Anode materials and methods for producing same

Abstract

Approximate oblate spheroid and D less than about 5 microns 50 1. An anode material comprising secondary graphite particles having primarily a shape having:

Description

[Technical Field]

[0001] The present invention relates to an anode material. More particularly, the anode material of the present invention is intended for use as an anode material in lithium-ion batteries.

[0002] In one highly preferred form, the anode material of the present invention approximates an oblate spheroid and has a D of less than about 5 microns. 50 The graphite particles comprise secondary graphite particles having a shape predominantly having a shape having a shape of

[0003] The present invention further relates to a method for producing the anode material. [Background technology]

[0004] Lithium-ion battery anode materials that utilize graphite are known to have limited battery performance at low temperatures. This is thought to be primarily due to issues with lithium plating and degradation of the solid electrolyte interface (SEI). That is, low temperatures can cause lithium metal deposits to form within the battery, leading to internal short circuits that can cause fires within the cell.

[0005] It is understood that lithium-ion batteries typically have lower capacity retention and cycling efficiency under frozen conditions, resulting in shorter operating times for devices such as laptop computers and mobile phones, or shorter driving ranges for electric vehicles (Non-Patent Document 1).

[0006] Li-ion batteries are widely used at room temperature due to their high specific energy and energy density, long cycle life, low self-discharge, and long storage life (Non-Patent Document 2). When charging a Li-ion battery, the lithium ions in the battery are absorbed (like a sponge) by a porous negative electrode (anode) made of graphite.

[0007] However, at temperatures close to freezing (0°C), lithium ions are not efficiently captured by the anode. Instead, many lithium ions are reduced to lithium metal and coat the surface of the anode (a process known as lithium plating), leaving less lithium available to carry the current. This results in a decrease in the battery's capacity and cycling efficiency, leading to poor performance (Non-Patent Document 3).

[0008] In cooler countries in the Northern Hemisphere, it has been measured that the driving range of electric vehicles can be reduced by 41% in real-world sub-zero conditions (Non-Patent Document 4).

[0009] The most significant adverse effect of low temperatures on Li-ion batteries is the development of lithium metal growths called dendrites, which can puncture the separator and cause short circuits or fires in the Li-ion cell. A well-known example of this was the 2013 grounding of the Boeing 787 Dreamliner aircraft, which suffered a series of electrical system failures, including fires. Investigations showed that cold winter nighttime temperatures promoted lithium plating within the battery cells, causing short circuits (Non-Patent Document 5).

[0010] One object of the anode material composites and methods of the present invention is to substantially overcome one or more of the aforementioned problems associated with the prior art, or at least to provide a useful alternative thereto.

[0011] The foregoing discussion of the background art is intended only to facilitate an understanding of the present invention and is not an admission that any of the materials referred to are or were part of the common general knowledge at the priority date of the application.

[0012] Throughout this specification and claims, unless the context clearly indicates otherwise, the term "comprise" or derivatives such as "comprises" or "comprising" will be understood to include a stated integer or group of integers but not to exclude other integers or groups of integers.

[0013] Throughout this specification and claims, unless the context requires otherwise, references to "milling" are understood to include references to "grinding" and references to "grinding" are understood to include references to "milling".

[0014] Throughout this specification and claims, unless the context requires otherwise, the term "oblate spheroid" or its derivatives means the surface of a solid of revolution obtained by rotating an ellipsoid about its minor axis. Briefly, an oblate spheroid is understood to be a flattened sphere that is wider than it is high. Summary of the Invention

[0015] According to the present invention, It is the surface of a solid of revolution obtained by rotating an ellipsoid around its minor axis. Approximate oblate spheroid and D less than about 5 microns 50 and secondary graphite particles having a shape predominantly having an anode material comprising: the secondary graphite particles comprise agglomerates of ground primary graphite particles; the ground primary graphite particles are spheroidized and coated with a carbon-based material, which may be one or more of pitch, polyethylene oxide, and polyvinyl oxide, and then pyrolyzed at 880°C to 1100°C for 12 to 40 hours to produce the secondary particles, which approximate oblate spheroids; The amount of carbon-based material in the secondary graphite particles is in the range of 2 to 10 wt % relative to the graphite. An anode material is provided.

[0016] Preferably, the secondary graphite particles have a D of about 3 to 5 microns. 50 More preferably, the secondary graphite particles have a D of about 3.5 microns. 50 It has.

