Negative electrode and electrochemical energy storage device

Abstract

This invention provides a negative electrode sheet and an electrochemical energy storage device. The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer located on at least one surface of the negative electrode current collector. The negative electrode active material layer includes an amorphous carbon material layer and a graphite-based negative electrode material layer. The amorphous carbon material layer contains a first negative electrode active material, which comprises a spherical amorphous carbon material with an average particle size D1 satisfying 0.2 μm ≤ D1 ≤ 4 μm. The graphite-based negative electrode material layer contains a second negative electrode active material, which comprises a graphite-based negative electrode material. This invention can effectively improve the power performance and low-temperature performance of electrochemical energy storage devices such as batteries.

Description

Technical Field

[0001] This invention relates to the field of power batteries, specifically to a negative electrode and an electrochemical energy storage device. Background Technology

[0002] Hybrid electric vehicles (HEVs) and plug-in hybrid electric vehicles (PHEVs) have advantages such as energy saving, environmental protection, short start-up time, and good driving experience, and have received widespread attention in recent years with the rise of electric vehicles. HEVs and PHEVs are driven by a hybrid of an internal combustion engine and an electric motor, reducing reliance on fossil fuels. The electric power generally provides power for instantaneous starting and recovers energy by converting potential energy into electrical energy when the car is going downhill. Both of these functions require the power battery to provide extremely high power. Furthermore, automotive start-stop batteries typically need to operate under low-temperature conditions (extreme low temperatures can reach around -30°C), thus placing extremely high demands on the power performance and low-temperature performance of the battery (cell). However, current electrochemical energy storage devices typically use graphite anodes (i.e., the anode material is mainly graphite). These electrochemical energy storage devices have poor power performance and low-temperature performance when used as power batteries (or start-stop batteries), especially unable to meet the operating conditions of HEVs and PHEVs under low-temperature conditions. Summary of the Invention

[0003] This invention provides a negative electrode sheet and an electrochemical energy storage device, which can effectively improve the power performance and low-temperature performance of electrochemical energy storage devices such as batteries, and meet the start-up performance requirements of HEVs and PHEVs under low-temperature conditions, especially under extreme low-temperature conditions of around -30°C.

[0004] In one aspect, the present invention provides a negative electrode sheet, comprising a negative electrode current collector and a negative electrode active material layer located on at least one surface of the negative electrode current collector. The negative electrode active material layer comprises an amorphous carbon material layer and a graphite-based negative electrode material layer. The amorphous carbon material layer contains a first negative electrode active material, which comprises a spherical amorphous carbon material, and the average particle size D1 of the amorphous carbon material satisfies: 0.2 μm ≤ D1 ≤ 4 μm. The graphite-based negative electrode material layer contains a second negative electrode active material, which comprises a graphite-based negative electrode material.

[0005] According to one embodiment of the present invention, the Raman spectrum Id / Ig peak ratio of the amorphous carbon material is 0.5-1.5; and / or, in the X-ray diffraction analysis results of the amorphous carbon material, the peak position of the diffraction peak is less than 26.5°.

[0006] According to one embodiment of the present invention, (7.5×D2 / D3)-1≥H1 / H2≥d / (7.5×D2-d) is satisfied, where H1 is the thickness of the amorphous carbon material layer, H2 is the thickness of the graphite-based anode material layer, D2 is the average particle size of the graphite-based anode material, and D3 is the maximum particle size of the graphite-based anode material.

[0007] According to one embodiment of the present invention, 1.15 > H1 / H2 > 0.04 is satisfied, where H1 is the thickness of the amorphous carbon material layer and H2 is the thickness of the graphite-based anode material layer.

[0008] According to one embodiment of the present invention, the particle size of the graphite-based anode material satisfies: D2≤10μm, D3 / D2≤5.3, where D2 is the average particle size of the graphite-based anode material and D3 is the maximum particle size of the graphite-based anode material.

[0009] According to one embodiment of the present invention, the graphite-based anode material includes graphite and / or a graphite-based core-shell structure material, wherein the graphite-based core-shell structure material includes a core formed of graphite and a shell present on the surface of the core.

[0010] According to one embodiment of the present invention, the shell of the graphite-based core-shell structure material comprises amorphous carbon material.

[0011] According to one embodiment of the present invention, the specific surface area of ​​the amorphous carbon material is 2-23 m². 2 / g; and / or, the specific capacity of the amorphous carbon material is 270-360 mAh / g.

