Secondary cell having low cobalt cathode active material and HF-gettering agent

Abstract

The present disclosure relates to secondary lithium-ion cells suitable for use at high voltage. The cells comprise a cathode active material which is stabilised by an HF gettering agent.

Description

[0001] SECONDARY CELL HAVING LOW COBALT CATHODE ACTIVE MATERIAL AND HF- GETTERING AGENT

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to secondary lithium-ion cells containing low cobalt cathode active material that have good cycle life.

[0004] BACKGROUND

[0005] Rechargeable or 'secondary' batteries find widespread use as electrical power supplies and energy storage systems. For example, in automobiles, battery packs formed of a plurality of battery modules, wherein each battery module includes a plurality of electrochemical cells, are provided as a means of effective storage and utilization of electric power.

[0006] Secondary cells such a lithium-ion cells comprise a positive active material, or "cathode active material", and a negative active material or "anode active material" that form the electrochemically active components of the cathode and anode, respectively.

[0007] Exemplary cathode active materials (CAM) include layered lithium metal oxide (LiMO?) intercalation materials, preferably wherein the metal is nickel. For example, lithium nickel manganese cobalt oxide (NMC) is a possible cathode active material for high-energy lithium-ion batteries. An alternative to traditional NMC chemistry and high-nickel cells is the use of CAMs based mainly on nickel-manganese cell chemistry. This technology is also known as NMX and is free from cobalt, which makes the cells more sustainable and cheaper than traditional NMC-containing cells.

[0008] High voltage lithium-ion batteries have been extensively studied to increase energy density of batteries. Investigations have included CAMs based on both conventional high-nickel NMC and more recently based on NMX technology. However, stability of the CAM under repeated charge and discharge is an ongoing challenge. Typically, the stability at high voltage is poor, despite various strategies being proposed to overcome the issues of high- potential cathodes.

[0009] Hence, there is a need to provide secondary lithium-ion cells with improved stability particularly at high voltage. In particular, it would be advantageous to provide secondary lithium-ion cells with increased discharge rate and longer cycle life. SUMMARY

[0010] The present disclosure relates to a secondary lithium-ion cell with improved performance particularly at high voltage. The cell comprises a cathode active material (CAM) comprising an intercalation material with a high content of manganese (Mn) compared to cobalt (Co) and a hydrofluoric acid (HF) getterer to keep the CAM stable during cycling and storage. In particular, leaching of Mn from the CAM is surprisingly efficiently reduced, thereby mitigating the gradual deterioration of the cell and resulting in improved initial discharge rate and improved cycle life.

[0011] Thus, an object of the present disclosure relates to provision of a secondary lithium-ion cell with improved performance and cycle life, particularly when operated at high voltage.

[0012] Moreover, it is an object of the present disclosure to provide a cheaper and more sustainable secondary lithium-ion cell.

[0013] Thus, an aspect of the present disclosure relates to a secondary lithium-ion cell comprising: a fluorine-containing electrolyte, a separator, an anode, a cathode comprising a cathode active material (CAM), and a hydrogen fluoride (HF) gettering agent, wherein the CAM comprises a material represented by the formula LibNii-x-yCOxMnyAzO2, wherein 0<x+y<0.4, 0<z<0.05, and 0.9<b< 1.2, wherein the ratio y / x is at least 1, and wherein A is one or more chosen from the group consisting of Al, B, Zr, Ba, Ca, Ti, Mg, Ta, Nb, V, Fe, Ru, Re, Pt, Mo and W.

[0014] Another aspect of the present disclosure relates to a battery comprising a plurality of secondary lithium-ion cells as described herein.

[0015] Yet another aspect of the present disclosure relates to a vehicle comprising the secondary lithium-ion cell or the battery as described herein.

[0016] A still further aspect of the present disclosure relates to a method for preparing a secondary lithium-ion cell as described herein, said method comprising the steps of:

[0017] (i) providing a separator, an anode, a fluorine-containing electrolyte, an HF gettering agent, and a cathode comprising a cathode active material (CAM), and (ii) assembling the secondary lithium-ion cell.

[0018] An even further aspect of the present disclosure relates to use of a hydrogen fluoride (HF) gettering agent for improving the cycle life efficiency (or the capacity retention), and / or the initial discharge capacity of a lithium-ion cell, and / or for reducing manganese leaching in a lithium-ion cell, said cell comprising a fluorine-containing electrolyte and a cathode active material represented by the formula

[0019] LibNii-x-yCOxMnyAzO2, wherein 0<x+y<0.4, 0<z<0.05, and 0.9<b< 1.2, wherein the ratio y / x is at least 1, and wherein A is one or more chosen from the group consisting of Al, B, Zr, Ba, Ca, Ti, Mg, Ta, Nb, V, Fe, Ru, Re, Pt, Mo and W.

[0020] BRIEF DESCRIPTION OF THE FIGURES

[0021] Figure 1 shows capacity retention as a function of cycle number of coin half cells (A) or prismatic cells (B) comprising a CAM mixture of 20% high-nickel and 80% high-manganese intercalation materials (Reference) or a CAM of 100% high-manganese intercalation material (NMX).

[0022] Figure 2 shows discharge capacity retention as a function of cycle number for prismatic cells comprising a CAM mixture of 20% high-nickel and 80% high-manganese intercalation materials with (light grey) or without (dark grey) the addition of a HF gettering agent.

[0023] The present disclosure will in the following be described in more detail.