[0017] Preferably, the secondary graphite particles are (i) Approximately 2 to 9 m 2 / g; or (ii) About 2~6m 2 / g surface area (BET) It has.

[0018] 75kf / cm 2 The compressed density of the secondary graphite particles is preferably about 1.0 to 1.5 g / cc (bulk density) The range is.

[0019] The electrical conductivity of the secondary graphite particles is preferably in the range of about 25 to 37 S / cm, for example, about 31 S / cm.

[0020] Preferably, the anode material further comprises a thickener.

[0021] In one embodiment, the thickening agent is carboxymethylcellulose (CMC).

[0022] Preferably, the anode material further comprises an aqueous binder.

[0023] In one embodiment, the water-based binder is styrene butadiene rubber (SBR).

[0024] Preferably, the anode material has a capacity retention of greater than 91% at a 2C rate discharge.

[0025] In one form of the invention, the anode material comprises about 97.5% wt / wt secondary graphite particles, about 1.5% wt / wt SBR, and about 1% wt / wt CMC.

[0026] The ground primary graphite particles preferably comprise: (i) less than about 15 microns; (ii) less than about 10 microns; or (iii) D in the range of about 4 to 6 microns 50 It has.

[0027] Preferably, the ground primary graphite particles have a size of about 2 to 9 mm. 2 / g, e.g., 7-9m 2 / g surface area (BET) It has.

[0028] Preferably, the ground primary graphite particles have XRD characteristics of one or more of d002 >3.35 Å, Lc >1000 Å, and La >1000 Å. In a preferred form, the ground primary graphite particles have XRD characteristics of each of d002 >3.35 Å, Lc >1000 Å, and La >1000 Å, and a purity of >99.9%.

[0029] The present invention further provides an anode comprising an anode material as described above in combination with a current collector.

[0030] Preferably, the anode material is distributed on the current collector in a random arrangement to facilitate the passage of lithium ions therethrough.

[0031] More preferably, the anode material is disposed on the current collector to a thickness of about 60 to 75 microns, for example, 71 microns.

[0032] According to the present invention, there is further provided a method for producing an anode material, said method comprising grinding a graphite material to produce ground primary graphite particles, said ground primary graphite particles comprising: The surface of a body of revolution is obtained by rotating an ellipsoid around its minor axis, the ellipsoid being spheroidized, coated with a carbon-based material, which is one or more of pitch, polyethylene oxide, and polyvinyl oxide, and then pyrolyzed at 800°C to 1100°C for 12 to 40 hours, and containing the carbon-based material in an amount ranging from 2 to 10 wt% relative to the graphite. Approximate oblate spheroid and D less than about 5 microns 50 to produce secondary graphite particles having a shape predominantly having 。

[0033] Preferably, the ground graphite particles are It is the surface of a solid of revolution obtained by rotating an ellipsoid around its minor axis. The secondary graphite particles are mainly oblate spheroids. Rua Agglomeration and / or surface modification process in It will be processed.

[0034] More preferably, the agglomeration and / or surface modification step comprises a spray drying process, which may preferably be achieved using a fluidized bed.

[0035] The ground primary graphite particles preferably comprise: (i) less than about 15 microns; (ii) less than about 10 microns; or (iii) D in the range of about 4 to 6 microns 50 It has.

[0036] Preferably, the ground primary graphite particles have a size of about 2 to 9 mm. 2 / g, e.g., 7-9m 2 / g of surface area.

[0037] Preferably, the secondary graphite particles have a D of about 3 to 5 microns. 50 More preferably, the secondary graphite particles have a D of about 3.5 microns. 50 It has.

[0038] Preferably, the secondary graphite particles are (i) Approximately 2 to 9 m 2 / g; or (ii) About 2~6m 2 / g of surface area.