[0012] According to one embodiment of the present invention, the graphite-based negative electrode material layer is located between the surface of the negative electrode current collector and the amorphous carbon material layer; or, the amorphous carbon material layer is located between the surface of the negative electrode current collector and the graphite-based negative electrode material layer.

[0013] In another aspect, the present invention provides an electrochemical energy storage device comprising the aforementioned negative electrode.

[0014] The negative electrode sheet provided by this invention, combining the aforementioned amorphous carbon material layer and graphite-based negative electrode material layer with different negative electrode active materials, can effectively improve the low-temperature performance and power performance of the negative electrode sheet, while ensuring its energy density and other characteristics. This improves the low-temperature performance, power performance, and energy density of the electrochemical energy storage device, enabling it to meet the start-up performance requirements of HEVs and PHEVs even under extreme low-temperature conditions of -30℃, which is of great significance for practical industrial applications. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the negative electrode sheet according to one embodiment of the present invention;

[0016] Figure 2This is a schematic diagram of the negative electrode sheet according to another embodiment of the present invention;

[0017] Figure 3 The image shows the Raman spectrum of an amorphous carbon material according to an embodiment of the present invention (the horizontal axis represents the Raman shift, and the vertical axis represents the peak intensity).

[0018] Figure 4 The image shows the XRD pattern of an amorphous carbon material according to an embodiment of the present invention (the horizontal axis is 2θ and the vertical axis is peak intensity).

[0019] Figure 5 A is a microscopic morphology image of an amorphous carbon material according to an embodiment of the present invention, measured by scanning electron microscopy (SEM); B is a microscopic morphology image of an amorphous carbon material according to a comparative example, measured by SEM.

[0020] Explanation of reference numerals in the attached figures: 1: Amorphous carbon material layer; 2: Graphite-based negative electrode material layer; 3: Negative electrode current collector. Detailed Implementation

[0021] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0022] In this invention, the average particle size (e.g., D1, D2) of the negative electrode material A can be determined as follows: Before fabricating the negative electrode sheet, the Dv50 (i.e., the average particle size of the negative electrode material A) is measured using a laser particle size analyzer. Dv50 is the particle size that reaches 50% of the volumetric particle size distribution of the material from the smallest particle size side; or, after fabricating the negative electrode sheet, a coating sample is taken from the negative electrode sheet, and the average particle size of the negative electrode material A in the sample is measured using a focused ion beam microscope (FIB-SIM); the negative electrode material A is, for example, an amorphous carbon material or a graphite-based negative electrode material.

[0023] In this invention, the maximum particle size (e.g., D3) of the negative electrode material A can be determined as follows: Before fabricating the negative electrode sheet, the Dv99 (i.e., the maximum particle size of the negative electrode material A) of the negative electrode material A is determined using a laser particle size analyzer. Dv99 refers to the particle size that reaches 99% of the volumetric particle size distribution of the material from the smallest particle size side; or, after fabricating the negative electrode sheet, a coating sample is taken from the negative electrode sheet, and the maximum particle size of the negative electrode material A in the sample is determined by focusing ion beam microscopy (FIB-SIM); the negative electrode material A is, for example, a graphite-based negative electrode material.

[0024] In this invention, "A / B" in the formula represents the ratio of A to B. For example, "H1 / H2" in the following text represents the ratio of H1 to H2, and "D3 / D2" represents the ratio of D3 to D2.

[0025] like Figure 1 and Figure 2 As shown, the negative electrode sheet of the present invention includes a negative electrode current collector 3 and a negative electrode active material layer located on at least one surface of the negative electrode current collector 3. The negative electrode active material layer includes an amorphous carbon material layer 1 and a graphite-based negative electrode material layer 2. The amorphous carbon material layer 1 contains a first negative electrode active material, which includes amorphous carbon material with a spherical structure. The average particle size D1 of the amorphous carbon material satisfies: 0.2μm≤D1≤4μm. The graphite-based negative electrode material layer 2 contains a second negative electrode active material, which includes graphite-based negative electrode material.

