Solvent-free cathode composition containing large surface area conductive additive

Abstract

The present disclosure relates to a solvent-free composition, electrodes formed from said composition, cells formed from said electrode, battery systems including said cell and vehicles containing said battery system. The present disclosure also relates to methods of preparing said composition and electrode. The composition comprises cathode active material, binder and conductive additive. The conductive additive has a high surface area, such as a specific BET surface area of 50m2 / g or greater. The electrodes formed using the composition show excellent electrochemical performance and stability including long cycle life, high capacity retention, good flexibility and good adhesion.

Description

[0001] SOLVENT-FREE CATHODE COMPOSITION CONTAINING LARGE SURFACE AREA CONDUCTIVE ADDITIVE

[0002] FIELD OF INVENTION

[0003] The present disclosure relates to a method of forming a cathode comprising an electroactive layer and a conductive foil, and to a solvent-free composition comprising a high surface area conductive additive for use in the method, and from which the electroactive layer is formed. The present invention is also related to a cell including the cathode of the invention, a battery system including the cell and a vehicle including the battery system.

[0004] BACKGROUND OF THE INVENTION

[0005] There has been significant interest in the use of rechargeable batteries for use in energy storage applications. In particular, lithium-ion batteries have been widely applied in diverse industries, such as electronic devices, power tools, satellites, utilityscale storage and electric vehicles.

[0006] Commercial lithium-ion battery electrodes are typically manufactured using wet processing techniques by coating a slurry onto a conductive foil. This process involves using significant amounts of solvent, such as N-methyl-2-pyrrolidone (NMP) or water. After casting the slurry onto the conductive foil, the electrode must be dried by evaporating the solvent. The drying process may take from several hours to days and is normally carried out at elevated temperatures to completely dry the electrode. Evaporated NMP also is generally recovered due to its high cost and potential as an environmental pollutant. Furthermore, the drying process may impart microstructural defects on the electrode surface as the solvent evaporates. As a result, the use of solvents and the required drying system contribute to significant production costs for lithium-ion battery electrodes.

[0007] In addition, electrodes prepared using wet coating methods often have an uneven distribution of binder and conductive additive due to non-uniform mixing. Electrodes prepared using wet methods may therefore have suboptimal properties due to conductive additive / binder agglomerates between the cathode active material particles, leadings to limited surface contact between the cathode active material particles and the binder and / or conductive additive. This is particularly problematic when components with a high surface area are used in the electrode, for example some carbon-based conductive additives. Components, such as conductive additives, with a high surface area often agglomerate in wet coating methods, leading to non-uniform mixing. Indeed, high surface area components often cannot be used in wet coating methods for this reason.

[0008] Whilst this is an issue most often seen for cathodes, it also applies to other electrodes or battery components comprising high surface area conductive additives such as anodes or solid electrolytes.

[0009] The elimination of solvents from the manufacture of lithium-ion battery electrodes is therefore an attractive approach to reduce production costs and processing times and improve electrode properties. A challenge that arises is how to develop a method that removes the need for the solvents (and thus drying), whilst also able to achieve uniform mixing, particularly when the composition includes high surface area components.

[0010] It is also desirable to provide a method of manufacturing lithium-ion battery electrodes that overcomes the issues associated with using high surface area components in the wet coating methods.

[0011] BRIEF DESCRIPTION OF FIGURES

[0012] Figure 1 is graph showing the relationship between the capacity degradation of an electrode with respect to the BET surface area of conductive additive comprised therein.

[0013] Figure 2 is a graph showing the relationship between capacity degradation of an electrode with respect to the OAN of the conductive additive comprised therein.

[0014] Figure 3 is a graph showing the relationship between the capacity degradation of an electrode and the Surface Index Number (BET surface area in m2 / g * Oil Absorption Number ml / lOOg) of the conductive additive comprised therein.

[0015] Figure 4 is a graph showing the relationship between the capacity degradation of an electrode and the porosity of the electrode. The BET surface area of the conductive additive (m2 / g) comprised within each of the electrodes is provided above the relevant data point in the graph.

[0016] BRIEF DESCRIPTION OF THE INVENTION This disclosure relates to a novel method of forming an electrode, wherein the method comprises providing a composition substantially free of solvent. In particular, this disclosure relates to a method comprising providing a substantially solvent-free composition comprising a high surface area conductive additive to form an electrode.

[0017] Given the issues identified with wet coating processes, the development of electrode manufacturing methods using dry processing conditions by coating conductive foils with dry particles represents an ideal fabrication process.

[0018] The authors have surprisingly discovered that the method of this disclosure may allow production of lithium-ion batteries with unexpectedly improved mechanical and electrochemical performance and stability, such as improved electrode adhesion strength, battery stability, cycle life and capacity retention.

[0019] According to an aspect of the present disclosure, there is provided an electroactive layer, the electroactive layer comprising; an active material; a a conductive additive; and a binder, wherein the conductive additive has a specific BET surface area of 50 m2 / g or greater.

[0020] According to an aspect of the present disclosure, there is provided a method of forming a cathode, the cathode comprising a conductive foil and an electroactive layer; the method comprising:

[0021] (a) providing a composition comprising a cathode active material; a binder; a conductive additive; wherein the conductive additive has a specific BET surface area of 50m2 / g or greater; and wherein the composition is substantially free of solvent; and

[0022] (b) depositing the composition on the conductive foil to form an electroactive layer.

[0023] Preferably, the composition is deposited on the conductive foil using an electrostatic deposition process. That is, preferably step (b) comprises an electrostatic deposition process. According to a further aspect of the present disclosure, there is provided a cathode formed via a method substantially free of solvent. The method includes the use of a conductive additive with a specific BET surface area of 50m2 / g or greater.

[0024] According to a further aspect of the present disclosure, there is provided a composition for spray deposition comprising;

[0025] 92-99 wt% cathode active material;

[0026] 0.05-7.95 wt% binder; and

[0027] 0.05-7.95 wt% carbon black; wherein the carbon black has a specific BET surface area of 50m2 / g or greater; and wherein the composition is substantially free of solvent.

[0028] Surprisingly, the inventors have found that the problems associated with non-uniform mixing in the conventional wet processing methods can be overcome by the method of the present invention. In particular, components with a high surface area (for example, a specific BET surface area of 50m2 / g or greater) may be more uniformly mixed in the method of the present disclosure, to form an electrode wherein the high surface area components are more uniformly distributed throughout. Without wishing to be bound by theory, the improved mixing and / or distribution of the components in the method of the present disclosure may be at least in part due to the reduction of the agglomeration of particles, especially the high surface area conductive additives.

[0029] Furthermore, the inventors have surprisingly found that the elimination of solvents from the manufacture of lithium-ion battery electrodes may reduce production costs and processing times and may improve electrode properties. In particular, the inventors have surprisingly found that eliminating solvents from the manufacture of lithium-ion battery electrodes may allow high surface area components to be incorporated into the composition without the problems associated with mixing (agglomeration) that are found in wet coating processes. Without wishing to be bound by theory, the incorporation of high surface area conductive additives may lead to improved conductivity of an electrode formed by the method of the invention. This may be due to the more uniform nature of the mixing leading to a more uniform distribution of the conductive additive.

[0030] The present invention will in the following be described in more detail.

[0031] DETAILED DESCRIPTION OF THE INVENTION 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 invention pertains.

[0032] The method of the disclosure comprises a first step (step (a)) of providing a composition, the composition comprising: a cathode active material; a binder; and a conductive additive, wherein the composition is substantially free of solvent.

[0033] The method of the disclosure also comprises a second step (step (b)) of depositing the composition on a conductive foil to form an electroactive layer.

[0034] Preferably, step (a) and step (b) are both substantially free of solvent.

[0035] Steps (a) and (b) may be carried out using standard methodologies, or by the methods described herein. The components of the composition may be combined in any order, unless otherwise specified.

[0036] An object of the present disclosure is generally to provide a substantially solvent-free method of forming a cathode, wherein the method overcomes one or more of the problems associated with the conventional wet processes. In particular, to overcome the agglomeration conductive additives, which often occurs during solvent-based preparation of cathode active layers, and makes high surface area conductive additives unsuitable for wet processes.

[0037] An advantage of the method of the present disclosure is that the conductive additive with a specific BET surface area of 50m2 / g or greater (and / or an OAN of 100 ml / lOOg or greater) can be used, and may also be uniformly distributed throughout the electrode.

[0038] For the avoidance of doubt, a 'solvent-free composition' or a composition 'free from solvent' is the be understood as a composition that it substantially free from solvent. The solvent-free composition may be an electroactive composition according to the disclosure. Solvent is preferably avoided in the composition, electroactive layer, electrode and / or fabrication / mixing processes. However, a solvent may be included in order to aid the processing of the components and / or facilitate the processing and / or mixing (e.g. components may be provided as a solution / emulsion). The composition, electroactive layer and / or electrode may comprise solvent, for example as a result of the manufacturing process, operation process and / or due to absorption of solvent from the atmosphere.

[0039] In the context of the disclosure, a solvent-free composition refers to a composition that comprises less than about 5 wt% solvent, for example less than about 4 wt% solvent, such as less than about 3 wt% solvent, for example less than about 2 wt% solvent, such as less than about 1 wt% solvent, for example less than about 0.5 wt% solvent, such as less about than 0.1 wt% solvent, based on the total weight of the composition.

[0040] In the context of the disclosure, a solvent is a liquid component. For example, a solvent may be an organic solvent, inorganic solvent, and / or aqueous solvent.

[0041] In some embodiments, a solvent is a volatile compound, wherein volatile may be defined as a compound having a high vapour pressure at room temperature, such as a compound that has a boiling point of from about 50 °C to about 250 °C.

[0042] In one embodiment, the composition is free from volatile organic compounds (VOCs), where VOCs are organic compounds that have high vapour pressure at room temperature, such as organic compounds that have a boiling point of from about 50 °C to about 250 °C.

[0043] A major advantage of using a solvent-free composition in the formation of an electroactive layer is that the composition may comprise a higher cathode active material wt% than typically possible in processes comprising a solvent. This may improve the energy capacity and energy density of an electroactive layer / cathode prepared from the solvent-free composition. The solvent-free composition is then deposited on a conductive foil to form an electroactive layer.

[0044] Furthermore, the use of a solvent-free composition allows for a high surface area conductive additive to be used, which further improves the properties of an electrode formed from the solvent-free composition, such as energy capacity and energy density. In a wet coating process, it is very challenging to uniformly distribute a conductive additive material due to agglomerations being formed, to the extent that a high surface area conductive additive cannot be used in wet coating processes.

[0045] In particular, in wet coating processes agglomerations of binder / conductive additive may form that do not contact the cathode active material (CAM). For example, the agglomerations of binder / conductive additive may exist alone in the porous space amongst the cathode active material. This is unfavourable as it reduces the surface area of the cathode active material available for intercalation / deintercalation of the lithium ion and reduces the conductivity of the cell. As a result, a wet coating process may require increased amounts of conductive additive to be used to counteract the conductive additive that is agglomerated and / or not in contact with the cathode active material. As conductive additives are often expensive, it is not economically favourable to include more conductive additive into the composition.

[0046] However, in methods of the present invention which involve a solvent-free composition (i.e. dry mixing and / or dry coating processes), the binder and conductive additive are able to be uniformly distributed in the composition so that they are in contact with the cathode active material, and the method allows high surface area conductive additives to be used. The use of a high surface area conductive additive is favourable as it allows a lower amount of conductive additive to be used compared to wet coating processes. The reduction of the amount of conductive additive in the composition is particularly desirable as this may make the process less expensive.

[0047] In the context of this disclosure, a "high surface area" in reference to a conductive additive is a specific BET surface area of 50 m2 / g or greater.

[0048] When the conductive additive is carbon black, a "high surface area" may also refer to a conductive addition with an Oil Absorption Number of 100 ml / lOOg or greater, and / or a Surface Index Number of 5,000 m2 / g * ml / 100g or greater.

[0049] A further advantage of the present invention is that solvent-free methods are typically greener by eliminating the need for toxic solvents that are associated with both health and environmental risks.