[0024] DETAILED DESCRIPTION

[0025] Definitions

[0026] Prior to outlining the present disclosure in more details, a set of terms and conventions is first defined:

[0027] Hydrogen fluoride (HF) gettering agent

[0028] In the present context, the term "HF gettering agent" relates to an entity which interacts chemically with hydrogen fluoride (HF) to remove it from a solution, such as an electrolyte solution. The HF gettering may interact with HF to form covalent or non-covalent complexes. In electrochemical cells, HF may form if a fluorine-containing electrolyte (particularly an electrolyte comprising LiPFe) comes into contact with any residual moisture in the cell. Hydrofluoric acid is a solution of hydrogen fluoride in water. Accordingly, the terms "hydrogen fluoride" and "hydrofluoric acid" may be used interchangeably herein, to denote any presence of HF in the electrochemical cell.

[0029] Fluorin e-containing electrolyte

[0030] In the present context, the term "fluorine-containing electrolyte" means an electrolyte system, which typically comprises a solvent, lithium salt and optional electrolyte additives) which contains a moiety having a fluorine atom. The moiety may be a lithium salt (Such as LiPFe), a solvent or an electrolyte additive.

[0031] The fluorine-containing electrolyte is preferably an electrolyte comprising LiPFe.

[0032] High-manganese

[0033] In the present context, the term "high-manganese" refers to an intercalation material or an electrochemical cell comprising the same, which have higher content of manganese than cobalt. Thus, for an intercalation material of the formula LibNii-x-yCOxMnyAzO2, a high- manganese version may be a ratio of y / x> l. High-manganese intercalation materials also include materials which are completely devoid of cobalt.

[0034] It is to be understood that a high-manganese intercalation material typically still comprises more nickel than manganese. In other words, in the above formula, 0 < x+y < 0.4, preferably 0 < x+y < 0.25. That is, preferably the high-manganese intercalation material comprises at least 60mol% nickel.

[0035] Mean particle size

[0036] In the present context, the term "mean particle size" refers to the d50 value of the population of particles, e.g. glass particles. The d50 value sets the value at which 50% of the particles within the population have a diameter below this value.

[0037] The particle diameter reported herein is preferably a d[4,3]diameter as measured by laser diffraction. Suitable apparatus for measuring the mean particle size include Malvern Mastersizer 3000.

[0038] High voltage

[0039] In the present context, the term "high voltage" when used in reference to a cell or battery refers to cells or batteries cycled at higher voltages than regular operating conditions for comparable electrochemical cells with NMC-based CAMs and graphite anodes. In particular, high voltage may be considered to be >4.3 V.

[0040] Capacity retention

[0041] In the present context, the term "capacity retention" refers to a value that is used to quantify cycle life. The capacity retention is given in percentage as the ratio of the discharge capacity after X cycles to the initial discharge capacity (after formation and preconditioning cycles).

[0042] About

[0043] Wherever the term "about" is employed herein in the context of amounts, for example absolute amounts, such as numbers, purities, concentrations, weights, sizes, etc., or relative amounts (e.g. percentages, equivalents or ratios), timeframes, and parameters such as temperatures, pressure, etc., it will be appreciated that such variables are approximate and as such may vary by ±10%, for example ± 5% and preferably ± 2% (e.g. ± 1%) from the actual numbers specified. This is the case even if such numbers are presented as percentages in the first place (for example 'about 10%' may mean ±10% about the number 10, which is anything between 9% and 11%).

[0044] Secondary lithium-ion cells

[0045] High voltage lithium-ion cells are an interesting route to expand the energy density of batteries but come with the challenge to provide enough stability to maintain long cycle life. Herein are described secondary lithium-ion cells with a cathode active material (CAM) comprising a high-manganese intercalation material that can handle high voltage and at the same time remain stable due to the inclusion of an HF gettering agent.

[0046] NMX materials without cobalt are known to be suitable cathode active materials for batteries operating at high voltage. However, there is still room for improvement of these types of cells, and knowledge relating to stability of cells with high content of manganese is scarce. The inventors tested CAMs comprising a high-manganese intercalation materials and found that the materials performed well in coin half-cells (Example 1, figure 1A). However, the desired performance surprisingly could not be transferred to a full cell (prismatic cell) setup for unknown reasons (Example 1, figure IB).

[0047] In one of many attempts to remedy the inability to prepare an efficient prismatic cell with a CAM comprising the high-manganese intercalation material, the inventors tried introducing an agent that could stabilize the cell by limiting the amount of HF formed as the fluorine-containing electrolyte (or component therein such as LiPFe) reacts with residual moisture in the cell. The introduction of a HF gettering agent surprisingly resulted in both markedly better cycle life and improved initial discharge capacity.

[0048] Without being bound by theory, it is contemplated herein that corrosion and dissolution of the CAM caused by HF is unexpectedly high when using a high-manganese intercalation material. It is postulated that leaching of manganese and / or nickel from the high- manganese intercalation material leads to a direct depletion of material on the cathode and possibly migration and deposition of manganese and / or nickel on the anode. Together these effects could induce impedance and reduce cyclability of the cell. These negative consequences could be further enhanced at high voltage and elevated temperatures.

[0049] Intercalation materials according to the disclosure wherein the y / x ratio is at least 1 are further surprisingly vulnerable to manganese leaching due to an increase in the number of unstable manganese sites.

