Binder for a secondary cell

Abstract

A binder for a cathode in a secondary cell, wherein the binder comprises a polyurethane- based polymer (which is a polyurethane or polyurethane urea) and an antioxidant; a cathode material as well as a cathode comprising said binder; a method to produce said cathode; a secondary cell comprising said cathode; and a vehicle comprising said secondary cell.

Description

[0001] BINDER FOR A SECONDARY CELL

[0002] FIELD OF THE DISCLOSURE

[0003] The present disclosure relates to a binder for a cathode in a secondary cell. More particularly, the present disclosure relates to a cathode binder comprising a polyurethane-based polymer (which is a polyurethane or polyurethane urea) and an antioxidant, a cathode material as well as a cathode comprising said binder, a method to produce said cathode, a secondary cell comprising said cathode, as well as a vehicle comprising said secondary cell.

[0004] TECHNICAL BACKGROUND

[0005] Rechargeable batteries having high energy density and discharge voltage, in particular Li-ion batteries, are a vital component in portable electronic devices and are a key enabler for the electrification of transport and large-scale storage of electricity. To reach higher energy densities, new types of batteries are being developed.

[0006] State of the art Li-ion batteries typically consist of stacks of secondary cells, wherein each cell is composed of a cathode comprising a cathode current collector, an electrolyte, an anode comprising an anode current collector, and optionally a separator positioned between the anode and cathode.

[0007] One of the limiting factors of the Li-ion battery is its cathode. In secondary cells where the anode is made of graphite-based materials, the cations extracted from the cathode material diffuse from the cathode material through the electrolyte and intercalate into the graphite material at the anode during charging. During discharge, this process is reversed. Regardless of the constitution of the cathode, this repeat process will tear on the cathode material, resulting in metal dissolution into the electrolyte. The coating of the cathode material is vital in reducing metal dissolution and prolonging cycle life.

[0008] Attempts have been made to use a binder to achieve better adherence of the cathode material and conducting agent and thereby improve the mechanical strength of the cathode. Conventional binders used for electrodes in batteries are polyvinylidene fluoride (PVDF), copolymers of vinylidene difluoride (VdF) and hexafluoropropene (HFP) monomers (Kynar or KynarFlex), carboxymethylcellulose (CMC) and its sodium salt (CMC-Na), poly(acrylic acid) (PAA) and its sodium salt (PAA-Na), and styrene-butadiene rubber (SBR). All of these have their inherent drawbacks, for example high fluoride content, and sodium carboxymethylcellulose and poly(acrylic acid) are rather brittle. Hence, there is a need for improving the performance of electrodes, cathodes in particular, and at the same time improving the electric conductivity.

[0009] LIST OF ABBREVIATIONS

[0010] C - charge rate

[0011] CC - constant current

[0012] CMC - carboxymethyl cellulose

[0013] CNT - carbon nanotubes

[0014] CNF - carbon nanofibers

[0015] CV - constant voltage den - denier

[0016] HNBR - hydrogenated nitrile butadiene rubber

[0017] ICP-MS - inductively coupled plasma mass spectrometry

[0018] LFP - lithium iron phosphate

[0019] LMNO - lithium manganese nickel oxide

[0020] LMO - lithium manganese oxide

[0021] M - molar min - minute

[0022] NBP - l-butylpyrrolidin-2-one

[0023] NMC - nickel manganese cobalt oxide

[0024] NMCA - nickel cobalt manganese aluminum

[0025] NMP - / V-methyl-2-pyrrolidone

[0026] PTFE - polytetrafluoroethylene

[0027] PVDF - polyvinylidene fluoride s - second

[0028] TEM - transmission electron microscopy

[0029] V - volt

[0030] SUMMARY OF THE DISCLOSURE

[0031] An object of the present disclosure is to provide a binder for a cathode in a secondary cell, wherein the binder may provide an improved electric conductivity (reduced DCIR), improved initial coulombic efficiency, improved capacity retention and good mechanical strength to maintain the structure of the cathode over time. A further object is the provision of a cathode with an improved electrochemical performance and cycle life while at the same time being more environmentally benign, cheaper and safer to assemble. The present disclosure provides a binder combination for a cathode in a secondary cell, wherein the binder comprises a polyurethane-based polymer and an antioxidant, and a method to prepare such a cathode.

[0032] BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 shows a plot of the metal dissolution from electrodes formed from, respectively, PVDF, spandex and spandex plus antioxidant binder.

[0034] Figure 2 shows the cycle life properties of electrodes formed from, respectively, PVDF, spandex and spandex plus antioxidant electrodes.

[0035] DETAILED DESCRIPTION OF THE DISCLOSURE

[0036] In a first aspect, the present disclosure relates to a cathode binder for a secondary cell, wherein the binder comprises a polyurethane-based polymer and an antioxidant.

[0037] Polyurethane-based polymer

[0038] The polyurethane-based polymer of the disclosure is environmentally benign compared to commonly used binder components, such as fluorinate PVDF or PTFE. Replacing such fluorinated binder components with a polyurethane-based polymer binder reduces the environmental impact of cells. In addition, the polyurethane-based polymer binder may be produced from recycled materials, further reducing the environmental impact.

[0039] The polyurethane-based polymer is a polyurethane or polyurethane urea.

[0040] The term "polyurethane" refers to a polyurethane-based polymer comprising urethane linkages. Typically, polyurethanes are prepared by reacting a polymeric isocyanate and a polyol (e.g. a diol) to form a urethane linkage.

[0041] The term "polyurethane urea" refers to a polyurethane-based polymer comprising urethane and urea linkages. Polyurethane urea are typically prepared in a reaction between polyols (e.g. diols) and diisocyanates that react to form a urethane linkage. Polyurethane ureas additionally comprise urea linkages that are often prepared by further reacting the diisocyanates with a diamine.

[0042] The polyurethane-based polymer (i.e. the polyurethane or polyurethane urea) is an elastomer, i.e. a flexible polymeric material. Preferably, the cathode binder comprises about 10-99.9 wt% polyurethane-based polymer (polyurethane or polyurethane urea), for example about 20-99.9 wt%, about 30-99.9 wt%, about 40-99.9 wt%, about 50-99.9 wt%, about 60-99.9 wt%, or about 70-99.9 wt% polyurethane-based polymer (polyurethane or polyurethane urea).

[0043] Even more preferably, the cathode binder comprises 90wt% or more polyurethane- based polymer (polyurethane or polyurethane urea), for instance 95wt% or more, or 98wt% or more.

[0044] In an embodiment, the cathode binder comprises a polyurethane-based polymer (polyurethane or polyurethane urea), antioxidant and additives.

[0045] The cathode binder may comprise up to 10wt% additives, for instance 5wt% or 2wt%. In the context of the disclosure, "additives" are compounds typically included to improve the physical properties of the binder.

[0046] Polymer formulations comprising polyurethane or polyurethane urea available from commercial suppliers often comprises additives. These additives may be stabilizers, residual solvent, delusterants, dispersants and / or lubricants for example.

[0047] An example of a residual solvent is dimethylacetamide.

[0048] An example of a delusterant is titanium dioxide.

[0049] An example of a lubricant is polydimethylsiloxane or a clay such as hydroxylated hydrotalcite.

[0050] Preferably, the cathode binder is free from delusterant such as titanium dioxide and residual solvent (such as dimethylacetamide). These additives can have a detrimental effect on the function of the polyurethane-based polymer, for instance it may reduce the adhesion of the cathode material and the substrate.

[0051] In a preferred embodiment, the cathode binder comprises polyurethane-based polymer (polyurethane or polyurethane urea) and does not comprise at least one of delusterant and residual solvent (such as, respectively, titanium dioxide and dimethylacetamide). For example, the cathode binder may comprise 90 wt% or more polyurethane-based polymer, for instance 95 wt% or more, or 98 wt% polyurethane-based polymer and does not comprise at least one of delusterant and residual solvent (such as, respectively, titanium dioxide and dimethylacetamide).

[0052] In some embodiments, the binder contains up to 5% by weight, or up to 3 wt% such as from 0.1 to 2 wt% or even 0.1 to 1 wt%, of a lubricant. Lubricants are typically added to the polyurethane-based polymer during production, for instance to aid in formation of the polymer during processes such as extrusion. These additives are typically not detrimental to the binder if present in small amounts.

[0053] In some embodiments, the binder contains up to 5% by weight, or from 0.1-3 wt% such as from 0.1-2 wt% or even 0.1 to 1 wt%, of polydimethylsiloxane.

[0054] In some embodiments, the binder contains up to 5% by weight, or from 0.1-3 wt% such as from 0.1-2 % by weight or even 0.1 to 1 wt%, of a clay such as hydroxylated hydrotalcite.

[0055] Dispersant

[0056] A particularly preferred additive is a dispersant.

[0057] Thus, the binder according to the present disclosure preferably comprises a polyurethane-based polymer such as spandex and a dispersant such as hydrogenated nitrile butadiene rubber (HNBR).