[0026] The microstructure of the aforementioned amorphous carbon materials is an irregular, disordered layer structure, exhibiting an irregular arrangement compared to graphite, with larger interlayer spacing. Furthermore, it differs from amorphous carbon materials with irregular morphologies (such as...). Figure 5 Compared to the amorphous carbon material shown in B, the amorphous carbon material particles have a small-diameter (0.2μm≤D1≤4μm) spherical structure with many end faces, high isotropy, and numerous channels for ion entry and exit, which is beneficial for ion (such as lithium ion) insertion / extraction / transport. Therefore, it has excellent power performance and low-temperature kinetic performance, specifically high discharge power and high low-temperature discharge lower limit voltage. The morphology of graphite-based anode material particles is generally irregular, and it has the characteristics of high initial efficiency / energy density. By combining the amorphous carbon material layer and the graphite-based anode material layer, the low-temperature high-power characteristics of the amorphous carbon material can be used to improve the electrical performance of the anode / electrochemical energy storage device, while also taking into account the energy density and other characteristics of the anode / electrochemical energy storage device. This results in the anode / electrochemical energy storage device having good low-temperature performance, power performance, and energy density.

[0027] Specifically, the macroscopic appearance of the aforementioned amorphous carbon material can be a powder composed of particles with the aforementioned spherical structure. According to the research of this invention, the Raman spectrum Id / Ig peak ratio of the amorphous carbon material (or spherical carbon material) is 0.5-1.5, and the peak position of the diffraction peak in its X-ray diffraction (XRD) analysis is less than 26.5°. It is a high-power carbon-based active material. By introducing it into the negative electrode through the above structural design, the low-temperature start-up and shutdown performance and power performance of the negative electrode / electrochemical device can be effectively improved.

[0028] Further research revealed that the following conditions were met: (7.5×D2 / D3)-1≥H1 / H2≥d / (7.5×D2-d), where H1 is the thickness of the amorphous carbon material layer, H2 is the thickness of the graphite-based anode material layer, D2 is the average particle size of the graphite-based anode material, and D3 is the maximum particle size of the graphite-based anode material. This is beneficial for further improving the low-temperature performance and power performance of the anode sheet / electrochemical device. At the same time, it can avoid scratches and scraping (pits, protrusions / particles) caused to the anode sheet during the manufacturing process, as well as the resulting defects such as poor processing performance of the anode sheet.

[0029] In some embodiments, the condition 1.15 > H1 / H2 > 0.04 can generally be satisfied. The value of H1 / H2 (i.e., the ratio of H1 to H2) can be, for example, 0.045, 0.07, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, or any combination of these values. According to the research of the present invention, as H1 / H2 increases, it is beneficial to improve the low-temperature performance and power performance of the negative electrode. However, if H1 / H2 is too large, it will reduce the energy density of the negative electrode to a certain extent. Controlling H1 / H2 within the above range is beneficial to simultaneously improve the power performance, low-temperature performance, and energy density of the negative electrode, and further ensure the function of the negative electrode.

[0030] Optionally, the thickness H1 of the amorphous carbon material layer 1 can be 2.5 μm to 30 μm, for example, 2.5 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 18 μm, 20 μm, 22 μm, 25 μm, 28 μm, 30 μm, or any combination of these values. The thickness H2 of the graphite-based anode material layer 2 can be... The thickness of the negative electrode active material layer is approximately equal to the sum of the thickness of the amorphous carbon material layer 1 and the thickness of the graphite-based negative electrode material layer 2, with a thickness ranging from 25μm to 65μm, such as 25μm, 28μm, 30μm, 32μm, 35μm, 38μm, 40μm, 42μm, 45μm, 48μm, 50μm, 52μm, 55μm, 58μm, 60μm, 62μm, 65μm, or any combination of two of these values.

[0031] In this invention, H, H1, and H2 all refer to the thickness of a single-sided coating, that is, the thickness of the negative electrode active material layer on one surface of the current collector, excluding the thickness of the current collector, and not the sum of the thickness of the negative electrode active material layer on one side of the current collector and the thickness of the negative electrode active material layer on the other side.

[0032] In some embodiments, the particle size of the graphite-based anode material satisfies: D2 ≤ 10 μm, where D2 can be, for example, a range of 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm or any combination of these values; D3 / D2 ≤ 5.3, where the minimum theoretical value of D3 / D2 is close to 1. In specific implementations, D3 / D2 can be, for example, a range of 3, 3.3, 3.5, 3.8, 4, 4.3, 4.5, 4.8, 5, 5.3 or any combination of these values. Controlling the graphite particle size within this range is beneficial for further improving the power performance and low-temperature performance of the anode sheet.