[0050] The properties of each of the components of the solvent-free composition are beneficial for providing a solvent-free composition that is homogeneously mixed, facilitate the formation of an electroactive layer via a solvent-free deposition method, and provide an electrode with improved properties. Cathode active material

[0051] The solvent-free composition of the disclosure comprises a cathode active material wherein the cathode active material may comprise a suitable material for use as an electrochemically active material in the cathode of a cell, particularly a lithium-ion cell.

[0052] The term "electrochemically active material" is to be understood as an 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.

[0053] The cathode active material may comprise an intercalation material, such as a lithium intercalation material, for example a lithium metal oxide which may include lithium and a transition metal.

[0054] 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).

[0055] Preferably, the cathode active material is a LNMO or an NMC material, i.e., a lithium nickel manganese oxide or a lithium nickel manganese cobalt oxide.

[0056] Exemplary cathode active materials include nickel-cobalt-manganese (NMC) composite oxides and lithium NMC (Li-NMC) composite oxides or lithium nickel cobalt manganese (NMC) oxides (LiNii-x-yCoxMnyO? (0<x+y<0.2)).

[0057] In some embodiments, the cathode active material comprises lithium nickel cobalt manganese oxides (NMC) (LibNii x-y-zCoxMnyAzO? (0<x+y+z<0.2)), 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.

[0058] In preferred embodiments, the NMC cathode materials is defined as LibNii-x-y-zCoxMnyAzO2, wherein 0<x+y+z<0.2, preferably 0<x+y+z<0.15, more preferably 0<x+y+z<0.12, 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.

[0059] The cathode active material may comprise a lithium metal oxide material that is coated with another material. For example, a lithium metal oxide may be coated with a different lithium metal oxide, carbon, graphene, or a combination thereof. Furthermore, the coating material may have been coated using atomic layer deposition (ALD) as a non-limiting example.

[0060] Typically, the D50 of the cathode active material particles is in the range of from about 5 pm to about 15 pm, such as from about 8 pm to about 12 pm, such as from about 9 pm to about 11 pm.

[0061] Additionally, the DIO of the cathode active material particles is typically in the range of from about 0.1 pm to 12 pm, such as from 5 pm to 10 pm, for instance from 6 pm to 9 pm.

[0062] The D90 of the cathode active material particles is typically in the range of from about

[0063] 8 pm to 20 pm, such as from 10 pm to 15 pm, for instance from 11 pm to 14 pm.

[0064] The cathode active material may have a bimodal particle size distribution. That is, it has two maximum values in the particle size distribution. The size of the small particles is typically in the range of from about 0.1 pm to 10 pm, preferably from about 4 pm to about 6 pm. The size of the large particles is typically in the range of from about 5 pm to 20 pm, preferably from about 10 pm to about 15 pm.

[0065] Preferably, the cathode active material of the present invention has a unimodal particle size distribution.

[0066] Typically, the D50 of the unimodal cathode active material particles is in the range of from about 5 pm to 15 pm, for example from 8 pm to about 12 pm, such as from about

[0067] 9 pm to about 11 pm.

[0068] Preferably, the unimodal particles have a D50 of about 8 pm, about 9 pm, about 10 pm, about 11 pm, or around 12 pm. Even more preferably, the D50 is about 10 pm. Preferably, the cathode active material particles are substantially spherical or spherical. Without wishing to be bound by theory, it is believed that the use of spherical or substantially spherical cathode active material compared to cuboid cathode active material allows for better packing, resulting in increased packing density.

[0069] By "substantially spherical" is meant a shape that is approximately a sphere, with only small deviations from a perfect sphere by no more than about 20% in any given dimension.

[0070] Typically, polycrystalline cathode active material particles are spherical, while single crystal cathode active material particles have a cuboid shape.

[0071] In an embodiment, the cathode active material comprises polycrystalline spherical particles.

[0072] To assess the shape of cathode active material particles, the aspect ratio is a key metric. This ratio compares the longest dimension to the shortest dimension of a particle, with a perfect sphere having an aspect ratio of 1.

[0073] The aspect ratio is determined by analyzing images captured via a microscope. For instance, using software like Image!, one can measure the longest and shortest dimensions of a particle.

[0074] The aspect ratio is then calculated as:

[0075] Shortest Dimension

[0076] Aspect Ratio = -

[0077] Longest Dimension

[0078] To obtain a representative value for a powder sample, the average aspect ratio is calculated from at least 10 particles.

[0079] Preferably, the cathode active material particles have an average aspect ratio below 1.5, preferably below 1.4, and more desirably below 1.3, 1.2, or even 1.1.

[0080] The cathode active material may be present in the composition in an amount of from about 85 to about 99.8 wt%, optionally from about 90 to about 99.5 wt%, from about 92 to about 99 wt%, from about 94 to about 99 wt%, from about 95 wt% to about 98 wt%, or from about 96 to about 98 wt%, based on the total weight of the composition.

[0081] Binder The composition of the disclosure comprises a binder.

[0082] The role of the binder is to adhesively connect all the electrode materials for long-term charge / discharge cycling.

[0083] The binder may improve the mechanical properties of the solvent-free composition e.g., by binding the components of the solvent-free composition within the active layer.

[0084] The binder may be selected from polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyethylene oxide (PEO), polypropylene (PP), paraffin wax, polylactic acid (PLA), acrylonitrile-butadiene-styrene (ABS), polypropylene carbonate, hydrogenated nitrile butadiene rubber, and mixtures thereof.

[0085] The binder may be selected based on which dry deposition process is used. Dry deposition processes include, but are not limited to, electrospray deposition (ESD), free-standing film (FSF) formation, and atomic layer deposition (ALD).

[0086] Preferably the binder is PVDF, (particularly when the deposition process is ESD).

[0087] The glass transition temperature (Tg) of the binder is preferably below room temperature. For example, the Tgof the binder may be below 26 °C, below 25 °C, below 24.5 °C, below 24 °C, below 23°C, below 22 °C, below 21 °C, and / or below 20 °C. Preferably, the Tgof the binder is below 25 °C.

[0088] A binder with a glass transition temperature within this range may be particularly suitable for the composition, since it may provide the composition with superior mechanical properties to facilitate preparation of the composition.

[0089] The glass transition temperature may be determined using a standard method, for example by differential scanning calorimetry (DSC) and following the standard practice as defined in ASTM E1356-23, for instance at a heating rate of 10°C / min.

[0090] For example, DSC may be carried out on a DSC Q100 Differential Scanning Calorimeter.

[0091] To avoid directly handling the samples, tweezers or other tools are used. The samples are placed into an aluminium pan and weighed to an accuracy of 0.01 milligram on an analytical balance. A lid is crimped over the material sample onto the pan. Typically, the nitrile rubber is placed directly in the weighing pan, and covered by the lid. The differential scanning calorimeter is calibrated using an indium metal standard and a baseline correction is performed, as described in the operating manual for the differential scanning calorimeter. A material sample is placed into the test chamber of the differential scanning calorimeter for testing, and an empty pan is used as a reference. All testing is run with a 55-cubic centimeter per minute nitrogen (industrial grade) purge on the test chamber. The heating and cooling program is a 2-cycle test that began with an equilibration of the chamber to -80 °C, followed by a first heating period at a heating rate of 10 °C per minute to a temperature of 100 °C, followed by equilibration of the sample at 100 °C for 3 minutes, followed by a first cooling period at a cooling rate of 10 °C per minute to a temperature of -80 °C, followed by equilibration of the sample at -80 °C for 3 minutes, and then a second heating period at a heating rate of 10 °C per minute to a temperature of 100 °C.

[0092] The results may be evaluated by identifying and quantifying the glass transition temperature of inflection, the endothermic and exothermic peaks, and the areas under the peaks on the DSC plots. The glass transition temperature is identified as the region on the plot-line where a distinct change in slope occurred.

[0093] The binder may have a melting temperature (Tm) of from about 120 °C to about 190 °C. For example, the binder may have a melting point of from about 130 °C to about 180 °C, and / or from about 140 °C to 175 °C.

[0094] For example, the melting point of PVDF is typically from about 130 °C to about 175 °C.

[0095] For nitrile rubber binders, the melting temperature of the binder may be determined using the capillary tube method in accordance with ASTM D-1519, for instance at a heating rate of 10°C / min. For other binders, the melting temperature may be determined using the capillary tube method in accordance with ISO 3146:2022, for instance at a heating rate of 10°C / min.

[0096] A binder with a melting temperature (Tm) within this range may be particularly suitable for the composition, since it may provide the composition with superior mechanical properties to facilitate preparation of the composition.

[0097] The binder for the method of the present invention is preferably provided in powder form. This is beneficial for the dry mixing processes that may be used in the present invention. The binder for the method of the present invention preferably has a small particle size, for example less than 3 pm, preferably less than 2.5 pm, preferably less than 2 pm, preferably less than 1.5 pm, more preferably less than 1 pm.

[0098] Typically, the binder of the disclosure is provided as small particles. By small particles is meant particles having a diameter of 0.5 micron or less.

[0099] For example, the binder may have a D50 of from about 10 nm to about 500 nm, such as from about 50 nm to about 300 nm, for example from about 75 nm to about 250 nm, such as from 90 nm to about 200 nm.

[0100] Even more preferably, the small particles are provided as small particles having a D50 of about 100 nm or about 200 nm.

[0101] Additionally, the binder particles may have a D90 of from about 60 nm to about 600 nm, such as from about 80 nm to about 325 nm, for example from about 90 nm to about 275 nm, such as from 100 nm to about 250 nm.

[0102] The binder particles are smaller than the cathode active material particles. For example, the ratio between the D50 of the binder particles and the D50 of the cathode active material particles may be from about 1 :5 to about 1:200, from about 1: 10 to about 1: 150, from about 1:20 to about 1: 100, from about 1:40 to about 1:75, or from about 1:45 to about 1:55. Preferably, the ratio between the D50 of the binder particles and the D50 of the cathode active material particles is about 1:50.

[0103] Without wishing to be bound by theory, it is believed that the use of smaller binder particles compared to the size of cathode active material particles, allows the smaller binder particles to coat the surface of the comparably large cathode active material particles. This in turn means that a smaller amount of binder is needed compared to traditional dry deposition methodologies. A low binder amount is desirable, as the binder does not contribute to energy storage. Hence, lowering the amount of binder, will increase the energy density of a cell.

[0104] Typically, the binder is prepared using emulsion polymerisation. The use of emulsion polymerisation ensures segregation of the propagating polymer chains which in turn suppresses termination of the chains. It is therefore possible to achieve relatively high molecular weight polymers. Further, the fact that the polymerisation reaction proceeds in micelles and droplets ensures that there is an upper boundary for the size of the produced polymer particles. That means that emulsion polymerisation may be used to obtain polymer particles having diameters ranging from 10 to 500 nm, with the particles typically containing relatively high molecular weight polymers.

[0105] Overall, the use of emulsion polymerisation allows for adequate control of the size distribution of the formed polymer particles.

[0106] The binder particles may loosely bind to one another to form agglomerates. The agglomerates typically have a D50 of about 1 pm to about 10 pm. The binding within the agglomerates is relatively weak, so mixing easily breaks up the agglomerates to release individual particles.

[0107] In some embodiments, the binder may initially be provided as larger particles. For example, the binder particles may have a size which is similar to or larger than the cathode active material particles. In such a case, pre-milling of the binder may be carried out ensure the binder particles are sufficiently small. By sufficiently small is meant particles which fulfil the above-mentioned size requirements. Pre-milling is however not essential, and typically any binder agglomerates will be broken apart when the binder is mixed with the cathode active material and optional conductive additive.

[0108] Preferably, the binder is present in a small amount such as below 5 wt%, for example below 3 wt%, such as below 1 wt%, for example below 0.5 wt% based on the combined weight of the cathode active material, binder and conductive additives.

[0109] To secure sufficient binding, at least 0.005 wt%, for example at least 0.05 wt%, such as at least 0.1 wt% needs to be present in the electroactive composition.

[0110] Preferably, the binder is present in an amount of about 0.05 wt% to about 3 wt% based on the combined weight of the cathode active material, the conductive additives and the binder. Even more preferably, the binder is present in an amount of about 2 wt%, 1 wt%, or 0.5 wt%. Most preferably, the binder is present in an amount of about 0.5 wt%.