[0039] Preferably, the ground primary graphite particles have XRD characteristics of one or more of d002 >3.35 Å, Lc >1000 Å, and La >1000 Å. In a preferred form, the ground primary graphite particles have XRD characteristics of each of d002 >3.35 Å, Lc >1000 Å, and La >1000 Å, and a purity of >99.9%. The present invention will now be described, by way of example only, with reference to certain embodiments thereof and the accompanying drawings, in which: [Brief explanation of the drawings]

[0040] [Figure 1a] FIG. 1a is a scanning electron microscope (SEM) image of an anode material of the present invention, which comprises secondary graphite particles primarily having a shape approximating an oblate spheroid. [Figure 1b] FIG. 1b is a scanning electron microscope (SEM) image of an anode material of the present invention, which comprises secondary graphite particles primarily having a shape approximating an oblate spheroid. [Figure 2] FIG. 2 is a schematic diagram of the steps used to manufacture an electrode according to an embodiment of the present invention, showing how secondary graphite particles (referred to as "Talnode-C") are processed through a series of process steps to provide a slurry to produce an electrode. [Figure 3] FIG. 3 is a graph of electrode density versus mechanical strength for an electrode prepared in accordance with the present invention and using secondary graphite particles thereof. [Figure 4] FIG. 4 is a cross-sectional view of a single layer laminate cell constructed in a known manner using the anode material of the present invention to provide an anode according to the present invention. [Figure 5] FIG. 5 is a Nyquist plot of resistance at 25° C. for a cell prepared with an anode material of the present invention providing an anode according to the present invention. [Figure 6] FIG. 6 is a Bode plot of resistance (Z' versus frequency) for a cell prepared with an anode material of the present invention providing an anode according to the present invention at 25° C. [Figure 7] FIG. 7 is a Bode plot of resistance (Z″ vs. frequency) for a cell prepared with an anode material of the present invention providing an anode of the present invention at 25° C. [Figure 8] FIG. 8 is a Nyquist plot of resistance in a cell prepared with an anode material of the present invention providing an anode of the present invention at 0° C. [Figure 9] FIG. 9 is a Bode plot of resistance (Z' vs. frequency) for a cell prepared with an anode material of the present invention providing an anode of the present invention at 0° C. [Figure 10] FIG. 10 is a Bode plot of resistance (Z″ vs. frequency) for a cell prepared with an anode material of the present invention providing an anode of the present invention at 0° C. [Figure 11]FIG. 11 is a schematic diagram of the limit load characteristics of cells prepared using anode materials of the present invention providing an anode according to the present invention, showing performance at 25° C. and 0° C. and using various C-rates. [Figure 12] FIG. 12 is a graphical representation of the efficiency of an anode according to the present invention at 25°C and 0°C. [Figure 13] FIG. 13 is a graphical representation of the voltage drop over time during durability testing of a cell according to the present invention at low temperature, comparing performance with a benchmark "market leader." [Figure 14] FIG. 14 is a graphical representation of the capacity of a cell according to the present invention at low temperature at different discharge rates, comparing performance with a benchmark "market leader." [Figure 15] FIG. 15 is a schematic diagram of the steps used in the manufacture of an electrode according to another embodiment of the present invention, showing how secondary graphite particles (referred to herein as "T-13") are processed through a series of process steps to provide a slurry to produce a coated electrode. [Figure 16] FIG. 16 is a graphical representation of the cycling performance of a pouch cell according to the present invention, showing its capacity retention. [Figure 17] FIG. 17 is a graphical representation of the discharge rate characteristics of a pouch cell according to the present invention.

[0041] BEST MODE FOR CARRYING OUT THE INVENTION The present invention provides an anode material comprising secondary graphite particles having a shape that primarily approximates an oblate spheroid, the secondary graphite particles having a D of less than about 5 microns. 50 , for example, a D of about 3 to 5 microns or about 3.5 microns 50 It has.

[0042] The secondary graphite particles are about 2 to 9 m 2 / g, for example, about 2 to 6 m 2 / g of surface area.

[0043] It is understood by applicants that the combination of graphite particle size and surface area described herein is particularly advantageous.

[0044] 75kf / cm 2 The compressed density of the secondary graphite particles is about 1.0 to 1.5 g / cc (bulk density) and the conductivity of the secondary graphite particles is in the range of about 25 to 37 S / cm, for example, about 31 S / cm.

[0045] The anode material further comprises a thickener, hi one embodiment, the thickener is carboxymethyl cellulose (CMC).

[0046] The anode material further comprises an aqueous binder, hi one embodiment, the aqueous binder is styrene butadiene rubber (SBR).

[0047] The anode material has a capacity retention of over 91% at a 2C rate discharge, assuming 100% capacity retention at 0.2C.

[0048] In one form of the invention, the anode material comprises about 97.5% wt / wt secondary graphite particles, about 1.5% wt / wt SBR, and about 1% wt / wt CMC.