[0033] Optionally, D3 can be 15-38μm, such as 15μm, 18μm, 20μm, 22μm, 25μm, 28μm, 30μm, 32μm, 35μm, 38μm or any combination of these values.

[0034] In some embodiments, the specific surface area of ​​the graphite-based anode material can be 1.5-3 m². 2 / g, for example 1.5m 2 / g、2m 2 / g, 2.5m 2 / g、3m 2 / g or a range consisting of any two of these values.

[0035] The graphite-based anode material described above can be a conventional graphite-based anode active material in the art. In some embodiments, the graphite-based anode material includes graphite and / or graphite-based core-shell structure material, which includes a core formed of graphite and a shell (or shell layer, shell membrane, etc.) existing on the surface of the core. It can be prepared according to conventional methods in the art, such as carbon coating method.

[0036] In comparison, the graphite-based core-shell structure material is more conducive to the combination with amorphous carbon materials, thereby improving the low-temperature performance and power performance of the negative electrode. In some preferred embodiments, the shell of the graphite-based core-shell structure material includes the amorphous carbon material. Specifically, the graphite-based core-shell structure material can be a core-shell structure with graphite as the core and the amorphous carbon material as the shell, which is conducive to further improving the low-temperature performance, power performance and energy density of the negative electrode.

[0037] In some embodiments, the average particle size D1 of the amorphous carbon material can be, for example, a range of 0.2 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, or any combination of two of these values.

[0038] In some embodiments, the specific surface area (BET) of the aforementioned amorphous carbon material can generally be 2-23 m². 2 / g, for example 2m 2 / g、3m 2 / g、4m 2 / g、5m 2 / g、6m 2 / g、7m 2 / g、8m 2 / g、9m 2 / g, 10m 2 / g、11m 2 / g、12m 2 / g、13m 2 / g、14m 2 / g, 15m 2 / g, 16m 2 / g、17m 2 / g、18m 2 / g、19m 2 / g、20m 2 / g、21m 2 / g、22m 2 / g、23m 2 / g or a range of any two of these values ​​is beneficial for improving the power performance and low-temperature performance of the negative electrode.

[0039] In some embodiments, the specific capacity of the amorphous carbon material is 270-360 mAh / g, for example, 270 mAh / g, 280 mAh / g, 290 mAh / g, 300 mAh / g, 310 mAh / g, 320 mAh / g, 330 mAh / g, 340 mAh / g, 350 mAh / g, 360 mAh / g, or any combination of these values.

[0040] Amorphous carbon materials can generally be prepared by a hydrothermal method, whereby a polymer undergoes a hydrothermal reaction in a homogeneous dispersion system to obtain a spherical precursor, which is then carbonized to obtain the amorphous carbon material. Alternatively, a precursor with a spherical structure can be directly carbonized (heat-treated) to obtain the amorphous carbon material. In some preferred embodiments of the present invention, the aforementioned amorphous carbon material can be prepared by carbonizing a phenolic resin with the aforementioned spherical structure (0.2 μm ≤ D1 ≤ 4 μm). The aforementioned hydrothermal reaction and carbonization processes are conventional procedures in the art and will not be described in detail further.

[0041] In some embodiments, the graphite-based negative electrode material layer 2 is located between the surface of the negative electrode current collector 3 and the amorphous carbon material layer 1, that is, the amorphous carbon material layer 1 is located on the surface of the graphite-based negative electrode material layer 2 (e.g., Figure 1As shown in the figure, it is beneficial to improve the power performance and low temperature performance of the negative electrode. At the same time, since the above-mentioned amorphous carbon material has the characteristics of large interlayer spacing, high hardness, low compaction density and low porosity of the coating, it is also beneficial to avoid problems such as expansion and easy formation of lithium dendrites during the use of the negative electrode, thereby improving the safety and service life of the electrochemical energy storage device.

[0042] In other embodiments, the amorphous carbon material layer 1 is located between the surface of the negative electrode current collector 3 and the graphite-based negative electrode material layer 2 (e.g.) Figure 2 As shown, compared to a simple graphite-based anode material layer, this method can also improve the low-temperature performance and power performance of the anode sheet. However, compared to the above-mentioned method where the amorphous carbon material layer 1 is located on the surface of the graphite-based anode material layer 2, this method has a relatively low effect on improving the low-temperature performance and power performance of the anode sheet.