[0050] Hydrogen fluoride (HF) can catalyse the conversion of Mn(III) to Mn4+and Mn2+ions. The Mn4+ions are insoluble and may deposit on the cathode, leading to interface impedance of the solid electrolyte interphase (SEI). Mn2+ions, on the other hand, may dissolve in the electrolyte and cause adverse side reactions on the anode. It is contemplated that the increased content of manganese in the CAM in combination with HF causes a particularly problematic and disproportionally large conversion of Mn(III) to Mn ions, resulting in the severe drop in performance observed herein.

[0051] The cells presented herein bridge the gap between good half-cell performance and poor prismatic cell performance by recognizing the requirement to include a HF gettering agent when working with high-manganese intercalation materials. The benefits of the cells described herein include prevention or reduction of manganese leaching, stabilization of the cathode, avoiding adverse side reactions at the anode, improved cycling performance, and increased initial discharge capacity.

[0052] The cells described herein are secondary lithium-ion cells. Such cells typically additionally comprise an anode, a separator disposed between the anode and cathode, said cathode, anode and separator forming an electrode assembly, the cell further comprising a housing for the electrode assembly. The cell will typically comprise an electrolyte to facilitate the transport of lithium ions between the cathode and anode. The housing is typically sealed to ensure the electrolyte is retained within the housing. Said housing usually includes terminals in electrical contact with the anode and cathode. Thus, an aspect of the present disclosure relates to a secondary lithium-ion cell comprising: a fluorine-containing electrolyte, a separator, an anode, a cathode comprising a cathode active material (CAM), and a hydrogen fluoride (HF) gettering agent, wherein the CAM comprises a material represented by the formula LibNii-x-yCOxMnyAzO2, wherein 0<x+y<0.4, 0<z<0.05, and 0.9<b< 1.2, wherein the ratio y / x is at least 1, and wherein A is one or more chosen from the group consisting of Al, B, Zr, Ba, Ca, Ti, Mg, Ta, Nb, V, Fe, Ru, Re, Pt, Mo and W.

[0053] Another aspect of the present disclosure relates to a secondary lithium-ion cell comprising: a fluorine-containing electrolyte, a separator, an anode, a cathode comprising a cathode active material (CAM), and a hydrogen fluoride (HF) gettering agent, wherein the CAM comprises a material represented by the formula LibNii-x-yCOxMnyAzO2, wherein 0<x+y<0.4, 0<z<0.05, and 0.9<b< 1.2, wherein the ratio y / x is at least 1, and wherein A is one or more chosen from the group consisting of Al, B, Zr, Ba, Ca, Ti, Mg, Ta, Nb, V, Fe, Ru, Re, Pt and Mo.

[0054] The high-manganese intercalation material comprises an predominant amount of nickel. However, the increased amount of manganese substituted in for cobalt impacts the energy density of the cell and its performance under high voltage conditions. By reducing the content of cobalt, then cells become both cheaper and more environmentally sustainable.

[0055] Thus, an embodiment of the present disclosure relates to the cell as described herein, wherein 0<x+y<0.35, such as 0<x+y<0.3, such as 0<x+y<0.25, such as 0<x+y<0.20. Another embodiment of the present disclosure relates to the cell as described herein, wherein x is less than 0.1, preferably less than 0.05, more preferably less than 0.02.

[0056] Yet another embodiment of the present disclosure relates to the cell as described herein, wherein x is 0. A further embodiment of the present disclosure relates to the cell as described herein, wherein y is at least 0.2.

[0057] Another embodiment of the present disclosure relates to the cell as described herein, wherein both x and y are greater than 0.

[0058] A still further embodiment of the present disclosure relates to the cell as described herein, wherein the ratio y / x is at least 1.2, such as at least 1.4, such as at least 1.6, such as at least 1.8, such as at least 2.

[0059] An even further embodiment of the present disclosure relates to the cell as described herein, wherein the ratio y / x is in the range of from about 1 to about 3, such as from about 1 to about 2.5, such as from about 1.5 to about 2.

[0060] The high-manganese intercalation material may be doped with one or more additional elements to gain new properties depending of the intended use of the cell. The stability of the cells may even be further improved by doping of the intercalation material.

[0061] Therefore, an embodiment of the present disclosure relates to the cell as described herein, wherein 0<z<0.03, preferably 0.001<z<0.01.

[0062] In particular, doping with Al and / or Zr may introduce strong AI-0 and Zr-0 bonds which may enhance the stability of the intercalation material.

[0063] Accordingly, an embodiment of the present disclosure relates to the cell as described herein, wherein A is Al and / or Zr.

[0064] The term "cathode active material" (CAM) is to be understood as a composition comprising one or more electrochemical species which can be oxidised and reduced in a system which enables a cell to produce electric energy during discharge. The role of the cathode active material is to reversibly intercalate (or otherwise bind) ions (such as lithium ions) during cell charge and discharge cycles.

[0065] The CAM may comprise only a single intercalation material or a combination of one or more intercalation materials. Therefore, an embodiment of the present disclosure relate to the cell as described herein, wherein there is only a single intercalation material in the CAM. It is to be understood that the single intercalation material is the high-manganese intercalation material.

[0066] However, the cathode active material may in other variants comprise one or more intercalation materials, i.e. one or more in addition to the high-manganese intercalation material. The additional intercalation material(s) may be a lithium intercalation material, for example a lithium metal oxide which may include lithium and a transition metal.

[0067] The cathode active material may comprise any one or a mixture of two or more of lithium manganese oxide, lithium nickel oxide, lithium cobalt oxide, lithium nickel manganese oxide (LNMO), lithium nickel cobalt oxide, lithium nickel manganese cobalt (NMC) oxide, lithium iron phosphate (LFP), lithium iron manganese phosphate (LFMP) and lithium nickel cobalt aluminium oxide (NCA).

