, for example from greater than 31 vol% to 35 vf. Compositions containing a single type of polymer to provide structural stability may be unable to incorporate such levels of electrolyte. By contrast, compositions containing a single type of polymer which can incorporate such levels of electrolyte may not provide the necessary structural stability and the electrodes are degraded by the cell electrolyte during use, shortening the lifetime of the cell. Indeed, compositions including only two types of polymers to provide structural stability and high levels of electrolyte may not provide sufficient longevity of the cell performance; that is, cell lifetime can be lower compared to cells containing compositions described herein. The present compositions can allow for a higher level of liquid electrolyte in the gel electrode (and thereby a higher level of alkali metal salt), while maintaining good structural stability and longevity compared to other compositions.

i) The polymer-electrolyte gel matrix phase comprises a gel matrix formed by the swelling of the swellable polymer blend when the polymer blend absorbs a liquid electrolyte. The polymer-electrolyte gel matrix phase therefore comprises a 0 comprising the polymer blend and absorbed liquid electrolyte.

In some embodiments, the polymer-electrolyte gel matrix phase consists of the polymer blend described herein and the liquid electrolyte described herein.

The skilled person will understand that the relative solubilities of the first, second and any further polymers in the liquid electrolyte can depend not only on the nature of the first, second and any further polymers chosen, but also on the choice of liquid electrolyte and/or choice of the components of the liquid electrolyte e.g. solvent.

In some embodiments, the liquid electrolyte is present ainount of at least 25 voi% of the total volume of the electrode precursor composition. In some embodiments, the liquid electrolyte is present in an amount of at least 28 vol%, at least 30 voi%, or at least 32 vol% of the total volume of the electrode precursor composition. In some embodiments the liquid electrolyte is present in an amount of up to 50 vol%, such as up to 48 vol%, up to 45 up to 42 voi% or up to 40 voi% of the total volume of the electrode precursor composition. Any combination of these values may be combined to form a suitable range, such as between 25 and 50 vol%, between 28 and 48 vol%, or between 32 and 45 vol%.

The liquid electrolyte contains organic solvent and an alkali metal alt.

In some embodiments, the oivte consists of the organic solvent 11!? al all:fetal salt, In some embodiments, the organic solvent comprises or consists of one or more cyclic or linear carbonate compounds. In some embodiments the solvent comprises one or more cyclic carbonate compounds. In some embodiments the solvent comprises one or more of ethylene carbonate, propylene carbonate; dimethyl carbonate, diethyl carbonate, ethyl-methyl carbonate: butylene carbonate, vinylene carbonate, f oroeihylene carbonate, fluoropropylene carbonate and y-butyrolactone In some embodiments the e solvent comprises one or more of ethylene carbonate, propylene carbonate, vinylene carbonate and fluoroethylene carbonate. In some embodiments the solvent comprises or consists of a mixture of ethylene carbonate, propylene carbonate; vinylene carbonate and fluoroethylene carbonate.

In some embodiments the solvent comprises a blend of at least two different compounds, thr example at least three or at least four different compounds. In some embodiments the solvent comprises a blend of at least two different organic carbonate compounds, for example at least three or at least four different organic carbonate compounds. In some embodiments the solvent is not a blend but consists of one compound. n L)

In some embodiments the solvent comprises ethylene carbonate in an amount of at least 50 it% based on the total weight of solvent, for example at least 55 wt%, at least 60 wt% ear at least 65 wt%. In some embodiments the solvent comprises ethylene carbonate in an amount of up to 80 wt% based on the total weight of solvent, for example up to 75 wt% or up to 70 wt%. In some embodiments the solvent comprises ethylene carbonate in an amount of from 50 to 80 wt% based on the total weight of solvent for example from 60 to wt%.