[0043] In some embodiments, the amorphous carbon material layer 1 includes a conductive agent, a binder, a thickener, and a first negative electrode active material, wherein the mass content of the first negative electrode active material is 88-98%, the mass content of the conductive agent is 0-5%, the mass content of the binder is 0.5%-4%, and the mass content of the thickener is 0.5%-3%.

[0044] In some embodiments, the graphite-based negative electrode material layer 2 includes a conductive agent, a binder, a thickener, and a second negative electrode active material, wherein the mass content of the second negative electrode active material is 88-98%, the mass content of the conductive agent is 0-5%, the mass content of the binder is 0.5%-4%, and the mass content of the thickener is 0.5%-3%.

[0045] In some embodiments, the negative electrode active material layer can be provided on only one surface of the negative electrode current collector, or the negative electrode active material layer can be provided on both the positive and negative surfaces of the negative electrode current collector. Relatively speaking, the latter is beneficial to improving the energy density and other characteristics of the negative electrode sheet. In specific implementation, the choice can be made according to the needs.

[0046] This invention also investigated the addition of silicon-based anode materials to a graphite-based anode material layer. The study found that controlling the amount of silicon-based anode material added to less than 5% (i.e., the mass content of silicon-based anode material in the second anode active material to less than 5%) had no significant negative impact on cell cycle performance, volume expansion characteristics, low-temperature cold start performance, and power performance. However, the volumetric energy density and gravimetric energy density of the cell were improved to some extent. Optionally, the silicon-based anode material may include at least one of silicon-oxygen anode materials (silicon oxide) and silicon-carbon anode materials. Relatively speaking, the cell cycle expansion is more pronounced when using silicon-carbon anode materials than when using silicon-oxygen anode materials. However, by controlling the amount of silicon-based material added within the aforementioned range, the cell cycle expansion phenomenon and its adverse effects on cell cycle performance can be overcome.

[0047] The electrochemical energy storage device of the present invention includes the above-mentioned negative electrode sheet. Optionally, the electrochemical energy storage device is, for example, a power battery, especially a power battery used in HEVs and PHEVs, specifically a lithium-ion battery.

[0048] The aforementioned electrochemical energy storage device also includes a positive electrode sheet, which comprises a positive current collector and a positive active material layer located on at least one surface of the positive current collector. The raw materials of the positive active material layer may include a positive active material, a conductive agent, and a binder. For example, the positive active material may include at least one of lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium nickel cobalt manganese oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadium oxide phosphate, lithium-rich manganese-based materials, and lithium nickel cobalt aluminum oxide. Among them, lithium nickel cobalt manganese oxide (NCM) may include at least one of NCM111, NCM523, NCM532, NCM622, and NCM811. Relatively speaking, NCMs with lower nickel content have a better effect on improving the low-temperature performance and power performance of the battery.

[0049] The aforementioned positive electrode active material can be a single crystal material and / or a polycrystalline material. Generally, single crystal materials have smaller particles, which makes the diffusion distance of ions (such as lithium ions) smaller, which is more conducive to the low temperature performance and power performance of the battery.

[0050] The aforementioned electrochemical energy storage device also includes a separator located between the positive and negative electrode plates to separate them. The separator has a porosity of 30-60%, which facilitates ion transport (such as lithium ions), thereby improving the low-temperature performance and power performance of the electrochemical energy storage device.

[0051] The separator used in this invention can be a conventional separator in the art. For example, in some embodiments, the separator includes a substrate and a coating layer located on at least one surface of the substrate. The thickness of the substrate is 2-22 μm, and the thickness of the coating layer is 0-10 μm. When the thickness of the coating layer is 0, the separator is an uncoated separator. When the thickness of the coating layer is not 0, the separator is a coated separator. Generally, the porosity of an uncoated separator is greater than that of a coated separator. Higher separator porosity is more conducive to the transport of ions (such as lithium ions) and is beneficial to the low-temperature performance and power performance of the battery. Therefore, in some embodiments, an uncoated separator is preferred.

[0052] Specifically, in some embodiments, the substrate may include at least one of polyethylene (PP) film, polypropylene (PE) film, and a composite film made of PP film and PE film. For example, the composite film may be a PP / PE / PP composite film formed by sequentially combining PP film, PE film, and PP film. The coating layer may include an adhesive coating layer on the surface of the substrate and a ceramic coating layer on the surface of the adhesive coating layer. The adhesive coating may be made from an adhesive, and the ceramic coating may be made from ceramic particles and an adhesive. The ceramic particles may include alumina, but are not limited thereto.