[0068] Preferably, the cathode active material (CAM) may comprise a lithium nickel manganese cobalt oxide (NMC), such as a high-nickel lithium nickel manganese cobalt oxide (high- nickel NMC).

[0069] 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%.

[0070] The high-manganese intercalation material may be mixed with one or more other intercalation materials to form the cathode active material (CAM). It is preferred that the CAM comprises a sizeable fraction of the high-manganese intercalation material to reap the benefits of the performance of the material. The remainder of the CAM may be comprised by high-nickel NMC.

[0071] Thus, an embodiment of the present disclosure relates to the cell as described herein, wherein said material represented by the formula LibNii-x-yCOxMnyAzO2 constitutes at least about 50 wt% of the CAM, such as at least about 60 wt% of the CAM, such as at least about 70 wt% of the CAM, such as at least about 80 wt% of the CAM, such as at least about 90 wt% of the CAM, such as at least about 95 wt% of the CAM.

[0072] Another embodiment of the present disclosure relates to the cell as described herein, wherein the cathode active material comprises about 50 wt% to about 95 wt% of said material represented by the formula LibNii-x-yCOxMnyAzO2 and about 5 wt% to about 50 wt% of high-nickel NMC.

[0073] The CAM is comprised in a cathode active layer which is coated onto the current collector (or conductive foil). The cathode active layer may in addition to the CAM comprise a binder and / or a conductive additive.

[0074] Accordingly, an embodiment of the present disclosure relates to the cell as described herein, wherein the cathode comprises said CAM, one or more binders and optionally a conductive additive.

[0075] To produce the cathode active layer, CAM, a binder and optionally a conductive additive are typically dispersed in a dispersant to form a slurry. The slurry is then deposited on a current collector to form the cathode active layer.

[0076] The binder adhesively connects all the electrode materials for long-term charge / discharge cycling. The role of the optional conductive additive is to improve the electronic properties of the cathode and to provide an electrical connection between the particles of cathode active material in the cathode.

[0077] Suitable binders are well known in the art and may be water-insoluble or water-soluble.

[0078] Therefore, an embodiment of the present disclosure relates to the cell as described herein, wherein, the cathode active layer comprises one or more water-insoluble binders selected from the group consisting of polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, an ethylene oxide-containing polymer, an ethylene propylene copolymer, polystyrene, polyvinylpyrrolidone, polyurethane, polytetrafluoro ethylene, polyvinylidene fluoride, polyethylene, polypropylene, and polyamideimide, polyimide.

[0079] Another embodiment of the present disclosure relates to the cell as described herein, wherein, the cathode active layer comprises one or more water-soluble binders selected from the group consisting of a rubber binder or a polymer resin binder.

[0080] A further embodiment of the present disclosure relates to cell as described herein, wherein the rubber binder is selected from the group consisting of a styrene-butadiene rubber, an acrylated styrene-butadiene rubber, an acrylonitrile-butadiene rubber, an acrylic rubber, a butyl rubber, and a fluororubber. A further embodiment of the present disclosure relates to cell as described herein, wherein the polymer resin binder is selected from the group consisting of polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, an ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, a polyester resin, an acrylic resin, a phenol resin, an epoxy resin, and polyvinyl alcohol.

[0081] A still further embodiment of the present disclosure relates to the cell as described herein, wherein the cathode active layer comprises, by weight, about 0.01-10 wt% binder, such as from about 0.02-8 wt%, from about 0.05-6 wt%, or from about 0.06-4 wt% binder, preferably from about 0.1 to 3 wt% binder, even more preferably about 0.2 wt% to about 2 wt% binder, such as from about 0.5 wt% to about 1.5 wt% binder, most preferably about 1 wt% binder.

[0082] An even further embodiment of the present disclosure relates to the cell as described herein, wherein the conductive additive is selected from one or more of the group consisting of acetylene black, carbon black, graphene, graphite, mesocarbon microbead (MCMB), pitch-based carbon, coke powders, carbon nanotubes and metallic powders.

[0083] Yet another embodiment of the present disclosure relates to the cell as described herein, wherein the cathode active layer comprises about 0.01-10 wt% conductive additive, such as from about 0.02-8 wt%, from about 0.05-6 wt%, or from about 0.06-4 wt% conductive additive, preferably from about 0.1 to about 3 wt% conductive additive, even more preferably about 0.2 wt% to about 2 wt% conductive additive, such as from about 0.5 wt% to about 1.5 wt% conductive additive, most preferably about 1 wt% conductive additive.

[0084] A further embodiment of the present disclosure relates to the cell as described herein, wherein the cathode active material (CAM) is present in an amount of, by weight, from about 60-99.9 wt%, for example from about 70-99.9 wt%, from about 80-99.8 wt%, from about 90-99.6 wt%, or from about 95-99.5 wt% of the total weight of the cathode active layer.

[0085] The cathode active layer is typically formed by forming a slurry of CAM, binder and optional conductive agent; and depositing the slurry on a current collector. Any suitable dispersing medium may be used for the slurry. The cathode is dried before assembly of the cell and addition of electrolyte, to ensure that the moisture level is kept at a minimum.