[0058] Hydrogenated nitrile butadiene rubber (HNBR) binder, hydrogenated nitrile butadiene rubber binder and HNBR binder may be used interchangeably.

[0059] The acrylonitrile content in HNBR may be from 17% to 50%, for example from 30% to 45%, such as from 35% to 43%, for example from 37% to 41%.

[0060] The hydrogenation process may be incomplete. Incomplete hydrogenation means that residual double bonds may be present in the HNBR. For example, the HNBR may comprise a maximum of 10% residual double bonds, for example a maximum of 7.5%, such as a maximum of 5%, for example a maximum of 2.5%, such as a maximum of 1%. The content of residual double bonds in HNBR may be determined using IR spectroscopy.

[0061] The HNBR of the present disclosure typically has a weight-average molecular weight Mw in the range of from about 50,000 to about 500,000 (measured by gel permeation chromatography (GPC) for polystyrene equivalents). For example, the HNBR has a Mwfrom about 75,000 to about 250,000, such as from about 100,000 to about 200,000, for example from about 125,000 to about 175,000.

[0062] HNBR may be obtained from a supplier.

[0063] For example, Arlanxeo sells HNBR under the tradename Therman® with product codes such as AT3904, AT3443, AT3404, and LT2004. Of these, AT3904 is preferred.

[0064] Presence of a dispersant such as HNBR in the binder together with a polyurethane-based polymer (such as spandex fibers) improves the uniformity of the cathode as the dispersion of the cathode material before coating is more uniform. The uniformity of the binder and its film forming property contributes to reducing metal dissolution from the cathode.

[0065] In a preferred embodiment, the binder comprises a polyurethane-based polymer (polyurethane or polyurethane urea) and HNBR.

[0066] The binder composition typically comprises from about 95 wt% to about 99.9 wt% polyurethane-based polymer (polyurethane or polyurethane urea), for example from about 98 wt% to about 99.9 wt%, such as from about 98.5 wt% to about 99.8 wt%, for example from about 99 wt% to about 99.5 wt%.

[0067] Additionally, the binder composition may comprise from about 0.1 wt% to about 5 wt% HNBR, for example from about 0.1 wt% to about 2 wt%, such as from 0.2 wt% to about 1.5 wt%, for example from about 0.5 wt% to about 1 wt%.

[0068] The weight ratio between HNBR and polyurethane-based polymer is typically from 1:999 to 5:995, for example from 1 :999 to 2:98, such as from 15:985 to 2:998, for example from 5:995 to 10:990. In a preferred embodiment, the ratio between HNBR and polyurethane-based polymer is 5:995.

[0069] These binders may optionally also contain a lubricant such as PDMS which, when present, is included at up to 3 wt% in place of the polyurethane-based polymer.

[0070] Thus, preferred formulation of the binder of the disclosure comprises (or consists of): from about 95 wt% to about 99.9 wt% polyurethane-based polymer; from about 0.1 to 3 wt% antioxidant; optionally from about 0.1 wt% to about 2 wt% HNBR; optionally up to 3 wt% lubricant such as PDMS or clay.

[0071] A particularly preferred formulation of the binder of the disclosure comprises (or consists of): from about 95 wt% to about 99.5 wt% polyurethane-based polymer; from 0.3 to 3 wt% antioxidant; optionally from about 0.2 wt% to about 1 wt% HNBR; optionally up to 1 wt% lubricant such as PDMS or clay.

[0072] The cathode binder of the disclosure comprising a polyurethane-based polymer is typically highly elastic.

[0073] The polyurethane-based polymer may be a block copolymer.

[0074] Preferably, the polyurethane-based polymer comprises a segmented polyurethane- based polymer. The terms "segmented polyurethane-based polymer" and "segmented polyurethane" may be used interchangeably herein.

[0075] Polyurethane-based block copolymers of a 'rigid' or 'hard' and a 'soft' polymer provide the excellent elastic properties. Without wishing to be bound by theory, it is considered that on stretching, the soft polymer expands and on release, springs back to its original form. The 'rigid' polymer does not expand, and therefore maintains the structural integrity of the polymer whilst the soft polymer undergoes deformation. Block copolymers of this structure are also referred to as segmented polymers or segmented copolymers. An example of a highly elastic segmented polyurethane-based polymer according to the disclosure is polyether-polyurea wherein the polyether is the 'soft' component and the polyurea is the 'rigid' component. The polyether-polyurea may in some embodiments be a polyether-polyurethane urea copolymer.

[0076] Preferably, the polyurethane-based polymer comprises a segmented polyurethane- based polymer.

[0077] In a preferred embodiment, the polyurethane-based polymer comprises 60-100wt% segmented polyurethane-based polymer. For instance, the polyurethane-based polymer comprises 70-95wt% segmented polyurethane-based polymer, such as 75- 90wt, or 80-88wt%. Preferably the polyurethane-based polymer comprises at least 85 wt% segmented polyurethane-based polymer.

[0078] Preferably, the segmented polyurethane-based polymer comprises a polyether and polyurea. That is, preferably the binder is a polyether-polyurethane urea binder.

[0079] Preferably, the segmented polyurethane-based polymer consists of polyether and polyurea segments.

[0080] In one embodiment, the polyurethane-based polymer is a polyether-polyurethane copolymer, for example a polyether-polyurethane urea copolymer. That is, in some embodiments, the cathode binder comprises for instance a polyether-polyurea copolymer wherein preferably, the polyurethane-based polymer binder is a blockcopolymer, for instance a block copolymer of polyether and polyurea (i.e. a polyether- polyurethane urea copolymer).

[0081] Preferably, the soft segment has a melting point of < 5 or 6°C.

[0082] Preferably, the polyurethane-based polymer has a number average molecular weight of 50k-1000k Da, for instance 100k-800k Da, 200k-500k Da, 200k-400k Da or 300-350k Da. The number average molecular weight can be determined via gel permeation chromatography (GPC).

[0083] For example, GPC may be performed on a Shimadzu Prominence LC system equipped with an R.I detector with a 300 mm x 75 mm, 5 pm PLgel 100 A and 300 mm x 7.5 mm, 5 pm PLgel 500 A column in series at 40 °C with a DMF eluent at 1.0 ml / min. The method can be calibrated with poly(styrene) standards with MW between 1000 and 10000.

[0084] A number average molecular weight within the defined range provides particularly beneficial results. For instance, improved peel strength, temperature stability and particle binding properties.

[0085] The properties of the segmented polymer may be controlled by varying the length and / or molecular weight of the hard and soft segments, and by controlling the weight percent or concentration of the hard / soft segments in the polymer.

[0086] In a conventional process of making segmented polyurethane-based polymers of polyether and polyurea, a glycol (diols of polyethers, polyesters or polycarbonates, including their copolymers or mixtures) is reacted with a diisocyanate in excess amount to form an isocyanate-terminated polyurethane or polyurethane urea prepolymer. This prepolymer is then diluted in a solvent and chain extended with a short chain diol or diamine to grow the polymer chain length. A terminator can be used to control the molecular weight of the polymer. In this type of conventional process, the soft segment is formed during the prepolymer formation stage and the hard segment is formed during the chain extension stage. Accordingly, the formed polymer chains consist only of alternating soft segments and hard segments.

[0087] The polyurethane-based polymer of the disclosure may comprise alternating hard and soft segments.

[0088] The polyurethane-based polymer of the disclosure may consist of alternating hard and soft segments. For example, the polyurethane-based polymer of the disclosure may consist of alternating polyurea and polyether segments.

[0089] The polyurethane-based polymer may be produced by an extended glycol process and / or under-capping process as disclosed in WO 2019 / 118604 Al. Such a process allows for the formation of a polymer wherein the molecular weight of the soft segment, even with the use of lower molecular weight glycol, can be increased without reducing molecular weight of the hard segment as typically observed in conventional prepolymer production processes. The extended glycol process comprises two step reactions to make the isocyanate- terminated prepolymer.

[0090] In the first step, excess amount of a lower molecular weight glycol (typical MW < 2500) is used to react with a diisocyanate to form a hydroxy-terminated glycol, or an extended glycol with typical MW > 2500.

[0091] This extended glycol is further reacted with excess amount of a diisocyanate in the second step reaction to produce an isocyanate-terminated prepolymer or capped glycol.

[0092] The diisocyanate used in the first step reaction to make the extended glycol can be same or different from the diisocyanate used in the second step reaction to make the capped glycol prepolymer. This capped glycol based on the extended glycol is then dissolved in a solvent and chain extended with a diamine extender and a monoamine as the terminator to form a segmented polyurethane urea polymer with engineered soft segment and hard segment molecular weights.

[0093] The molecular weight of the extended glycol and the capping ratio thereafter in making the capped glycol prepolymer should be controlled in order to provide the desired molecular weight ratio (SSMW / HSMW) of the soft segment to the hard segment and the urea hard segment weight percent (HSWT%) for the segmented polyurethane or polyurethane ureas according to the present disclosure.