In some embodiments the solvent comprises propylene carbonate in. an amount of at least 10 wt% based on the total weight of solvent, for example at least 15 vt%, at east 20 wt% or at least 22 wt%. Iii some embodiments the solvent comprises propylene carbonate in an amount of up to 45 wt % based on the total weight of solvent, for example up to 42 wt% or up to 40 wt%. In some embodiments the solvent comprises propylene carbonate in an amount of from 10 to 45 wt% based on the total weight of solvent, for example from 20 to 40 ?v&;) n L) In some emboa inents, the liquid electrolyte further comprises one or more lithium salts. Examples of suitable lithium salts include LiPF6, LiBF4, lithium bis(fluorosulfonyl) imide.

(IbilFSI), lithium 2-trilluoromethyl-4,5-clicyanoimidazote (IMMO, and lithium bis(trifluoromethanesulfonypimide In some embodiments, ts, the liquid electrolyte comprises one or more lithium salts selected from LiPF6, Lirift, lithitm2 bis(fluorosulfonyl) imide (LiFSI), bis(trifluoromethanesulfonypimide (LiTFSI) and lithium 2-trifluoromethyI-4,5-di cyanoirni dazol e (Li I'D°. In some embodiments, the liquid electrolyte comprises a solvent as described above and a lithium salt component comprising or consisting of one or more lithium salts selected from LiPF6, UBE', LiFSI, LiTFSI and LIM!. hi some embodiments, the liquid electrolyte comprises a solvent as described above and a lithium salt component comprising or consisting of one or more lithium salts selected from LAMS! and Li MI.

In some embodiments, the liquid electrolyte comprises or consists of an organic solvent and an alkali metal salt; wherein the organic solvent consists of one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl-methyl carbonate, butylene carbonate, vinylene carbonate, fluoroethylene carbonate, fluoropropylene carbonate and y-butyrolactone; and the alkali metal salt consists of one or more of LiPF6, UBF4,I.iI St, LiTFSI and LiTDI. In some embodiments, the liquid electrolyte comprises or consists of an organic solvent and an alkali metal salt; wherein the orimnic solvent comprises or consists of one or more of ethylene carbonate, propylene carbonate, vinylene carbonate and fluoroethylene carbonate; and the alkali metal salt comprises or consists of one or more of ti F SI and LiTDI.

In some embodiments, the l quid electrolyte comprises or consists of a mixture of at least two different lithium salts. In some embodiments the solvent comprises or consists of a blend of at least two different organic carbonate compounds, for example at least two or at least three or at least four different organic carbonate compounds, and the liquid electrolyte comprises or consists of a mixture of at least two different lithium salts. In some embodiments, the liquid electrolyte consists of one kind of alkali metal salt and one kind of solvent, such as one kind of lithium salt and one kind of organic carbonate compound. In some embodiments, the liquid electrolyte contains only one kind of alkali metal salt, and a blend of at least two different organic carbonate compounds. In some embodiments, the liquid electrolyte comprises a mixture of at least two different alkali metal salts, such as two different lithium salts, and only one kind of organic carbonate compound as solvent. In some embodiments, the liquid electrolyte comprises or consists of a mixture of two different alkali metal salts, such as LIFSI and LiTDI, and at least two kinds of organic carbonate compounds as solvent.

In some embodiments, the total concentration of the lithium saltfs) in the organic solvent is at least 10 wt%, based on the total weight of liquid electrolyte, for example at least 11 wt%, at least 12. wt%, at least 13 wt%, at least 14 wt% or at least 15 wt%. In some embodiments, the total concentration of the lithium salt(s) in the organic.: solvent is up to 50 wt%, based on the total weight of liquid electrolyte, for example up to 40 w up to 30 wt%, up to 2.5 wt% or up to 24 wt%.

In some embodiments, the total concentration of the lithium salt1s) in the organic solvent is from 10 to 30 wt%, based on the total weight of liquid electrolyte, for example from 12 to 25 wt.% or from 15 to 25 wt%.

it dispersed phase comprises an electrochemically active mated' In some embodiments, the electrochemit ally achy,aloes up at least 50 voi°/h or the total volume of the electrode precursor composition, such as at least 52 vol%, at least 0 55 vol%, or at least 57 vol%. In some embodiments, the electrochemically active material makes up up to 75 voi°,4 of the total volume of the electrode precursor composition, such as up to 73 vote, up to 70 volri/b or up to 68 vol%. Any combination of these values may be combined to form a suitable range, such as between 50 and 75 vol%, between 50 and 73 vol%, or between 52 and 73 vol% of the total volume of the electrode precursor composition In some embodiments, the dispersed phase consists of an i-ctro-het ly active material.