[0086] HF is formed when the fluorine-containing electrolyte (or component therein such as LiPFe) comes in contact with residual moisture in the cell. Moisture may be introduced during battery production and despite careful efforts to avoid water, most cells typically contain at least 100-1000 ppm of residual moisture in the electrolyte. Since fluorine readily reacts with water, highly corrosive HF is quickly formed within the cell, which ultimately decreases the performance of the cell. Damage caused by HF may happen both during use and storage of the cell.

[0087] The cells described herein comprises a hydrogen fluoride (HF) gettering agent to protect the cathode from manganese leaching and dissolution. It has been found that glass particles works as a surprisingly effective HF gettering agent for use in cells with high content of manganese intercalation material. Upon contact with the glass particles, the fluorine ions are chemically trapped on the particle surface and prevent formation of HF in the electrolyte.

[0088] Accordingly, an embodiment of the present disclosure relates to the cell as described herein, wherein the HF gettering agent comprises glass particles.

[0089] The glass is silicon-based and preferably comprises barium and / or lithium. Without being bound by theory, it is contemplated that glass particles comprising lithium may facilitate transfer of lithium to the anode, e.g. a graphite anode, to increase the initial discharge capacity of the cell.

[0090] Therefore, an embodiment of the present disclosure relates to the cell as described herein, wherein the glass particles comprises SiOx, such as SiO?.

[0091] Another embodiment of the present disclosure relates to the cell as described herein, wherein the glass particles comprises barium and / or lithium.

[0092] The glass particles may be selected so that the particle size is suitable for either dispersion in the CAM or for coating onto the CAM.

[0093] Therefore, an embodiment of the present disclosure relates to the cell as described herein, wherein the mean particle size (d50) of the glass particles is in the range of from about 0.6 pm to about 1.1 pm, preferably about 1 pm.

[0094] Preferably, the glass particles have a d90 of 5 pm or below.

[0095] A glass suitable for use as a getting agent according to the disclosure has the following composition (in % by weight based on oxide): 48-58 % SiO2;

[0096] 7-13 % B2O3;

[0097] 7-13 % AI2O3;

[0098] 22-28 % BaO; and

[0099] 0.1-8 % ZrO2.

[0100] The material can in principle contain alkali metal oxides, but preferably contains IJ2O as the only alkali metal oxide, apart from accidental impurities.

[0101] It can therefore contain IJ2O (for instance from 0 to 5 wt% IJ2O), but preferably no Na2O, K2O, Rb2O, or CS2O.

[0102] By "accidental impurities" is meant less than 0.1% by weight, in particular less than 0.05 % by weight or even less than 0.01 % by weight.

[0103] A particularly suitable glass is available from Schott AG under glass code G018-405.

[0104] Another glass suitable for use as a getting agent according to the disclosure has the following composition (in % by weight based on oxide):

[0105] 0.1-1 % AI2O3;

[0106] 50-85 % BaO;

[0107] 0.1-1 % U2O;

[0108] 1-10 % P2O5; and

[0109] 10-50 % SiO2.

[0110] The HF gettering agent may comprise other components beyond the glass particles to induce the HF gettering effect. In particular, the glass particles may be mixed with other components that may induce a synergistic HF gettering effect.

[0111] The HF gettering agent may be included in the cell in several different configurations. The HF gettering agent may also be included in the cell at several positions simultaneously to maximise reduction of HF build up.

[0112] Therefore, an embodiment of the present disclosure relates to the cell as described herein, wherein the HF gettering agent is integrated in the cell in a configuration selected from group consisting of coated on the cathode active material particles, adhered to the separator, intermixed with the cathode active material in the cathode layer, coated on the cathode layer, and dispersed in the electrolyte preferably where said HF gettering agent is intermixed with the cathode active material in the cathode layer.

[0113] The anode of the cells presented herein are not limited to any particular type of anode, but may be any anode suitable for use in a secondary lithium-ion cell. Depending on the type of anode, however, the cell will benefit more or less from the inclusion of the HF gettering agent. As an example, the performance of a cell with a lithium metal anode is not expected to be reduced much by HF corrosion because the lithium of the anode will interact with residual moisture to produce LiOH, thereby minimising the amount of available water for HF formation.

[0114] However, the cells described herein preferably comprise an anode with an anode active material comprising a carbonaceous material as these perform well in secondary lithium- ion cells and in combination with the high-manganese intercalation material. In particular, graphite has favourable structural stability and great lithium ion storage capacity, which makes it a good anode active material.

[0115] Thus, an embodiment of the present disclosure relates to the cell as described herein, wherein the anode comprises an anode active material comprising a carbonaceous material.

[0116] Another embodiment of the present disclosure relates to the cell as described herein, wherein the carbonaceous material is selected from the group consisting of synthetic graphite, natural graphite, mesophase carbon, soft carbon, hard carbon, amorphous carbon, polymeric carbon, coke, meso-porous carbon, carbon fiber, graphite fiber, carbon nano-fiber, carbon nano-tube, and expanded graphite platelets or nano graphene platelets containing multiple graphene planes bonded together, and combinations thereof.

[0117] A preferred embodiment of the present disclosure relates to the cell as described herein, wherein the anode active material is graphite.

[0118] Charging and discharging of the secondary lithium-ion cell involves transport of lithium ions from the cathode to the anode and vice versa. Lithium ions are carried in an electrolyte. Typically, the electrolyte comprises a lithium salt such as LiPFe and one or more solvents, preferably one solvent. The choice of electrolyte may be guided by the rest of the components, such as the active materials. Thus, an embodiment of the present disclosure relates to the cell as described herein, wherein the electrolyte comprises LiPFe and at least one solvent.