[0053] The aforementioned electrochemical energy storage device also includes an electrolyte. This invention can employ conventional electrolytes in the art. For example, the electrolyte used may include a non-aqueous electrolyte, the raw materials of which may include a non-aqueous solvent, lithium salt, and additives. The non-aqueous solvent includes at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethyl acetate, ethyl propionate, propyl propionate, and propyl acetate. The lithium salt includes lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium difluorooxalate borate, etc. At least one of lithium (trifluoromethanesulfonyl)imide and lithium bis(oxalato)borate, with additives including at least one of vinyl sulfite, lithium bis(oxalato)borate, vinyl sulfate, tris(trimethylsilane)borate, 1,3-propenesulfonate lactone, 1,3-propanesulfonate lactone, ethylene carbonate, ethylene sulfite, lithium difluorophosphate, lithium difluorobis(oxalato)phosphate, lithium tetrafluorooxalatophosphate, lithium difluorophosphate, vinyl sulfate, and boron phosphate lithium oxalate, and ethyl 3-methoxypropionate.

[0054] The electrochemical energy storage device of the present invention can be manufactured according to conventional methods in the art. For example, the positive electrode, separator and negative electrode can be stacked in sequence and then wound (or stacked) to form a cell. Then, after processes such as encapsulation, cell baking, electrolyte injection (i.e., injection of electrolyte), and hot pressing formation, a battery is obtained. These steps / processes are all conventional operations in the art and will not be described in detail.

[0055] The electronic device of the present invention includes the above-mentioned electrochemical energy storage device, which is, for example, an automobile, specifically a HEV and a PHEV.

[0056] Unless otherwise specified, the conductive agent used in this invention may include at least one of superconducting carbon black (SP), graphene, carbon nanotubes, fullerene, graphene nanoribbons, and sheet graphite, wherein the carbon nanotubes may include single-walled carbon nanotubes and / or multi-walled carbon nanotubes; the binder may include at least one of polyvinylidene fluoride (PVDF), a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, polyhexafluoropropylene, and styrene-butadiene rubber (SBR); the thickener may include sodium carboxymethyl cellulose (CMC). However, this invention is not limited to these materials, and other suitable conductive agents, binders, thickeners, etc., may also be selected.

[0057] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described below through specific embodiments and comparative examples.

[0058] Unless otherwise specified, in the following examples, the specific surface area (BET) of the materials was measured using a Tristar 3020 McMill surface area analyzer; the thickness of the negative electrode active material layer was measured using a micrometer. The properties of the amorphous carbon material used in the following examples are as follows: its Raman spectrum Id / Ig peak ratio is 1.09; the elution position of the diffraction peak in the X-ray diffraction (XRD) analysis is approximately 22.445°; and the specific capacity is 330 mAh / g. The Raman spectrum of this amorphous carbon material is shown below. Figure 3 ( Figure 3 (The results are from three tests.) XRD patterns are shown in the image. Figure 4 SEM image as follows Figure 5 As shown in A.

[0059] In the following embodiments, the negative electrode, positive electrode, and battery are all prepared according to the following process:

[0060] (1) Amorphous carbon material, SBR, superconducting carbon black, and CMC are placed in deionized water at a mass ratio of 94.3:1.5:1.5:2.7 to prepare a first negative electrode slurry; graphite-based negative electrode material, binder, conductive agent, and CMC are placed in deionized water at a mass ratio of 94.3:1.5:1.5:2.7 to prepare a second negative electrode slurry; the first and second negative electrode slurries are coated on the front and back surfaces of the negative electrode current collector (copper foil) using a double-layer coating machine. After drying and rolling, a negative electrode active material layer (which includes an amorphous carbon material layer formed by the first negative electrode slurry and a graphite-based negative electrode material layer formed by the second negative electrode slurry) is formed on the front and back surfaces of the negative electrode current collector to obtain a negative electrode sheet;

[0061] (2) NCM111 (single crystal), SBR and superconducting carbon black are placed in N-methylpyrrolidone at a mass ratio of 94:3.5:2.5 to prepare a positive electrode slurry. The positive electrode slurry is coated on both the front and back surfaces of the positive electrode current collector (aluminum foil). After drying and rolling, a positive electrode active material layer is formed on both the front and back surfaces of the positive electrode current collector to obtain a positive electrode sheet.