[0049] The present invention further provides an anode comprising an anode material as described above in combination with a current collector, for example a copper current collector.

[0050] The anode material is distributed on the current collector in a random arrangement, which facilitates lithium ion absorption.

[0051] In one embodiment, the anode material is disposed on the current collector to a thickness of about 60 to 75 microns, for example, 71 microns.

[0052] The secondary graphite particles include ground primary graphite particles, and the ground primary graphite particles further include a carbon-based material, such as one or more of pitch, polyethylene oxide, and polyvinyl oxide, in an amount ranging from 2 to 10 wt % relative to the graphite.

[0053] The ground primary graphite particles are (i) less than about 15 microns; (ii) less than about 10 microns; or (iii) D in the range of about 4 to 6 microns 50 It has.

[0054] The ground primary graphite particles are about 2 to 9 mm in size. 2 / g, for example, about 7 to 9 m 2 / g of surface area.

[0055] The ground primary graphite particles have XRD characteristics of one or more of d002 >3.35 Å, Lc >1000 Å, and La >1000 Å. For example, the ground primary graphite particles have XRD characteristics of d002 >3.35 Å, Lc >1000 Å, and La >1000 Å, respectively, and a purity of >99.9%.

[0056] The present invention further provides a method for producing an anode material, the method comprising grinding a graphite material to produce ground primary graphite particles, the ground primary graphite particles approximating oblate spheroids and having a D of less than about 5 microns. 50 The graphite is processed to produce secondary graphite particles having a shape predominantly having a

[0057] In one form of the invention, the ground primary graphite particles are spheroidized, coated with a carbon-based material, and then pyrolyzed to produce the secondary particles, which approximate oblate spheroids.

[0058] The carbon-based material is one or more of pitch, polyethylene oxide, and polyvinyl alcohol, and the amount of carbon-based material used to coat the ground primary graphite particles ranges from 2 to 10 wt % relative to the graphite.

[0059] The pyrolysis temperature is about 880° C. to 1100° C. The pyrolysis time is in the range of about 12 to 40 hours.

[0060] The ground primary graphite particles have a D of less than about 15 microns, e.g., less than about 10 microns, or in the range of about 4 to 6 microns. 50 It has.

[0061] The ground primary graphite particles are about 2 to 9 mm in size. 2 / g, e.g., 7-9m 2 / g of surface area.

[0062] The ground primary graphite particles are (i) less than about 15 microns; (ii) less than about 10 microns; or (iii) D in the range of about 4 to 6 microns 50 It has.

[0063] The secondary graphite particles have a D of about 3 to 5 microns, e.g., about 3.5 microns. 50 It has.

[0064] The ground primary graphite particles have XRD characteristics of one or more of d002 >3.35 Å, Lc >1000 Å, and La >1000 Å. For example, the ground primary graphite particles have XRD characteristics of d002 >3.35 Å, Lc >1000 Å, and La >1000 Å, respectively, and a purity of >99.9%.

[0065] In a further aspect of the invention, the ground primary graphite particles are treated by an agglomeration and / or surface modification process to produce secondary graphite particles having a shape predominantly approximating an oblate spheroid. The agglomeration and / or surface modification process may comprise a spray drying process. In one embodiment, the spray drying process may be accomplished utilizing a fluidized bed.

[0066] In the typical arrangement of graphite flakes relative to the current collector in prior art anodes, the anisotropic graphite flake or particle orientation relative to the current collector results in high resistance to lithium ion diffusion therethrough. The anisotropic graphite particle orientation simply does not provide a physical opportunity for lithium ion diffusion. As a result, prior art attempts to randomly orient the graphite and create spheroidized graphite to overcome the apparent anisotropy limitations. This is why the shape of most current anode materials is generally spherical. The generally spherical shape of prior art graphite anode materials is also intended to provide the packing density needed for the current collector to increase its volumetric capacity for storing lithium.

[0067] Without limiting the scope of the present invention, it is envisioned that the secondary graphite particles of the present invention are ideally largely randomly oriented relative to the current collector, thereby providing lower resistance to lithium ion diffusion therethrough. The oblate spheroidal nature of the secondary particles of the present invention means that they do not orient in the same manner as prior art graphite flakes. Rather, the secondary particles of the present invention aggregate randomly, creating agglomerates of secondary particles that provide a level of porosity and relatively high packing density in the anode materials and anodes of the present invention. It has been understood by applicants that the expansion and lithium ion resistance in the anodes of the present invention are reduced compared to the prior art.

