Electrodes comprising a synthetic graphite additive

Abstract

The present invention relates to an electrode comprising an electrode active material, and a synthetic graphite additive, wherein the synthetic graphite additive has: a through-plane thermal conductivity of at least about 10 W / (m･k); and a d90 / d10 particle size ratio of at most about 8, wherein the particle size is measured by laser light scattering. The present invention further relates to a method of producing and using such an electrode, and a battery comprising such an electrode.

Description

[0001] Electrodes comprising a synthetic graphite additive

[0002] FIELD OF THE INVENTION

[0003]

[0001] The present invention relates to an electrode comprising an electrode active material and a synthetic graphite additive, a method of producing such an electrode, use of such an electrode and a battery comprising such an electrode.

[0004] BACKGROUND OF THE INVENTION

[0005]

[0002] Electrodes are commonly prepared by mixing an electrode active material, a binder, and a suitable solvent to form an electrode slurry, coating said electrode slurry onto a current collector, such as an aluminium or copper sheet, mesh, film or foil, and drying the electrode slurry at a high temperature to remove the solvent.

[0006]

[0003] Prepared electrodes may then be stacked or rolled together with a separator to form a battery.

[0007]

[0004] Controlling water and solvent content is considered to be important when fabricating electrodes, as high water or solvent content may result in severe attenuation of electrochemical performance and affect battery stability. The structure and properties of electrodes are affected by the manufacturing processes, including the drying process. For example, drying an electrode slurry too quickly, or at too high a temperature can lead to poor adhesion between the coated electrode slurry layer and the current collector, as well as reduced electrolyte diffusion and high ionic resistance from the electrode. Therefore, care needs to be taken when drying an electrode slurry to ensure high quality electrodes are fabricated, as it is a complex combination of heat and mass transfer processes. As such, the process of drying an electrode slurry is often expensive and can be very time consuming.

[0008]

[0005] There are a multitude of factors that affect the drying process, such as the electrode slurry preparation, electrode slurry composition and the equipment and temperature used for drying the electrode slurry.

[0009]

[0006] With current drying technologies, the primary focus has been on how to enhance the thermal-mass exchange during the drying. All of the optimizations are made through modifications to the drying equipment and drying conditions. However, due to the thickness and low through-plane thermal conductivity of as-coated electrode layers, it makes it difficult to achieve fast heat-mass exchange. Thus, it is difficult to achieve uniform drying of the electrode slurry, which makes it easy for the electrode to crack and break, affecting the performance and lifetime of any resultant battery. As such, there is an emerging need to control the drying of the electrode slurry to achieve improved quality control of the electrodes.

[0010]

[0007] It is therefore desirable to provide electrodes with wider process windows (such as temperature) that also have good properties. It is also desirable to provide improved methods of producing such electrodes.

[0011] SUMMARY OF THE INVENTION

[0012]

[0008] The present invention is defined in the appended claims.

[0013]

[0009] In accordance with a first aspect, the present invention provides an electrode comprising an electrode active material and a synthetic graphite additive, wherein the synthetic graphite additive has: a through-plane thermal conductivity of at least about 10 W / (m-k); and a dgo / d particle size ratio of at most about 8, wherein the particle size is measured by laser light scattering. The laser light scattering method used is described below.

[0014]

[0010] Particle size properties referred to herein, such as the d , dso and dgo particle size of the synthetic graphite additive, are measured by wet Malvern laser scattering (standard ISO 13320-1). In this technique, the size of particles in powders, suspensions and emulsions may be measured using the diffraction of a laser beam, based on the application of Mie theory. Such a machine, for example a Malvern Mastersizer 2000 (as supplied by Malvern instruments) provides measurements and a plot of the cumulative percentage by volume of particles having a size, referred to in the art as the “equivalent spherical diameter” (e.s.d), less than given e.s.d values. The mean particle size dso is the value determined in this way of the particle e.s.d. at which there are 50% by weight of the particles which have an equivalent spherical diameter less than that dso value. For the avoidance of doubt, the measurement of particle size using laser light scattering is not an equivalent method to a sedimentation method.

[0015]

[0011] The inventors surprisingly found that high quality electrodes, with low electrode tortuosity and high peel strength were able to be fabricated from a combination of an electrode active material and a synthetic graphite additive, where the synthetic graphite additive has a through-plane thermal conductivity of at least about 10 W / (m-k) and a dgo / dw particle size ratio of at most about 8, wherein the particle size is measured by laser light scattering. The inventors found that electrodes according to the present invention had improved microstructure properties and subsequently improved performance when used in battery cells, which is considered to be due, at least in part, to the synthetic graphite additive used.

[0016]

[0012] Examples of the present invention showed that the electrodes comprising an electrode active material, and the synthetic graphite additive having a through-plane thermal conductivity of at least about 10 W / (m-k) and a dgo / d particle size ratio of at most about 8, produced coin cells with higher charging performance than coin cells fabricated using a commercially available synthetic graphite additive commonly used in electrodes. In many cases, the inventors observed an interrelation between the electrode tortuosity, drying speed, peel strength, and charging performance, and the synthetic graphite additive used in the present invention to form the electrodes.

[0017]

[0013] In accordance with a second aspect, the invention further provides a method of producing an electrode comprising:

[0018] - providing an electrode slurry comprising an electrode active material and the synthetic graphite additive according to the first aspect and a solvent;

[0019] - applying the electrode slurry to a substrate; and

[0020] - drying.

[0021]

[0014] In accordance with a third aspect, the invention further provides the use of an electrode according to the first aspect in a battery.

[0022]

[0015] In accordance with a fourth aspect, the invention further provides a battery comprising the electrode according to the first aspect.

[0023]

[0016] In accordance with a fifth aspect, the invention further provides an electrode comprising an electrode active material and the synthetic graphite additive, wherein the synthetic graphite additive has: a through-plane thermal conductivity of at least about 10 W / (m- k); and a d9o / dio particle size ratio of at most about 8; and wherein the synthetic graphite additive has a dso particle size of up to about 10 pm, as measured by laser light scattering.

[0024]

[0017] Certain embodiments of the present invention may provide one or more of the following advantages:

[0025] • high quality electrodes;

[0026] • reduced electrode tortuosity;

[0027] • improved adhesion between the applied electrode slurry layer and substrate when dried; • improved drying homogeneity of the electrode surface;

[0028] • reduced surface defects in the electrode surface;

[0029] • reduced cracking and / or breaking of electrode surface;

[0030] • improved discharge capacity retention of resultant battery cells;

[0031] • increased efficiency of resultant battery cells;

[0032] • reduced energy consumption;

[0033] • reduced production cost of resultant battery cells;

[0034] • increased production efficiency of battery cells; and

[0035] • reduced cell surface temperature increases during cell charging / discharging at high current densities.

[0036]

[0018] The details, examples and preferences provided in relation to any particular one or more of the stated aspects of the present invention apply equally to all aspects of the present invention. Any combination of the embodiments, examples and preferences described herein in all possible variations thereof is encompassed by the present invention unless otherwise indicated herein, or otherwise clearly contradicted by context.

[0037] BRIEF DESCRIPTION OF THE DRAWINGS

[0038]

[0019] The disclosure will further be illustrated by reference to the following figure:

[0039] Figure 1: shows the cycling performance of pouch cells CPC (comparative) and IPC 1 (inventive) fabricated using a comparative electrode and an electrode according to the present invention, respectively.

[0040] Figure 2: shows pouch cell temperature vs. charging time for pouch cells CPC (comparative) and IPC 1 (inventive).

[0041] Figure 3: shows pouch cell temperature vs. discharge time for pouch cells CPC (comparative) and IPC 1 (inventive).