[0094] The under-capping process comprises adding controlled amount of a second diisocyanate to an isocyanated-terminated prepolymer which is produced by reacting a glycol at a low capping ratio (typically less than 1.50) with a first diisocyanate. The first diisocyanate and the second diisocyanate can be the same or different.

[0095] The mixture including the added second diisocyanate and the capped glycol prepolymer from the first diisocyanate is dissolved into a solvent, and a diol or diamine chain extender and a monoamine terminator are then added to produce the polyurethane or polyurethane urea polymer with engineered soft and hard segment molecular weights.

[0096] The capping ratio in making the capped glycol prepolymer and the amount of second diisocyanate added to the capped glycol should be controlled in order to provide the desired molecular weight ratio (SSMW / HSMW) of the soft segment to the hard segment and the urea hard segment weight percent (HSWT%) for the segment polyurethanes or polyurethane ureas according to the present disclosure.

[0097] In a preferred embodiment, the cathode binder comprises a polyurethane-based polymer comprising segments of polyether and polyurea, wherein the polymer is based on glycols with a number average molecular weight less than 2500 as measured by GPC. Preferably, the polymer has a molecular weight ratio of the soft segment to the hard segment larger than 12.0, and a urea hard segment weight percent less than 7.8%. The weight ratio of the soft and hard segments may be determined according to the methods outlined below.

[0098] For example, when the formed polymer chains consist only of alternating soft segments and hard segments, and the number average soft segment molecular weight and hard segment molecular weight of the polymer can be estimated mathematically as shown below:

[0099] SSMW = R X (MWgi + MWdi) / (R-l) (1)

[0100] HSI« = R x (MWex + MWdi) (2) where in equation (1) and (2), SSMW and HSMW stand for soft segment molecular weight and hard segment molecular weight, respectively; MWgl, MWdi and MWex represent the number average molecular weight of the glycol, the formula weight of the diisocyanate and the extender or their averages in the situation of mixed diisocyanates or extenders, respectively; and R in the equations is the capping ratio, the molar ratio of the diisocyanate to the glycol.

[0101] Combining equation (1) and (2) provides a correlation of the SSMW and the HSMW referred to as the segment molecular weight ratio, as shown in equation (3).

[0102] SSMW / HSMW =(l / (R-l))x(MWgi+ MWdi) / (MWex + MWdi) (3)

[0103] Based on equation (3), once the ingredient type is determined, such as poly(tetramethylene ether) glycol (PTMEG), methylene bis(4-phenylisocyanate) (MDI) and ethylenediamine (RDA), the SSMW and HSMW are dependent to each other with a function of the capping ratio R and the number average molecular weight of the glycol. There are at least two ways of achieving a polymer with the preferred molecular weight distribution.

[0104] A first method comprises an extended glycol approach wherein a glycol with lower MW is extended to a higher MW before making the isocyanate-terminated prepolymer. This can be achieved by reacting excess glycol with a diisocyanate which functions as a linker connecting two or more glycol molecules. The desired molecular weight of the extended glycol is determined by the relative molar ratio (r> 1) of the glycol to the diisocyanate. The diisocyanate used for glycol extension can be the same or different from the diisocyanate used for making the prepolymer.

[0105] Extended Glycol MWegi= (r x MWgi+ MWdi) / (r-l) (4)

[0106] For example, to extend PTMEG from 1800 to 3500 MW with MDI, the r should be 2.2060. This extended glycol can be used for the conventional prepolymer formation and chain extension processes to provide the SSMW and HSMW following equation (1) and (2) except where the MWgishall be substituted by the extended glycol MWegi.

[0107] A second method comprises an under-capping process wherein a prepolymer is made for the desired soft segment MW and then an extra amount of diisocyanate is added into the capped glycol prepolymer prior to the chain extension step. In this process, the SSMW still follows equation (1) determined by the capping ratio R, and the HSMW is determined by the unreacted diisocyanate in the prepolymer and the extra amount of diisocyanate added into the prepolymer by equation (5). Again, the diisocyanate used to make the prepolymer and the diisocyanate added into the prepolymer for tuning the HSMW can be the same or different.

[0108] HSMW = Rx(MWex + MWdi) + K(R2 / (R-l))x(MWex, + MWxdi) (5) where K is the molar ratio of extra added diisocyanate to the original diisocyanate in making the prepolymer. The MWdi is the molecular weight of the extra added diisocyanate. In the event that the type of the extra amount of diisocyanate added before chain extension is the same as the type of the original diisocyanate used in making the prepolymer, then MWxdi is equal to MWdi.

[0109] The HSMW is very much dependent on how much extra diisocyanate is added into the prepolymer. The weight percent of the soft segment content (SSWT%) in the polymer can be calculated by equation (6) based on the ingredient weights in making the prepolymer and the total weight of the polymer solids:

[0110] SSWT% = (WTgl + WTdi / R) X 100 I WTpolymer (6) where WTgiand WTdi are the respective weight of the glycol (or extended glycol) and the diisocyanate, R is the molar ratio of the diisocyanate to the glycol (or the extended glycol) in making the isocyanate-terminated prepolymer, and WT polymer is the total weight of the polymer solids consisting of all components in making the segmented polyurethane-based polymer.

[0111] Accordingly, the weight percent of the hard segment content in the polymer can be estimated by equation (7).

[0112] HSWT% 100 - SSWT% (7)

[0113] Preferably, the polyurethane-based polymer also has a number average molecular weight of 200k-500k Da, 200k-400k Da or 300k Da as measured by gel permeation chromatography.

[0114] The molecular weights referred to in this description, including the glycol molecular weight, the segmental molecular weights and the polymer molecular weight, are number average molecular weights.

[0115] In a non-limiting example, the polyurethane-based polymer may be prepared in a method comprising:

[0116] (a) adding a diisocyanate to a glycol at a capping ratio of less than 1.5 to produce an under-capped capped glycol;

[0117] (b) adding additional diisocyanate to the capped glycol; and

[0118] (c) adding a chain extender to produce the polymer with engineered hard and soft segment molecular weights; wherein the glycol is polytetramethylene ether glycol (PTMEG).

[0119] Nonlimiting examples of diisocyanates useful in the present disclosure include 4,4'- methylene bis(phenyl isocyanate) (also referred to as 4,4-diphenylmethane diisocyanate (MDI)), 2,4'- methylene bis(phenyl isocyanate, 4,4'- rnethylenebis(cyclohexyl isocyanate), 1,4-xylenediisocyanate, 1,4- bis(isocyanatomethyl)cyclohexane, 2,6-toluenediisocyanate, 2,4- toluenediisocyanate, and mixtures thereof. Examples of specific diisocyanates include Takenate® 500 and FORTIMOO 1,4-116XDI (Mitsui Chemicals), Mondur® MB (Bayer), Lupranate® M (BASF), and Isonate® 125 MDR (Dow Chemical), and combinations thereof. Nonlimiting examples of glycols useful according to the present disclosure include polyether glycols such as poly(tetramethylene ether) glycols (PTMEG), copolyether glycols such as poly(tetramethyleneether-co-ethyleneether) glycol and poly(tetramethylene ether-co- 2-methyltetramethylene ether) glycol, polyester and copolyester glycols such as polycaprolactone diol and those produced by condensation polymerization of aliphatic dicarboxylic acids and diols, or their mixtures, oflow molecular weights with no-more than 12 carbon atoms in each molecule, and polycarbonate glycols produced by condensation polymerization of aliphatic diols with phosgene, dialkylcarbonates or diarylcarbonates. Examples of specific commercially available glycols are Terathane® glycols (INVISTA of Wichita, Kansas, USA), PTG-L glycols (Hodogaya Chemical Co., Ltd., Tokyo, Japan), ETERNACOLL® diols (Ube Industries, Ltd., Tokyo, Japan) and STEPANPOL® polyols (Stepan, Illinois, USA).