[0068] 1a and 1b, many approximately oblate spheroidal secondary graphite particles of the present invention are shown, and their D 50 is in the range of about 3 to 5 microns.

[0069] The process of the present invention can be better understood with reference to the following non-limiting examples. [Example]

[0070] As previously mentioned, the present invention further provides a method for producing an anode material, said method comprising grinding a graphite material to produce ground primary graphite particles, said ground primary graphite particles being processed to produce secondary graphite particles predominantly having a shape approximating an oblate spheroid.

[0071] Table A below provides examples of suitable ground primary graphite particles for / to be used in the method of the present invention, and Table B provides the elemental analysis thereof. Table A JPEG0007779483000001.jpg97144 Table B JPEG0007779483000002.jpg20127

[0072] The ground primary graphite particles are spheroidized, coated with a carbon-based material, and then pyrolyzed to produce secondary particles that approximate oblate spheroids. The carbon-based material is one or more of pitch, polyethylene oxide, and polyvinyl alcohol. The amount of carbon-based material used to coat the ground primary graphite particles ranges from 2 to 10 wt% relative to the graphite. The pyrolysis temperature is approximately 880°C to 1100°C. The pyrolysis time, including both heating and cooling periods, ranges from approximately 12 to 40 hours.

[0073] FIG. 2 illustrates a method for slurrying an anode material according to the present invention for application to a current collector in a known manner to produce an anode according to one embodiment of the present invention. As previously described, 29.25 g of secondary graphite particles according to the present invention (referred to herein as Talnode-C) are mixed with 0.21 g of CMC to provide a 1.0% HO solution (21 g). This is mixed three times for 2 minutes at 2000 rpm. Next, 0.45 g of CMC (1.0% HO solution; 4.5 g) is added twice and mixed twice for 2 minutes at 2000 rpm, as shown. Additionally, 0.45 g of SBR (48% HO solution; 0.928 g) is added and mixed once for 2 minutes at 2000 rpm. This process provides a slurry of an anode material according to the present invention with a solids content of 49.9% and a viscosity of 41 mPa·s. Application of the resulting slurry to a current collector and drying are then accomplished by known methods. This process provides an anode composition of 97.5% wt / wt secondary graphite particles, about 1.5% wt / wt SBR, and about 1% wt / wt CMC.

[0074] Table 1 below lists the properties of anodes made in accordance with the present invention, and Figure 3 shows a graph of electrode density versus mechanical strength. The density and mechanical strength of the anodes of the present invention are good relative to equivalent prior art anodes, with a reversible capacity of 350-365 mAh / g being understood by applicants to be "industry standard," depending on cell configuration. [Table 1]

[0075] Table 2 below and Figure 4 show a full cell 10 including an anode material and an anode according to the present invention. The full cell 10 includes an aluminum laminate film or outer package 12, a negative electrode or anode 14 according to the present invention, a positive electrode or cathode 16, and a separator 18, each arranged substantially in a known manner. The anode 14 further includes a copper current collector 20, and the cathode 16 further includes an aluminum current collector 22. Importantly, there is no gassing during the initial charge / discharge of the full cell 10, with minimal discharge observed at a 3.6 V charge (0.04 cc). [Table 2]

[0076] 5-7 show plots of the resistance of cell 10 at 25°C, which can be compared with FIGS. 8-10, which show plots of the resistance of cell 10 at 0°C. Importantly, cell 10 exhibits a 15% lower cell resistance at 25°C compared to a typical or known cell using a current graphite anode. For example, the resistance value, which is largely related to the negative electrode reaction resistance, is 0.29, which, as noted above, is approximately 15% lower than a typical or known cell resistance at 25°C using a current graphite anode. At 0°C, cell 10 exhibits the lowest level of a typical or known cell using a current graphite anode.