[0042] Figure 4: shows moisture content vs. time measured while drying electrode slurry IES 5 according to the present invention, and comparative electrode slurry CES 12.

[0043]

[0020] It is understood that the following description and references to the figure concern exemplary embodiments of the present invention and shall not be considered in any way limiting to the scope of the claims. DETAILED DESCRIPTION

[0044]

[0021] The present invention is based on the surprising finding that electrodes with improved microstructures can be obtained when the electrode comprises an electrode active material and a synthetic graphite additive with specific properties. Not only can the electrodes of the present invention have improved physical properties, it was also found that by using the synthetic graphite additive(s) with specific properties, uniform drying of the electrode could be achieved. It is considered that such uniform drying may reduce or avoid deviations or defects within the electrode surface.

[0045]

[0022] In particular, the present inventors found that an electrode comprising an electrode active material and the synthetic graphite additive, wherein the synthetic graphite additive has a through-plane thermal conductivity of at least about 10 W / (m-k) and a d9o / dio particle size ratio of at most about 8, has improved material and drying characteristics such as drying speed, adhesion and electrode tortuosity. The present inventors found that both the through-plane thermal conductivity and d9o / dio ratio within the synthetic graphite additive was important to achieve a high quality electrode with good peel strength and electrode tortuosity.

[0046]

[0023] When ranges are used herein, all combinations and sub-combinations of ranges and specific embodiments therein are intended to be included.

[0047]

[0024] As used herein, the term "about" when referring to a number or a numerical range means that the number or numerical range referred to is an approximation within experimental variability (or within statistical experimental error), and thus the number or numerical range may vary. Typical experimental variabilities may stem from, for example, changes and adjustments necessary during scale-up from laboratory experimental and manufacturing settings to large scale, GMP manufacturing conditions as is known to those familiar with the art of electrode development and manufacturing. Such changes can vary between 1% and 10% of the stated number or numerical range.

[0048]

[0025] As used herein, the term "comprising" (and related terms such as "comprise" or "comprises" or "having" or "including") has an open meaning and therefore an electrode slurry composition or an electrode composition comprising described features may comprise additional components in addition to the described features.

[0049]

[0026] Abbreviations used herein have their conventional meaning within the chemical and electrochemical arts, unless otherwise indicated. Electrode

[0050]

[0027] The present invention provides an electrode comprising an electrode active material and a synthetic graphite additive, wherein the synthetic graphite additive has: a through-plane thermal conductivity of at least about 10 W / (m-k); and a dgo / d particle size ratio of at most about 8, wherein the particle size is measured by laser light scattering.

[0051]

[0028] In some embodiments, the electrode may be for use in a battery. In particular embodiments, the battery is a rechargeable battery. For example, the battery may be an alkaline battery, a lead acid battery or a lithium-ion battery. For example, an electrode according to the present invention in a lead acid battery may lead to an improvement of the cycle life and charge acceptance. Lithium-ion batteries have attracted widespread attention, particularly over the past two decades, due to the increased demand for the use of alternative energy or clean energy, and alternative forms of power generation and storage. High-performance, low-cost lithium-ion batteries currently offer one of the most promising options for large-scale energy storage equipment. Therefore, it would be advantageous to be able to prepare high quality electrodes for use in lithium-ion batteries.

[0052]

[0029] In alternative embodiments, the electrode may be used in any electrochemical cell, for example, in a fuel cell such as a proton-exchange membrane fuel cell. It is envisaged the electrode according to the present invention may be suitable for use in any field using electrodes comprising carbonaceous materials such as synthetic graphite additives, for example, the field of electrolysis.

[0053] Thermal Conductivity and Particle Size

[0054]

[0030] The synthetic graphite additive of the electrode has a through-plane thermal conductivity of at least about 10 W / (m-k). In some embodiments, the synthetic graphite additive of the electrode has a through-plane thermal conductivity of at least about 11 W / (m-k), for example, at least about 12 W / (m-k), at least about 13 W / (m-k), or at least about 13.5 W / (m-k). The through-plane thermal conductivity, as referred to herein, is measured according to ASTM E1461 using a Laser Flash Analyzer by NETZSCH (LFA 447 analyzer).

[0055]

[0031] In some embodiments, the synthetic graphite additive of the electrode has a through-plane thermal conductivity in the range of about 10 W / (m-k) to about 30 W / (m- k). For example, in embodiments, the synthetic graphite additive of the electrode has a through-plane thermal conductivity in the range of about 12 W / (m-k) to 25 about W / (m- k), or in the range of about 13.5 W / (m-k) to 19.0 W / (m-k).

[0056]

[0032] The synthetic graphite additive of the electrode has a dgo / dw particle size ratio of at most about 8, wherein the dgo / d is determined by laser light scattering. For example, in some embodiments, the synthetic graphite additive of the electrode has a dgo / dw of particle size ratio of at most about 7.5, at most about 7, at most about 6.5, at most about 6, at most about 5.5, at most about 4.5, or at most about 4. In some embodiments the synthetic graphite additive of the electrode has a d90 / dw particle size ratio of at least 0.1 , at least 0.5, at least 1 , at least 1.5 or at least 2.0.

[0057]

[0033] In some embodiments, the synthetic graphite additive of the electrode has a through-plane thermal conductivity of at least about 11 W / (m-k) and a dgo / dw particle size ratio of at most about 8. For example, in some embodiments, the synthetic graphite additive of the electrode has a through-plane thermal conductivity of at least about 12 W / (m-k) and a dgo / dw particle size ratio of at most about 8, or a through-plane thermal conductivity of at least about 13 W / (m-k) and a dgo / dw particle size ratio of at most about 8, or a through-plane thermal conductivity of at least about 13.5 W / (m-k) and a dgo / dw particle size ratio of at most about 8. In certain embodiments, the synthetic graphite additive of the electrode has a through-plane thermal conductivity of at least about 10 W / (m-k) and a d90 / dw particle size ratio of at most about 7, or a through-plane thermal conductivity of at least about 10 W / (m-k) and a dgo / dw particle size ratio of at most about 6, or a through-plane thermal conductivity of at least about 11 W / (m-k) and a dgo / dw particle size ratio of at most about 6, or a through-plane thermal conductivity of at least about 12 W / (m-k) and a dgo / dw particle size ratio of at most about 6, or a through-plane thermal conductivity of at least about 13 W / (m-k) and a dgo / dw particle size ratio of at most about 6, or a through-plane thermal conductivity of at least about 13.5 W / (m-k) and a d90 / dw particle size ratio of at most about 6.

[0058]

[0034] In certain embodiments, the synthetic graphite additive of the electrode has a through-plane thermal conductivity in the range of about 13.5 W / (m-k) to 19.0 W / (m-k), and a dgo / dw particle size ratio of at most about 6.

[0059]

[0035] In some embodiments, the synthetic graphite additive of the electrode has a dw particle size, determined by laser light scattering, of up to about 5 pm, for example, up to about 4 m, up to about 3 pm, up to about 2.5 pm, or up to about 2 pm. For example, the synthetic graphite additive of the electrode has a dw particle size, determined by laser light scattering, of about 0.5 pm or more, for example of about 1.0 pm or more, or about 1.5 pm or more. For example, the synthetic graphite additive of the electrode has a d particle size of from about 0.5 pm to about 5 pm, or from about 1.0 pm to about 4 pm, or from about 1.5 pm to about 3 pm.