[0111] As used herein, "particle size" is the D[4,3]50 particle size (i.e. Dv50, for example the maximum D[4,3] particle diameter below which 50% of the sample volume exists) of the particles. Particle sizes disclosed herein may be measured, for instance, using a Mastersizer 3000 from Malvern Panalytical Ltd.

[0112] Preferably, the binder will have a sufficient level of tackiness to ensure adhesion of the composition during mixing, for instance above room temperature.

[0113] A particularly preferred binder has a particle size less than 2 pm, a Tgbelow room temperature (for example, below 25 °C) and a Tmfrom about 130 °C to about 175 °C.

[0114] The binder may be present in the composition in an amount of from about 0.01 wt% to about 8 wt%, for example from about 0.05 wt% to about 5 wt%, from about 0.1 wt% to about 4 wt%, such as from about 0.2 wt% to about 3 wt%, preferably from about 0.5 wt% to about 2 wt%, based on the total weight of the composition.

[0115] Particle size analysis

[0116] The D10, D50 and D90 of the particles may be measured by any method known to the person skilled in the art. Suitably however laser diffraction is used. Suitable methodologies for measuring particle size and particle size distributions by laser diffraction are detailed in ISO 13320:2020.

[0117] The size distribution may be determined by laser diffraction for instance using a Malvern Mastersizer 3000 + .

[0118] Laser diffraction measures particle size distributions by measuring the angular variation in intensity of light scattered as a laser beam passes through a dispersed particulate sample. Large particles scatter light at small angles relative to the laser beam and small particles scatter light at large angles. The angular scattering intensity data is then analysed to calculate the size of the particles responsible for creating the scattering pattern, using the Mie theory of light scattering. The particle size is reported as a volume equivalent sphere diameter (i.e. D[4,3] value).

[0119] When using a Mastersizer, typically, the particle properties (D10, D50 and D90 particle sizes) are measured in a solid dispersion.

[0120] Preferably, the particle properties (D10, D50 and D90 particle sizes) are measured when dispersed in water. Alternatively, a dry dispersion can be used. Suitably, the Mastersizer 3000+ Ultra allows particle size measurement using a dry powder, for instance dispersed in air.

[0121] When measured using laser diffraction, the particle size is reported as a volume equivalent sphere diameter (i.e. the D[4,3] value).

[0122] In an example, the particles are suspended in water and analysed using a Mastersizer 3000, wherein the Mastersizer 3000 is set a follows:

[0123] Mode: Single mode

[0124] Laser light: Red and blue laser light

[0125] Measurement time: 10 seconds per measurement

[0126] Obscuration range: 4 to 7%

[0127] Stabilization time: 30 seconds

[0128] The particle size analysis is then be carried out using Mie theory (volume equivalent sphere). To use Mie theory, it is usually necessary to know the refractive index and adsorption index of the sample. These may be determined by any suitable method.

[0129] Fibrillated binders

[0130] In an embodiment where the deposition process is a free-standing film (FSF) formation process, the binder is a fibrillated material.

[0131] The binder may be provided as a fibrillated material and / or the material may be fibrillated during any step of the preparation of the composition and / or film. The fibrillated material may be a fibrillated version of any of the materials listed as suitable binders for the composition of the present disclosure. Typically, the binder for FSF processes is fibrillated polytetrafluoroethylene (PTFE).

[0132] Fibrillation of the binder may be carried out using a fibrillation process, e.g. a (dry) high-shear method. For example, the material may undergo fibrillation to form a fibrillated material (or is fibrillated to a certain degree). The fibrillation process may include solvent to aid in fibrillation. Fibrillation may occur as part of step (a) or step (b) of the disclosed process, or fibrillation may occur in a separate step.

[0133] Without wishing to be bound by theory, it is proposed a fibrillated material may have a high binding affinity and / or surface area, so that the fibrils can link with other components of the film and / or electrode (e.g. electrode active material and / or optional conductive additive). The fibrillated material may provide fibrils that grip the particles with the core fibre linking two or more particles together. These features may provide advantageous properties to the electrode, in particular to the microstructure of the electrode, for example high packing density, low porosity, reduced incidence of defects (e.g. holes, cracks and / or surface pits), high tensile strength, resistance to shear stress, resistance to compressive stress, resistance to twisting stress, short diffusion paths and / or fast electronic and / or ionic transfer. For example, the fibrillated material may be fibre-like and form an interconnected network throughout the film and / or electrode and bind strongly to the electrode active material (e.g. thereby affecting the pore structure, microstructure and / or mesostructured and minimising void space).

[0134] The fibrillated material may be a fibre, for example with a fibre core length that is significantly larger than the fibre core width. In this way, the material may form an interconnected network throughout the film and / or electrode.

[0135] Preferably, the fibrillated material fibre core comprises a fibre core with fibrils (e.g. nano- and / or microfibrils) extending from the surface of the fibre core. The fibrillation process may provide the fibrillated material with an increased number of fibrils, greater fibril surface area and / or longer fibrils. The fibrillated material may comprise fibrils, in particular microfibrils, on the surface of the fibre core.

[0136] In cases where the fibrillated material fibres are staple fibres of a discrete length (e.g. in a millimetre to centimetre range), then the fibres may be cut down to a smaller fibre length.

[0137] The length of the fibrillated material fibre core may be from about 5-200 pm, such as from about 10-150 pm, including from about 20-50 pm. The width of the material fibre core may be from about 0.1-10 pm, such as from about 0.5-5 pm, for example from about 1-2 pm.

[0138] In one embodiment, the fibrillated material fibre core has an aspect ratio of from about 10-100, such as from about 20-50. The aspect ratio of a fibre may be understood to be the ratio of the fibre core length to the fibre core width.

[0139] It is advantageous if the length of the material fibre core is larger than the size of the electrode active material particle, and / or the width of the material fibre core is smaller than the size of the electrode active material particle. This allows the material fibre to act as a binder and form an interconnected network throughout the free-standing electrode film and / or electrode, with the fibrils aiding in adhesion to the individual particles. In this way, the fibres may link the electrode active particles together with fibrils gripping each particle, and provide superior mechanical properties (e.g. a high binding and / or adhesive strength) to the film and / or electrode.

[0140] Conductive additive

[0141] The solvent-free composition comprises a conductive additive. The conductive additive is included to improve the electronic properties of the resultant electroactive layer. It may for example provide an electrical connection between the particles of the electrode active material in the electrode.

[0142] In some embodiments, the conductive additive is a carbon-based material.

[0143] By carbon-based material, this is understood to be a material comprising carbon. However, the carbon-based material may also contain elements other than carbon, such as hydrogen, oxygen, nitrogen, boron, sulphur, halogens, and metals, including alkali metals, such as lithium. For example, the carbon-based material may contain elements other carbon that may be selected from one or more of hydrogen, oxygen, nitrogen, and mixtures thereof.

[0144] In one embodiment, the conductive additive is a carbon allotrope.

[0145] For example, the conductive additive may be selected from one or more of graphene, graphene fiber, fibrous graphene, porous graphene, nanoporous graphene, nanoporous graphene fiber, holey graphene, perforated graphene, graphene foam, graphene aerogel, carbon nanofiber (CNF), porous carbon nanofiber, carbon nanofoam, carbon microfoam, graphite, amorphous carbon, carbon black, acetylene black, mesocarbon microbead (MCMB), pitch-based carbon, coke powders, single-walled carbon nanotube, thin-walled carbon nanotube, multi-walled carbon nanotube, and mixtures thereof.

[0146] Preferably, the conductive additive is selected from one or more of nanoporous graphene, nanoporous graphene fiber, holey graphene, carbon nanofiber (CNF), porous carbon nanofiber, carbon black and mixtures thereof. More preferably, the conductive additive is carbon black. Preferably, the carbon black is Ketjenblack®. N? gas sorption may be used to calculate the Brunauer-Emmett-Teller (BET) specific surface area (or BET surface area). The BET surface area may be measured by use of ASTM method D3663-03.

[0147] The conductive additive has a specific BET surface area of 50 m2 / g or greater. In particularly preferred embodiments, the conductive additive has a specific BET surface area which is greater than 50 m2 / g. For example, preferred embodiments include those in which the conductive additive has a specific BET surface area of 60 m2 / g or greater, 70 m2 / g or greater, 80 m2 / g or greater, 90 m2 / g or greater, 100 m2 / g or greater, 120 m2 / g or greater, 150 m2 / g or greater, 180 m2 / g or greater, 200 m2 / g or greater, 250 m2 / g or greater, 300 m2 / g or greater, 350 m2 / g or greater, 400 m2 / g or greater, 450 m2 / g or greater, more preferably 500 m2 / g or greater, 600 m2 / g or greater, 700 m2 / g or greater, even more preferably 800 m2 / g or greater.

[0148] For instance, the conductive additive may have a specific BET surface area of from 50 to 2000 m2 / g, such as from 60 to 2000 m2 / g, from 70 to 2000 m2 / g, from 80 to 2000 m2 / g, from 90 to 2000 m2 / g, from 70 to 1900 m2 / g, from 75 to 1800 m2 / g, from 80 to 1700 m2 / g, from 85 to 1600 m2 / g or from 90 to 1500 m2 / g.

[0149] Surprisingly, it has been found that the BET surface area of the conductive additive correlates with an electrode's cyclability.

[0150] The Oil Absorption Number (OAN) may also be used as a measure of the specific surface area of the conductive additive. The OAN is a measure of a material's ability to absorb liquids, specifically oils.

[0151] The OAN of the conductive additive may be determined by measuring the absorption of dibutyl phthalate (DBP) using an absorptometer according to ASTM D2414-22. Typically, OAN is a property associated with carbon black.

[0152] The conductive additive may have an Oil Absorption Number (OAN) of 100 ml / lOOg or greater. In particularly preferred embodiments, the conductive additive has an OAN which is greater than 100 ml / lOOg. For example, preferred embodiments include those in which the conductive additive has an OAN of 200 ml / lOOg or greater, such as 210 ml / lOOg or greater, 220 ml / lOOg or greater, 230 ml / lOOg or greater, 240 ml / lOOg or greater, 250 ml / lOOg or greater, 300 ml / lOOg or greater, or 330 ml / lOOg or greater. For instance, the conductive additive may have an OAN of from 100 ml / lOOg to 600 ml / lOOg, for instance 200 to 500 ml / lOOg, such as from 220 to 450 ml / lOOg, from 230 to 400 ml / lOOg, from 240 to 350 ml / lOOg, from 250 to 340 ml / lOOg, or from 300 to 330 ml / lOOg.

[0153] The preferred OAN numbers disclosed herein preferably refer to embodiments wherein the conductive additive is carbon black.

[0154] Surprisingly, the correlation between OAN of the conductive additive and cyclability of an electrode does not always correlate in the same way as the BET surface area, particularly at low OAN values. See Figure 2.

[0155] The conductive additive may have a Surface Index Number of 5,000 m2 / g * ml / 100g or greater, wherein the SIN is the product of the BET surface area in m2 / g * ml / 100g and the OAN (ml / lOOg).

[0156] The Surface Index Number (SIN) may be calculated according to Equation (1):

[0157] SIN = BET surface area) * OAN ) (1)

[0158] The conductive additive may have an SIN of 5,000 m2 / g or greater. In particularly preferred embodiments, the conductive additive has a specific BET surface area which is greater than 5,000 m2 / g * ml / 100g. For example, preferred embodiments include those in which the conductive additive has an SIN of 6,000 m2 / g * ml / 100g or greater, 7000 m2 / g * ml / 100g or greater, 8000 m2 / g * ml / 100g or greater, 9,000 m2 / g * ml / 100g or greater, 10,000 m2 / g * ml / 100g or greater, 11,000 m2 / g * ml / 100g or greater, 12,000 m2 / g * ml / 100g or greater, 20,000 m2 / g * ml / 100g or greater, such as 25,000 m2 / g * ml / 100g or greater, 50,000 m2 / g * ml / 100g or greater, 75,000 m2 / g * ml / 100g or greater, 100,000 m2 / g * ml / 100g or greater, 200,000 m2 / g * ml / 100g or greater, or 400,000 m2 / g * ml / 100g or greater.