[0077] The test protocol for testing the limit load characteristics (initial load and simulated load after aging) of cell 10 at both 25°C and 0°C, 10 cycles per setting, and variable depth of charge, is shown in Figure 11. The depth of charge was varied by changing the charge voltage, and the cell was only partially charged / discharged to allow for different voltages. Details of the resistance and depth of charge are shown in Table 3 below. Performance evaluation of cell 10 was performed as shown in Table 3, considering different C-rates at each different temperature. The test details included using 10 cycles per setting, and cell 10 was only partially charged / discharged to allow for various voltages. [Table 3]

[0078] Further examination of the limit load characteristics of cell 10 in terms of efficiency is shown in Figure 12. Tables 4 and 5 below provide relevant capacity data. [Table 4] [Table 5]

[0079] At 25° C., the efficiency of cell 10 is seen to be similar to that of leading known anode products. However, it is important to note that at 0° C., the capacity retention of leading known anode products is less than 98% and then rapidly declines to marginal levels. The anode material of the present invention, instead, has a cycling efficiency of 99% at low load (4.1 V) and achieves 100% cycling efficiency even at high load (4.15 V) and after 60 cycles.

[0080] At 25° C., the efficiency of cell 10 is seen to be similar to that of leading known anode products. However, it is important to note that at 0° C., the capacity retention of leading known anode products is less than 98% and then rapidly declines to marginal levels. The anode material of the present invention, instead, has a cycling efficiency of 98% at low load (4.1 V) and achieves 100% capacity retention even at high load (4.15 V) and after 60 cycles.

[0081] Tests were also conducted to determine the durability of cell 10 (generally referred to herein as Talnode or Talnode-C) under high power and fast charging conditions compared to benchmark "market leader" products. The results of these tests are shown in Figures 13 and 14. A cyclic test was conducted, designed to simulate driving a car up a mountain at high speed. This cyclic test measures the ability of cell 10 to efficiently harvest fast charging regenerative current (due to braking) after high power discharge (or acceleration) in cold conditions.

[0082] Figure 13 shows the time until the cell voltage drops below 3.2V at 14°C. The test cycle consisted of 3 seconds of discharge at 3C, 1 second of charge at 1C, 4 seconds of rest, and repeated until voltage drop or thermal / cell temperature limit was reached. Figure 14 shows that cell 10 provides higher capacity than the benchmark "Market Leader" or "Commercial Composite" at all C-rates.

[0083] FIG. 15 illustrates a method for slurrying an anode material according to the present invention for application to a current collector by known methods to produce an anode according to a further embodiment of the present invention. As previously described, secondary graphite particles according to the present invention (herein referred to as T-13) are mixed in an amount of 4.3 g with 2 g of CMC to provide a 1.0% HO solution. This is mixed once at 2000 rpm for 2 minutes. Next, as shown, 0.2 g to 0.8 g of CMC (1.0% HO solution) is added five times and mixed twice or three times at 2000 rpm for 2 minutes. Another mixing step is performed in 0.5 g of HO for 2 minutes at 2000 rpm. Furthermore, 0.14 g of SBR is added (48.5% HO dispersion) and mixed once at 2000 rpm for 2 minutes. This process provides a slurry of an anode material according to the present invention with a solids content of 47.2% and a viscosity of 200 mPa·s. Application of the resulting slurry to a current collector and drying are then accomplished by known methods. This process provides an anode composition of 97.5% wt / wt secondary graphite particles, about 1.5% wt / wt SBR, and about 1% wt / wt CMC.

[0084] Table 6 below lists the properties of anodes prepared according to the present invention. [Table 6]

[0085] Figure 16 shows the cycling performance or capacity retention of a 30 x 50 mm pouch cell (with an NMC cathode) containing the same anode composition as in Table 6 over 100 cycles at 50°C, showing that the capacity retention only decreased to 90.1% over 100 cycles. Cycles 1, 15, 50, 75, and 100 are charged at 0.2 C, 4.2 V-CC; discharged at 0.2 C, 2.7 V-CC. Cycles 2-24, 26-49, 51-74, and 76-99 are charged at 0.5 C, 4.2 V-CC; discharged at 0.5 C, 2.7 V-CC.

[0086] Figure 17 shows the discharge rate of the cell of Figure 15 at 25°C in terms of the relationship between capacity and voltage. Assuming 100% capacity retention at 0.2C, the discharge rate is 3.8 mAh / cm 2 Using an electrode load capacity of 91.2%, a capacity retention rate of 91.2% is achieved at 2 C. Charging was performed at 4.2 V CCCV at 0.2 C with a lower current limit of 0.05 C.