[0060]

[0036] In some embodiments, the synthetic graphite additive of the electrode has a dso particle size, determined by laser light scattering, of up to about 10 pm. For example, in some embodiments, the synthetic graphite additive of the electrode has a dso particle size of up to about 8.0 pm, up to about 6.0 pm, up to about 5.0 pm, up to about 4.0 pm, or up to about 3.5 pm. For example, the synthetic graphite additive of the electrode has a d5o particle size, determined by laser light scattering, of about 0.5 pm or more, for example of about 1.0 pm or more. For example, the synthetic graphite additive of the electrode has a d5o particle size of from about 0.5 pm to about 10 pm, or from about 0.5 pm to about 9.0 pm, or from about 0.5 pm to about 8.0 pm, or from about 0.5 pm to about 7.0 pm, or from about 0.5 pm to about 4.0 pm, or from about 0.5 pm to about 3.5 pm, or from about 0.8 pm to about 3.5 pm.

[0061]

[0037] In some embodiments, the synthetic graphite additive of the electrode has a dgo particle size, determined by laser light scattering, of up to about 25 pm, for example, up to about 22.5 pm, up to about 20 pm, up to about 17.5 pm, or up to about 15.5 pm. For example, the synthetic graphite additive of the electrode has a dgo particle size, determined by laser light scattering, of about 2 pm or more, for example of about 4 pm or more, or about 6 pm or more. For example, the synthetic graphite additive of the electrode has a dgo particle size of from about 2 pm to about 20 pm, or from about 4 pm to about 17.5 pm, or from about 6 pm to about 15.5 pm.

[0062]

[0038] In certain embodiments, the synthetic graphite additive of the electrode has a through-plane thermal conductivity in the range of about 13.5 W / (m-k) to 19.0 W / (m-k), a dgo / d particle size ratio in the range of about 3.5 to about 6, and a d5o particle size, determined by laser light scattering, of up to about 10 pm.

[0063] Interlayer Spacing c / 2

[0064]

[0039] In embodiments, the synthetic graphite additive has a c / 2 value of about 0.3360 nm or less. For example, in embodiments the synthetic graphite additive has a c / 2 value of about 0.3359 nm or less, or a c / 2 value of about 0.3358 nm or less. A lower c / 2 may be beneficial as it denotes a higher crystallinity of graphite, which can lead to improved thermal conductivity.

[0065]

[0040] The interlayer space c / 2 was determined by X-ray diffractometry. The angular position of the peak maximum of the

[0002] reflection profiles were determined and, by applying the Bragg equation, the interlayer spacing was calculated (Klug and Alexander, Xray diffraction Procedures, John Wiley & Sons Inc., New York, London (1967)). To avoid problems due to the low absorption coefficient of carbon, the instrument alignment and nonplanarity of the sample, an internal standard, silicon powder, was added to the sample and the graphite peak position was recalculated on the basis of the position of the silicon peak. The synthetic graphite additive sample was mixed with the silicon standard powder by adding a mixture of polyglycol and ethanol. The obtained slurry was subsequently applied on a glass plate by means of a blade with 150 pm spacing and dried.

[0066] Crystallite Size Lc

[0067]

[0041] In some embodiments, the synthetic graphite additive has a crystallinity (Lc) of about 50 nm or more. For example, in some embodiments, the electrode comprises a synthetic graphite additive having a crystallinity Lcof about 60 nm or more, or a crystallinity Lcof about 65 nm or more, or even a crystallinity Lcof about 70 nm or more. In some embodiments, the synthetic graphite additive has a crystallinity Lcof about 100 nm or less. For example, the electrode comprises a synthetic graphite additive having a crystallinity Lcof about 95 nm or less. As used herein, the crystallinity Lcdesignates the average crystallite size of the synthetic graphite additive. A larger crystallinity Lcmay be beneficial, as a larger Lcvalue denotes less crystal boundaries, and thus improved thermal conductivity.

[0068]

[0042] Crystallite size Lc is determined by analysis of the (002) and (004) diffraction profiles. For the present invention, the method suggested by Iwashita (N. Iwashita, C. Rae Park, H. Fujimoto, M. Shiraishi and M. Inagaki, Carbon 42, 701-714 (2004)) was used. The algorithm proposed by Iwashita has been specifically developed for carbon materials. The widths of the line profiles at the half maximum of sample and reference are measured. By means of a correction function, the width of pure diffraction profile can be determined. The crystallite size is subsequently calculated by applying Scherrer's equation, L=KA / pcos0, where K is a dimensionless shape factor, L is the crystallite size, A is the X-ray wavelength, is the line broadening at half the maximum intensity, and 0 is the Bragg angle. (P. Scherrer, Gottinger-Nachrichten 2 (1918) p. 98).

[0069] BET Surface Area

[0070]

[0043] In some embodiments of the present invention, the electrode comprises an electrode active material and a synthetic graphite additive, where the synthetic graphite additive has a BET surface area of about 30.0 m2 / g or less. For example, the synthetic graphite additive comprised in the electrode according to the present invention may have a BET surface area of about 25.0 m2 / g or less, or a BET surface area of about 22.5 m2 / g or less, or a BET surface area of about 20.0 m2 / g or less. In some embodiments of the present invention, the electrode comprises a synthetic graphite additive having a BET surface area of about 10.0 m2 / g or more. For example, the synthetic graphite additive comprised in the electrode according to the present invention may have a BET surface area of about 12.0 m2 / g or more, or about 20.0 m2 / g or more.

[0071]

[0044] The method of measuring BET is based on the registration of the absorption isotherm of liquid nitrogen in the range p / p0=0.04-0.26, at 77 K. The nitrogen gas adsorption was performed using a Quantachrome Autosorb-1. Following the procedure proposed by Brunauer, Emmet and Teller (Adsorption of Gases in Multimolecular Layers, J. Am. Chem. Soc., 1938, 60, 309-15 319), the monolayer capacity can be determined. On the basis of the cross-sectional area of the nitrogen molecule, the monolayer capacity and the weight of sample, the specific surface can then be calculated. Reference: Ravikovitch, P., Vishnyakov, A., Russo, R., Neimark, A., Langmuir 16 (2000) 2311-2320; Jagiello, J., Thommes, M., Carbon 42 (2004) 1227-1232.

[0072] Composition

[0073]

[0045] In embodiments, the electrode active material is selected from: synthetic graphite, natural graphite, hard carbon, a silicon-carbon composite, a silicon monoxidecarbon composite, or combinations thereof. In embodiments, the electrode may comprise from about 70 wt% to about 99 wt% or from about 80 wt% to about 98 wt% or from about 87 wt.% to about 98 wt.% or from about 89 wt.% to about 97.5 wt.% or from 91 wt.% to about 95 wt.% of the electrode active material, based on the total weight of the electrode.

[0046] In embodiments, the electrode may comprise from about 0.1 wt.% to about 10 wt.%, or from about 0.5 wt.% to about 8 wt.%, or from about 1 wt.% to about 6 wt.% of the synthetic graphite additive, based on the total weight of the electrode.

[0074]

[0047] In some embodiments, the combination of the electrode active material and the synthetic graphite additive are present in the electrode in an amount of from about 70.1 wt% to about 99 wt% or about, or from about 80 wt% to about 98 wt% or from about 87.1 wt.% to about 98.1 wt.% or from about 90 wt.% to about 98 wt.% or from about 92 wt.% to about 97 wt.%, or from about 92 wt% to about 95 wt% based on the total weight of the electrode.

[0075]

[0048] The electrode may further comprise other materials suitable for use in an electrode. In some embodiments, the electrode further comprises a conductive carbonaceous material, selected from any one of carbon black, carbon nanotube and combinations thereof. In embodiments, the electrode may comprise from about 0 wt.% to about 2 wt.%, or from about 0.25 wt.% to about 1.75 wt.%, or from about 0.5 wt.% to about 1.5 wt.% of the conductive carbonaceous material, based on the total weight of the electrode.