[0120] Nonlimiting examples of diamine chain extenders useful in making the segmented polyurethane ureas according to the present disclosure include one or more diamines selected from 1,2-ethylenediamine; 1,4-butanediamine; 1,2-butanediamine; 1,3- butanediamine; 1,3- diamino-2,2-dimethylbutane; 1,6-hexamethylenediamine; 1,12- dodecanediamine; 1,2- propanediamine; 1,3-propanediamine; 2-methyl-l,5- pentanediamine; l-amino-3,3,5-trimethyl-5-aminomethylcyclohexane; 2,4-diamino- 1 -methylcyclohexane; N-methylamino-bis(3- propylamine); 1,2-cyclohexanediamine; 1,4-cyclohexanediamine; 4,4'-methylene-bis (cyclohexylamine); isophorone diamine;

[0121] 2.2-dimethyl- 1,3-propanediamine; meta-tetramethylxylenediarnine; l,3-diamino-4- methylcyclohexane; 1,3-cyclohexane-diamine; 1,1- methylene-bis(4,4'- diaminohexane); 3-aminomethyl-3,5,5-trimethylcyclohexane; 1,3- pentanediamine(l,3-diaminopentane); m-xylylene diamine; and Jeffamine® (Texaco). When a segmented polyurethane with urethane hard segments is desired, the chain extender is a diol. Examples of such diols that may be used include, but are not limited to, ethylene glycol, 1,3- propanediol, 1,2-propylene glycol, 3-methyl-l,5-pentanediol,

[0122] 2.2-dimethyl-l,3-trimethylene diol, 2,2,4-trimethyl-l,5-pentanediol, 2-methyl-2- ethyl-l,3-propanediol, l,4-bis(hydroxyethoxy)benzene, and 1,4-butanediol and mixtures thereof. Nonlimiting examples of useful chain terminators for the present disclosure include one or more monofunctional amines selected from ethylamine, propylamine, isopropylamine, n-butylamine, sec-butylamine, tert-butylamine, isobutylamine, isopentylamine, 1-hexylamine, 1-octylamine, 2-ethyl-l-hexaneamine, cyclohexylamine, N,N-diethylamine, N-ethyl-N-propylamine, N,N-diisopropylamine, N- tert-butyl-N-methylamine, N-tert-butyl-N-benzylamine, N,N-dicyclohexylamine, N- ethyl-N-isopropylamine, N-tertbutyl-N-isopropylamine, N-isopropyl-N-cyclohexylamine, N-ethyl-N-cyclohexylamine, N,Ndiethanolamine, and 2,2,6,6-tetramethylpiperidine.

[0123] A non-limiting example of the solvent used in the present disclosure is N,N- dimethylacetamide (DMAc).

[0124] In one nonlimiting embodiment, the process steps involved in making the segmented polyurethanes or polyurethane ureas of the present disclosure can be a batch process or a continuous process or their combinations. In one nonlimiting embodiment, an extended glycol is made by a batch process, which is further supplied to make the isocyanate-terminated capped glycol prepolymer and to make the polymer with chain extension and termination in a solvent by a continuous polymerization process. For another example, adding and mixing a diisocyanate to a capped glycol prepolymer in the under-capping process can be conducted in a batch process or a continuous process.

[0125] In another nonlimiting embodiment, steps involved in making an extended glycol and / or a capped glycol prepolymer are performed with heat, with or without the use of a catalyst, typically in a temperature range of 50 to 100°C.

[0126] In some nonlimiting embodiments, the process further comprises the step of extending a glycol of low molecular weight to a hydroxy-terminated polyurethane or polyurethaneurea or an extended glycol, prior to making an isocyanate-terminated or capped glycol prepolymer followed by chain extension, so that both molecular weights of the soft segment and the hard segment can be increased without limitation by the low molecular weight of the starting glycol.

[0127] In some nonlimiting embodiments, the process further comprises the step of adding an additional diisocyanate to an isocyanate-terminated or capped glycol prepolymer so that molecular weight of the hard segment is not affected by the low capping ratio prior to the addition of a chain extender. Fibers of polyether-polyurea block copolymers are commonly referred to as Spandex, Elastane or Lycra. Spandex / elastane / Lycra are exemplary polyurethane-based polymer fibers according to the disclosure. Spandex / elastane / Lycra typically comprises at least 85% segmented polyurethane-based polymer, and may additionally comprise pigments, stabilizers, lubricants, antioxidants, other additives and solvents.

[0128] One example of a polyurethane-based polymer is spandex.

[0129] Spandex is a versatile material that is manufactured by a continuous two-step process where a prepolymer of choice having terminal isocyanates is reacted with a suitable diol, diamine or hydrazine. The production method allows for finetuning of the material depending on the specific need. Spandex fibers provide excellent adhesion, flexibility and chemical resistance that are all desired properties for binder materials. Spandex is not fluorinated, as compared to other binder materials, such as PVDF and PTFE, which both uses and can potentially leach components or break down to per- and polyfluoroalkyl substances (PFAS). Using spandex as a binder is thus a more environmentally friendly alternative. Spandex is also considerably cheaper compared to its fluorinated counterparts.

[0130] As used herein, spandex is defined as the generic term as defined by the US federal trade commission. In one embodiment spandex is a fiber comprising at least 85% by weight of a segmented polyurethane. That is, a polyurethane-based polymer fiber comprising at least 85wt% segmented polyurethane-based polymer according to the disclosure may be referred to as spandex.

[0131] In one embodiment, the polyurethane-based polymer fiber is spandex. Suitable spandex fibers are for example Arachra® from TK chemical Corp, Korea; Roica™ from Asahi Kasei, Japan; Elafit™ from Taekwang Indsutrial Co, Ltd., Korea; and creora® from Hyosung TNC, Korea. The spandex is preferably from a recycled material, such as recycled textiles.

[0132] The polyurethane-based polymer of the disclosure may be in fiber form, particle form, or granules.

[0133] In one embodiment, the polyurethane-based polymer fibers are spun from a composition of the segmented polyurethane-based polymer. The fibers may be, for example, but not limited to, dry spun, wet spun or melt spun. In one nonlimiting embodiment, the fibers are dry spun.

[0134] The polyurethane-based polymer fiber may be a staple fiber.

[0135] Preferably the length of polyurethane-based polymer fiber is larger than the largest dimension of the ceramic material particle, more preferably more than 5 times larger.

[0136] Preferably, the polyurethane-based polymer fiber has a length of between 100-1000 pm, for instance 100-800 pm, or 200-600 pm.

[0137] In one embodiment, the thickness of the polyurethane-based polymer fiber is from about 2 den to about 60 den, preferably from about 10 den to about 60 den, more preferably from about 20 den to about 50 den, even more preferably from about 30 den to about 50 den, most preferably from about 35 den to about 45 den. The thickness may be determined by any suitable method, for example ASTM D2591 - 07(2020).

[0138] In a further embodiment, the thickness of the polyurethane-based polymer fiber is about 40 den.

[0139] By "elastomer" or "elastomeric" is meant that the polyurethane-based polymer is deformable and may return to its original shape if deformed. In other words, polyurethane-based polymer is not rigid and may be deformed.

[0140] When in fiber form, the polyurethane-based polymer according to the disclosure typically has an excellent elongation at break, for instance as measured with the general method of ASTM D 2731-72.

[0141] In an example, three fibers, a 2-inch (5-cm) gauge length and a 0-300% elongation cycle are used for each of the measurements. The samples are cycled five times at a constant elongation rate of 50 centimeters per minute. Load power (5TP300), the stress on the polyurethane-based polymer binder during the fifth cycle at 300% extension, is reported as gram-force for a given decitex. Unload power (5TM100) is the stress at an extension of 100% for the fifth unload cycle and is also reported in gram-force. Percent elongation at break is measured on a sixth extension cycle. Percent set was also measured on samples that had been subjected to five 0-300% elongation / relaxation cycles. The percent set, %SET, was then calculated as % SET = 100 x Lf - Lo / Lo where Lo and Lf are respectively the fiber length when held straight without tension before and after the five elongation / relaxation cycles.

[0142] The flatness index of stretch and recovery of the polyurethane-based polymer fibers may be determined by the ratio of 5TM100 / 5TP300, which was the ratio of the recovery power or unload power at 100% extension to the stretch power or load power at 300% extension measured in the fifth 0-300% stretch / recovery cycles.

[0143] Preferably the polyurethane-based polymer fiber has an elongation at break of at least 300%, for example at least 400%, at least 500%, or at least 600%.

[0144] The term "elongation at break" may be used interchangeably with the phrase "possible elongation" within the context of the disclosure.

[0145] In one embodiment, the possible elongation of the polyurethane-based polymer fiber is from about 500% to about 800%, or from about 600% to about 700%.

[0146] In a further embodiment, the possible elongation of the polyurethane-based polymer fiber is about 650%.

[0147] Preferably, polyurethane-based polymer fiber has an excellent flat stretch / recovery determined by a 5TM100 / 5TP300 ratio of greater than 0.09.

[0148] Preferably, the polyurethane-based polymer when in fiber form has a SET% of less than 20, more preferably less than 16%.

[0149] In the context of the disclosure "elastomeric" usually refers to a polyurethane-based polymer that when in the form of a fiber has;

[0150] (i) an elongation at break of at least 300%, for example at least 400%, at least 500%, or at least 600%; and / or

[0151] (ii) a possible elongation of the fiber from about 500% to about 800%, or from about 600% to about 700%; and / or

[0152] (iii) flat stretch / recovery determined by a 5TM100 / 5TP300 ratio of greater than 0.09; and / or

[0153] (iv) a SET% of less than 20, more preferably less than 16%.

[0154] Antioxidant The binder of the disclosure further comprises an antioxidant, wherein the antioxidant is a compound comprising a sterically hindered amine or sterically hindered phenol group.

[0155] The antioxidant of the disclosure is preferably an oligomeric or polymeric compound comprising a sterically hindered amine or sterically hindered phenol group.