[0087] Anodes fabricated from the anode materials of the present invention and cells containing them exhibit reduced electrode expansion during lithiation and delithiation compared to the expansion exhibited by prior art natural and synthetic electrodes. This is despite the higher capacities of anodes fabricated from the anode materials of the present invention. For example, anodes of the present invention have capacities in excess of about 360 mAh / g, while prior art synthetic anodes typically have capacities on the order of 340-350 mAh / g. Despite this, anodes of the present invention exhibit approximately 5% lower anode expansion than prior art synthetic anodes, on the order of 16% compared to approximately 21% for the prior art.

[0088] Table 7 below summarizes the electrochemical characteristics and performance of the 30x50mm single layer pouch cells (with NMC cathode) described above. [Table 7] 1. Applicant has observed some variation in 1°C cycling efficiency depending on NMC manufacturer and cell construction (i.e., electrolyte, additives used, type of binder used, cell manufacturer). Capacity retention at 2.0°C is based on limit load characterization testing after 50 cycles.

[0089] As can be seen from the above description, electrochemical characterization by impedance spectroscopy and galvanostatic charge-discharge cycling tests indicates that the anode materials of the present invention, anodes prepared therefrom, and cells containing the same exhibit fast charging and high power with inherently good charge transfer properties, low electrical resistance, and high diffusion of lithium into the secondary graphite particles, which in particular allows for potential use in high power / fast charging batteries in certain applications at low temperatures.

[0090] It is reasonably assumed that the anode materials of the present invention substantially overcome the problem of lithium plating formation at low temperatures, thereby improving the safety of lithium-ion batteries. Furthermore, it is understood that the anode materials of the present invention substantially overcome the cold cranking amperage (CCA) problem in lithium-ion battery systems, enabling starter batteries using lithium-ion technology. Furthermore, the lower impedance of the anode materials of the present invention produces cells with lower impedance, requiring less "thermal management" of lithium-ion cells at the "battery pack" level. Furthermore, the improved low-temperature performance of the anode materials and cells of the present invention improves the life of such cells on a single charge.

[0091] Furthermore, the anode materials of the present invention, anodes made therefrom, and cells containing same exhibit relatively low electrode expansion, particularly relative to prior art anodes and cells.

[0092] The foregoing discussion further demonstrates that improvements are realized with respect to the low temperature performance of the anode materials of the present invention, while being achieved without significantly affecting performance at high temperatures (eg, 50° C.).

[0093] It is contemplated that the anode materials of the present invention may comprise primarily secondary graphite particles having shapes that are primarily larger in two dimensions than in their three dimensions. It is understood that an oblate spheroidal shape meets such criteria. It is further understood that the secondary graphite particles of the present invention, as described, may consist of agglomerates of primary graphite particles of indeterminate and / or variable shape, while still exhibiting a generally oblate spheroidal shape.

[0094] Such modifications and variations as would be apparent to one skilled in the art are deemed to be within the scope of the present invention. [Prior art documents] [Non-patent literature]

[0095] [Non-Patent Document 1] Temperature effect and thermal impact in lithium-ion batteries: A Review, Progress in Natural Science: Materials International, Shuai Ma et al., December 2018 [Non-patent document 2] The Limits of Low-Temperature Performance of Li-Ion Cells, Huang et al., Journal of The Electrochemical Society, 147 (8) 2000 [Non-patent document 3] Final Technical Report: Internal Short Circuits in Lithium-Ion Cells for PHEVs” Sriramulu & Stringfellow, 2014 [Non-patent document 4] Electric Vehicle Range Testing: AAA proprietary research into the effect of ambient temperature and HVAC use on driving range and MPGe, American Automobile Association, Feb 2019 [Non-patent document 5] Aircraft Serious Incident Investigation Report, All Nippon Airways Ltd, JA804A., Sep 2014

Claims

1. It approximates an oblate spheroid, which is the surface of a body of revolution obtained by rotating an ellipsoid around its minor axis, and has a D of less than 5 microns. ５０ 1. An anode material comprising secondary graphite particles having primarily a shape having the secondary graphite particles comprise agglomerates of spherical primary graphite particles; the primary graphite particles are coated with a pyrolytic carbon material; An anode material, wherein the amount of the pyrolytic carbon material in the secondary graphite particles is in the range of 2 to 10 wt % relative to the graphite.

2. the secondary graphite particles are (i) 3 to 5 microns; or (ii) 3.5 microns D ５０ The anode material of claim 1 having the formula:

3. the secondary graphite particles are (i) 2 to 9 m ２ / g; or (ym)2~6m ２ / g 3. The anode material according to claim 1, having a surface area (BET) of

4. 75 kf / cm ２ 4. The anode material according to claim 1, wherein the secondary graphite particles have a compressed density in the range of 1.0 to 1.5 g / cc (bulk density).