[0076]

[0049] In embodiments, the electrode comprises a dispersing agent and / or viscosity enhancer used in the electrode slurry used to prepare the electrode. In embodiments, the dispersing agent and / or viscosity enhancer may be selected from carboxymethyl cellulose (CMC), block co-polymers, naphthalene sulfonates, lignosulfonates, and combinations thereof. As used herein, the term "dispersing agent" refers to a substance used to help disperse the carbonaceous material particles and avoid aggregation, as more uniform distribution generally has a positive effect on battery performance. As used herein, the term “carbonaceous material particles” refers to materials containing or composed of carbon, in particular, the synthetic graphite additive and in embodiments, the electrode active material and / or conductive carbonaceous material. Well-dispersed carbon particles may reduce the viscosity of an electrode slurry during production, which may improve handling and processing. In some embodiments, the binder may act as a dispersing agent and / or viscosity enhancer. In embodiments, the electrode may comprise from about 0.8 wt.% to about 2 wt.%, or from about 1 wt.% to about 1.8 wt.% of the dispersing agent, based on the total weight of the electrode.

[0077]

[0050] In embodiments, the electrode comprises a binder, for example, a polymer binder. In embodiments, the polymer binder may be selected from styrene-butadiene rubber (SBR), polyvinyl alcohol (PVA) and polyvinylidene fluoride or polyvinylidene difluoride (PVDF) and combinations thereof. As used herein, the term "binder" refers to a substance used to make other substances in an electrode slurry adhere tightly and uniformly to the surface of a substrate, so that the active materials do peel off during the charge / discharge processes, to ensure the stable cycle performance and good electrochemical performance. In embodiments, the electrode may comprise from about 1 wt.% to about 2 wt.%, or from about 1.2 wt.% to about 1.7 wt.% of binder, based on the total weight of the electrode.

[0078]

[0051] In embodiments, the electrode has an electrode tortuosity in the range of about 0.1 T to about 2.0 T. For example, in certain embodiments, the electrode has an electrode tortuosity in the range of about 0.2 T to about 1.9 T, in the range of about 0.3 v to about 1.8 T, in the range of about 0.4 T to about 1.75 T, or in the range of about 0.5 T to about 1.7 T.

[0079]

[0052] In embodiments, the electrode has a peel strength equal to or higher than about 35 mN / 20mm. In some embodiments, for example, the electrode has a peel strength equal to or higher than about 37.5 mN / 20mm, higher than about 40 mN / 20mm, higher than about 42.5 mN / 20mm, higher than about 45 mN / 20mm.

[0080]

[0053] In certain embodiments, the electrode has an electrode tortuosity of in the range of about 0.1 T to about 2.0 T and a peel strength equal to or higher than about 35 mN / 20mm. In some embodiments, the electrode has an electrode tortuosity of in the range of about 0.1 T to about 1.7 T and a peel strength equal to or higher than about 45 mN / 20mm.

[0081] Method of Preparing an Electrode

[0082]

[0054] The present invention further provides a method of producing an electrode comprising:

[0083] providing an electrode slurry comprising the electrode active material and the synthetic graphite additive according to the present invention, and a solvent; applying the electrode slurry to a substrate; and

[0084] drying.

[0085]

[0055] In certain embodiments, the substrate is a current collector. In some embodiments, the substrate comprises a current collector selected from a copper sheet, titanium sheet, carbon sheet, copper mesh, titanium mesh, carbon mesh, a copper film, titanium film, carbon film, copper foil, titanium foil, carbon foil, copper foam, titanium foam, carbon foam, or combinations thereof.

[0086]

[0056] In embodiments, the electrode slurry comprises a binder, for example, a polymer binder. In embodiments, the polymer binder may be selected from styrenebutadiene rubber (SBR), polyvinyl alcohol (PVA) and polyvinylidene fluoride or polyvinylidene difluoride (PVDF) and combinations thereof. As used herein, the term "binder" refers to a substance used to make other substances in the slurry adhere tightly and uniformly to the surface of a substrate, so that the active materials do peel off during the charge / discharge processes, to ensure the stable cycle performance and good electrochemical performance. In embodiments, the electrode slurry may comprise from about 0.4 wt.% to about 1 wt.%, or from about 0.55 wt.% to about 0.85 wt.% of the binder, based on the total weight of the electrode slurry.

[0087]

[0057] In certain embodiments, such as when the binder used is water soluble, such as a binder selected from at least one of styrene-butadiene rubber (SBR) and polyvinyl alcohol (PVA), the solvent may be deionized water. In certain embodiments, such as when the binder has low water solubility, such as a binder selected from at least one of polyvinylidene fluoride or polyvinylidene difluoride (PVDF), the solvent may be selected from any suitable organic solvent. For example, suitable organic solvents may be selected from at least one of N-methyl-2-pyrrolidone (NMP), dimethyl formamide (DMF), dimethylacetamide (DMAC) or dimethyl sulfoxide (DMSO).

[0088]

[0058] In some embodiments, the electrode slurry may comprise from about 20 wt% to about 70 wt% or from about 40 wt% to about 70 wt% or from about 25 wt% to about 65 wt% or from about 45 wt% to about 65 wt% or from about 30 wt% to about 60 wt% or from about 50 wt% to about 60 wt% or from about 35 wt% to about 50 wt% or from about 40 wt.% to about 50wt.% of electrode active material based on the total weight of the electrode slurry, for example, from about 45 wt.% to about 47 wt.% of electrode active material based on the total weight of the electrode slurry.

[0089]

[0059] In some embodiments, the electrode slurry may comprise from about 0.03 wt% to about 7 wt% or from about 0.1 wt% to about 6 wt% or from about 0.2 wt% to about 5 wt% or from about 0.3 wt.% to about 5 wt.% or from about 0.4 wt% to about 4 wt% or from about or from about 1.4 wt.% to about 3 wt.% of synthetic graphite additive based on the total weight of the electrode slurry.

[0090]

[0060] In some embodiments, the electrode slurry may comprise the combination of the electrode active material and the synthetic graphite additive in the range of from about 21 wt% to about 60 wt% or from about 25 wt % to about 55 wt% of from about 30 wt% to about 50 wt% or from about 35 wt% to about 45 wt%.

[0091]

[0061] In embodiments, the electrode slurry comprises a conductive carbonaceous material, selected from any one of carbon black, carbon nanotube and combinations thereof. In embodiments, the electrode slurry may comprise from about 0 wt.% to about 1 wt.% or from about 0.2 wt.% to about 0.75 wt.% of the conductive carbonaceous material, based on the total weight of the electrode slurry.

[0092]

[0062] In embodiments, the electrode slurry comprises a dispersing agent and / or viscosity enhancer. In embodiments, the dispersing agent and / or viscosity enhancer may be selected from carboxymethyl cellulose (CMC), block co-polymers, naphthalene sulfonates, lignosulfonates, and combinations thereof. As used herein, the term "dispersing agent" refers to a substance used to help disperse the carbonaceous material particles and avoid aggregation, as more uniform distribution generally has a positive effect on battery performance. Well-dispersed carbon particles may reduce the viscosity of an electrode slurry during production, which may improve handling and processing. In some embodiments, the binder may act as a dispersing agent and / or viscosity enhancer. In embodiments, the electrode slurry may comprise from about 0.3 wt.% to about 1 wt.% or from about 0.5 wt.% to about 0.9 wt.% of the dispersing agent, based on the total weight of the electrode slurry.