[0159] For instance, the conductive additive may have an SIN of from 20,000 to 600,000 m2 / g * ml / 100g, such as from 25,000 to 550,000 m2 / g * ml / 100g, from 50,000 to 500,000 m2 / g * ml / 100g, from 75,000 to 490,000 m2 / g * ml / 100g, from 100,000 to 480,000 m2 / g * ml / 100g or from 200,000 to 480,000 m2 / g * ml / 100g.

[0160] Both the BET surface area and the OAN provide a measure of the surface area of the conductive additive. However, the BET surface area is a measure of the amount of gas (nitrogen) that can be absorbed by a material, whereas the OAN provides a measure of how much oil that can be absorbed by a material (carbon black).

[0161] Typically, an electroactive layer according to the disclosure will be used in a cell comprising an organic electrolyte. Accordingly, the OAN can provide an indication of the conductive additive-electrolyte interaction and may therefore be correlated with the electronic performance e.g. cyclability.

[0162] The SIN provides a measure of both gas and oil absorption of the conductive additive. Without wishing to be bound by theory, it is considered that for materials with a low OAN, providing a high BET surface area can compensate and ensure good cyclability compared to a material with the same OAN but a lower BET, and vice versa.

[0163] Accordingly, in some instances the SIN provides a more accurate correlation to the electroactive layer's performance.

[0164] Using a conductive additive with a high surface area (for example, a specific BET surface area of 50 m2 / g or greater) is beneficial in the manufacture of an electrode. Without wishing to be bound by theory, using a conductive additive with a high surface area may allow for less conductive additive to be included in the composition whilst maintaining a high conductivity of the electrode and / or electroactive layer. Including a lower amount of conductive additive in the composition also may have the benefit of increasing the proportion of active materials in the battery composition, for example increasing the proportion of cathode active material in the composition, which in turn increases the capacity of the battery. It may also be possible to reduce the amount of binder that is required without negatively affecting the properties of the battery.

[0165] Without wishing to be bound by theory, due to the dry processing conditions and / or by using a high surface area conductive additive, an advantage of the present invention is that a greater amount of the surface of the cathode active material remains accessible to charge transfer species (e.g. lithium ions). In contrast, if wet processing conditions and / or a conductive additive with a lower surface area were used, the surface of the cathode active material may become blocked, for instance due to agglomerations forming during wet processing or due to using increased amounts of binder as required in wet processes.

[0166] As a result, the combination of the high surface area conductive additive and the dry processing conditions, the cathode may have a higher capacity, higher energy density, faster charge and discharge rate, higher rate capacity, higher integrity and / or higher adhesive strength compared to a cathode formed from a composition with a conductive additive with a lower surface area and / or using a wet manufacturing method.

[0167] In some embodiments, the conductive additive may be porous. For the avoidance of doubt, 'porous' here may refer to a material containing pores and that has a porous structure.

[0168] The conductive additive may be present in the composition in an amount of from about 0.01 wt% to about 8 wt%, for example from about 0.05 wt% to about 5 wt%, from about 0.1 wt% to about 4 wt%, such as from about 0.2 wt% to about 3 wt%, preferably from about 0.5 wt% to about 2 wt%, based on the total weight of the composition.

[0169] A composition of the present disclosure, wherein the composition is substantially solvent free, may be prepared by step (a) of the method of the present disclosure.

[0170] Typically, step (a) comprises: providing a composition comprising an electrode active material, a binder and a conductive additive, wherein the conductive additive has a specific BET surface area of 50m2 / g or greater, wherein the composition is substantially free of solvent.

[0171] When the conductive additive is carbon black, step (a) may preferably comprise: providing a composition comprising an electrode active material, a binder and a conductive additive, wherein the conductive additive has a specific BET surface area of 50m2 / g and / or greater and / or an OAN of 100 ml / lOOg or greater, wherein the composition is substantially free of solvent.

[0172] Typically, step (a) comprises: forming a composition comprising an electrode active material, a binder and a conductive additive, wherein the conductive additive has a specific BET surface area of 50m2 / g or greater (and / or an OAN of 100 ml / lOOg or greater if the conductive additive is carbon black) wherein the composition is substantially free of solvent.

[0173] Step (a) of the method may involve mixing the electrode active material, binder and conductive additive under a shear force, preferably resulting in a homogeneous distribution of components throughout the composition and / or avoiding excessive agglomeration.

[0174] A method for preparing the composition substantially free of solvent of the present disclosure, such as step (a) of the method of the present disclosure, may comprise the steps of:

[0175] (i) providing a combination of a cathode active material, a binder, and conductive additive; and

[0176] (ii) mixing the combination under a shear force to obtain the composition, preferably wherein step (ii) is a dry mixing process.

[0177] Step (i) of the method comprises providing a combination of cathode active material, binder and conductive additive, wherein the conductive additive has a specific BET surface area of 50m2 / g or greater (and / or OAN of 100 ml / lOOg or greater if the conductive additive is carbon black), and the resulting composition is substantially free of solvent. These ingredients may be combined in any order.

[0178] In some embodiments, step (i) of the method comprises the steps of:

[0179] (x) combining a binder (preferably PVDF) and an electroactive material in a first step to form a precursor composition; and

[0180] (y) combining the precursor composition and a conductive additive to form the composition.

[0181] Preferably the precursor composition is solvent-free.

[0182] Preferably, both steps (x) and (y) are dry mixing steps.

[0183] Carrying out steps (x) and (y) may result is better mixing of the components. For instance, two-step mixing may result in the binder covering the electroactive material particles. For instance, the binder may cover from about 5% to about 50% of the surface of the cathode active material particle, for example from about 10% to about 40%, such as from 20% to about 30%.

[0184] In some embodiments, step (i) comprises the steps of: providing

[0185] 1. a binder with a D50 particle diameter of 500 nm or less, 2. a cathode active material with a D50 particle diameter of about 5 to about 15 microns;

[0186] 3. a conductive additive, wherein the conductive additive has a BET surface area of 50 m2 / g or greater (and / or an OAN of ml / lOOg or greater if the conductive additive is carbon black).

[0187] In particularly preferred embodiments, step (i) of the method for preparing the composition substantially free of solvent of the present disclosure comprises the steps of:

[0188] (x) combining a binder (preferably PVDF) and an electroactive material in a first step to form a precursor composition; and

[0189] (y) combining the precursor composition and the conductive additive to form the composition; wherein,

[0190] 1. the binder has a D50 particle diameter of 500 nm or less;

[0191] 2. the electroactive material has a D50 particle diameter of about 5 to about 15 microns; and

[0192] 3. the conductive additive has a BET surface area of 50 m2 / g or greater.

[0193] Methods comprising steps (x) and (y), and comprising components according to 1-3, are particularly associated with a high packing density electroactive layer.

[0194] The ingredients for the combination may be supplied as a solution or a dispersion, and therefore solvent or dispersing medium may be added to prepare the substantially solvent-free composition.

[0195] Step (ii), step (x) and / or step (y) of the method involves mixing the combination under a shear force. The shear force applied during mixing is preferably sufficient to create a uniform, or near-uniform mixing of the ingredients provided in step (i), when the method comprises steps (i) and (ii). Step (ii), step (x) and / or step (y) are typically done at a rate which ensures even and thorough mixing of the combination, thereby resulting in a homogeneous distribution of ingredients throughout the resulting composition.

[0196] Step (ii), step (x) and / or step (y) of the method may comprise a dry mixing process. A dry mixing process is a mixing process that is substantially free of solvent. Typically, a high shear force is required to enable homogeneous dry mixing. The shear force may be calculated from a measurement of shear stress detected during the dry mixing process (for instance, in a high shear mixer).

[0197] Preferably, the shear force employed may result in the conductive additive and / or binder arranging around, surrounding and / or attaching to the surface of the electrode active material particles. Preferably, the shear force may result in the surface of the electrode active material not being completely covered by binder / conductive additive.

[0198] Typically, the (dry) mixing process of step (ii), steps (x) and / or step (y) utilises a mixer is selected from the group consisting of a high shear mixer, high shear reactor, rotorstator mixer, and a high-shear homogenizer.

[0199] Preferably, mixing the combination results in a homogeneous mixture. The mixing process is important since it may be advantageous to obtain an even distribution of the components of the composition throughout the mixture.

[0200] Typically, step (ii) steps (x) and / or step (y) comprises: mixing the combination for about 5 minutes to about 5 hours, such as for about 20 minutes to about 4 hours, for example for about 40 minutes to about 3 hours, such as for about 1 to about 2 hours.

[0201] Typically, step (ii), steps (x) and / or step (y) comprises: mixing the combination in a shear mixer, wherein the rotor tip speed of the shear mixer is from about 10 to about 50 m / s.

[0202] Preferably, step (ii) steps (x) and / or step (y) comprises: mixing the combination in a shear mixer, wherein the shear rate is from about 20,000 to about 100,000 s-1.

[0203] When the method of the disclosure comprises steps (x) and (y), the steps may be carried out using the same mixing parameters, for instance the same time or using the same shear force.

[0204] Alternatively, steps (x) and (y) may be carried out using different mixing parameters.

[0205] For instance, step (y) may be carried out at a higher shear force than step (x). This is particularly beneficial for the production of a high-density electroactive layer with well- distributed components (for instance, binder covering the electroactive material and / or homogenous distribution of conductive additive).

[0206] Wet processing may result in the binder and / or conductive active material completely covering the surface of the electrode active material (and / or conductive active material) and / or blocking space around the electrode active material particles, thereby reducing the accessibility of the particles and / or hindering the movement of the lithium ions throughout the electrode. Therefore, wet processing methods may result in unfavourably increasing the ionic resistance of the resulting electrode.

[0207] Without wishing to be bound by theory, due to the dry processing, such as dry mixing, and / or the properties of the high surface area conductive additive of the present disclosure, the binder and conductive additive material may have a reduced tendency to cover the surface of the active material and / or fill the void spaces of the electroactive layer, in comparison to an electroactive layer formed via wet processing methods. Furthermore, the binder may have a reduced tendency to form agglomerations with itself and / or the conductive additive. The reduced tendency to coat the cathode active material, and / or reduced tendency to form agglomerations may improve the amount of contact (i.e. increases the surface area of contact between the cathode active material particles, by increasing the number of contact points and / or by increasing the surface area of individual contact points) between the particles of cathode active material (and / or the conductive additive), allowing for greater conductivity.

[0208] Therefore, compared to wet processing methods, methods of the present disclosure may reduce the impedance and / or resistance to lithium conduction into and out of active material particles (due to greater accessibility of the particles), and may affect the ionic and / or electronic conductivity of the electroactive layer, for example by resulting in a reduced ionic tortuosity and an improved heterointerface between the components, and / or the mechanical strength of the electroactive layer. Ionic tortuosity should be understood to mean the trajectory for ion conduction through the electroactive layer. There may also be a reduced ionic resistance of the composition when in a cell, and a faster potential charging rate of the cell.

[0209] Accordingly, the method of the disclosure may provide an improved electroactive layer and / or electrode than those formed with methods comprising wet mixing and / or wet deposition steps.

[0210] Forming the electroactive layer (step b) Once the composition substantially free from solvent has been provided, the composition is deposited on a conductive foil to form an electroactive layer, for example, according to step (b) of the method of the present disclosure.

[0211] Any suitable method may be used for depositing the composition on the current collector to form an electroactive layer. For example, the electroactive layer may be a free-standing layer, the composition may be laminated to the current collector, the electroactive layer may be formed directly on the current collector, or it may be fibrillated.

[0212] The composition may be mixed with fluidising air prior to and / or during deposition (e.g. using a powder feeding hopper). The composition may be charged prior to and / or during the deposition process (e.g. in the form of charged particles).

[0213] Typically, step (b) of the present disclosure comprises: electrostatically depositing the composition onto a conductive foil to form a coated conductive foil.

[0214] The coated conductive foil then may undergo further processing steps to form an electroactive layer and / or an electrode. Any suitable method may be used to prepare the electroactive layer and / or the electrode of the disclosure, for example extrusion, calendering, pressing and / or rolling.

[0215] It is preferable that step (b) is substantially free of solvent. Dry preparation of the electroactive layer avoids any issues arising during solvent evaporation, for example microstructural defect formation in the electroactive layer.