[0156] For instance, in a preferred embodiment, the antioxidant is a compound with a high molecular weight. For instance, the antioxidant may have a molecular weight of 1000 g / mol or more. For example, the antioxidant may have a molecular weight of 1100 g / mol or more, 1250 g / mol or more, or 1500 g / mol or more.

[0157] A high molecular weight prevents the antioxidant from migrating out of the cathode layer and into the electrolyte due to a strong interaction between the antioxidant and the polyurethane-based polymer binder.

[0158] Examples of oligomeric or polymeric antioxidant compounds comprise polyester, polyurethane or polyamide compounds and derivatives thereof.

[0159] The antioxidant of the disclosure comprises a sterically hindered amine or sterically hindered phenol. The term "sterically hindered" is given its common meaning in the art.

[0160] Steric hindrance occurs when the size of one or more substituents affect the chemical reactivity of other nearby substituents within the same molecule, for instance by making it more difficult for reactive species to approach the nearby substituent.

[0161] Sterically hindered phenols are physically shielded from the approach of reactants. Sterically hindered phenols comprise a tertiary or quaternary carbon in the ortho position(s) with respect to the phenol group. That is, when the phenol is in the 1 position, positions 2 and 6 are substituted with tertiary or quaternary carbons.

[0162] In the context of the disclosure, a secondary carbon is a carbon atom that is bonded to two other carbon atoms, a tertiary carbon is a carbon atom that is bonded to three other carbon atoms, and a quaternary carbon is a carbon atom that is bonded to four other carbon atoms. Thus, the central carbon in a tert-butyl group bonded to a phenyl ring would be a quaternary carbon, as it is attached to the phenyl ring (1 carbon) and three other carbon atoms (namely, the three methyl groups of the tert-butyl).

[0163] Similarly, sterically hindered amines are compounds in which the nitrogen atom of the amine molecule is physically shielded by neighbouring groups so that large molecules cannot easily approach and react with the nitrogen. For example, a sterically hindered amine may be a secondary amine in which the amino group is bonded to at least one secondary or tertiary carbon, or it may be a tertiary amine comprising sterically hindering substituents.

[0164] In the context of the disclosure, a secondary amine is an amine wherein the nitrogen atom is attached to two carbon atoms, and a tertiary amine is an amine wherein the nitrogen atom is bonded to three carbon atoms.

[0165] Accordingly, antioxidants according to the disclosure may comprise at least one of: a phenol comprising a tertiary or quaternary carbon in the position(s) ortho to the phenol group; a phenol comprising a long chain alkyl group (e.g. Cs-Cie), optionally containing an ether or thioether linkage (such as CFhOCs-Cie-alkyl or CFhSCs-Cie-alkyl); a secondary amine wherein the amino group is bonded to at least one tertiary carbon; a secondary amine wherein the amino group is part of a ring structure, wherein at least one ring carbon bonded to the amine group is a secondary or tertiary carbon; or a tertiary amine wherein the amino group is bonded to at least one alkyl group comprising at least 4 carbon atoms.

[0166] In some embodiments, the antioxidant is a sterically hindered phenol with a structure according to Formula (I) :

[0167]

[0168] Formula (I)

[0169] In Formula (I), A represents the remainder of the antioxidant molecule.

[0170] In Formula (I) at least one of Rxand R2denotes an alkyl or alkenyl group. Preferably both of R1and R2denote an alkyl or alkenyl group. R1and R2may be the same alkyl group, or they may be different.

[0171] To provide sufficient steric hindrance, preferably at least one of R1and R2denote an alkyl or alkenyl group comprising at least 4 carbon atoms (C4). For instance, the alkyl or alkenyl group may comprise a C4-C12 carbon chain.

[0172] The alkyl or alkenyl group may be linear, branched or in ring form.

[0173] Preferably, the alkyl group is a branched. In exemplary embodiments, R1and / or R2are branched alkyl groups independently selected from n-propyl, n-butyl, sec-butyl, isobutyl and tertbutyl.

[0174] In an exemplary embodiment, the antioxidant has a structure according to Formula (I) wherein:

[0175] R1and R2denote tert-butyl.

[0176] In some embodiments, the alkyl or alkenyl group of R1and / or R2comprises a heteroatom containing group, for example an O, S or N-containing group may be present in the form of an amide, ketone or ester substituent may be present, or the alkyl or alkenyl group of R1and / or R2may comprise a sulphur linkage.

[0177] For instance, the phenol may contain a long chain alkyl group (e.g. Cs-Cie-alkyl), optionally containing an ether or thioether linkage at a position ortho to the phenol group. Suitable substituents include Cs-Cie-alkyl, CFhOCs-Cie-alkyl, and CH2SC8-C16- alkyl.

[0178] The benzene ring of the sterically hindered phenol also comprises further substituents, denoted by A.

[0179] The group denoted by A must be suitable for use in a cathode e.g. preferably it does not degrade and / or negatively interact with the other cell components during use or storage. The chemical nature of the group denoted by A is not important other than that is it compatible for use in a cathode.

[0180] A may be bonded to the sterically hindered phenol at any vacant position on the ring. Preferably, the group denoted by A is bonded to the sterically hindered phenol in the position para to the phenol group.

[0181] In some embodiments, A denotes an organic chain that is oligomeric or polymeric. Examples of oligomeric or polymeric antioxidant compounds comprise polyester, polyurethane or polyamide compounds and derivatives thereof. Preferably the group denoted by A in such embodiments results in the antioxidant compound having a high molecular weight according to the disclosure.

[0182] In some embodiments, the antioxidant is a sterically hindered amine with a structure according to Formula (II):

[0183] Rt R3

[0184] R I5

[0185] Formula (II)

[0186] In Formula (II) both R4and R5denote alkyl or alkenyl groups. R4and R5may denote the same alkyl or alkenyl group, or they may denote different alkyl or alkenyl groups.

[0187] In some embodiments, R3is H. That is, the sterically hindered amine may be a secondary amine.

[0188] In some embodiments, R3also denotes an alkyl or alkenyl group. That is, the sterically hindered amine may be a tertiary amine. In such embodiments, R3may represent an organic chain that is oligomeric or polymeric and is therefore analogous to A of Formula (I) and Formula (III). That is, the nature of the R3group in such embodiments must be suitable for use in cathode e.g. preferably it does not degrade and / or negatively interact with the other cell components during use or storage. The chemical nature of the group is not important in such embodiments other than that is it compatible for use in a cathode.

[0189] Examples of oligomeric or polymeric antioxidant compounds comprise polyester, polyurethane or polyamide compounds and derivatives thereof. Preferably the group denoted by R3in such embodiments results in the antioxidant compound having a high molecular weight according to the disclosure.

[0190] R4and / or R5are preferably alkyl or alkenyl groups comprising at least 4 carbon atoms (C4). For instance, the alkyl or alkenyl group may comprise a C4-C12 carbon chain.

[0191] The alkyl or alkenyl group may be linear, branched or in ring form.

[0192] When the alkyl or alkenyl group is linear, preferably the sterically hindered amine is a tertiary amine. For instance, when R4and R5denote a linear alkyl or alkenyl group, R3is part of an alkyl or aryl ring. In some embodiments, the ring structure is aromatic and / or comprises heteroatoms. For instance, the ring may be a heterocycle comprising one, two or three heteroatoms. Preferably, the heteroatom is nitrogen.

[0193] In an exemplary embodiment, the antioxidant has a structure according to Formula (II), wherein:

[0194] R4and R5are linear C4 alkyl groups,

[0195] R3is part of an alkyl or aryl ring and wherein the compound of Formula (II) is a tertiary amine.

[0196] Preferably, when R4and / or R5are alkyl groups, the alkyl group is a branched. In exemplary embodiments, R4and / or R4are branched alkyl groups independently selected from n-propyl, n-butyl, sec-butyl, isobutyl and tertbutyl.

[0197] In some embodiments, the alkyl or alkenyl group comprises a hetero-atom containing group, for example an O or N-containing group may be present in the form of an amide, ketone or ester substituent as an example. In some embodiments, R4and R5combine to form a ring, for instance a five, six or seven-membered alkyl, alkenyl or aryl ring. In such embodiments, the amine may be a secondary or tertiary amine. Preferably R3is H when R4and R5combine to form a ring. That is, preferably the amine is a secondary amine when R4and R5combine to form a ring.

[0198] When R4and R5combine to form a ring, the carbon atom bonded to N in at least one of R4and R5is a secondary or tertiary carbon. Preferably, the carbon atom bonded to N in both R4and R5are tertiary carbons.

[0199] For example, if the ring is a 6-membered alkyl ring formed from R4and R5, the carbon atoms bonded to N in one or both of R4and R5may comprise an alkyl or alkenyl substituent. Preferably, the carbon atoms bonded to N in both of R4and R5comprise an alkyl or alkenyl substituent. Even more preferably, when the ring is an alkyl ring formed from R4and R5, the carbon atoms bonded to N of both of R4and R5comprise two alkyl or alkenyl substituents, wherein most preferably both comprise two alkyl substituents.