[0093]

[0063] In certain embodiments, the method comprises combining the electrode active material, the synthetic graphite additive and optionally the conductive carbonaceous material in a container followed by dry mixing for about 3 or more minutes. For example, the electrode active material, synthetic graphite additive and optionally the conductive carbonaceous material may be mixed for about 5 minutes or more, or about 7 minutes or more. The mixing process may be carried out at a low rpm by various mixers that are commonly used to produce electrode slurries for coating, such as a TH INKY ARE-310® mixer (low rpm for this mixer is from about 100 to about 1000 rpm) or a Primix 2P-03 type mixer (low rpm for this mixer is from about 50 to about 20 rpm -maximum speed of about 100 rpm).

[0094]

[0064] In some embodiments, a solvent solution of the dispersing agent (water or organic solvent) may be added to the mixed dry electrode active material, synthetic graphite additive and optionally conductive carbonaceous material. The resulting mixture with the dispersing agent may then be mixed at an rpm in the range of about 1000 rpm to about 5000 rpm for about 5 minutes or more. Additional solvent may then be added, followed by further mixing step at an rpm of about 1000 rpm to about 5000 rpm for about 5 minutes or more. Finally, a binder in a solvent solution may be added, and the resulting mixture may be subjected to a final mixing at an rpm of about 1000 rpm to about 5000 rpm for about 5 minutes or more, followed by a degassing process at an rpm of about 2000 rpm to about 5000 rpm for about 2 minutes or more, to form an electrode slurry. In embodiments, a resulting electrode slurry may have a solid content of from about 30 wt.% to about 70 wt.%, for example about 40 wt.% to about 60 wt.% based on the total weight of the electrode slurry.

[0095]

[0065] The prepared electrode slurry comprising the electrode active material and the synthetic graphite additive is applied to the substrate. In embodiments, the electrode slurry is coated. For example, the electrode may be coated using a bar coater or a roll to roll coater. In such embodiments, the coating speed may be in the range of about 10 mm / s to about 100 mm / s, for example about 20 mm / s to about 80 mm / s.

[0096]

[0066] The method according to the invention comprises a drying step. In some embodiments, the drying step is carried out to obtain an electrode with a solvent content of about 5 wt.% or less, based on the total weight of the electrode. For example, a drying step is carried out to obtain an electrode with a solvent content of about 4.5 wt.% or less, about 4.0 wt.% or less, about 3.5 wt.% or less, about 3.0 wt.% or less, about 2.5 wt.% or less, about 2.0 wt.% or less, about 1.5 wt.% or less, about 1.0 wt.% or less, or about 0.5 wt.% or less based on the total weight of the electrode. In certain embodiments, the drying step is carried out to obtain an electrode which is primarily solvent free.

[0097]

[0067] In some embodiments the drying step is carried out at a temperature of about 30 °C to about 100 °C. For example, the drying step is carried out at a temperature of about 35 °C to about 95 °C, about 40 °C to about 90 °C, or about 45 °C to about 85 °C. For example, the drying step is carried out at a temperature of about 95 °C, about 90 °C, about 85 °C, or about 80 °C.

[0098] Use

[0099]

[0068] The present invention also provides the use of an electrode according to the present invention in a battery.

[0069] In some embodiments, the battery is a rechargeable battery. For example, in some embodiments, the battery may be an alkaline battery, a lead acid battery or a lithium-ion battery.

[0100]

[0070] In alternative embodiments, the electrode may be used in any electrochemical cell, for example, in a fuel cell such as a proton-exchange membrane fuel cell.

[0101] Battery

[0102]

[0071] The present invention also provides a battery comprising an electrode according to the present invention.

[0103]

[0072] In embodiments, the battery has a 3C discharge rate performance vs 0.2C% of at least about 95, at least about 96, or at least about 96.5.

[0104]

[0073] In embodiments, the battery has a 2C charge rate performance vs 0.2C% of at least about 20, at least about 21, at least about 22, at least about 23, at least about 24 or at least about 24.5.

[0105]

[0074] The details, examples and preferences provided in relation to any particular aspect of the present invention apply equally to all aspects of the present invention. Any combination of the embodiments, examples and preferences described herein in all possible variations thereof are encompassed by the present invention unless otherwise indicated herein, or otherwise clearly contradicted by context.

[0106]

[0075] In certain embodiments, the electrode, method of producing the electrode, use of the electrode and / or the battery comprising the electrode may have one or more of the following effects:

[0107] - high quality electrodes;

[0108] - good electrode tortuosity;

[0109] - good adhesion between the applied electrode slurry layer and substrate when dried;

[0110] - good drying homogeneity of the electrode surface;

[0111] - good surface defects in the electrode surface;

[0112] - low cracking and / or breaking of electrode surface;

[0113] - good discharge capacity retention of resultant battery cells;

[0114] - high efficiency of resultant battery cells;

[0115] - low energy consumption;

[0116] - low production cost of resultant battery cells; good production efficiency of battery cells; and

[0117] low cell temperature increases during cell charging / discharging at high current densities.

[0118] Having described the various aspects of the present invention in general terms, it will be apparent to those of skill in the art that many modifications and slight variations are possible without departing from the scope of the present invention.

[0119] EXAMPLES

[0120]

[0076] The following illustrates examples of synthetic graphite additive materials, electrodes and batteries, and related aspects described herein. Thus, these examples should not be considered to restrict the present disclosure, but are merely in place to teach how to carry out the present disclosure.

[0121] EXAMPLE 1

[0122] Coin Cell Test Procedure

[0123] Electrode Slurry Preparation

[0124]

[0077] Six Electrode Surries were prepared using the components described in Table 1 below (Inventive Electrode Slurries (IES) 1 and 2; and Comparative Electrode Slurries (CES) 1 - 4). The weight % values in Table 1 represent the amounts of each component included in the electrode slurry formulations, based on the total weight of the dry components in the electrode slurry. The particle size distribution, BET, crystallinity and through-plane thermal conductivity for the Electrode Active Material and synthetic graphite additives (“SG Additive(s)”) used in each Electrode Slurry are shown in Table 2. Table 1 - Materials used in the Preparation of the Electrode Slurries

[0125]

[0126] a - Commercial synthetic graphite having product name FSN-1, manufactured by Shanshan Co.

[0127] b - Super P carbon black manufactured by Imerys; having a BET Surface area of 62 m2 / g and an adsorption stiffness number of 32 ml / 5g.

[0128] c - Product name MAC500LC from Nippon Paper Group

[0129] d - Product name TRD102A from JSR Corporation Table 2 - Properties of Carbonaceous Materials used in Preparation of the Electrode Slurries

[0130] >

[0131]

[0132]

[0078] For each of the Electrode Slurries IES 1, IES 2, and CES 1 to CES 4, the Electrode Active Material, the SG Additive (if present) and the Carbon Black from Table 1 were weighed in the wt.% values in Table 1 and put into a container, and the total weight of SG Active and SG Additive materials in the container was 40 grams. The Carbon Black amounts for each Electrode Slurry was 0.41 grams. The combined dry components were then mixed for 5 minutes at a low mixing speed (500 rpm). The mixing process could be carried out by various mixers that are used for the production of electrode slurries for coating, for example, in this Example, a TH INKY ARE-310® mixer was used.

[0133]

[0079] A 40.82 gram quantity of a water solution containing 1 wt% carboxy methyl cellulose was then added into the container and blended with the combined dry components. The contents of the container was then mixed at 2000 rpm for 5 mins. A 6 gram quantity of DI water was added into the container. The contents of the container were then mixed again at 2000rpm for 5 mins. Finally, an aqueous Styrene-Butadiene Rubber (SBR, 48.5 wt. %) suspension was added into the container. The contents of the container were subjected to a final mixing at 2000 rpm for 5 mins, followed by a degassing process at 2200 rpm for 2 mins to form the electrode slurries. The resulting Electrode Slurries each had a solid content of 46 wt.% based on the total weight of the electrode slurry. Each of the prepared Electrode Slurries was then coated onto a 20 pm copper foil and dried at 80 °C to form Inventive Electrodes (IE) 1 and 2, and Comparative Electrodes (CE) 1 to 4 from IES 1, IES 2, and CES 1 to CES 4, respectively. The average loading mass of graphite (combination of Electrode Active Material and SG Additive) per Electrode was 8 mg / cm2. For the coin cell tests described below, the electrodes were pressed to a density of 1.5 to 1.6 g / cm3using a rolling press machine. A rolling press machine typically uses two rollers with adjustable pressure and adjustable gap between the two rollers. The rolling press machine may be of different sizes and specifications. If the targeted electrode density is achieved, there is no impact from the choice of different rolling press machines.