The electroe heroicallyactive material is a particulate material, i.e. a material made up of a plurality of discrete particles. The particles may comprise primary particles and/or secondary particles formed from the agglomeration of a plurality of primary particles.

In some embodiments, the electrochemically active match al is a positive ac ve na al. Such materials may suitably be used to form an electrode which is a cathode.

In some embodiments., the positive active material is a lithium transition metal oxide material. In some embodiments, the positive active material is a lithium transition metal oxide material comprising a mixed metal oxide of lithium and one or more transition metals, optionally further comprising one or more additional non-transition metals. In some embodiments, the positive active material is a lithium transition metal oxide material comprising lithium and one or more transition metals selected from nickel, cobalt and manganese. In some embodiments, the positive active material is selected from one or more of lithium cobalt oxide (LCO), lithium manganese oxide (LMO), lithium nickel cobalt oxide (NCO), aluminium-doped lithium nickel cobalt oxide (NC:A), lithium nickel manganese cobalt oxide (NMC), lithium nickel oxide (LNO), lithium nickel manganese oxide (LIMO), lithium iron phosphate (1_213), lithium manganese iron phosphate (LEP) and lithium nickel vanadate (LNV). In some embodiments, the positive active material is lithium nickel manganese cobalt oxide (NMC), optionally doped with another metal such as aluminium.

In some cases, the electrochemically active material may comprise carbon, suitably graphite, graphene or a blend of carbon and a si icon oxide.

Such electroclrernically active commercially available or may be manufactured by methods known to the skilled person, for example through the precipitation of mixed metal hydroxide intermediates from a reaction mixture containing different precursor metal salts, followed by calcination to form a mixed metal oxide and optionally lithiation to incorporate lithium into the oxide.

The electrochemically active materials undoped or uncoated or may contain one or more dopants and/or a coating. For example, the electrochemically active material may be doped with small amounts of one or more metal elements. The electrochemically active material may comprise a carbon coating on the surface of the particles of the material.

In some embodiments, the electrochemically active material is a negative active material. Such compositions may suitably he used to prepare an electrode which is an anode.

In some embodime s the electrochemically active material las a bimodal particle size distribution.

In some embodiments, the electrode precursor composition is for a lithium-ion secondary electrochemical cell. In some embodiments, the electrode precursor composition is a cathode precursor composition. n L)

Electrode Also provided herein is an electrode use in an i ocaii metal ion secondary cell. The electrode comprises a polymer-electrolyte gel matrix phase and a dispersed phase, wherein the polymer-electrolyte gel matrix phase comprises a polymer blend and a liquid electrolyte, the polymer blend comprising a first polymer which is polymethylmethacrylate (PMMA) having a weight average molecular weight of at least lx105 Da, and a second polymer which comprises at least 75 molt)/0-vinylidene fluoride (VDF) as constituent monomer, and wherein the liquid electrolyte elei trolyte coinpriSCS an organic solvent and an alkali metal salt; wherein the dispersed phase comprises an electrochemically active material; and wherein the first polymer makes up between 0.1 and 10 vol% of the total volume of the polymer blend.

In sonic embodiments electrode comprises or is y processing an electrode precursor composition described herein to form a film.

In some embodiments, the electrode is an extruded electrode. In other embodiments, the electrode is a hot-rolled electrode. In other embodiments, the electrode is prepared by extruding an electrode precursor composition described herein through a die to form a film.

In some embodiments, the electrode is a cathode or an anode. In some embodiments, the electrode is a cathode.

All of the compositional options set out for the electrode precursor compositio described herein apply equally to the electrode described herein, including the identities and the relative amounts of the various components of the composition which are not typically, expected to change during the processing of the precursor composition into the electrode.