[0119] Another embodiment of the present disclosure relates to the cell as described herein, wherein the at least one lithium salt is 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 (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 (LiBF4), lithium nitrate (LiNOs) lithium 2-trifluoromethyl-4,5-dicyanoimidazole (LiTDI).

[0120] The concentration of the lithium salt can be adjusted to optimise performance of the secondary lithium-ion cell. For efficient transfer of lithium ions the electrolyte should have sufficient conductivity and viscosity.

[0121] Thus, an embodiment of the present disclosure relates to the cell as described herein, wherein the concentration of lithium salt is in the range of about 0.1 M to about 2.0 M.

[0122] For the purpose of the cells described herein, the electrolyte should be in a non-aqueous organic solvent to limit any available water for HF formation. The non-aqueous organic solvent may include a carbonate-based, ester-based, ether-based, ketone-based, alcohol- based, or aprotic solvent.

[0123] Therefore, an embodiment of the present disclosure relates to the cell as described herein, wherein the at least one solvent is a non-aqueous organic solvent.

[0124] Another embodiment of the present disclosure relates to the cell as described herein, wherein the at least one solvent is selected from the group consisting of 1,2- dimethoxyethane (DME), N-propyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide (PYR13-FSI), N-propyl-N-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), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), ethylene carbonate (EC), and propylene carbonate (PC), and their fluorinated equivalents.

[0125] Once the separate components has been prepared, they can be assembled to a battery. A battery comprises an array of connected secondary lithium-ion cells. While cycling in mid- state-of-charge would yield the best longevity, the batteries presented herein are suitable for use under stressful conditions due to the high performing CAM and stabilised design. Stressful conditions include exposure to elevated temperatures and keeping the cell at high charge voltage. A battery dwelling above 30°C is considered elevated temperature and a voltage of >4.3 V is deemed as high voltage.

[0126] Thus, an aspect of the present disclosure relates to a battery comprising a plurality of secondary lithium-ion cells as described herein.

[0127] An embodiment of the present disclosure relates to the battery as described herein, wherein the battery is a high voltage battery.

[0128] An embodiment of the present disclosure relates to the battery as described herein, wherein the battery can cycled at high voltage, such as at least 4.1 V, such as at least 4.2 V, preferably at least 4.3 V.

[0129] A further embodiment of the present disclosure relates to the battery as described herein, wherein the battery is suitable for use and storage at elevated temperatures, such as at least 30°C.

[0130] The secondary lithium-ion cells described herein may also be used for charging larger electrical devices, such as a vehicle comprising a cell (or battery system). The vehicle is preferably an electric vehicle, such as a car, truck, bus, scooter, motorbike, bicycle or the like, preferably a car, truck or bus. If the battery is used for powering larger electrical devices, the battery may comprise many smaller batteries connected in a series-parallel configuration ( / .e. a battery system).

[0131] Accordingly, an aspect of the present disclosure relates to a vehicle comprising the secondary lithium-ion cell or the battery as described herein.

[0132] The secondary lithium-ion cell may be prepared by any conventional method for manufacture of electrochemical cells. The HF gettering agent is added during preparation of the cell, either in the cathode slurry, as a coating on the CAM or separator, or in the electrolyte. Preferably, the HF gettering agent is included in the cathode slurry or coated on the CAM.

[0133] Therefore, an embodiment of the present disclosure relates to a method for preparing a secondary lithium-ion cell as described herein, said method comprising the steps of:

[0134] (i) providing a separator, an anode, a fluorine-containing electrolyte, a cathode active material (CAM), and an HF gettering agent, and

[0135] (ii) assembling the secondary lithium-ion cell.

[0136] An embodiment of the present disclosure relates to the method as described herein, wherein the HF gettering agent is mixed as a slurry with the CAM and deposited to form a cathode.

[0137] The HF gettering agent is mixed with the CAM by including it in the wet slurry or mixing the HF gettering agent and CAM in dry powder form before adding the dispersing medium of the slurry. Mixing the HF gettering agent with the CAM requires minimal extra processing in comparison to fabricating the cell without the HF gettering agent.

[0138] A further embodiment of the present disclosure relates to the method as described herein, wherein the slurry comprises N-methyl-2-pyrrolidone (NMP) as dispersing media.

[0139] The HF gettering agent may be coated onto the CAM to provide a protective layer. Coating increases processing time to prepare the cell, but could overall increase the protective effect as the electrolyte has to pass the film before getting in direct contact with the CAM, i.e. HF formed in the electrolyte would be trapped by the HF gettering agent before damaging the cathode.

[0140] If provided as a coating on the CAM, such a coating is preferably thin, such as less than 10 nm.

[0141] To achieve thin and uniform layers, atomic layer deposition (ALD) is used for the coating process.

[0142] ALD is based on sequential deposition of monolayers on a surface using a gas-phase chemical process. The surface on which the film is to be deposited is sequentially exposed to different precursors followed by purging of the growth reactor to remove any residual chemically active source gas or by-products. When the growth surface is exposed to a precursor, it gets completely saturated by a monolayer of that precursor. The thickness of a monolayer depends on the reactivity of that precursor with the growth surface. This results in a number of advantages such as excellent uniformity, and easy and accurate film thickness control.

[0143] Thus, an embodiment of the present disclosure relates to the method as described herein, wherein the HF gettering agent is coated onto the CAM by atomic layer deposition (ALD).