[0200] Preferably the alkyl or alkenyl substituent comprises a C1-C4 carbon chain.

[0201] Preferably the alkyl substituent is branched. For instance, the alkyl substituent may be n-propyl, n-butyl, sec-butyl, isobutyl and tertbutyl.

[0202] Preferably, when R4and R5combine to form a ring, each carbon atom in R4and R5bonded to N comprises the maximum number of alkyl or alkenyl substituents. For example, when R4and R5combine to form a ring, each of the positions in R4and R5bonded to N may comprise two substituents. Alternatively, when R4and R5combine to form a ring, each of the positions in R4and R5bonded to N may comprise one substituent.

[0203] In an exemplary embodiment, the antioxidant has a structure according to Formula (II), wherein:

[0204] R4and R5combine to form a 6-membered alkyl ring, wherein both R4and R5are tertiary carbons each comprising two methyl groups (with the remaining carbon substituents being the alkylene chains that combine to form the ring).

[0205] For instance, the antioxidant may have a structure according to Formula (III) :

[0206]

[0207] Formula (III)

[0208] In Formula (III), A represents the remainder of the antioxidant molecule.

[0209] As with the sterically hindered phenols with a structure according to Formula (I), the group denoted by A must be suitable for use in a cathode e.g. preferably it does not degrade and / or negatively interact with the other cell components during use or storage. The chemical nature of the group denoted by A is not important other than that is it compatible for use in a cathode.

[0210] For instance, A may denote an organic chain that is oligomeric or polymeric. Examples of oligomeric or polymeric antioxidant compounds comprise polyester, polyurethane or polyamide compounds and derivatives thereof. Preferably the group denoted by A in such embodiments results in the antioxidant compound having a high molecular weight according to the disclosure.

[0211] The bond between A and the sterically hindered amine may be at any vacant position on the sterically hindered amine. Preferably, the bond between A and the sterically hindered amine is at the 4-position relative to the amine group, in embodiments wherein R4and R5combine to form a 6-membered ring.

[0212] Preferably, the antioxidant comprises a plurality of sterically hindered amine and / or sterically hindered phenol groups. Taking Formula (III) as an example, the group denoted by A may therefore be an oligomeric or polymeric group that comprises a further sterically hindered amine or sterically hindered phenol group.

[0213] Surprisingly, antioxidants according to the disclosure can bind leached transition metals. Without wishing to be bound by theory, antioxidants according to the disclosure bind transition metals such as Ni, Co and Mn from the cathode active material thereby preventing leaching of the metals and breakdown of the cathode. Accordingly, providing a cathode comprising an antioxidant provides a cell with improves electronic properties and improved thermal stability as shown in the Examples. Specifically, the binders comprising an antioxidant of the disclosure provide improved initial coulombic efficiency, improved electrical conductivity (reduced DCIR), and improved capacity retention under cycling.

[0214] Typically, the binding between the antioxidant and the transition metal forms an antioxidant-transition metal complex in which the antioxidant and the transition metal are strongly bound. This is beneficial as it is less likely that the transition metal is released during battery operation. However, this also means that once a complexation occurs at a particular site, said site is no longer able to bind further transition metals. It is therefore beneficial to provide multiple binding sites per antioxidant compound to ensure that sufficient transition metals are bound.

[0215] Preferably, the antioxidant has multiple transition metal binding sites. Such antioxidants may be described as multi-faceted or multi-dentate binding sites.

[0216] In some embodiments, the antioxidant is an oligomeric or polymeric compound. An oligomeric or polymeric structure allows for the antioxidant to be securely lodged within the polyurethane-based polymer binder and also have transition metal binding sites protruding into the electrolyte. This provides excellent and secure binding of leached transition metals.

[0217] In an embodiment, the antioxidant is an oligomeric or polymeric compound that is multidentate.

[0218] Exemplary antioxidants are compounds with the following structures:

[0219]

[0220] Exemplary antioxidants include those sold under the registered trade names Irganox® 1098, Irganox 1726®, Chimassorb® 2020, Tinuvin® 770, Tinuvin® 622, Tinuvin® 249, however any suitable antioxidant can be used.

[0221] Preferably, the binder comprises 0.1-10wt% antioxidant. For instance, binder may comprise 0.1-5wt%, 0.1-3wt%, 0.2-3wt% antioxidant, 0.3 to 3 wt% antioxidant, 0.5 to 3 wt% antioxidant, 1 to 2.5 wt% antioxidant, or 1.5 to 2.5 wt% antioxidant.

[0222] The antioxidant may be one compound, or it may be a mixture of different antioxidant compounds.

[0223] For instance, the antioxidant may comprise two compounds in a weight ratio of from 20:80 to 80:20, for instance 30:70 to 70:30, such as 40_60 to 60:40, such as about 50:50. Preferably, when the antioxidant comprises a mixture of antioxidant compounds, wherein the antioxidant comprises at least 50 wt% of an antioxidant with a high molecular weight, more preferably at least 60 wt%, such as at least 70 wt% or even at least 80 wt%. That is, the antioxidant may comprise a mixture of compounds wherein at least 50 wt% is made up of a compound with a molecular weight of 1000 g / mol or more, for example 1100 g / mol or more, 1250 g / mol or more, or 1500 g / mol or more.

[0224] In some embodiments, the binder further comprises a secondary antioxidant compound. In the context of the disclosure, a secondary antioxidant is a compound that can regenerate the antioxidant of the disclosure.

[0225] As discussed above, upon binding a transition metal, the antioxidant of the disclosure is consumed and can no longer bind further metal ions. The role of a secondary antioxidant compound is to regenerate the antioxidant so that it can once again bind transition metals.

[0226] An example of a suitable secondary antioxidant is a phosphite compound or "phosphite antioxidant". Phosphite antioxidants are particularly effective at reviving antioxidants comprising sterically hindered phenols.

[0227] An example of a suitable secondary antioxidant is 2,2'-methylenebis (4,6-di-tert- butylphenyl) octylphosphite (CAS no. 126050-54-2).

[0228] Exemplary antioxidants are those sold under the registered trade names ADK STAB HP 10 ®, Irganox PS 800 FL®, Irfanos 126®, Irganox 1726®.

[0229] In an embodiment is a binder comprising : a polyurethane-based polymer; and an antioxidant, wherein the antioxidant is a compound comprising a sterically hindered phenol or a sterically hindered amine; and a secondary antioxidant, wherein the secondary antioxidant is a phosphite antioxidant.

[0230] Particularly advantageous combinations of antioxidant and secondary antioxidant include:

[0231] • Irganox 1726® and Irganox 1098®;

[0232] • Irgafos 126® and Irganox 1098®; and Irganox PS 800 FL® and Irganox 1098.

[0233] In some embodiments, the same compound may act as a primary and secondary antioxidant. That is, in some embodiments, the antioxidant is self-regenerative. An example of such an antioxidant is the compound sold under the trade name Irganox 1726®.

[0234] By including a secondary antioxidant, improved transition metal binding may be achieved. In some instances, less of the antioxidant needs to be included in the cathode due to the improved transition metal binding properties.

[0235] In some embodiments, the secondary antioxidant may lead to a further improved thermal stability of the binder.

[0236] In an embodiment is a composition for a cathode comprising a polyurethane-based polymer, an antioxidant, a cathode active material and optionally a conductive material.

[0237] Preferably, the conductive material comprises CNT, CNF, graphene, carbon black, or a combination thereof.

[0238] The cathode active material may comprise active material selected from at least one of nickel manganese cobalt oxide (NMC), lithium iron phosphate (LFP), nickel cobalt manganese aluminum (NMCA), lithium manganese nickel oxide (LMNO), or a lithium manganese oxide (LMO).

[0239] Preferably, the cathode active material is a transition metal complex such as layered lithium metal oxide (LiMO?) cathode materials, wherein the metal is typically nickel. Even more preferably, the cathode active material is a lithium nickel manganese cobalt oxide (NMC), such as a high nickel lithium nickel manganese cobalt oxide (high Ni NMC) or lithium rich lithium nickel manganese cobalt oxide (Li rich NMC).

[0240] In some embodiments, the cathode active material comprises lithium nickel cobalt manganese oxides (NMC) (LibNii x-yCoxMnyAzO? (0<x+y< 1)), where A is an element other than Li, Ni, Co, Mn or O and wherein 0<z<0.05, preferably 0<z<0.03, more preferably 0.001<z<0.01, and wherein 0.9<b< 1.2. A is one or more chosen from the group Al, B, Zr, Ba, Ca, Ti, Mg, Ta, Nb, V, Fe, Ru, Re, Pt and Mo. Preferably, A is chosen from the group Al and Zr. In preferred embodiments, the NMC cathode materials are lithium rich. As such, the cathode active material typically comprises lithium nickel cobalt manganese oxides (NMC) represented by the formula LibNii-x-yCoxMnyAzO2 (0<x+y< l), where A is an element other than Li, Ni, Co, Mn or O and wherein 0<z<0.05, preferably 0<z<0.03, more preferably 0.001<z<0.01, and wherein 1.05<b< 1.2. A is one or more chosen from the group Al, B, Zr, Ba, Ca, Ti, Mg, Ta, Nb, V, Fe, Ru, Re, Pt and Mo. Preferably, A is chosen from the group Al and Zr.