[0062] (3) After stacking the positive electrode, separator and negative electrode in sequence, they are wound to form a cell. Then, after the processes of encapsulation, cell baking, liquid injection and hot pressing, a battery (with a cell capacity of about 2Ah) is obtained. The separator used is a PP / PE / PP composite film with a thickness of 9μm and a porosity of about 43.43%.

[0063] In each embodiment and comparative example, the average particle size D1, specific capacity, and specific surface area (BET) of the amorphous carbon material are shown in Table 1; the average particle size D2 and the maximum particle size D3 of the graphite-based anode material are shown in Table 1; and the thickness H1 of the amorphous carbon material layer, the thickness H2 of the graphite-based anode material layer, and the thickness H of the anode active material layer are shown in Table 1.

[0064] In Examples 1 to 8, Examples 11 to 16, and Comparative Example 4, the graphite-based anode material layer is located between the surface of the anode current collector and the amorphous carbon material layer; in Examples 9 and 10, the amorphous carbon material layer is located between the surface of the anode current collector and the graphite-based anode material layer.

[0065] The graphite-based anode materials used in Examples 1 to 15 are graphite-based core-shell structure materials with graphite as the core and the above-mentioned amorphous carbon material as the shell. The graphite-based anode material used in Example 16 is graphite.

[0066] The difference between Comparative Example 1 and Example 1 is that the negative electrode active material layer only has a graphite-based negative electrode material layer (i.e., does not include the amorphous carbon material layer), and the thickness H and other parameters of the negative electrode active material layer are shown in Table 1.

[0067] The difference between Comparative Example 2 and Example 16 is that the negative electrode active material layer only has a graphite-based negative electrode material layer (i.e., does not include the amorphous carbon material layer), and the thickness H and other parameters of the negative electrode active material layer are shown in Table 1.

[0068] The difference between Comparative Example 3 and Example 8 is that the negative electrode active material layer only has a graphite-based negative electrode material layer (i.e., does not include the amorphous carbon material layer), and the thickness H and other parameters of the negative electrode active material layer are shown in Table 1.

[0069] The difference between Comparative Example 4 and Example 1 is that the amorphous carbon material used is different. The SEM image of the amorphous carbon material (with an irregular morphology) used in Comparative Example 4 is shown below. Figure 5 The average particle size, specific gravity, BET and other parameters of B are shown in Table 1.

[0070] Apart from the differences mentioned above, the remaining conditions of each embodiment and comparative example are basically the same.

[0071] In each embodiment and comparative example, battery performance was tested through the following process:

[0072] (1) -30℃ discharge lower limit voltage test: Adjust the battery capacity to 50% SOC, stand at -30℃ for 4h, then discharge at 3C for 2s, and record the battery lower limit voltage. The test results (-30℃ discharge lower limit voltage) of each embodiment are shown in Table 2.

[0073] (2) Power test: With a fixed discharge time of 10s, different current rates were adjusted for discharge. When the lower limit voltage after 10s of discharge was exactly 2.7V, the current was the maximum discharge current. The actual discharge end voltage was the lower limit voltage. The power calculation formula was: Power = Lower limit voltage × Maximum discharge current. The test results (discharge power) of each embodiment and comparative example are shown in Table 2.

[0074] (3) Based on the principle that energy density = capacity × open circuit voltage / cell mass, the energy density of the batteries in each embodiment and comparative example was measured and is shown in Table 2.

[0075] Table 1

[0076]

[0077] Table 2

[0078]

[0079] As can be seen from the results in Table 2, the batteries from Examples 1 to 16 all possess good power performance, low-temperature performance, and energy density.

[0080] As can be seen from Examples 1 to 4 and Comparative Example 1, and Example 16 and Comparative Example 2, combining the graphite-based anode material layer and the amorphous carbon material layer can significantly improve the power performance and low-temperature performance of the battery.

[0081] As can be seen from Examples 2 and 9, Examples 7 and 10, and Comparative Examples 1 and 2, compared with graphite anode material layers containing only graphite as the anode active material, combining graphite-based anode material layers and amorphous carbon material layers can improve the power performance and low-temperature performance of the battery. In particular, the amorphous carbon material layer has a more significant effect on the surface of the graphite-based anode material layer.