[0216] Dry deposition processes include, but are not limited to, electrospray deposition (ESD), free-standing film (FSF) formation, and atomic layer deposition (ALD). Electrospray deposition may also be referred to electrostatic deposition within the context of the disclosure.

[0217] The composition may be applied to the conductive foil, for example by using an electrostatic deposition (ESD) process or a free-standing film (FSF) process.

[0218] Free-Standing Film

[0219] In an embodiment where the dry deposition process is a free-standing film (FSF) process, the binder is a fibrillated material, (preferably fibrillated PTFE). For example, when a fibrillated binder is used to provide the composition in step (a), the composition provided may form a free-standing film.

[0220] When step (b) is a FSF deposition process, an electrode may be obtained by providing the composition of step (a) (wherein the binder is a fibrillated material), and forming an electrode (for example, a cathode) from the free-standing electrode film and the conductive foil.

[0221] Typically, when step (b) is a FSF deposition process, step (b) involves bringing the free-standing electrode film into contact with the conductive foil.

[0222] Typically, when step (b) is a FSF deposition process, step (b) comprises: laminating the free-standing electrode film onto the conductive foil to form an electrode.

[0223] Spray deposition

[0224] Preferably, the method of the disclosure comprises an ESD process.

[0225] Spray deposition, in particular ESD, is a promising approach for the preparation of electrodes for lithium-ion batteries. This method may provide numerous advantages to the resulting electrodes, such as increased production efficiency, lower environmental footprint, improved flexibility and / or peel strength, higher energy density, capacity and / or charge / discharge rate, greater control over electrode properties (e.g. thickness and / or density), more uniform distribution of the components (i.e. binder, electrode active material and / or conductive additive) throughout the electrode and / or better distribution of the binder and / or conductive additive around the electrode active material.

[0226] Without wishing to be bound by theory, when deposition process of step (b) comprises ESD, it is proposed that an electrode with fast charging can be prepared without requiring carbon nanotubes as the conductive additive. For example, carbon black may be used as the conductive additive, whilst still achieving an electrode with charging properties as good as or better than an electrode prepared via a wet coating process which comprises carbon nanotubes as a conductive additive. It may be beneficial to use carbon black instead of carbon nanotubes, as carbon nanotubes are typically expensive. ESD may involve depositing and / or spray coating the composition onto the conductive foil, for example using a spray gun system. Typical process parameters are used to control the deposition process in order to achieve an electrode and / or electroactive layer with the desired properties, for example spray gun voltage, spray gun current, coating time, coating speed, deposition rate, nozzle size, air flow, coating passes (i.e. cycles), etc.

[0227] Typically, in ESD, particles are charged as they pass through a charging gun, and are deposited onto a substrate, wherein the substrate may be grounded. ESD provides further advantages, for example it may be used with a variety of different materials that have different particle shapes and / or sizes, it may be scaled up for large-scale manufacturing and / or it offers high deposition rates onto large surfaces.

[0228] ESD may involve depositing and / or spray coating the composition onto the conductive foil, for example using a spray gun system comprising a charging gun. Typical process parameters are used to control the deposition process in order to achieve an electrode with the desired properties, for example spray gun voltage, spray gun current, coating time, coating speed, deposition rate, nozzle size, air flow, coating passes (i.e. cycles), etc.

[0229] The composition may be mixed with fluidising air prior to and / or during deposition (e.g. using a powder feeding hopper). The composition may be charged prior to and / or during the deposition process (e.g. in the form of charged particles).

[0230] Accordingly, the solvent-free composition of the disclosure is formulated to be a suitable consistency for preparation of an electroactive layer and / or electrode. Due to the properties of the components, typically no additional binder or solvent is required for forming the electroactive layer. For example, for ESD, the composition provided in step (a) should be suitable for spraying. For example, for FSF, the composition provided in step (a) should be suitable for forming a free-standing film.

[0231] The processing conditions employed may be used to control the properties of the electroactive layer, for example the thickness, density and bonding strength. The processing conditions may therefore be varied to produce electroactive layer and / or electrode with tuned properties for different applications. For example, higher pressing forces and longer pressing times may result in thinner / denser layers, which may be optimal for certain applications and / or devices. Properties of the electroactive layer

[0232] The electrode active material, the binder and the conductive additive combine to form an electroactive composition.

[0233] Upon deposition of the electroactive composition unto a conductive foil, an electroactive layer is formed on said conductive foil.

[0234] In one embodiment, the electroactive composition consists of or comprises from 60 to 99.9 wt% cathode active material, from 0 to 10 wt% conductive additive, and from 0.005 to 5 wt% binder, for example from 90 to 99.8 wt% cathode active material, from 0.02 to 6 wt% conductive additive, and from 0.05 to 3 wt% binder, such as from 94 to 99 wt% cathode active material, from 0.5 to 3 wt% conductive additive, and from 0.1 to 1 wt% binder.

[0235] In an embodiment, the mass ratio of cathode active material:binder:conductive additive is about 96:2:2, more preferably about 98: 1: 1, even more preferably about 98.5:0.75:0.75.

[0236] The optimal mass ratio of cathode active material :binder:conductive additive may differ depending on the types of and the size of the materials used. Therefore, the optimal mass ratio for one set of cathode active material, binder and conductive additive may differ from the optimal mass ratio for another set of cathode active material, binder and conductive additive.

[0237] Prior to deposition of the electroactive composition, the components of the electroactive composition are mixed. For example, mechanochemical mixing may be used.

[0238] Typically, the mixing results in the coating of binder onto the cathode active material. This means that all the components of the electroactive composition are equally distributed.

[0239] The binder covers from about 5% to about 50% of the surface of the cathode active material particle, for example from about 10% to about 40%, such as from 20% to about 30%. An electroactive layer prepared using the method of the present disclosure, such as by a method comprising ESD, may have a lower porosity and / or higher packing density compared to one prepared using wet processing methods.

[0240] The density and / or porosity of the electroactive layer may be determined using various techniques, for example 3D imaging techniques, X-ray tomography, focused ion-beam scanning electron microscopy (FIB-SEM), pycnometry (e.g. helium), gas sorption techniques (e.g. nitrogen) and / or porosimetry (e.g. mercury) techniques.

[0241] The porosity may be defined as the percentage of volume of the material occupied by pores. For instance, the porosity of the electroactive layer may be defined as the fraction of the void volume of the electroactive layer over the total sample volume of the electroactive layer.

[0242] In one embodiment, the electroactive layer has a porosity of from about 1-50%, for example from about 15-40%, such as from about 15-35%, such as from about 20- 30%.

[0243] In one embodiment, the electroactive layer has a porosity of 30% or less, such as 28% or less, 25% or less, or 22% or less.

[0244] In some embodiments, the electroactive layer has a packing density of from about 0.8- 5.0 g / cm3, such as from about 1.0-4.0 g / cm3, such as from about 1.1-3.0 g / cm3, for example from about 1.2-1.75 g / cm3.

[0245] In preferred embodiments, the electroactive layer has a packing density of from about 0.8-6.0 g / cm3, such as from 1.5-5.6 g / cm3, such as from 2.0-5.0 g / cm3, such as from 2.5-4.5 g / cm3, for example from 3.0-4.0 g / cm3.

[0246] In the context of the disclosure, the terms "packing density" and "density" of an active layer may be used interchangeably.

[0247] One option for determining the porosity and packing density is by mercury intrusion porosimetry by measuring the diameter of mercury filled pores at a predetermined pressure according to ASTM UOP578-11, for example by using a mercury porosimeter such as Autopore produced by Micromeritics and PoreMaster produced by Quantachrome. The packing density here may be understood to be the bulk density as measured by mercury intrusion porosimetry. In this technique, a non-wetting liquid (i.e. mercury) is intruded into the material at high pressure and a porosity / density calculation is made based on Washburn's equation and the critical pressure needed to force the liquid into the material. The diameter of the fine pores may be measured at each predetermined pressure while continuously applying a pressure of up to 0.5- 60,000 psi. In this case, mercury intrusion porosimetry measurements are limited to the measurement of pores with a diameter greater than 50 nm (i.e. macropores).

[0248] A preferred method for determining the porosity / pa eking density of the electroactive layer is by calculating the values from the known bulk density of the materials. In the context of the disclosure, this may be referred to as the "bulk density reference method". This is the most preferred method of determining the porosity / packing density.

[0249] Accordingly, in a preferred embodiment, the density / porosity of the electroactive layer is calculated using the bulk density reference method.

[0250] Bulk density reference method

[0251] The electroactive layer of the disclosure is preferably a cathode active layer.

[0252] For cathode active layers, the density of the cathode active material is the greatest contributor to the density of the layer. The contribution of the conductive additive and binder can therefore be ignored for the purpose of calculating the density of the layer within the context of this disclosure.

[0253] Preferably, the electroactive layer of the disclosure comprises a cathode active material selected from the group consisting of NMC, LCO, NCA, LMO, LFP and LMP.

[0254] In the bulk density reference method, the porosity / packing density of the electroactive layer (e.g. cathode active layer) is determined by calculating the porosity based on a table of known cathode active material density values.

[0255] The relationship between the electrode density and cathode active material density is as follows:

[0256] Electroactive layer density = Bulk Cathode Material Density x (1-Porosity) Equation 2 can be used to calculate the porosity of the electroactive layer from the electroactive layer density and the density of the active material: ioo (2) wherein De is the electroactive layer density and DAM is the bulk density of the active material.

[0257] In most cases, the electroactive layer is deposited on a conductive foil to form an electrode. Accordingly, De may be measured as set out below.

[0258] The dimensions of the electrode comprising foil and active layer, and the dimensions of the foil alone are measured in order to determine the dimensions of the electroactive layer alone. For both measurements, the thickness may be measured by thickness gauge, LITEMATIC (Ball tip) VL-50S-B (MITUTOYO).

[0259] The mass of the electrode is measured by load cell. Again, the mass of the electrode comprising foil and electroactive layer, and the mass of the foil alone is measured in order to determine the mass of the electroactive layer alone.

[0260] De (density of the electroactive layer alone) can then be calculated from the mass and thickness measurements.

[0261] When the active material is a cathode active material, DAM (DCAM) is the bulk density of the cathode active material as defined in Table 1. Table 1

[0262] If the electroactive layer comprises a cathode active material that is not listed in Table 1, the bulk density of the cathode active material in Table 1 with the most similar chemical composition is chosen.

[0263] For instance, if the electroactive layer comprises an NMC732 material, the bulk density value of NMC811 as set out in Table 1 is selected.

[0264] For electroactive layers comprising a mixture of cathode active materials or a composite particle, the density of each of the components should be weighted according to the wt% of the material comprise in the layer.

[0265] That is, is an electroactive layer comprises 20 wt% LCO and 80 wt% NMC111, the DCAM in equation (2) is:

[0266] (0.2 * 5.06) + (0.8 * 4.8) = 4.825 0 / cm3

[0267] The desired porosity / packing density of the electroactive layer may be arrived at using any suitable method. For instance, after deposition of the electroactive layer, a calendaring step may be implemented in order to increase the density of the electroactive layer. In some embodiments, multiple calendaring steps may be implemented to increase the density of the electroactive layer in stages.

[0268] An embodiment of the disclosure refers to a method of forming an electroactive layer according to the disclosure wherein the electroactive layer is calendared after deposition in order to obtain the desired porosity and / or packing density.

[0269] In an embodiment, the electroactive layer may be calendared at a pressure of up to 150 bar, for instance up to 200 bar, up to 220 bar or up to 240 bar per calendaring step.

[0270] In addition, the calendar rolls may also be heated such that the calendaring step simultaneously compressed and heats the electroactive layer. Heating may assist with increasing the density of the electroactive layer. In an embodiment, the calendaring rolls may be heating to a temperature of 100°C or more, for instance 120°C or more, 150°C or more, 160°C or more, 170°C or more or 180°C or more.

[0271] The pressure and / or temperature of the calendaring step may depend on the composition of the electroactive layer. For instance, the particle size of the electroactive material may dictate the maximum calendaring pressure in order to avoid cracking the particles and / or the thermal properties of the binder may determine the calendaring temperature.

[0272] In addition to obtaining the desired porosity / packing density, calendaring may be used to increase adhesion of the electroactive layer to the current collector.