In some embodiments, the processing comprises thermal processing or extrusion.

In some embodiments the thermal processing comprises passing the electrode precursor composition through a roller assembly at a temperature of at least 50 'C, for example at least 60 0C, at least 70 °C, at least 80 °C, at least 90 °C or at least 100 °C. In some n L) embodiments the ther.mal proceusing comprises passing; the electrode precursor composition through rollers at a temperature of up to 150 "I. example up to 140 °C or up to 130 °C. In some embodiments the thermal processing comprises passing the electrode precursor composition through rollers at a temperature of from 50 "C to 150 "(1, for example from 60 °C to 150 "C, from 70 °C to 150 °C, from 80 °C to 150 °C, from 80 °C. to 140 °C, from 90 ctm, to 140 "C, from 100 citil to 140 "C or from 110 r)C to 130 "C.

The roller assembly may comprise two, sr,pprated by a small distance suds tlsat the electrode is pressed into a thi passed through the rollers.

In some embodiments the thermal processing comprises extruding the electrode. hi some embodiments the thermal processing comprises extruding the electrode using an extrusion apparatus comprising one or more screw feeding sections sad an extrusion die. In some embodiments, the temperature of the die is at least 50 °C, for example at least 60 "C, at least 70 "C, at least 80 "C, at least 90 OC or at least 100 °C. In some embodiments the temperature of the die is up to 150 'DC, for example up to 140 "C or up to 130 °C. In some embodiments the temperature of the die is from 50 "C to 150 'C, for example from 60 "C to 150 °C, from 70 °C to 150 °C, from 80 °C to 150 °C, from 80 °C to 140 °C, from 90 °C to 140 °C, from 100 °C to 140 "C or from 110 "C to 130 °h. n L)

In sonic embodiments the electrode has a thickness of less than 150 pm, for example less than 100 p.m, less than 90 pm, less than 80 p.m or less than 70 pm. In some embodiments the electrode has a thickness of from 40 to 150 pm, for example from 40 to 100 pm, from 40 to 90 p.m, from 40 to 80 pm, from 40 to 70 pm or from 50 to 70 p.m.

In some embodiments the electrode has a thickness of from 40 to 150 pm, for example from 40 to 100 pm, from 40 to 90 pm, from 40 to 80 pm, from 40 to 70 pm or from 50 to 70 urn, In some embodiments the electrode has a porosity of less than about 5% bye volume. In some cases, the porosity of the electrode is less than 5 voi%, less than 3 vol% or less than 2 yol%. To phrase in another manner, the volumetric density of the electrode may be at least 2 suitably at least about 97% or 9S% of the density of a. perfectly non-porous electrode.

In some cases, the extruded electrode may for part of an extruded monolith which includes one or more further layers which are present in an electrochemical battery. For instance, the monolith may include a separator layer, and/or may include the other electrode (i.e. the extruded monolith may include both a cathode and anode). The different layers may be coexxr'uded and have different compositions from one another.

Cell and Device Also provided herein is an electrochemical secondary cell comprising an electrode described herein.

In some embodiments, the cell is an alkali all<ali metal ion secondary cell, for example a sodium-ion secondary cell or a lithium-ion secondary cell. In some embodiments, the cell is a urn-ion secondary cell n L) In some embodiments, the electrochemical secondary cell comprises one electrode as described herein In some embodiments, the electrochemical secondary cell comprises more than one, such as two or more than two, electrodes as described herein.

In some embodiments the electrochemical secondary cell comprises a first electrode described herein, wherein the first electrode is a cathode, and a second electrode described herein, wherein the second electrode is an anode, and an electrolyte between the cathode and the anode. In some embodiments the electrochemical secondary cell comprises an electrode described herein laminated with a current collector, for example a metallic foil.

Also provided herein is an electrochemical energy storage device comprising an electrochemical secondary cell described herein. in some embodiments, the electrochemical energy storage device is a battery In some embodiments:, the electrochemical energy storage device is a lithium-ion battery.