[0134] Coin Cell Assembly

[0135]

[0080] Inventive Coin Cells (InvCC) 1A and 2A, and Comparative Coin Cells (CompCC) 1A - 4A of the CR2032 type were prepared using the electrodes IE 1, IE 2, and CE 1 to CE 4, respectively, to test the charge rate performance in coin cells. A piece of Li metal was used as both the counter and reference electrode. The electrolyte was 200pl 1M LiPF6EC / ECM / DMC (3 / 5 / 2 in weight). The separator used was a piece of celgard ® 2500 monolayer microporous membrane (obtainable from Celgard LLC). Charge Rate Performance Test

[0136]

[0081] For the discharge rate test of coin cells InvCC 1A, InvCC 2A and CompCC 1A to CompCC 4A, the subject coin cell was first charged at a constant current of 0.2C to 0.005V until the current dropped to 0.01 C. The cell was then discharged at a constant current of 3C. The capacity retention at 3C is the ratio between constant current charged capacities at 3C versus 0.2C. For the charge rate test of coin cells InvCC 1A, InvCC 2A and CompCC 1A to CompCC 4A, the subject coin cell was charged at 2.0C to 0.005V and at a constant current until the current dropped to 0.01 C. The cell was then discharged at 0.2C. The charge rate performance at 2C rate is the ratio between constant current charged capacities at 2C versus 0.2C. The coin cell testing, as referred to herein, is performed using a machine called a charge-discharge cycler, model number TOSCAT-3100, obtained from Toyo system Co. Ltd. The results of such testing are shown in Table 3 below.

[0137] Table 3 - Coin cell performance

[0138]

[0139] Electrode Tortuosity Test

[0140]

[0082] Inventive Coin Cells (InvCC) 1B and 2B, and Comparative Coin Cells (CompCC) 1B - 4B of the CR2032 type were prepared using the electrodes IE 1, IE 2, and CE 1 to CE 4, respectively, to test for electrode tortuosity. Two pieces of the electrodes were assembled in the coin cell. The electrolyte was 200pl 1M LiPFe EC / EMC / DMC (3 / 5 / 2 in weight) (ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate). The separator used was a piece of celgard ® 2500 monolayer microporous membrane (obtainable from Celgard LLC).

[0141]

[0083] The coin cells were tested using an electrochemical impedance tester (BioLogic Potentiostation VMP3). The voltage amplitude was set to be + / - 10mV and the frequency was sweeping from 1M Hz to 10 mHz. The electrochemical impendence spectroscopy (EIS) curves were fitted by the Z-view software based on a transmission line model. Effective ionic resistance of the electrolyte within the pores of the electrode (Rion) was calculated from the difference between the impendence of the electrode (Zelec) and the high frequency resistance (Rhfr).

[0142]

[0084] The tortuosity of the electrode was calculated based on the following equation: T = (Rlon ■ A E K ) / t

[0143] the conductivity of the electrolyte (K), the porosity (E) of the electrode, electrode thickness (t), the area of the electrode (A) and the effective ionic resistance of the electrolyte within the pores of the electrode (Rion). Porosity (E) is determined by the ratio between the actual density and the theoretical density. Electrode tortuosity test is detailed in: Ref. Journal of The Electrochemical Society, 165(10)A2008-A2018(2018) and Journal of The Electrochemical Society, 159 (7) A1034-A1039 (2012).

[0144] The electrode tortuosity test results are shown in Table 4 below. Table 4 -Tortuosity of Coin Cells

[0145]

[0146] Peel strength Test

[0147]

[0092] For each of the electrodes IE 1, IE 2, and CCE 1 to CE 4 prepared above (and pressed to a density of 1.5 to 1.6 g / cm3), a peel strength test was carried out using an Instron® 3343 series apparatus. The test was performed as per the following:

[0148] Pressed electrodes with a width of 20 mm and a length of 21 cm were prepared. A 150 mm-length x 35 mm-width double-face tape was set onto the test plate. A metal roller was used to ensure good adhesion of tape to the plate. The right end of electrode was set onto the tape with the same method. The metal plate was then put onto an Instron® 3343 series apparatus and the left end of electrode was attached to the test clip. After aligning the electrode strip and test clips in a vertical line direction, peel strength was acquired from a 180° peeling with a peeling speed of 100 mm / min. The peel strength results are shown in Table 5 below. Table 5 - Peel strength of electrodes

[0149]

[0150]

[0093] The inventors found that the charging rate performance of the coin cells showed a negative correlation with the electrode tortuosity. The coin cells InvCC 1A and InvCC 2A fabricated from inventive electrodes IE 1 and IE 2 advantageously displayed a higher charging performance than the coin cells CompCC 1A to CompCC 4A fabricated from comparative electrodes CE 1 to CE 4 at a 2C charge rate vs 0.2C%. The inventors interestingly found that the higher the electrode tortuosity, the lower charging performance. The inventors found that the charging process was directly related to the Li ion diffusion from the electrolyte to the graphite, as tortuous pathways may cause slow diffusion thus affecting the charging rate

[0151]

[0094] The inventors found that for the discharge rate performance, minimum variation could be observed within all the coin cell examples, as the Li ions diffuse from the graphite into the electrolyte, which is only governed by the graphite material itself. However, the coin cells InvCC 1A and InvCC 2A fabricated from inventive electrodes IE 1 and IE 2 beneficially displayed a comparable discharge rate performance at a 3C discharge rate vs 0.2C% to the coin cell CompCC 4A, fabricated from comparative electrode CE 4, which is a commercially available carbonaceous material commonly used in electrodes.

[0152]

[0095] Electrode tortuosity is a parameter for the characterization of the microstructure of electrodes. Low tortuosity indicates better electrolyte diffusion and lower ionic resistance from the electrode. The inventors found that inventive electrodes IE 1 and IE 2 demonstrated the lowest tortuosity. The inventors found that the carbonaceous material, in these examples, the synthetic graphite additive, used to fabricate electrodes may help to greatly improve the microstructure of the electrodes, and subsequently help to improve battery performance.

[0153]

[0096] Peel strength was also a parameter investigated by the inventors, as the peeling of materials results in scraps, and increased dust generation during downstream processes. These side effects are not favourable for battery production from both a safety and economic point of view. As such, peel strength is a way of quantifying electrode quality.

[0154]

[0097] The inventors found that for through-plane thermal conductivity <10W / (m-k), the intrinsic through-plane thermal conductivity is not sufficient to trigger a homogeneous drying process for the solvent. As a result, the inventors found the electrode tortuosity increased as the movement of the materials blocks part of the lithium ion diffusion pathways during the solvent evaporation. This was found by the inventors to increase electrode tortuosity and subsequently decrease the rate performance of the electrodes. As shown in Tables 4 and 5, the present inventors found that the use of Inventive SG Additives 1 and 2, each having higher thermal conductivities as compared to Comparative SG Additives 2 and 3, resulted in higher electrode adhesion (peel strength) and lower electrode tortuosity.