[0273] A high packing density / low porosity is often desired as it reduces the 'dead-weight' within a cell. The higher the packing density of the electroactive layer, the higher the potential capacity due to an increased volumetric energy density. However, electrodes comprising electroactive layers with a high packing density are often associated with poor electrolyte penetration and poor cyclability (see Figure 3 and Example 1.3).

[0274] Accordingly, it is advantageous to provide an electrode comprising a low porosity / high packing density electroactive layer that has improved cyclability.

[0275] In the context of the disclosure, the term "cyclability" may be used to refer to the change in specific capacity of an electrode and includes parameters such as first cycle efficiency, capacity degradation and capacity retention.

[0276] It has been surprisingly found that an electroactive layer comprising a high surface area conductive additive has improved cyclability (see Figures 1-2 and Examples 1.1- 1.2). This effect surprisingly extends even when a low porosity electroactive layer is provided.

[0277] Without wishing to be bound by theory, it is considered that the high surface area of the conductive additive mitigates the problems associated with low porosity, such as electrolyte penetration, and provides excellent electrical connection between the electroactive material particles over a number of cycles. For instance, Figure 3 shows that for electrodes of similar porosity (around 20-22%), providing a conductive additive with a higher surface area (1425 m2 / g compared to 62 m2 / g) results in a significant improvement in capacity degradation. In this instance, the high surface area conductive additive provides an improvement in capacity degradation of around 0.06% per cycle (average of degradation per cycle for cycle numbers 9-160).

[0278] A low porosity electroactive active layer comprising a high surface area conductive additive that is deposited in a substantially solvent-free method is considered to provide even greater advantages.

[0279] In order to obtain good cyclability, it is beneficial to provide an electroactive layer with consistent electrical connection throughout the layer. This can be achieved by providing a homogenously distributed conductive additive. For high surface area conductive additives, this is challenging in wet deposition methods due to agglomeration of the conductive additive during solvent mixing leading to poor distribution. Accordingly, the benefits associated with low porosity and a high surface area conductive additive are most effectively realised when preparing the electroactive layer via a substantially solvent-free deposition method.

[0280] A particularly preferred substantially solvent-free deposition method is electrospray deposition (ESD).

[0281] It has surprisingly been found that a density of over 3.6 g / cm3can easily be achieved in electrodes formed by electrospray deposition (ESD) and a cathode active material with a D50 particle diameter of 8 to 12 pm, and a binder with a particle size (diameter) of less than 500 nm. This is particularly advantageous as densities of over 3.6 g / cm3are often associated with wet processing conditions with bimodal cathode active material particles.

[0282] Preferably, the electroactive layer of the disclosure has a thickness of from about 10 pm to about 1 mm, for example from about 50 pm to about 750 pm, such as from about 100 pm to about 500 pm.

[0283] Preferably, the electroactive layer has a uniform thickness. For example, the thickness variation of the electroactive layer may be about 10% or less, for example about 5% or less, such as about 2.5% or less, preferably about 1% or less. By thickness variation, it should be understood to be the difference between the maximum thickness of the electroactive layer and the minimum thickness of the electroactive layer.

[0284] The electroactive layer according to the present disclosure may also display good electrolyte penetration, which can facilitate processing of the electrode and preparation of the cell. The penetrability of the electrolyte into the electroactive layer may be measured using an electrolyte drop test. For example, electrolyte may be applied to the electroactive layer and the spreading of the electrolyte observed. The spreading rate of the electrolyte on the electroactive layer may be from about 1-100 mm / min, for example from about 5-50 mm / min, such as from about 10-30 mm / min.

[0285] In some embodiments, the electroactive layer comprises about 85-99.5 wt% of an electrode active material (for example, a cathode active material), about 0.5-8 wt% of a binder and about 0.05-6 wt% of a conductive additive, based on the total weight of the electroactive layer.

[0286] In another embodiment, the electroactive layer comprises about 90-99 wt% of an electrode active material (for example, a cathode active material), about 0.7-6 wt% of a binder and about 0.05-4 wt% of a conductive additive, based on the total weight of the electroactive layer.

[0287] In a preferred embodiment, the electroactive layer comprises about 95.5-98.5 wt% of an electrode active material (for example, a cathode active material), about 1-2.5 wt% of a binder and about 0.25-2.5 wt% of a conductive additive, based on the total weight of the electroactive layer.

[0288] Electrode

[0289] The combination of binder, electrode active material and conductive additive of the present disclosure enables the preparation of an electrode to be carried out under solvent-free processing conditions. Electrodes prepared in said manner provide unique advantages compared with conventional wet processing methods as a result of the solvent-free process. This includes greater environmental friendliness, lower cost, enhanced compatibility, higher production efficiency and improved electrode performance.

[0290] Furthermore, the dry processing conditions may overcome multiple issues that arise with wet processing methods, either during wet mixing, such as instability of mixtures / compositions, rheological instabilities, binder degeneration, agglomeration, gas generation, and / or during wet coating, such as the formation of pin holes, curling, cracks and binder migration.

[0291] In particular, dry processing conditions overcome the agglomeration issues associated with conventional wet processing conditions. Dry processing methods may also enable a wider and / or alternative range of materials (such as high surface area particles), which would not be compatible with wet processing methods, and / or may also avoid any issues arising during solvent evaporation, for example microstructural defect formation on the electrode surface.

[0292] The electrode may be substantially free of solvent and / or substantially solvent-free, and / or prepared in such a manner.

[0293] The electrode of the present disclosure comprises a conductive foil. The type of conductive foil will depend on the choice of the type of electrode active material and whether the electrode is a cathode or an anode. For an anode, the conductive foil is typically copper.

[0294] In a preferred embodiment, the electrode of the disclosure is a cathode, and the conductive foil is a positive current collector.

[0295] The cathode conductive foil may comprise a metal, such as aluminium, nickel or stainless steel. Preferably, the positive conductive foil is an aluminium foil.

[0296] The conductive foil may have a coating such as a carbon coating, which can improve conductivity at the interface with the electrode active material. The coating may also improve the peel strength (or adhesive properties) of layers coated thereon, reducing delamination of the electrode.

[0297] The conductive foil may be a primer-coated conductive foil. Preferably, the conductive foil is coated with a primer, such as carbon and / or binder (e.g. acrylic binder). The primer-coated conductive foil may provide better adhesive properties compared to a non-coated conductive foil, and therefore better adhesion of electroactive layer and the current collector. Primer coatings may also provide enhanced electrical connection between the electroactive layer and the current collector.

[0298] The processing conditions may also affect the electrochemical properties of the electrode. Therefore, the processing conditions may be varied in order to tune the electrochemical properties of the electrode and the cell, such as capacity retention, cycle life and rate capacity.

[0299] In some embodiments, the electrode has a specific capacity on charge or discharge of from about 100-4200 mAh / g, such as from about 150-3400 mAh / g, for example from about 200-2000 mAh / g, such as from about 250-600 mAh / g, for example from about 300-500 mAh / g.

[0300] The electrode may be prepared from the electroactive layer or the composition of the present disclosure using any standard fabrication process. For example, the process may include mixing, milling, dosing, spraying, depositing, curing (e.g. chemical, thermal and / or UV), charging, ionisation, atomising, pre-calendering, calendering, preheating, winding, slitting and / or assembly.

[0301] Dry processing allows other active materials that are sensitive to solvents, such as NMP-sensitive or water-sensitive active materials, and high surface area conductive additives to be used.

[0302] Additionally, elimination of solvent or dispersing medium from the composition avoids the use of toxic and environmentally hazardous chemicals, and it can help to reduce electrode manufacturing costs associated with material resources, disposal of waste products, use of special production equipment, such as drying equipment, and time involved in electrode drying processes.

[0303] Electrodes prepared using the methods disclosed herein exhibit excellent structural and electrochemical properties in lithium-ion cells, especially due to the use of high surface area conductive additives.

[0304] To form an electrode, pre-calendering and / or calendering may be carried out on the coated conductive foil (i.e. after deposition of the composition onto the conductive foil), for example by roll-to-roll calendering.

[0305] Typically, step (b) comprises: pre-calendering and / or calendering the coated conductive foil to form an electrode, said electrode comprising the conductive foil having an electroactive layer thereon.

[0306] In other words, the calendering of the coated conductive foil compacts and bonds the coating on the conductive foil, forming an electroactive layer which is bonded to the underlying conductive foil. The electrode may comprise the electroactive layer and the conductive foil. The adhesion or peel strength of an electrode prepared by a method of the present invention, such as a method comprising deposition by ESD, may typically be very high. The adhesion strength of the coating onto the conductive foil may be measured using a peel test. The peel strength of the electrode comprising the components of the invention (i.e. an electrode active material, a binder and a conductive additive) may be about 5 N / m or greater, such as from about 10-150 N / m, for example from about 30-140 N / m.

[0307] The peel strength may be measured in accordance with ASTM D3330. The peeling strength test may be carried out on a Universal Testing Machine (e.g. Instron 3345), for example, using an electrode sample having a width of 25 mm. Each of the electrode plates in which the coating layers were located on both surfaces of the current collectors may be cut to a size of 25 mm x 150 mm. After an adhesive was coated on a glass substrate at room temperature, the electrode plate was adhered to the adhesive and roll-pressed. After one end of the electrode plate was folded 180°, a force applied to the sample was measured while pulling the sample in a direction opposite to the one end at a speed of 100 mm / min. The peel strength may be an average of 20 samples.

[0308] The remaining features of the cell of the present disclosure will be briefly described.

[0309] Cell

[0310] The present disclosure also relates to cells comprising the electrode of the disclosure, for example a secondary lithium-ion cell. Such cells typically comprise a cathode, an anode, a separator disposed between the anode and the cathode, wherein the cathode comprises the composition of the electrode disclosed herein.

[0311] The anode may comprise anode active material such as any one or a mixture of two or more of metallic lithium, lithium / aluminium alloys, lithium / tin alloys, carbon, hard carbon, graphite, black lead, lithium / titanium oxide, silicon, SiOx, silicon-carbon composites, prelithiated silicon or its composites and oxides and silicon / silicon composites. Preferably, the anode active material comprises carbon and / or silicon.

[0312] Said cathode, anode and separator may form 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 the 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. The cell may be a cylindrical, prismatic, coin cell or pouch cell. The cell may be a lithium-ion cell, such as a secondary lithium-ion cell. Preferably, the cell is a cylindrical secondary lithium-ion cell.

[0313] Battery System

[0314] The cell may be included in a battery system. The battery system may include one or more individual cells. The cells may be configured in a series, parallel or a mixture thereof, in order to achieve the desired voltage, energy capacity and / or power density. The battery system may include battery modules, wherein the battery modules include one or more individual cells. The battery system may include interconnects which provide electrical conductivity between the cells. The battery system may further include cooling and heating systems. The battery system may also include software for managing the battery system, for example a battery management system (BMS).

[0315] Vehicle

[0316] The battery system may be included in a vehicle. The vehicle may have an onboard power system that is integrated with the battery system. The battery system may also be included in a vehicle accessory, such as a trailer or roof-top box.

[0317] The following items describe embodiments of the invention

[0318] Item 1. A method of forming a cathode, the cathode comprising a conductive foil and an electroactive layer; the method comprising:

[0319] (a) providing a composition comprising a cathode active material; a binder; a conductive additive; wherein the conductive additive has a specific BET surface area of 50m2 / g or greater and / or wherein the conductive additive is carbon black and has an OAN of 100 ml / lOOg; and wherein the composition is substantially free of solvent; and

[0320] (b) depositing the composition on the conductive foil to form an electroactive layer.

[0321] Item 2. The method of item 1, wherein step (a) and / or step (b) is substantially free of solvent, preferably wherein step (a) and step (b) are substantially free of solvent. Item 3. The method of item 1 or item 2, wherein the composition is deposited on the conductive foil using an electrostatic deposition process, preferably electrostatic spray deposition.