Methods Also provided herein is a method of preparing an electrode precursor.omposition set out herein. The method comprises mixing the electrochemically active material with the first, second and optional further poiytner(s) and the electrolyte. Other components, such as any conductive additive, may be mixed at the same time or later. Mixing may be carried out by any suitable means, in particular any suitable kind of n faxing apparatus for any suitable time. In some embodiments, the mixing is carried out at room temperature (roughly 18-25 "c") at atmospheric pressure.

0 Also provided herein is the use of between 0.1 and 10 vol% of the first polymer in a polymer-electrolyte gel matrix phase of a composition for an alkali metal ion secondary cell, the composition comprising the polymer-electrolyte gel matrix phase and a dispersed phase, wherein the polymer-electrolyte gel matrix phase comprises a polymer blend and a liquid electrolyte, the polymer blend compri sing the first poiymer which is polymethylmethacrylate (1)MMA) having a weight average molecular weight of at least 1x105 Da, and a second polymer which comprises at least lidene fluoride IDE) as constituent monomer, and wherein the liquid electrolyte comprises an organic solvent and an alkali metal salt; and wherein the dispersed phase comprises an electrochemically active material Accordingly, the use provides the first polymer as rr processing additive to gel electrode compositions. Typically, the use results in a composition as described herein.

Also provided herein s a method of producing an electrode. The method comprises processing an electrode precursor composition described herein to form a film or a coating.

In sonic embodiments, the processing forms a film.

In some embodiments, the method is a method of producing an electrode for an alkali metal ion secondary cell.

In some embodiments, the processing comprises thermal processing or emulsion.

In some embodiments, the method comprises: mixing polymers, an electrolyte and an electrochemically active material to form an electrode precursor composition described herein; and thermally processing or extruding the electrode precursor composition to form an electrode film or coating. in some embodiments, the processing forms a film. In some embodiments, the processing comprises thermal processing.

In some embodiments; the electrode film has a thickness of from 500 to 700 um.

In some embodin eats, the method further comprises cutting the electrode film to form an electrode of predetermined dimensions.

In some embodiments, the method further comprises performing a second thermal processing step on the cut film to reduce the thickness of the film to within a range of 50 to 70 urn in some embodiments, the film is provided at the desired thickness without a second thermal processing step i.e. the thermal processing or extrusion step resul film of desired thickness.

In some embodiments, the ure during thermal processing is from 100 to 140 °C.

Examples

Electrode precursor compositions were prepared according to the formulations shown in Table 1 below. The electrode precursor compositions were subjected to processing steps and the resulting compounded material subjected to pressure at room temperature (between 20 and 25°C) to reduce target thickness. The same pressure was applied to each example and its respective comparative example (i.e. Example 1 and Comparative Example I had the same pressure applied; Example 2 and Comparative Example 2 had the same pressure applied; and Example 3 and Comparative Example 3 had the same pressure applied). After subjecting the compounded materials to pressure, a visual assessment was carried out.

The mass amounts of the components to he the composition was calculated based on the target vol.% amount to he used, and the determined density of the component, using the known formula mass density x volume.

In general, density may be determined by available data (in a. textbook or similar) or from first principles using a suitable method known to a skilled person. For solid components such as particulate solids, polymers, conductive carbon -density can be determined using a method such as helium wycnornetry to measure the volume and material weight accurately (this is not powder density or tap density). For liquid components, density measurements can be taken using suitable liquid density apparatus such as a volumetric flask. Density measurements as used herein are at 25°C and atmospheric pressure.

The examples used the following components: - the second polymer is an ultra-high molecular weight PVDF copolymer, the polymer comprising VDF as constituent monomers; - the third polymer is a high molecular weight PV,DF copolymer, the polymer comprising VDF as constituent monomer units; -the first polymer isPhiliMA; - additive I is carbon black; and additive 2 is carbon nanotubes; - electrolytes 1 and 2 are each present at I M. Electrolyte] has the following comp( her e the funs provided are a proportion of the total electrOlyte, which is 100 wt%: Proportion of component % Ethylene carbonate 19% Fluoroct e carbonate 2 29'10 Li FM 12.47% Propylene carbonate 19.40% LiTD1 3 2 0 % ene carbonate 4.45% Electrolyte 2. xture of two carbonate solvents and two Mum salts.