[0241] In preferred embodiments, the NMC cathode materials are high in nickel. As such, the cathode active material typically comprises lithium nickel cobalt manganese oxides (NMC) represented by the formula LibNii-x-yCoxMnyAzO2, wherein 0<x+y<0.4, preferably 0<x+y<0.25, and wherein 0<z<0.05, preferably 0<z<0.03, more preferably 0.001<z<0.01, and wherein 0.9<b< 1.2. A is one or more chosen from the group Al, B, Zr, Ba, Ca, Ti, Mg, Ta, Nb, V, Fe, Ru, Re, Pt and Mo. Preferably, A is chosen from the group Al and Zr.

[0242] The ratio of the nickel of the high-nickel NMC material may range from 33 mol% to 98 mol %. Preferably, the ratio may range from 60 mol% to 95 mol%. Even more preferably, the ratio may range from 80 mol% to 95 mol%.

[0243] In preferred embodiments, the NMC cathode materials is defined as LibNii-x-yCoxMnyAzO2, wherein 0<x+y<0.4, preferably 0<x+y<0.25, and wherein 0<z<0.05, preferably 0.002<z<0.03, more preferably 0.001<z<0.01, and wherein 0.9<b< l. l. A is one or more chosen from the group Al, B, Zr, Ba, Ca, Ti, Mg, Ta, Nb, V, Fe, Ru, Re, Pt and Mo. Preferably, A is chosen from the group Al and Zr.

[0244] In some embodiments, the composition for a cathode is a slurry and further comprises a solvent such as NMP or NBP.

[0245] The slurry may be used to prepare a cathode.

[0246] That is, in an embodiment, is a method for preparing a cathode comprising a binder according to the disclosure, the method comprising :

[0247] • providing a cathode active material, a polyurethane-based polymer, an antioxidant, optionally HNBR and optionally a conductive additive; • dispersing the cathode material, polyurethane-based polymer, antioxidant, optional HNBR and optional conductive additive in a solvent to form a slurry;

[0248] • coating a substrate with the slurry; and

[0249] • removing the solvent.

[0250] When the composition for a cathode is a slurry, the HNBR (when present) may be considered a dispersant for the components of the slurry or the components of the binder.

[0251] In a third aspect, the present disclosure relates to a cathode for a secondary cell comprising a cathode binder wherein the binder comprises a polyurethane-based polymer and an antioxidant.

[0252] Typically, the conductive material is present in the cathode from 0.1 to 3 wt%, such as from 0.1 to 2 wt%, or from 0.2 to 1.5 wt%, such as from 0.3 to 1.2 wt%.

[0253] Typically, the cathode binder is present in the cathode from 0.1 to 3 wt%, such as from 0.1 to 2 wt%, or from 0.2 to 1.5 wt%, such as from 0.3 to 1.2 wt%.

[0254] Typically, the cathode active material is present in the cathode from 94 to 99.8 wt%, such as from 96 to 99.8 wt%, or from 97 to 99.6 wt%, such as from 97.6 to 99.4 wt%.

[0255] In one embodiment, the cathode is an NMC-, LFP-, NMCA-, LMNO-, or an LMO-cathode, preferably an NMC- or LFP- cathode, more preferably an NMC-cathode.

[0256] The cathode may have a surface layer comprising a thin layer comprising an inert material selected from the group consisting of Al, B, Cu, AI2O3, TiO?, ZnO, LiF, La2Os, NbO2, ZrO2, IJ2O, HfO2, GaO2, GeO2, CeO2 , MgO, CaO, AIF3, IJAIF4, MgF2, Zn2<3F2, LisFO, LiCFs, Li3N, TiN, U2CO3, CaCO3, ZnCO3, La2(CO3)3, Nb(CO3)2, MgCO3, U2S, ZnS, GaS2, TiS2, NbS2, HfS2, CaS, La2S3, BaSO4, U3PO4, AIPO4, WF4, W(PO4)2, SiO2, SiC, Si, carbon, or mixtures of any two or more thereof. In some embodiments, the inert material comprises a hafnium oxide, lithium hafnium oxide, a lithium fluoride-lithium carbonate composite, or composite materials containing LiF, La2Os, NbC>2, ZrC>2, Li2<D, G GaC>2, GeO2, CeO2, MgO, CaO, AIF3, LiAIF4, MgF2, Zn2OF2, Li3FO, LiCFs, Li3N, TiN, U2CO3, CaCO3, ZnCO3, La2(CO3)3, Nb(CO3)2, MgCO3, Li2S, ZnS, GaS2, TiS2, NbS2, HfS2, CaS, La2Ss, BaSO4, U3PO4, AIPO4, WF4, W(PO4)2, lithium niobium oxides, lithium hafnium oxides and lithium lanthanum oxides, lithium silicon oxide, or lithium aluminum phosphate (LixAly(PO4)z), or mixtures of any two or more thereof.

[0257] As stated above, the polyurethane-based polymer, for instance spandex fibers, used in the present disclosure are environmentally benign compared to other binder components, such as fluorinate PVDF or PTFE. Replacing those fluorinated binder components to a polyurethane-based polymer such as spandex is an improvement of the environment at large, but also an improvement of the working environment during assembly of the cells. In addition, the polyurethane-based polymer such as spandex fibers may be produced from recycled materials using much cheaper processes as compared to the production of the PVDF or PTFE.

[0258] Solvent

[0259] In addition, the inventors have found that the process for preparing the cathode material may be significantly improved as well, such as by using less toxic components. The cathode material of the present disclosure may be prepared by dispersing the cathode material in a safe solvent such as l-butylpyrrolidin-2-one (NBP), rather than in the conventional solvent / V-methyl-2-pyrrolidone (NMP). The process improvements of this substitution are large. Not only does the polyurethane-based polymer such as spandex disperse significantly quicker in the safe solvents such as NBP than PVDF does in NMP, safe solvents also provide a number of other benefits. For example, NBP is also considered non-toxic, biodegradable and has a lower volatility compared to NMP. Furthermore, NMP has been classified as a developmental- or geno-toxic solvent that is facing increasing regulatory pressure. The main benefit of NBP is its non-toxic nature, greatly improving the working environment and reducing costs for precautionary measures that otherwise needs to be taken.

[0260] A secondary cell comprising a binder according to the present disclosure and prepared by using NBP will considerably increase its sustainability.

[0261] Thus, in a fourth aspect, the present disclosure relates to a method for preparing a cathode comprising a binder, wherein the binder comprises a polyurethane-based polymer and an antioxidant, and wherein the method comprises dispersing a cathode material comprising said binder and a conductive material in a solvent such as NBP, followed by coating a substrate and removing the solvent. In a fifth aspect, the present disclosure relates to a secondary cell comprising an anode, a cathode, an electrolyte, and optionally a separator, characterized in that the secondary cell further comprises a cathode binder and a conductive material, wherein the binder comprises a polyurethane-based polymer and an antioxidant.

[0262] The electrolyte used in the secondary cell according to the present disclosure is a liquid electrolyte comprising at least one lithium salt and at least one or more solvents selected from the group consisting of carbonate solvents and their fluorinated equivalents, diCi- 4 ethers and their fluorinated equivalents and ionic liquids. The lithium salt is preferably one or more selected from the group consisting of lithium hexafluorophosphate (LiPFe), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium (fluorosulfonyl) (trifluoromethanesulfonyl) imide (LiFTFSI), lithium bis(pentafluoroethanesulfonyl)imide (LiBETI), lithium

[0263] (pentafluoroethanesulfonyl)(trifluoromethanesulfonyl)imide (LiPTFSI), lithium trifluoromethanesulfonate (LiOTf), lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiDFOB), lithium difluorobis(oxalato)phosphate (LiDFOP), lithium tetrafluoro(oxalato)phosphate (LiTFOP), lithium tetrafluoroborate (UBF4), lithium nitrate (LiNOs) lithium 2-trifluoromethyl-4,5-dicyanoimidazole (LiTDI). In one embodiment, the solvent is selected from the group consisting of 1,2-dimethoxyethane (DME), / V-propyl- / V-methylpyrrolidinium bis(fluorosulfonyl)imide (PYR13-FSI), / V-propyl- / V-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR13-TFSI), 1-butyl-l- methylpyrrolidinium bis(fluorosulfonyl)imide (PYR14-FSI), 1-butyl-l- methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR14-TFSI), l-ethyl-3- methylimidazolium bis(fluorosulfonyl)imide (EMIM-FSI), l-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMIM-TFSI). The solvent is preferably one or more selected from dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), ethylene carbonate (EC), and propylene carbonate (PC), and their fluorinated equivalents.