[0144] Dry coating may also be a suitable process for coating the HF getting agent onto the CAM. Therefore, an embodiment of the present disclosure relates to the method as described herein, wherein the HF gettering agent is coated onto the CAM by dry coating.

[0145] Another embodiment of the present disclosure relates to the method as described herein, wherein the thickness of the coating layer is less than 10 nm.

[0146] The coating layer may be on the particles of CAM, or as a layer coated on the surface of the cathode.

[0147] Preferably, the coating layer of HF gettering material is a layer on the surface of the cathode.

[0148] Alternatively the HF gettering agent may be coated onto the separator. Therefore, an embodiment of the present disclosure relates to the method as describe herein, wherein the HF gettering agent is coated onto the separator.

[0149] Instead, the HF gettering agent may be dispersed in the electrolyte solution. Accordingly, an embodiment of the present disclosure relates to the method as describe herein, wherein the HF gettering agent is comprised in the fluorine-containing electrolyte.

[0150] It is to be understood that the HF gettering agent may also be included in the cell in any of the configurations at the same time, with the configurations being (i) dispersion of said HF gettering agent into the CAM, (ii) coating of said HF gettering agent onto the CAM, (iii) coating of said HF gettering agent onto the separator, and (iv) comprised in the fluorine- containing electrolyte.

[0151] Independent of how the HF gettering agent is included in the cell, it is preferable that the HF gettering agent is handled in the absence of water. This is because the glass particles are hygroscopic and could therefore inadvertently introduce moisture into the cell if handle under humid conditions during any processing step. Thus, the HF gettering agent is preferably handled under dehumidified conditions.

[0152] Therefore, an embodiment of the present disclosure relate to the method as described herein, wherein adding the HF gettering agent to the CAM, the separator, or the electrolyte is performed in absence of water.

[0153] Another aspect of the present disclosure relates to use of a hydrogen fluoride (HF) gettering agent for improving the cycle life efficiency (or the capacity retention), ), and / or the initial discharge capacity of a lithium-ion cell, and / or for reducing manganese leaching in a lithium-ion cell, said cell comprising a fluorine-containing electrolyte and a cathode active material represented by the formula

[0154] LibNii-x-yCOxMnyAzO2, wherein 0<x+y<0.4, 0<z<0.05, and 0.9<b< 1.2, wherein the ratio y / x is at least 1, and wherein A is one or more chosen from the group consisting of Al, B, Zr, Ba, Ca, Ti, Mg, Ta, Nb, V, Fe, Ru, Re, Pt, Mo and W.

[0155] The listing or discussion of an apparently prior published document in this specification should not necessarily be taken as an acknowledgement that the document is part of the state of the art or is common general knowledge.

[0156] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains.

[0157] Preferences, options and embodiments for a given aspect, feature or parameter of the disclosure should, unless the context indicates otherwise, be regarded as having been disclosed in combination with any and all preferences, options and embodiments for all other aspects, features and parameters of the disclosure. This is especially true for the description of the secondary lithium-ion cell and the battery comprising the same, and all its features, which may readily be part of the method for preparing the secondary lithium- ion cell as described herein. EXAMPLES

[0158] EXAMPLE 1: EVALUATION OF HIGH-MANGANESE CATHODE ACTI E MATERIAL

[0159] Coin half cells were prepared to determine the performance of during cell cycling at high voltage and elevated temperature.

[0160] Slurry compositions of cathode active material were prepared using N-methyl-2- pyrrolidone (NMP) as dispersing media. Two types of half cells were prepared; a first type comprising a CAM mixture of 20% high-nickel NMC and 80% high-manganese intercalation material ("reference CAM"), and a second type comprising a CAM of 100% high-manganese intercalation material ("high-manganese CAM"). The ratio between CAM, binder, and conductive additive was 97: 1.5: 1.5.

[0161] The anode used in the coin half cell was lithium metal. A ceramic-coated separator was used to separate the anode and cathode. Stainless steel was used for the positive and negative casing elements of the cell.

[0162] The formed cell was cycled between 3.0 V and 4.3 V at 45 °C. The rate was 0.5 C for charging and 1 C for discharging.

[0163] The discharge capacity retention of the coin half cells prepared as described above is seen in Figure 1A. It is clear that the half cell with high-manganese CAM performs better than the half cell with reference CAM, approx. 3-4% better capacity retention after 50 cell cycles.

[0164] Full prismatic cells were assembled for testing of capacity retention. Two types of cells with different CAMs were prepared as described for the coin half cells above with the exception that the anodes in the prismatic cells were graphite.

[0165] The prismatic cells were cycled between 3.0 V and 4.3 V at 45 °C. The rate was 0.5 C for charging and 1 C for discharging.

[0166] The results are shown in figure IB and surprisingly show that the prismatic cell comprising the reference CAM performed significantly better than the prismatic cell comprising the high-manganese CAM. After 440 cycles, the prismatic cell with reference CAM showed approx. 6% better capacity retention than the prismatic cell with the high-manganese CAM.

[0167] In conclusion, there is some unknown effect that hinders the positive traits of the high- manganese CAM to be transferred from a coin half cell setup to a prismatic cell. EXAMPLE 2: TEST OF SECONDARY LITHIUM-ION CELL COMPRISING HYDROFLUORIC ACID GETTERING AGENT

[0168] Prismatic cells were prepared to test influence of the addition of a hydrogen fluoride (HF) gettering agent on cell performance.

[0169] A prismatic cell comprising the reference CAM material was prepared as described in Example 1.