Table I

Example I_ Comparative Example 1 Example 2 Comparative Example 2 Example 3 0.08 Comparative First POKillef (vol%) 0.34 0.17 Example 3 Second Polymer 0 /0 (i.48 0.48 0 47 G.47 7 3.32 0 47 O: 47 Third Polymer (vol%) 3.04 3.38 3.15 323 3.32 Amount of first polymer ' based on total volume of 2.1 noluner blend vol%) 8.8 Electrolyte I (x))1(11)) 30.86 30.86 30.32 0 30.32 30.32 vie 2 lvol% j Cathode active material 64.00 64.00 64.00 6 00 64 00 vol %) 64.00 Additive 1 (val/U) 1.29 i9 Additive 2 (vol%) 1.89 1.89 1.89 1.89 It was found that, after application of pressure, electrolyte squeezed out from the compounded material of Comparative Examples 1, 2 and 3. After application of corresponding pressure to the compounded material of Example 1, electrolyte was not observed to be squeezed out. After application of pressure to the compounded material of Example 2, it was observed that electrolyte retention was considerably improved compared to the result of Comparative Example 2. Similarly, after application of pressure to the compounded material of Example 3, it was observed that the electrolyte retention was considerably improved compared to the result of Comparative Example 3.

Figure 1(a) shows the result of Comparative Example I i.e, a composition having polymer, and subsequently processed and pressed as described above. The circled portion shows areas of the compounded material in which electrolyte loss can be observed visually. Other areas are also visible, though not indicated. Figure (b) shows the result of Example I i.e. a composition as described herein containing a first polymer as an additive reposition used to form the material of Figure 1(a). The material shown in Figure was processed and pressed in the same way as the material of Figure Figure 104 shows no area of visible electrolyte loss. It is noted that these images are taken with overlying polymer film (used when pressure is applied) carefully removed, for ease of 00111pari son.

Claims (2)