[0264] In one embodiment, the secondary cell comprises an NMC cathode.

[0265] In a further aspect, the present disclosure relates to a vehicle comprising a secondary cell according to the fifth aspect of the present disclosure.

[0266] As used herein, the term "about" refers to a value or parameter herein that includes (and describes) embodiments that are directed to that value or parameter per se. For example, description referring to "about 50" includes description of "50." Numeric ranges are inclusive of the numbers defining the range. Generally speaking, the term "about" refers to the indicated value of the variable and to all values of the variable that are within the experimental error of the indicated value (e.g., within the 95% confidence interval for the mean) or within 10 percent of the indicated value, whichever is greater.

[0267] All aspects and embodiments disclosed herein can be combined with any other aspect and / or embodiment disclosed herein.

[0268] EXAMPLES

[0269] Example 1. Transition metal elution

[0270] The elution of transition metals from the cathodes was investigated using NMC cathodes comprising a polyurethane-based polymer binder (referred to herein as spandex) with and without an antioxidant according to the disclosure. A cathode comprising PVDF binder was used as a reference. Three half cells comprising the three difference cathodes and lithium metal counterparts were prepared, which will be referred to as NMC-SPDX- AO, NMC-SPDX and NMC-REF respectively.

[0271] The three coin half cells were charged to 4.3 V, and then stored for 2 weeks at 70 °C, after which measurements were made using inductively coupled plasma mass spectrometry (ICP MS), the results of which are shown in Table 1.

[0272] Table 1. Percentage metal dissolution from cathodes.

[0273] Figure 1 shows a graph of results of Table 1.

[0274] As can be seen from both Table 1 and Figure 1, both cathodes comprising polyurethane- based polymer outperforms the reference sample comprising PVDF binder. That is, the polyurethane-based polymer binder reduces metal elution during storage compared to a PVDF binder. The effect of reduced metal elution for the polyurethane-based polymer vs PVDF is greatest for cobalt, and the smallest effect is seen for manganese. The effect is however significant for all metals tested. Surprisingly, including an antioxidant in the cathode further decreases the degree of metal elution when the binder comprises a polyurethane-based polymer. The effect is seen across all three metals, however it is particularly significant for manganese. This is highly beneficial as a binder comprising polyurethane-based polymer without an antioxidant is least effective for preventing metal elution.

[0275] Example 2. Initial coulombic efficiency

[0276] The initial coulombic efficiency (ICE) is a parameter associated with the amount of redundant cathode materials in a cell. A high initial coulombic efficiency is associated with a low amount of redundant material.

[0277] The ICE of NMC REF, NMC-SPDX and NMC-SPDX-AO were tested, the results of which is shown in Table 2 below.

[0278] Table 2. ICE for cathodes.

[0279] Table 2 demonstrates that a binder comprising polyurethane-based polymer and an antioxidant provides an excellent ICE and is therefore indicative of a highly efficient cathode material. That is, when a polyurethane-based polymer is used as the binder, the amount of cathode active material available for use is increased. This effect is enhanced by also including an antioxidant in the composition. Without wishing to be bound by theory, this is likely due to a decreased degree of metal elution for cathodes comprising and antioxidant leading to improved electrochemical availability.

[0280] Example 3. DCIR

[0281] The direct current internal resistance (DC IR) of a cell is indicative of the electronic properties. Internal resistance is one of the parameters that indicate a battery's ability to carry current. When the value of internal resistance is low, the battery is able to carry a significant amount of current. On the other hand, a battery with high internal resistance can only carry a small amount of current. Accordingly, a low DCIR is desirable.

[0282] The DCIR of NMC REF, NMC-SPDX and NMC-SPDX-AO was tested, the results of which is shown in Table 2 below.

[0283] Table 3. DCIR for cathodes

[0284] As can be seen from Table 3, using a polyurethane-based polymer binder instead of PVDF provides a decreased DCIR. Without wishing to be bound by theory, this is considered to be because of the excellent distribution and binding of particles in the cathode.

[0285] In addition, including an antioxidant in the cathode further decrease the DCIR leading to a further improved cell. Without wishing to be bound by theory, this is likely due to a decreased degree of metal elution for cathodes comprising and antioxidant leading to improved electronic properties of the cathode active material.

[0286] Example 4. Capacity retention

[0287] Capacity retention is a measure of the lifetime of a cell with respect to performance. In order to provide batteries with excellent lifetimes, thereby reducing the need to replace batteries, a high capacity retention is required. The capacity retention of NMC-REF, NMC-SPDX and NMC-SPDX-AO cells was tested. Table 4 and Figure 2 shows the capacity retention of each of the samples after 50 cycles at a temperature of 45°C.

[0288] As can be seen, providing a binder comprising polyurethane-based polymer increases the capacity retention of a cathode. This is thought to be due to the elastic properties protecting the cathode active material for degradation during cycling. In addition, including an antioxidant in the binder further improved the properties. This is thought to be due to the prevention of metal dissolution during the 50 cycles leading again to less material degradation during use.

[0289] Accordingly, providing an antioxidant in a cathode is shown to increase battery lifetime. Table 4. Capacity retention for cathode

Claims

CLAIMS1. A cathode for a secondary cell comprising a cathode binder, wherein the binder comprises a polyurethane-based polymer and an antioxidant, wherein the polyurethane-based polymer is a polyurethane or polyurethane urea, and wherein the antioxidant is a compound comprising a sterically hindered amine or sterically hindered phenol group.

2. The cathode according to claim 1, wherein the polyurethane-based polymer comprises segments of polyether and polyurea, and that has a molecular weight ratio of the soft segment to the hard segment larger than 12.0, and a urea hard segment weight percent less than 7.8.

3. The cathode according to any preceding claim, wherein the antioxidant has a molecular weight of 1000 g / mol or more.

4. The cathode according to any preceding claim, wherein the antioxidant comprises at least one of a phenol comprising a tertiary or quaternary carbon in the position(s) ortho to the phenol group; a phenol comprising a long chain alkyl group (e.g. Cs-Cie), optionally containing an ether or thioether linkage (such as ChhOCs-Cie-alkyl or ChhSCs-Cie-alkyl); a secondary amine wherein the amino group is bonded to at least one tertiary carbon; a secondary amine wherein the amino group is part of a ring structure, wherein at least one ring carbon bonded to the amine group is a secondary or tertiary carbon; or a tertiary amine wherein the amino group is bonded to at least one alkyl group comprising at least 4 carbon atoms.

5. The cathode according to any preceding claim, wherein the binder further comprises a secondary antioxidant compound.

6. The cathode according to any preceding claim, wherein the binder further comprises HNBR.

7. The cathode according to any preceding claim, wherein the binder comprises (or consists of)from about 95 wt% to about 99.9 wt% polyurethane-based polymer; from about 0.1 to 3 wt% antioxidant; optionally from about 0.1 wt% to about 2 wt% HNBR; optionally up to 3 wt% lubricant such as PDMS or clay.

8. The cathode according to any preceding claim, wherein the cathode further comprises a conductive material selected from CNT, CNF, graphene, carbon black, or a combination thereof.

9. The cathode according to any preceding claim, wherein the cathode further comprises a cathode active material selected from at least one of nickel manganese cobalt oxide (NMC), lithium iron phosphate (LFP), nickel cobalt manganese aluminum (NMCA), lithium manganese nickel oxide (LMNO), or a lithium manganese oxide (LMO).

10. The cathode according to claim 9, wherein the cathode active material is a lithium nickel cobalt manganese oxides (NMC) represented by the formula LibNii-x-yCoxMnyAzO2, wherein 0<x+y<0.4, wherein 0<z<0.05, wherein 0.9<b<1.2, and wherein A is one or more chosen from the group Al, B, Zr, Ba, Ca, Ti, Mg, Ta, Nb, V, Fe, Ru, Re, Pt and Mo.

11. A secondary cell comprising the cathode of any preceding claim.

12. A vehicle comprising the secondary cell according to claim 11.

13. A method for preparing a cathode according to any one of claims 1-10, comprising providing a cathode material, a polyurethane-based polymer, optionally HNBR and optionally a conductive additive; dispersing the cathode material, polyurethane-based polymer, optional HNBR and optional conductive additive in a solvent such as l-butylpyrrolidin-2-one (NBP) to form a slurry; coating a substrate with the slurry; and removing the solvent.

14. A cathode binder comprising (or consisting of) from about 95 wt% to about 99.9 wt% polyurethane-based polymer; from about 0.1 to 3 wt% antioxidant, wherein the antioxidant is a compound comprising a sterically hindered amine or sterically hindered phenol group; optionally from about 0.1 wt% to about 2 wt% HNBR;optionally up to 3 wt% lubricant such as PDMS or clay.

15. The cathode binder of claim 14, wherein the antioxidant is as defined in any one of claims 3-6.

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