5. The electrical conductivity of the secondary graphite particles is (i) in the range of 25 to 37 S / cm; or (ii) 31S / cm 5. The anode material according to claim 1, wherein

6. The anode material according to claim 1 , further comprising a thickener.

7. 7. The anode material of claim 6, wherein the thickener is carboxymethyl cellulose (CMC).

8. The anode material according to claim 6 , further comprising an aqueous binder.

9. 9. The anode material of claim 8, wherein the aqueous binder is styrene butadiene rubber (SBR).

10. 10. The anode material of claim 1, wherein the anode material has a capacity retention of greater than 91% at a 2C rate discharge.

11. 10. The anode material of claim 9, wherein the anode material comprises 97.5% wt / wt of the secondary graphite particles, 1.5% wt / wt of SBR, and 1% wt / wt of CMC.

12. the primary graphite particles are (i) less than 15 microns; (ii) less than 10 microns; or (iii) in the range of 4 to 6 microns D ５０ 12. The anode material according to claim 1, wherein

13. the primary graphite particles are (i) 2 to 9 m ２ / g; or ())) ２ / 13. The anode material according to claim 1, having a surface area (BET) of 14. The anode material of any one of claims 1 to 13, wherein the primary graphite particles have one or more of the following XRD characteristics: d002 >3.35 Å, Lc >1000 Å, and La >1000 Å.

15. 15. The anode material of claim 1, wherein the primary graphite particles have XRD characteristics of d002 >3.35 Å, Lc >1000 Å, and La >1000 Å.

16. 16. An anode comprising the anode material of any one of claims 1 to 15 in combination with a current collector.

17. 17. The anode of claim 16, wherein the anode material is distributed on the current collector in a random arrangement to facilitate the passage of lithium ions therethrough.

18. the anode material is (i) 60 to 75 microns; or (ii) 71 microns 18. The anode according to claim 16, wherein the anode is disposed on the current collector to a thickness of 0.1 μm or more.

19. 1. A method for producing an anode material, comprising grinding a graphite material to produce primary graphite particles, the primary graphite particles being spheroidized and coated with a carbon-based material, the carbon-based material being one or more of pitch, polyethylene oxide, and polyvinyl oxide, and then pyrolyzed at 800° C. to 1100° C. for 12 to 40 hours to produce a graphite anode material comprising the carbon-based material in an amount ranging from 2 to 10 wt % relative to the graphite, the graphite anode material approximating an oblate spheroid, the surface of which is obtained by rotating an ellipsoid about its minor axis, and having a D of less than 5 microns. ５０ 1. A method for producing secondary graphite particles having a shape predominantly having a shape having

20. 20. The method of claim 19, wherein the primary graphite particles are subjected to an agglomeration and / or surface modification process to produce the secondary graphite particles having a shape that primarily approximates an oblate spheroid, which is the surface of a body of revolution obtained by rotating an ellipsoid about its minor axis.

21. 21. The method of claim 20, wherein the agglomeration and / or surface modification step comprises a spray drying process.

22. 22. The method of claim 21, wherein the spray drying process is accomplished using a fluidized bed.

23. The primary graphite particles comprising: (i) less than 15 microns; (ii) less than 10 microns; or (iii) in the range of 4 to 6 microns D ５０ 23. The method of any of claims 19 to 22, comprising:

24. the primary graphite particles are (i) 2 to 9 m ２ / g; or ())) ２ / 24. The method of any one of claims 19 to 23, wherein the surface area (BET) of

25. the secondary graphite particles are (i) 3 to 5 microns; or (ii) 3.5 microns D ５０ 25. The method of any of claims 19 to 24, comprising:

26. the secondary graphite particles are (i) 2 to 9 m ２ / g; or (ym)2~6m ２ / g 26. The method of any one of claims 19 to 25, wherein the surface area (BET) of

27. the primary graphite particles are (i) one or more of d002 > 3.35 Å, Lc > 1000 Å, and La > 1000 Å; or (ii) d002 > 3.35 Å, Lc > 1000 Å, and La > 1000 Å, respectively 27. The method of any one of claims 19 to 26, having an XRD characteristic of:

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