1. CLAIMSAn electrode precursor composition for an alkali metal ion secondary cell, comprising: a polymer-electrolyte gel matrix phase and a dispersed phase, wherein the polymer-electrolyte gel matrix phase comprises a polymer blend and a liquid electrolyte, the polymer blend comprising a first polymer which is polymethylmethacrylate (1)MMA) having a weight average molecular weight of at least 1x10' Da, and a second polymer which comprises at least 75 mol% vinylidene fluoride (VDF) as constituent monomer, and wherein the liquid electrolyte comprises an organic solvent and an alkali metal salt; wherein the dispersed phase comprises an electrochemically active material; and wherein the first polymer makes up between 0.1 and 10 vol% of the total volume of the polymer blend.
2. 2. An electrode precursor composition according to claim 1, wherein the first polymer is present in an amount of at least 0.5 vol% of the total volume of the polymer blend and/or up to 9 vol% of the total volume or the polymer blend.n L) CCUr SO * composition according to any one of the preceding claims, er has a e molecular weight of at least 1 xl06Da.4 An electrode precursor composition according to any one of the preceding claims, wherein the second polymer has a weight average molecular weight of at least lx105 Da.5. An electrode precursor composition according; to any one of the preceding claims, wherein the polymer blend comprises a third polymer which is different from the first and second polymers and which optionally comprises at least 75 mot% vinylidene fluoride (V131) as constituent monomer.6. An electrode precursor composition according to claim 5, wherein the first polymer has a weight average molecular weight which is greater than that of the second polymer, and optionally wherein the third polymer has a weight average molecular weight which is lower than that of the second polymer.7. An electrode precursor composition according to any one of the preceding claims, wherein at least one of the second polymer or an optional further polymer comprises hexafluoropropylene (HIM as a constituent monomer and optionally up to 2 Ind.% of one or more constituent monomers other than \IDE. and HI 8. An electrode precursor composition according o any one of the preceding claims, wherein the elect Gaily active material is present in an amount of 50 to 75 vol% of the total volume of the electrode precursor composition.electrode precursor composition according to claim 8, wherein the electrochemically active material is present in an amount of at least 60 vol% of the total volume of the electrode precursor composition.10. An electrode precursor composition according to any one of the preceding claims, wherein the dispersed phase further comprises a conductive additive.11. n electrode n precursorecursor composition according to any one of the preceding claims, wherein the liquid electrolyte is present in an amount of at least 25 vol% of the total volume of the electrode precursor composition.An electrode precursor composition according to any one of the preceding claims, wherein the organic solvent comprises one or more cyclic or linear carbonate compounds.13. An electrode precursor composition according to any one of the preceding claims, wherein the organic solvent comprises one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, carbonate, ethyl-methyl carbonate, butylene carbonate, vinylene carbonate, fluoroethylene carbonate, fluoropropylene carbonate and y-butyrolactone. n L)4. An electrode precursor composition according to any one of the preceding claims, wherein the alkali metal salt comprises one or more of LiPF6, LiE1Fx, lithium bis(fluorosulfony0 imide (LilESO, lithium bisOrifluoromethanesulfonypimide (LiTFS1) and lithium 2-tritluoromethyl-4,5-di cyanoimidazole (Li TD l).15. An electrode precursor composition according to any one of the preceding wherein the electrode precursor composition comprises from 20 vol% to 50 vol% of the polymer-electrolyte gel matrix phase, based on the total composition volume.16. An electrode precursor composition according to any one of the preceding, claims, wherein the polymer-electrolyte gel matrix phase comprises 3 to 30 yol% of the polymer blend, based on the total volume of polymer-electrolyte gel matrix phase.17. An electrode precursor composition according to any one of the preceding, claims, which is for a lithium-ion secondary electrochemical cell 13. A method of preparing an electrode precursor composition according to any one of the preceding claims, comprising mixing the electrochemically active material with the first and second polymers, and optionally a further polymer, and the electrolyte. n L)19. Use of between 0.1 and 10 vol% of a first polymer in a polymer-electrolyte gel matrix phase of a composition for an alkali metal ion secondary cell, the composition comprising: the polymer-electrolyte gel matrix phase and a dispersed phase, wherein the polymer-electrolyte gel matrix phase comprises a polymer blend and a liquid electrolyte, the polymer blend comprising the first polymer which is polymethylmethacrylate (PAWA) having a weight average molecular weight of at least 17(105 Da, and a second polymer which comprises at least 75 mol% vinylidene fluoride (VDF) as constituent monomer, and wherein the liquid electrolyte comprises an organic solvent and an alkali metal salt; and wherein the dispersed phase comprises an electrochemically active material.20. An electrode for use in an alkali metal ion secondary cell, comprising a polymer-electrolyte gel matrix phase and a dispersed phase, wherein the polymer--electrolyte gel matrix phase comprises a polymer blend and a liquid electrolyte, the polymer blend comprising a first polymer which is poiymethylmethacrylate (FNMA) having a weight average molecular weight of at least 1x105 Da, and a second polymer which comprises at least 75 mol% vinylidene fluoride (ME) as constituent monomer, and wherein the liquid electrolyte comprises an organic solvent and an alkali metal salt; wherein the dispersed phase comprises an electrocliemieally active material; anc wherein the first polymer makes up between 0.1 and Io vol% of the fora] volume of the polymer blend.21. An electrode according to claim 20, comprising or produced from an electrode precursor composition according to any one of claims 1 to 19.22. A method of producing an electrode comprising processing an electrode precursor composition according to any one of claims 1 to 19 to form a film or coating.23. A method according to claim z wherein the processing comprises thermal processing or extrusion.24. An electrochemical secondary cell comprising an electrode according, to any one of claims 20 or 211; or as produced by a method according to any one of claims 22 or 23.25. An electrochemical energy storage device comprising an electrochemical secon cell according to claim 24. n L)