[0155]

[0098] The present inventors found that both the through-plane thermal conductivity and dgo / dw ratio within the synthetic graphite additive was important to achieve a high quality electrode with a good peel strength and electrode tortuosity. In particular, the comparison between the use of Inventive SG Additives 1 and 2 and Comparative SG Additive 1 in electrodes and coin cells indicates the effect of the dgo / d ratio. Referring to Tables 2, 4 and 5, although Comparative SG Additive 1 has a high through-plane thermal conductivity, and a faster drying speed, the peel strength of the comparative electrode CE 1 was decreased. The tortuosity of the comparative coin cell CompCC 1B increased compared to the inventive electrodes IE 1 and 2. and inventive coin cells InvCC 1B and 2B prepared using Inventive SG Additives 1 and 2, respectively. EXAMPLE 2

[0156] Laminated Cell Test Procedure

[0157] Electrode Preparation

[0158]

[0099] For laminated cell tests, negative and positive electrodes for use in each of the pouch cell assemblies were prepared according to the following steps.

[0159] Negative Electrode Formation

[0160]

[0100] To prepare the Inventive Negative Electrode Slurries IES 3 to IES 5, and the Comparative Negative Electrode Slurry CES 5, the Elextrode Active Material, the SG Additive (if present) and the Carbon Black were weighed in the wt.% values in Table 6 and put into a container. The powders were then mixed for 5 minutes at low mixing speed (20 RPM). The mixing process may be carried out by various mixers that are used for the production of electrode slurries for coating. For this example, in this Example a Primix 2P-03 type mixer was used with a mixing speed of 20 rpm.

[0161]

[0101] A quantity of a 1 wt.% CMC solution was added until the solid content of the slurry reached 64.5 wt.%. The slurry was then mixed at 100 rpm for 30 min. Another portion of 1% CMC solution was added into the mixer until the solid content reached a calculated amount of 56.3 wt.% based on the total weight of the electrode slurry. The slurry was then mixed at 100 rpm for 30 min. Another portion of 1% CMC solution was added into the mixer until the solid content reached a calculated amount of 50 wt.% based on the total weight of the electrode slurry. The slurry was then mixed at 100 rpm for 30 min. Finally, a Styrene-Butadiene Rubber (SBR, 48.5 wt.%) suspension in water was added into the container. The slurry was stirred at 80 rpm for 30 min and then degassed at 20 rpm for 10 min. The final solid content of the electrode slurries was 49.5 wt.% based on the total weight of the electrode slurry.

[0162] Inventive Negative Electrodes 3 to 5 (INE 3 to INE 5) and Comparative Negative Electrode 5 (CNE 5) were prepared from slurries IES 3 to IES 5, and CES 5, respectively, by the following method. Each of the prepared Electrode Slurries IES 3 to IES 5 and CES 5 were coated onto a 20 pm copper foil using a roll to roll coater (having a first roller for feeding the copper foil and a second roller on which the coated copper foil is rolled) and then dried as described below to form Electrodes INE 3 to INE 5 and CNE 5, respectively. The coating speed (i.e. roll to roll coater speed) was set to 600 mm / min. There were two drying ovens (a first oven and a second oven) positioned between the first and second rollers. Following the coating, the coated Electrode is then passed through the first oven of 1.2 meters in length operated at 40°C and is then passed through the second oven of 1.2 meters in length operated at 60 C, and is then rolled onto the second roller. The copper foil was coated on both sides, the loading mass of graphite (combination of SG Active Material and SG Additive) on each side for the material was 9 mg / cm2. The electrode material (INE 3 to INE 5 and CNE 5) was pressed to a density of 1.5 to 1.6 g / cm3.

[0163] Table 6 - Materials used in Preparation of the Electrode Slurries

[0164]

[0165] a - Commercial synthetic graphite having product name FSN-1, manufactured by Shanshan Co.

[0166] b - Super P carbon black manufactured by Imerys; having a BET Surface area of 62 m2 / g and an adsorption stiffness number of 32 ml / 5g.

[0167] c - Product name MAC500LC from Nippon Paper Group

[0168] d - Product name TRD102A from JSR Corporation

[0169] Positive Electrode (“PE”) Formation

[0170]

[0102] Positive electrodes for use in each of the pouch cell assemblies were prepared from lithium nickel cobalt manganese oxide, C65T carbon black (available from Imerys Graphite & Carbon), PVDF HSV1810 binder obtained from Arkema, using a Primix 2P-03 type mixer was used with a mixing speed of 20 rpm. The final slurry composition for the positive electrode was lithium nickel cobalt manganese oxide: carbon black: binder in a 96.5:2:1.5 ratio respectively, with a solid content of 72 wt.% based on the total weight of the electrode slurry. The solvent used in positive electrode preparation was N-Methyl-2-pyrrolidone (NMP).

[0171]

[0103] The slurry was then coated onto aluminum foil (20 pm in thickness) with a roll to roll coater (having a first roller for feeding the aluminum foil and a second roller on which the coated aluminum foil is rolled) forming a coated Electrode. The coating speed (roll to roll coater speed) was set to 600 mm / min. There were two drying ovens (a first oven and a second oven) positioned between the first and second rollers. Following the coating, the coated Electrode is then passed through the first oven of 1.2 meters in length operated at 40°C and is then passed through the second oven of 1.2 meters in length operated at 60 C, and is then rolled onto the second roller. The aluminum foil was coated on both single side and double sides, the loading mass for the material on each coated side was 15 mg / cm2. The electrode material was pressed to a density of 3.4 g / cm3.

[0172] Assembly of the Pouch Cell

[0173]

[0104] To assemble each of the Pouch Cells, the pressed negative electrode was punched into a 54mm*44mm size with a tab for further electrical connection. The pressed positive electrode was punched into a 50mm*40mm size with a tab for further electrical connection. Cellgard ® 2500 separators were punched into 56mm*46mm size for future use.

[0174]

[0105] Inventive Pouch Cells 1 to 3 (IPC 1 to IPC 3) and a Comparative Pouch Cell (CPC) were prepared using Electrodes INE 3 to INE 5 and CNE 5, respectively, as follows. 500mAh pouch cells were assembled in a dry room with a dew point of below -40°C. The Negative electrodes INE 3 to INE 5 and CNE 5, as prepared above, Cellgard ® 2500 separators, and the Positive Electrode (“PE”) prepared as described above were aligned in a mold with alternating layers of negative electrode- separator as above - positive electrode - separator - repeat. There are a total 5 pieces of positive electrodes, 10 pieces of separators, 3 pieces of negative double side electrodes and 2 pieces of single side negative electrodes. A nickel tab was welded onto the negative electrode tabs and an aluminum tab was welded onto the positive electrode tabs. A piece of aluminum pouch was then used to seal the electrodes.

[0175]

[0106] Finally, 3 ml of electrolyte was injected into the Pouch Cell. The Pouch Cell was then vacuum sealed. The electrolyte was 1M LiPF6 EC / EMC / DMC (1 / 3 each in volume) with 1 wt.% vinylene carbonate (VC).

[0176] Formation of the Pouch Cells (using electrical current)

[0177]

[0107] The assembled Pouch Cells (I PC 1 to I PC 3 and CPC) were first charged to 3.6V with a constant current and constant voltage (CC-CV) charging protocol. The charging protocol was set to end at 0.05C. The charged Pouch Cells were then put in an oven with a constant temperature of 60°C and stored for 18 hrs. After that, the Pouch Cells were cut open in the dry room to release the gas and then resealed. The Pouch Cells were then charged to 4.2V CC-CV and discharged to 2.5V with a 0.1 C constant current (CC) protocol.