[0322] Item 4. The method of any preceding item, wherein the conductive additive is selected from one or more of graphene, graphene fiber, fibrous graphene, porous graphene, nanoporous graphene, nanoporous graphene fiber, holey graphene, perforated graphene, graphene foam, graphene aerogel, carbon nanofiber (CNF), porous carbon nanofiber, carbon nanofoam, carbon microfoam, graphite, amorphous carbon, carbon black, acetylene black, mesocarbon microbead (MCMB), pitch-based carbon, coke powders, single-walled carbon nanotube, thin-walled carbon nanotube, multi-walled carbon nanotube, and mixtures thereof.

[0323] Item 5. The method of item 4, wherein the conductive additive is selected from one or more of nanoporous graphene, nanoporous graphene fiber, holey graphene, carbon nanofiber (CNF), porous carbon nanofiber, carbon black and mixtures thereof, preferably wherein the conductive additive is carbon black.

[0324] Item 6. The method of any preceding item, wherein the conductive additive has a specific BET surface area of 100 m2 / g or greater, preferably 200 m2 / g or greater, more preferably 500 m2 / g or greater, even more preferably 800 m2 / g or greater; and / or wherein the conductive additive is carbon black and has an OAN of 105 ml / lOOg or greater, 110 ml / lOOg or greater, 115 ml / lOOg or greater, 120 ml / lOOg or greater, 125 ml / lOOg or greater, 130 ml / lOOg or greater, 135 ml / lOOg or greater, 140 ml / lOOg or greater, 145 ml / lOOg or greater, 150 ml / lOOg or greater, 155 ml / lOOg or greater, or 160 ml / lOOg or greater.

[0325] Item 7. The method of any preceding item, wherein the composition comprises the conductive additive in an amount of from about 0.01 wt% to about 8 wt%, optionally from about 0.05 wt% to about 5 wt%, from about 0.1 wt% to about 4 wt%, about 0.2 wt% to about 3 wt%, preferably from about 0.5 wt% to about 2 wt%, based on the total weight of the composition.

[0326] Item 8. The method of any preceding item, wherein the cathode active material comprises a lithium nickel manganese oxide or a lithium nickel manganese cobalt oxide. Item 9. The method of any preceding item, wherein the composition comprises the cathode active material in an amount of from about 85 to about 99.8 wt%, optionally from about 90 to about 99.5 wt%, from about 92 to about 99 wt%, from about 94 to about 99 wt%, from about 95 wt% to about 98 wt%, or from about 96 to about 98 wt%, based on the total weight of the composition.

[0327] Item 10. The method of any preceding item, wherein the cathode active material has a D50 particle size in the range of from about 5 pm to about 15 pm, such as from about 8 pm to about 12 pm, such as from about 9 pm to about 11 pm.

[0328] Item 11. The method of any preceding item, wherein the cathode active material has a DIO particle size in the range of from about 0.1 pm to 12 pm, such as from 5 pm to 10 pm, for instance from 6 pm to 9 pm.

[0329] Item 12. The method of any preceding item, wherein the cathode active material has a D90 particle size in the range of from about 8 pm to 20 pm, such as from 10 pm to 15 pm, for instance from 11 pm to 14 pm.

[0330] Item 13. The method of any preceding item, wherein cathode active material has a bimodal particle size distribution.

[0331] Item 14. The method of any preceding item, wherein cathode active material has a unimodal particle size distribution.

[0332] Item 15. The method of any preceding item, wherein the binder has a particle size less than 2 pm, a Tgbelow room temperature, and a Tmfrom about 130 °C to about 175 °C.

[0333] Item 16. The method of any preceding claim wherein the binder is provided as particles having a diameter of 0.5 micron or less.

[0334] Item 17. The method of any preceding item wherein the binder has a D50 particle size of from about 10 nm to about 500 nm, such as from about 50 nm to about 300 nm, for example from about 75 nm to about 250 nm, such as from 90 nm to about 200 nm.

[0335] Item 18. The method of any preceding item wherein the binder has a D50 particle size of about 100 nm or about 200 nm. Item 19. The method according to any preceding item wherein the binder has a D90 particle size of from about 60 nm to about 600 nm, such as from about 80 nm to about 325 nm, for example from about 90 nm to about 275 nm, such as from 100 nm to about 250 nm.

[0336] Item 20. The method of any preceding item wherein the binder particles are smaller than the cathode active material particles.

[0337] Item 21. The method of any preceding item wherein the ratio between the D50 of the binder particles and the D50 of the cathode active material particles is from about 1:5 to about 1 :200, from about 1 : 10 to about 1 : 150, from about 1:20 to about 1: 100, from about 1:40 to about 1:75, or from about 1:45 to about 1:55, preferably wherein the ratio between the D50 of the binder particles and the D50 of the cathode active material particles is about 1 :50.

[0338] Item 21. The method of any preceding item, wherein the binder is one or more selected from polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyethylene oxide (PEO), polypropylene (PP), paraffin wax, polylactic acid (PLA), acrylonitrile- butadiene-styrene (ABS), polypropylene carbonate, hydrogenated nitrile butadiene rubber, and mixtures thereof; preferably wherein the binder is PVDF.

[0339] Item 22. The method of any preceding item, wherein the composition comprises the binder in an amount of from about 0.01 wt% to about 8 wt%, optionally from about 0.05 wt% to about 5 wt%, from about 0.1 wt% to about 4 wt%, about 0.2 wt% to about 3 wt%, preferably from about 0.5 wt% to about 2 wt%, based on the total weight of the composition.

[0340] Item 23. A composition for spray deposition comprising

[0341] 92-99 wt% cathode active material;

[0342] 0.05-7.95 wt% binder; and

[0343] 0.05-7.95 wt% conductive additive; wherein the conductive additive has a specific BET surface area of 50m2 / g or greater; and wherein the composition is substantially free of solvent. Item 24. A method for preparing the composition of item 23 or the composition as provided in step (a) of the method of any of items 1-22; the method comprising the steps of:

[0344] (i) providing a combination of a cathode active material, a binder, and conductive additive; and

[0345] (ii) mixing the combination under a shear force to obtain the composition, preferably wherein step (ii) is a dry mixing process.

[0346] Item 25. The method according to item 24 wherein step (i) of the method comprises the steps of:

[0347] (x) combining a binder (preferably PVDF) and an electroactive material in a first step to form a precursor composition; and

[0348] (y) combining the precursor composition and a conductive additive to form the of item 23 composition or the composition as provided in step 8a9 of the method of any of items 1-22.

[0349] Item 26. The method according to item 25 wherein the precursor composition is solvent-free.

[0350] Item 27. The method according to item 26 wherein step (i) comprises the steps of: providing

[0351] 1. a binder with a D50 particle diameter of 500 nm or less,

[0352] 2. a cathode active material with a D50 particle diameter of about 5 to about 15 microns;

[0353] 3. a conductive additive, wherein the conductive additive has a BET surface area of 50 m2 / g or greater (and / or an OAN of ml / lOOg or greater if the conductive additive is carbon black).

[0354] Item 28. The method of item 24-27, wherein step (i) and / or step (ii) is substantially free of solvent, preferably wherein step (i) and step (ii) are substantially free of solvent.

[0355] Item 29. A cathode formed from the method of any one of items 1-22 or 24-28.

[0356] Item 30. A cathode comprising, or formed from, the composition of item 23.

[0357] Item 31. An electroactive layer comprising; a cathode active material; a a conductive additive; and a binder, wherein the conductive additive has a specific BET surface area of 50 m2 / g or greater.

[0358] Item 32. The electroactive layer according to item 31 wherein the conductive additive has a specific BET surface area of 60 m2 / g or greater, 70 m2 / g or greater, 80 m2 / g or greater, 90 m2 / g or greater, 100 m2 / g or greater, 120 m2 / g or greater, 150 m2 / g or greater, 180 m2 / g or greater, 200 m2 / g or greater, 250 m2 / g or greater, 300 m2 / g or greater, 350 m2 / g or greater, 400 m2 / g or greater, 450 m2 / g or greater, more preferably 500 m2 / g or greater, 600 m2 / g or greater, 700 m2 / g or greater, even more preferably 800 m2 / g or greater.

[0359] Item 33. The electroactive layer according to items 31-32 wherein the conductive additive has a specific BET surface area of from 50 to 2000 m2 / g, such as from 60 to 2000 m2 / g, from 70 to 2000 m2 / g, from 80 to 2000 m2 / g, from 90 to 2000 m2 / g, from 70 to 1900 m2 / g, from 75 to 1800 m2 / g, from 80 to 1700 m2 / g, from 85 to 1600 m2 / g or from 90 to 1500 m2 / g.

[0360] Item 34. The electroactive layer according to items 31-33 wherein the conductive additive is selected from one or more of nanoporous graphene, nanoporous graphene fiber, holey graphene, carbon nanofiber (CNF), porous carbon nanofiber, carbon black and mixtures thereof.

[0361] Item 35. The electroactive layer according to item 34 wherein the conductive additive is carbon black.

[0362] Item 36. The electroactive layer according to item 35 wherein the conductive additive has an Oil Absorption Number (OAN) of 100 ml / lOOg or greater.

[0363] Item 37. The electroactive layer according to item 36 wherein the conductive additive has an OAN of 200 ml / lOOg or greater, such as 210 ml / lOOg or greater, 220 ml / lOOg or greater, 230 ml / lOOg or greater, 240 ml / lOOg or greater, 250 ml / lOOg or greater, 300 ml / lOOg or greater, or 330 ml / lOOg or greater.

[0364] Item 38. The electroactive layer according to item 36-37 wherein the conductive additive may have an OAN of from 100 ml / lOOg to 600 ml / lOOg, for instance 200 to 500 ml / lOOg, such as from 220 to 450 ml / lOOg, from 230 to 400 ml / lOOg, from 240 to 350 ml / lOOg, from 250 to 340 ml / lOOg, or from 300 to 330 ml / lOOg. Item 39. The electroactive layer according to item 35-38 wherein the conductive additive has a Surface Index Number (SIN) of 5,000 m2 / g * ml / 100g or greater, wherein the SIN is the product of the BET surface area in m2 / g and the OAN (ml / lOOg).

[0365] Item 40. The electroactive layer according to item 39 wherein the conductive additive has an SIN of 6,000 m2 / g * ml / 100g or greater, 7000 m2 / g * ml / 100g or greater, 8000 m2 / g * ml / 100g or greater, 9,000 m2 / g * ml / 100g or greater, 10,000 m2 / g * ml / 100g or greater, 11,000 m2 / g * ml / 100g or greater or 12,000 m2 / g * ml / 100g or greater, 20,000 m2 / g * ml / 100g or greater, such as 25,000 m2 / g * ml / 100g or greater, 50,000 m2 / g * ml / 100g or greater, 75,000 m2 / g * ml / 100g or greater, 100,000 m2 / g * ml / 100g or greater, 200,000 m2 / g * ml / 100g or greater, or 400,000 m2 / g * ml / 100g or greater.

[0366] Item 41. The electroactive layer according to item 39-40 wherein the conductive additive has an SIN of from 20,000 to 600,000 m2 / g * ml / 100g, such as from 25,000 to 550,000 m2 / g * ml / 100g, from 50,000 to 500,000 m2 / g * ml / 100g, from 75,000 to 490,000 m2 / g * ml / 100g, from 100,000 to 480,000 m2 / g * ml / 100g or from 200,000 to 480,000 m2 / g * ml / 100g.

[0367] Item 42. The electroactive layer according to item 31-41 wherein the electroactive layer has a porosity of from 1-50%, for example from about 15-40%, such as from about 15-35%, such as from about 20-30%.

[0368] Item 43. The electroactive layer according to item 42 wherein the electroactive layer has a porosity of 30% or less, such as 28% or less, 25% or less, or 22% or less.

[0369] Item 44. The electroactive layer according to items 31-43 wherein the electroactive layer has a packing density of from about 0.8-5.0 g / cm3, such as from about 1.0-4.0 g / cm3, such as from about 1.1-3.0 g / cm3, for example from about 1.2-1.75 g / cm3.

[0370] Item 45. The electroactive layer according to items 31-44 wherein 0.8-6.0 g / cm3, such as from 1.5-5.6 g / cm3, such as from 2.0-5.0 g / cm3, such as from 2.5-4.5 g / cm3, for example from 3.0-4.0 g / cm3.