[0082] As can be seen from Examples 1 to 4 and Comparative Example 4, compared with amorphous carbon materials with non-spherical structures and larger particle sizes, the use of the above-mentioned amorphous carbon materials with small particle sizes and spherical structures can significantly improve the power performance and low-temperature performance of the battery.

[0083] As can be seen from Examples 1 to 4, the particle size of amorphous carbon materials has a significant impact on the power performance and low-temperature performance of the battery. It is speculated that the reason is that as the particle size of amorphous carbon materials increases, the lithium-ion solid-phase diffusion ability weakens, leading to a decrease in the battery's low-temperature discharge performance.

[0084] As can be seen from Examples 6 to 8, the particle size of the graphite-based anode material has a significant impact on the power performance and low-temperature performance of the battery. It is speculated that the reason is that as the particle size of the graphite-based anode material increases, the lithium-ion solid-phase diffusion ability weakens, leading to a decrease in the battery's low-temperature discharge performance.

[0085] As can be seen from Examples 11 to 15, increasing H1 / H2 (increasing the thickness of the amorphous carbon material layer) is beneficial to the power performance and low-temperature performance of the battery, but it will also affect the energy density of the battery to some extent.

[0086] According to the test results of Examples 5, 11 and 15, the battery has good power performance and low temperature performance. However, if D3 is too large (D3 / D2>5.3) and H1 / H2 is too large or too small (not satisfying (7.5×D2 / D3)-1≥H1 / H2≥d / (7.5×D2-d)), scratches will appear on the negative electrode, posing a great safety risk and resulting in poor processing performance of the negative electrode.

[0087] As can be seen from Examples 7 and 16, compared with using pure graphite, using a core-shell structure material with graphite as the core and amorphous carbon material as the shell is more conducive to improving the power performance and low-temperature performance of the battery.

[0088] The preferred embodiments and experimental verifications of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. An electrochemical energy storage device, characterized in that, include: A negative electrode and a positive electrode; the negative electrode includes a negative current collector and a negative active material layer located on at least one surface of the negative current collector, the negative active material layer including an amorphous carbon material layer and a graphite-based negative electrode material layer, the amorphous carbon material layer containing a first negative active material, the first negative active material including amorphous carbon material with a spherical structure, the average particle size D1 of the amorphous carbon material satisfying: 0.2μm≤D1≤4μm; the graphite-based negative electrode material layer containing a second negative active material, the second negative active material including graphite-based negative electrode material; the amorphous carbon material layer is located between the surface of the negative current collector and the graphite-based negative electrode material layer; The positive electrode sheet includes a positive current collector and a positive active material layer located on at least one surface of the positive current collector, wherein the positive active material layer includes a positive active material; The positive electrode active material is lithium nickel cobalt manganese oxide NCM111; The Raman spectrum Id / Ig peak ratio of the amorphous carbon material is 0.5-1.5; in the X-ray diffraction analysis results of the amorphous carbon material, the peak position of the diffraction peak is less than 26.5°. The particle size of the graphite-based anode material satisfies: D2≤10μm, D3 / D2≤5.3, where D2 is the average particle size of the graphite-based anode material and D3 is the maximum particle size of the graphite-based anode material. The graphite-based anode material includes a graphite-based core-shell structure material, which includes a core formed of graphite and a shell existing on the surface of the core. The shell of the graphite-based core-shell structure material comprises the amorphous carbon material.

2. The electrochemical energy storage device according to claim 1, characterized in that, The following conditions must be met: (7.5×D2 / D3)-1≥H1 / H2≥D1 / (7.5×D2-D1), where H1 is the thickness of the amorphous carbon material layer, H2 is the thickness of the graphite-based anode material layer, D2 is the average particle size of the graphite-based anode material, and D3 is the maximum particle size of the graphite-based anode material.

3. The electrochemical energy storage device according to claim 1 or 2, characterized in that, The condition 1.15 > H1 / H2 > 0.04 is satisfied, where H1 is the thickness of the amorphous carbon material layer and H2 is the thickness of the graphite-based anode material layer.

4. The electrochemical energy storage device according to claim 1, characterized in that, The specific surface area of ​​the amorphous carbon material is 2-23 m². 2 / g; and / or, the specific capacity of the amorphous carbon material is 270-360 mAh / g.

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