[0178] Testing of the Pouch Cells for Direct Current Resistance (DCR) at 50% State of Charge (SOC)

[0179]

[0108] The Pouch Cells (I PC 1 to I PC 3 and CPC) were charged to a SOC of 50% and rested for one hour. The DCR was tested by a pulse current of 0.2C for 5s, 0.5C for 5s, and finally 1C for 5s. The DCR was calculated from the slope of the V-l curve. The DCR was tested first at 25°C and then at -10°C. Results of the DCR tests are found in Table 7 below.

[0180] Test of -10°C Discharge Energy Output for the Pouch Cells

[0181]

[0109] The Pouch Cells were fully charged with a CC-CV protocol to 4.2 V (cut-off at 0.02 C). The Pouch Cells were then discharged at a constant 1C rate to 2.5V under 25°C. The energy output A in Wh was recorded by the charge and discharge machine. Then the Pouch Cells were fully charged with a CC-CV protocol to 4.2 V (cut-off at 0.02 C). The cells were cooled to -10°C and maintained for three hours. The Pouch Cells were then discharged at a constant 1C rate to 2.5V. The energy output B Wh was recorded by the charge and discharge machine. B / A is the ratio of the energy output at -10°C vs 25°C. Results found in below Table 7. Table 7

[0182]

[0183] Cycling test - capacity retention

[0184]

[0110] The Pouch Cells from above were each subjected to cycling tests, as described using the following protocol:

[0185] a 0.5C CC-CV charge, cut off at 0.05C and a constant 0.2C discharge capacity confirmation cycle

[0186] 1C CC-CV charge, cut off at 0.05C and a constant 1C discharge, 100 cycles Repeat the above protocol for 10 times

[0187] Direct Current Reistance and Discharge Energy Output

[0188]

[0111] As can be seen in Table 7, inventive Pouch Cells IPC 1 to IPC 3 were found by the inventors to lead to an improvement in ddirect current resistance and capacity retention at 25°C and at -10°C, compared to comparative Pouch Cell CPC which incorporated a commercially available carbonaceous material commonly used in electrodes.

[0189]

[0112] The low temperature discharge energy output was also found to be improved for inventive Pouch Cells IPC 1 to IPC 3. Use of 3.88 wt.% of the SG Additive according to inventive Pouch Cell IPC 1 was shown to be the minimum amount to achieve the largest performance improvement.

[0190] The battery cycling performance of the pouch cells was also investigated with 3.88 wt.% of the SG Additive according to inventive Pouch Cell IPC 1 (using the Cycling test - capacity retention method protocol as described above). Figure 1 shows the capacity retention ratio over 1000 cycles of a pouch cell fabricated using inventive pouch cell IPC 1 and comparative pouch cell CPC. As can be seen from Figure 1, the cycling performance of the inventive pouch cell IPC 1 was shown to be improved compared to comparative pouch cell CPC, which incorporates a commercially available carbonaceous material commonly used in electrodes. The inventive pouch cell IPC 1 had a capacity retention ratio of about 96% over 1000 cycles, compared to the comparative pouch cell CPC which had a capacity retention ratio of about 93% over 1000 cycles.

[0191]

[0113] Figure 2 shows the cell surface temperatures, as measured using a thermocouple, for Pouch Cells inventive IPC 1 and comparative CPC vs. charging time, and shows reduced cell surface temperature increases during cell charging at high current densities for IPC 1. Figure 3 shows the cell surface temperatures as measured for Pouch Cells inventive IPC 1 and comparative CPC vs. discharge time, and shows reduced cell surface temperature increases during cell discharging at high current densities for IPC 1. Table 8 below shows the peak temperatures for Pouch Cells IPC 1 and CPC, and that they are lower for IPC 1.

[0192] Table 8

[0193]

[0194] EXAMPLE 3

[0195] Electrode Drying Speed Testing

[0196] Electrode Preparation

[0197]

[0114] Step 1: Formation of an electrode slurry. Electrode Slurries IES 5, IES 6, and CES 9 to CES 12 were prepared in the same manner as the electrode slurries in Example 1.

[0198]

[0115] Step 2: Applying the electrode slurry to the surface of a copper substrate. For each of the electrode slurries IES 5, IES 6, and CES 9 to CES 12, a 7cm*5cm copper foil was coated with the subject slurry by a bar coater (ZEHNTNER ZAA2300) with a 300-|jm coating gap at a speed of 20mm per second.

[0199]

[0116] Step 3: Drying the electrode slurry. The coated electrode was then dried at 80C by a moisture analyser. The drying speed of each electrode slurry on the substrate was measured using a Halogen Moisture Analyzer HE53 (“moisture analyser”). The solvent loss vs time data was recorded every 10 seconds The drying speed, in mg / minute, were calculated from the collected data starting at the point where the mass was decreasing linearly with time, (had reached heat-mass transfer balance). The drying speed is the slope of the plot of mass (moisture content) vs. time in the linear section of the data. Figure 4 is a plot of moisture content vs. time for IES 5 and CES 12, and it is from these types of plots that the drying speed (slope of the plot) is derived. Results shown in the Table 9 below. Table 9 - Drying speed of the electrode slurries

[0200]

[0201]

[0117] The inventive slurries IES 5 and IES 6 were seen to have comparable drying speeds to the comparative slurries CES 9 to CES 12. The solvent drying process is an energy consuming process, and the drying speed of electrode slurries is a parameter directly linked to the production efficiency (the line speed) and often the quality of the electrode. As such, a comparable drying speed was found to be beneficial.

[0202]

[0118] The drying process is a complex combination of heat and mass transfer processes. Fast drying at high temperature has in the art be associated with to poor adhesion between the coated materials layer and the substrate.

Claims

CLAIMS1. An electrode comprising an electrode active material, and a synthetic graphite additive, wherein the synthetic graphite additive has:a through-plane thermal conductivity of at least about 10 W / (m-k); and a dgo / d particle size ratio of at most about 8, wherein the particle size is measured by laser light scattering.

2. The electrode according to claim 1, wherein the electrode is for use in a battery.

3. The electrode according to claim 2, wherein the battery is a rechargeable battery.

4. The electrode according to any preceding claim, wherein the synthetic graphite additive has a d5o particle size of up to about 10 pm, as measured by laser light scattering.

5. The electrode according to any preceding claim, wherein the synthetic graphite additive has a through-plane thermal conductivity in the range of about 10 W / (m-k) to about 30 W / (m-k).

6. The electrode according to any preceding claim, wherein the synthetic graphite additive has a c / 2 value of 0.3360 or less.

7. The electrode according to any preceding claim, wherein the electrode active material comprises a synthetic graphite, a natural graphite, a hard carbon, a siliconcarbon composite, a silicon monoxide-carbon composite, or combinations thereof.

8. The electrode according to any preceding claim, comprising a conductive carbonaceous material selected from any one of carbon black, carbon nanotube and combinations thereof.

9. The electrode according to any preceding claim, wherein the electrode comprises about 87 to about 96.9 wt.% of the electrode active material, based on the total weightof the electrode, and wherein the electrode comprises about 0.1 to about 10 wt.% of the synthetic graphite additive, based on the total weight of the electrode.

10. The electrode according to any preceding claim, wherein the electrode has an electrode tortuosity of in the range of about 0.1 to about 2.0 T.

11. The electrode according to any preceding claim, comprising a peel strength equal to or higher than about 35 mN / 20mm.

12. A method of producing an electrode comprising:providing an electrode slurry comprising the electrode active material and the synthetic graphite additive according to any one of claims 1 to 11 and a solvent;applying the electrode slurry to a substrate; anddrying.

13. Use of an electrode according to any one of claims 1 to 11 in a battery.

14. The use according to claim 13, wherein the battery is a rechargeable battery.

15. A battery comprising the electrode as claimed in any one of claims 1 to 11.

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