[0371] Item 46. The electroactive layer according to items 31-45 wherein the active material is a cathode active material, optionally wherein the cathode active material is selected from the list comprising NMC, LCO, NCA, LMO, LFP, LMP and combinations thereof. Item 47. The electroactive layer according to item 46 wherein the cathode active material is a cathode active material according to items 10-14 or 21.

[0372] Item 48. The electroactive layer according to items 31-47 wherein the binder is a binder according to items 16-21.

[0373] Item 49. The electroactive layer according to items 31-48 wherein the electroactive layer is prepared according to the method of any of items 1-22 or 24-28, or from the composition of item 23.

[0374] Item 50. The cathode according to items 29-30 wherein the cathode comprises an electroactive layer according to items 31-49.

[0375] Item 51. A cell comprising: a cathode, wherein the cathode comprises an electroactive layer according to any of items 31-49; an anode; a separator; and an electrolyte; preferably wherein the cell is a lithium-ion cell, even more preferably wherein the cell is a secondary lithium-ion cell.

[0376] Item 52. A cell comprising: the cathode of item 29 or 30; an anode; a separator; and an electrolyte; preferably wherein the cell is a lithium-ion cell, even more preferably wherein the cell is a secondary lithium-ion cell.

[0377] Item 53. A cell according to items 51-53 wherein the cell has an average capacity retention of 99.5% or more per cycle for cycles 10-100, for instance the cell may have an average capacity retention of 99.6% or more, such as 99.7% or more, 99.8% or more, 99.9% or more, or 99.94% or more per cycle cycles 10-100.

[0378] Item 54. A cell according to item 53 wherein the cell has an average capacity retention of 80% or more for cycle 160 compared to the first cycle, for instance, 82% or more, such as 84% or more or 85% or more for cycle 160 compared to the first cycle. Item 55. A cell according to items 51-54 wherein the cell has a capacity degradation of 0.5% or less per cycle for cycles 10-100, for instance the cell may have an average capacity degradation of 0.4%, such as 0.3% or less, 0.2% or less, 0.1% or less or 0.06% or less for cycles 10-100.

[0379] Item 56. A cell according to item 53 wherein the cell has a capacity degradation of 20% or less for cycle 160 compared to the first cycle, for instance, 18% or less, such as 16% or less or 15% or less for cycle 160 compared to the first cycle.

[0380] Item 57. A battery system comprising the cell according to items 51-56.

[0381] Item 58. A vehicle comprising the battery system according to item 57.

[0382] Item 59. Use of a conductive additive with a BET specific surface area of 50m2 / g or greater or an OAN of 100 ml / lOOg or greater to increase the capacity of a cell, preferably wherein the conductive additive is used in the cell according to items 51- 56.

[0383] Item 60. Use of a conductive additive with a BET specific surface area of 50m2 / g or greater or an OAN of 100 ml / lOOg or greater to increase the cyclability of a cell, preferably wherein the conductive additive is used in the cell according to items 51- 56.

[0384] Item 61. The use according to item 60 wherein "cyclability of a cell" refers to capacity retention with cycle number.

[0385] Item 62. Use of a conductive additive with a BET specific surface area of 50m2 / g or greater or an OAN of lOOml / lOOg or greater to increase the capacity of a battery system, preferably wherein the conductive additive is used in the battery system according to item 57.

[0386] Item 63. Use of a conductive additive with a BET specific surface area of 50m2 / g or greater or an OAN of 100 ml / lOOg or greater to increase the cyclability of a battery system, preferably wherein the conductive additive is used in the battery system according to item 57. Item 64. The use according to item 63 wherein "cyclability of a battery" refers to capacity retention with cycle number.

[0387] The high surface area conductive additive (for instance, with a BET specific surface area of 50m2 / g or greater) may be used to increase the capacity of an electrode (preferably a cathode), a cell, and / or a battery system comprising the cell. In particular, the capacity may be increased compared to an electrode (preferably a cathode), a cell, and / or a battery system comprising the cell, which are prepared with wet processing methods, and / or with a lower surface area conductive additive.

[0388] The high surface area conductive additive may further be used to increase the cyclability of an electroactive layer compared to an electroactive layer of the same comprising a conductive additive with a lower surface area. This is particularly true when the porosity of the electroactive layer is low. This advantage may be particularly obtained when the electrode is prepared in a solvent-free method and as such, the cyclability of an electroactive layer prepared in the solvent-free method may be improved compared to an electrode with the same porosity and comprising the same conductive additive but deposited using a wet deposition technique.

[0389] For example, the high surface area conductive additive may be used in any of the methods of the invention to increase the capacity of a battery / and or cell. The high surface area conductive additive may also be used in any of the compositions of the invention. For example, it may be used in a composition for spray deposition, and / or in a composition to form a cathode, cell, battery system and / or vehicle.

[0390] 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 invention pertains.

[0391] All embodiments of the invention and particular features mentioned herein may be taken in isolation or in combination with any other embodiments and / or particular features mentioned herein (hence describing more particular embodiments and particular features as disclosed herein) without departing from the disclosure of the invention.

[0392] As used herein, the term 'comprises' will take its usual meaning in the art, namely indicating that the component includes but is not limited to the relevant features (i.e. including, among other things). As such, the term 'comprises' will include references to the component consisting essentially of the relevant substance(s).

[0393] Wherever the word 'about' is employed herein in the context of amounts, for example absolute amounts, weights, volumes, sizes, diameters etc., or relative amounts (e.g. percentages) of individual constituents in a composition or a component of a composition (including concentrations and ratios), timeframes, and parameters such as temperatures 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 herein. 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%).'

[0394] Examples

[0395] Four electroactive layer samples were prepared comprising an NMC811 cathode active material (CAM D50 = 10pm), a PVDF binder (D50 = 2-5pm (agglomerates)) and a conductive additive. All samples had a cathode active material: binder : conductive additive weight ratio of 98: 1: 1.

[0396] The properties of the conductive additive for Samples 1-4 are provided in Table 2:

[0397] Table 2

[0398] The electroactive layers were prepared by combining the cathode active material, binder and conductive additive and deposited on a conductive foil using ESD. The samples were then calendared using heated rollers.

[0399] The cyclability of the electroactive layer was then tested in a coin cell experiment according to the following protocol:

[0400] • Anode: Lithium metal

[0401] • Cathode: NMC811: PVDF: = 98: 1: 1

[0402] • Electrolyte: 1.2M LiPF6

[0403] • Cycle rate: 0.2C

[0404] • Discharge rate: 1.0C

[0405] • Voltage range 4.3V - 2.8V

[0406] • No of cycles: 160

[0407] The properties of the electroactive layers of Samples 1-4 are provided in Table 3:

[0408] * The degradation per cycle is reported for the 9th-160thcycles due to inconsistency in early cycles due to SEI formation. Figures 1-4 show the results of testing the samples. Figures 1 and 3 show that the surface area of the conductive additive is related to the cyclability of the electroactive layer; Figure 1 demonstrates that a BET high surface area provides improved cyclability and Figure 3 demonstrates that for the surface area as represented by the SIN is also excellently correlated with improved cyclability.

[0409] In addition, Table 2 and Figure 4 shows that the surface area of the conductive additive improves cyclability even when electroactive layer has a low porosity, (see for example Sample 1 vs 3). This is highly beneficial to high energy density and fast-charging applications.

Claims

CLAIMS1. An electroactive layer comprising; a cathode active material; a a conductive additive; and a binder, wherein the conductive additive has a specific BET surface area of 50 m2 / g or greater.

2. The electroactive layer according to claim 1 wherein the conductive additive has a specific BET surface area of 60 m2 / g or greater, 70 m2 / g or greater, 80 m2 / g or greater, 90 m2 / g or greater, 100 m2 / g or greater, 120 m2 / g or greater, 150 m2 / g or greater, 180 m2 / g or greater, 200 m2 / g or greater, 250 m2 / g or greater, 300 m2 / g or greater, 350 m2 / g or greater, 400 m2 / g or greater, 450 m2 / g or greater, more preferably 500 m2 / g or greater, 600 m2 / g or greater, 700 m2 / g or greater, even more preferably 800 m2 / g or greater.

3. The electroactive layer according to claims 1 or 2 wherein the conductive additive is carbon black, wherein the conductive additive has an Oil Absorption Number (OAN) of 100 ml / lOOg or greater, such as 200 ml / lOOg or greater, 210 ml / lOOg or greater, 220 ml / lOOg or greater, 230 ml / lOOg or greater, 240 ml / lOOg or greater, 250 ml / lOOg or greater, 300 ml / lOOg or greater, or 330 ml / lOOg or greater.

4. The electroactive layer according to claims 1 to 3 wherein the conductive additive is carbon black, wherein the conductive additive has a Surface Index Number (SIN) of 5,000 m2 / g * ml / 100g or greater, wherein the SIN is the product of the BET surface area in m2 / g and the OAN (ml / lOOg).

5. The electroactive layer according to claims 1 to 4 wherein the electroactive layer has a porosity of 1-50%, for example from about 15-40%, such as from about 15- 35%, such as from about 20-30%, or for example, wherein the electroactive layer has a porosity of 30% or less, such as 28% or less, 25% or less, or 22% or less.

6. The electroactive layer according to claims 1 to 5 wherein the density of the electroactive layer is from 0.8-6.0 g / cm3, such as from 1.5-5.6 g / cm3, such as from 2.0-5.0 g / cm3, such as from 2.5-4.5 g / cm3, for example from 3.0-4.0 g / cm3.

7. The electroactive layer according to claims 1 to 6 wherein cathode active material has a D50 particle size in the range of from about 5 pm to about 15 pm, such as from about 8 pm to about 12 pm, such as from about 9 pm to about 11 pm.

8. The electroactive layer according to claims 1 to 7 wherein the binder has a D50 particle size of from about 10 nm to about 500 nm, such as from about 50 nm to about 300 nm, for example from about 75 nm to about 250 nm, such as from 90 nm to about 200 nm.

9. The electroactive layer of any of claims 1 to 8 wherein the ratio between the D50 of the binder particles and the D50 of the cathode active material particles is from about 1: 5 to about 1:200, from about 1: 10 to about 1 : 150, from about 1 :20 to about 1: 100, from about 1:40 to about 1:75, or from about 1:45 to about 1:55, preferably wherein the ratio between the D50 of the binder particles and the D50 of the cathode active material particles is about 1 :50.

10. A method of forming a cathode, the cathode comprising a conductive foil and an electroactive layer according to any of claims 1 to 9, the method comprising:(a) providing a composition comprising a cathode active material; a binder; a conductive additive; wherein the conductive additive has a specific BET surface area of 50m2 / g or greater; and wherein the composition is substantially free of solvent; and(c) depositing the composition on the conductive foil to form an electroactive layer.

11. The method of claim 10, wherein step (a) and / or step (b) is substantially free of solvent, preferably wherein step (a) and step (b) are substantially free of solvent.

12. The method of claim 11 wherein step (a) comprises:(i) providing a combination of a cathode active material, a binder, and conductive additive; and(ii) mixing the combination under a shear force to obtain the composition, wherein step (i) comprises:(x) combining the binder (preferably PVDF) and cathode material in a first step to form a precursor composition; and(y) combining the precursor composition and the conductive additive to form the composition.

13. The method of claims 10 to 12 wherein step (c) comprises depositing the composition via electrostatic spray deposition.

14. A cell comprising: a cathode according to claims 10 to 13; an anode; a separator; and an electrolyte; preferably wherein the cell is a lithium-ion cell, even more preferably wherein the cell is a secondary lithium-ion cell.

15. The cell according to claim 14 wherein the cell has a capacity degradation of 0.5% or less per cycle for cycles 10-100, for instance the cell may have an average capacity degradation of 0.4%, such as 0.3% or less, 0.2% or less, 0.1% or less or 0.06% or less for cycles 10-100.

16. The cell according to claims 14-15 wherein the cell has a capacity degradation of 20% or less for cycle 160 compared to the first cycle, for instance, 18% or less, such as 16% or less or 15% or less for cycle 160 compared to the first cycle.

17. A battery system comprising the cell according to claim 14-16, optionally wherein the battery system is for a vehicle.

18. Use of a conductive additive with a BET specific surface area of 50m2 / g or greater, to increase the capacity and / or cyclability of an electrode (preferably a cathode), cell and / or battery system.

Images