[0170] In addition to this, a prismatic cell wherein the CAM further contained a HF gettering agent comprising glass particles (Schott, Mainz, Germany, product code G018-405). The HF gettering agent was added to the slurry compositions of cathode active material upon preparation of the cell.

[0171] The two types of prismatic cells were cycled between 3.0 V and 4.3 V at 45 °C. The rate was 0.2 C for charging and 1 C for discharging.

[0172] The discharge capacity retention of the prismatic cells is displayed in Figure 2. It is immediately apparent that the prismatic cell containing the HF gettering agent performs markedly better that the prismatic cell with no HF gettering agent. After 50 cell cycles the prismatic cell containing a HF gettering agent shows approx. 3-4% better discharge capacity retention.

[0173] Surprisingly, a pouch cell containing a HF gettering agent also displayed a improved initial discharge capacity compared to the pouch cell without an HF gettering agent. The increase in initial discharge capacity was approx. 0.5% (see Table 1).

[0174] Table 1. Data for test of pouch cells with and without a HF gettering agent in the CAM. In conclusion, it is evident that the performance of the prismatic cell is significantly enhanced with respect to cycle life and initial discharge capacity by introduction of the HF gettering agent.

Claims

CLAIMS1. A secondary lithium-ion cell comprising: a fluorine-containing electrolyte, a separator, an anode, a cathode comprising a cathode active material (CAM), and a hydrogen fluoride (HF) gettering agent, wherein the CAM comprises a material represented by the formula LibNii-x-yCOxMnyAzO2, wherein 0<x+y<0.4, 0<z<0.05, and 0.9<b< 1.2, wherein the ratio y / x is at least 1, and wherein A is one or more chosen from the group consisting of Al, B, Zr, Ba, Ca, Ti, Mg, Ta, Nb, V, Fe, Ru, Re, Pt, Mo and W.

2. The cell according to claim 1, wherein x is less than 0.1, preferably less than 0.05, more preferably less than 0.02.

3. The cell according to any one of the preceding claims, wherein y is at least 0.2.

4. The cell according to any one of the preceding claims, wherein the HF gettering agent comprises glass particles.

5. The cell according to claim 4, wherein the glass particles have the following composition (in % by weight based on oxide):0.1-1 % AI2O3;50-85 % BaO;0.1-1 % U2O;1-10 % P2O5; and10-50 % SiO2.

6. The cell according to any one of the preceding claims, wherein the HF gettering agent are integrated in the cell in a configuration selected from group consisting of:(i) intermixing said HF gettering agent with the CAM in the cathode,(ii) coating of said HF gettering agent onto the cathode,(iii) coating of said HF gettering agent onto the separator, and(iv) comprised in the fluorine-containing electrolyte preferably where said HF gettering agent is intermixed with the CAM in the cathode.

7. The cell according to any one of the preceding claims, wherein the anode comprises an anode active material comprising a carbonaceous material, such as graphite.

8. The cell according to any one of the preceding claims, wherein the fluorine-containing electrolyte comprises a solvent and LiPFe.

9. A battery comprising a plurality of secondary lithium-ion cells according to any one of the preceding claims.

10. A vehicle comprising the secondary lithium-ion cell according to any one of claims 1-8 or the battery according to claim 9.

11. A method for preparing a secondary lithium-ion cell according to any one of claims 1- 8, said method comprising the steps of:(i) providing a separator, an anode, a fluorine-containing electrolyte, an HF gettering agent, and a cathode comprising a cathode active material (CAM), and(ii) assembling the secondary lithium-ion cell.

12. The method according to claim 11, wherein the HF gettering agent is intermixed with the CAM in the cathode or coated onto the cathode, preferably intermixed with the CAM in the cathode.

13. The method according to claim 12, wherein a slurry comprising the HF gettering agent and CAM is deposited to form a cathode.

14. Use of a hydrogen fluoride (HF) gettering agent for improving the cycle life efficiency (or the capacity retention) of a lithium-ion cell comprising a fluorine-containing electrolyte and a cathode active material represented by the formulaLibNii-x-yCOxMnyAzO2, wherein 0<x+y<0.4, 0<z<0.05, and 0.9<b< 1.2, wherein the ratio y / x is at least 1, and wherein A is one or more chosen from the group consisting of Al, B, Zr, Ba, Ca, Ti, Mg, Ta, Nb, V, Fe, Ru, Re, Pt, Mo and W.

15. Use of a hydrogen fluoride (HF) gettering agent for improving the initial discharge capacity of a lithium-ion cell comprising a fluorine-containing electrolyte and a cathode active material represented by the formulaLibNii-x-yCOxMnyAzO2,wherein 0<x+y<0.4, 0<z<0.05, and 0.9<b< 1.2, wherein the ratio y / x is at least 1, and wherein A is one or more chosen from the group consisting of Al, B, Zr, Ba, Ca, Ti, Mg, Ta, Nb, V, Fe, Ru, Re, Pt, Mo and W.

16. Use of a hydrogen fluoride (HF) gettering agent for reducing manganese leaching in a lithium-ion cell comprising a fluorine-containing electrolyte and a cathode active material represented by the formula LibNii-x-yCOxMnyAzO2, wherein 0<x+y<0.4, 0<z<0.05, and 0.9<b< 1.2, wherein the ratio y / x is at least 1, and wherein A is one or more chosen from the group consisting of Al, B, Zr, Ba, Ca, Ti, Mg, Ta, Nb, V, Fe, Ru, Re, Pt, Mo and W.

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