Battery and electric equipment

Abstract

The invention provides a battery and electric equipment, the battery comprises a positive plate, a negative plate and an electrolyte, the negative plate comprises a negative current collector and a negative coating located on the surface of the negative current collector, the negative coating comprises a silicon carbon material, and the silicon carbon material comprises porous carbon and silicon particles deposited in porous carbon channels; the negative electrode coating comprises a first active material layer and a second active material layer, the first active material layer is located on at least one side surface of the negative electrode current collector, and the second active material layer is located on one side, deviating from the negative electrode current collector, of the first active material layer; the mass percentage content of the silicon element in the second active material layer is greater than that of the silicon element in the first active material layer, the electrolyte comprises carboxylic ester, the carboxylic ester comprises ethyl butyrate, and the mass percentage content of the ethyl butyrate in the electrolyte is 5-35%. The rate capability and the cycle performance of the battery can be improved.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, specifically relating to a battery and an electrical device. Background Technology

[0002] With the ever-increasing demand for energy, high-performance, high-energy-density batteries have become crucial for modern technological development. Silicon possesses a high theoretical specific capacity (approximately 4200 mAh / g), far exceeding that of traditional graphite anodes (approximately 372 mAh / g). Using silicon-carbon materials as anodes is an important means of improving battery energy density. However, silicon undergoes a volume expansion of over 300% during lithiation, leading to capacity decay, reduced rate performance, and decreased cycle performance. Therefore, improving the rate performance and cycle performance of silicon-containing battery systems is a pressing technical challenge in this field. Summary of the Invention

[0003] The present invention provides a battery and an electrical device, wherein the battery has both excellent rate performance and cycle performance.

[0004] In one aspect, the present invention provides a battery comprising a positive electrode, a negative electrode, and an electrolyte; the negative electrode comprises a negative current collector and a negative electrode coating located on the surface of the negative current collector, the negative electrode coating comprising a silicon-carbon material comprising porous carbon and silicon particles deposited in the porous carbon channels; the negative electrode coating comprises a first active material layer and a second active material layer; the first active material layer is located on at least one side of the surface of the negative current collector, and the second active material layer is located on the side of the first active material layer opposite to the negative current collector; the mass percentage of silicon in the second active material layer is greater than the mass percentage of silicon in the first active material layer; the electrolyte comprises a carboxylic acid ester, the carboxylic acid ester comprising ethyl butyrate, and the mass percentage of ethyl butyrate in the electrolyte is 5%-35%.

[0005] According to one embodiment of the present invention, the mass percentage of silicon in the second active material layer is n% of 3%-50%, and the mass percentage of silicon in the first active material layer is w% of 0%-20%; preferably, n is 5-40 and w is 0-10.

[0006] According to one embodiment of the present invention, the thickness of the first active material layer is x1 μm, the thickness of the second active material layer is x2 μm, and x2 > x1; preferably, 0.1 ≤ x1 / (x1+x2) ≤ 0.49; preferably, 70 μm ≤ x1+x2 ≤ 150 μm.

[0007] According to one embodiment of the present invention, the carboxylic acid ester further includes one or more of methyl formate, methyl acetate, propyl acetate, ethyl propionate, propyl propionate, methyl butyrate, ethyl acetate, methyl levulinate, methyl pyruvate, and ethyl difluoroacetate; and / or, the electrolyte further includes carbonates, the carbonates including one or more of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethylene carbonate, and propylene carbonate.

[0008] According to one embodiment of the present invention, the first active material layer comprises hard carbon; preferably, the mass percentage of hard carbon in the first active material layer is 1% to 10%.

[0009] According to one embodiment of the present invention, the second active material layer comprises hard carbon; preferably, the mass percentage of hard carbon in the second active material layer is 1% to 10%.

[0010] According to one embodiment of the present invention, the electrolyte further includes a first additive, which includes one or more of lithium difluorophosphate, vinyl sulfate, and lithium difluorooxalate borate; preferably, the mass percentage of the first additive in the electrolyte is 0.01%-3%, more preferably 0.1%-2%.

[0011] According to one embodiment of the present invention, the electrolyte further includes a second additive, the second additive including an unsaturated nitrile additive, the unsaturated nitrile additive including 1,4-dicyano-2-butene; preferably, the mass percentage of the second additive in the electrolyte is 0.01%-2%.

[0012] According to one embodiment of the present invention, the surface of the negative electrode coating is provided with a recess; preferably, the distance between two adjacent recesses is 0.5mm-10mm; preferably, the depth of the recess is 5μm-60μm.

[0013] According to one embodiment of the present invention, the negative electrode current collector satisfies at least one of the following conditions: a) the thickness of the negative electrode current collector is 4 μm to 12 μm; b) the tensile strength of the negative electrode current collector is 400 MPa to 1000 MPa; c) the elongation of the negative electrode current collector is 2% to 15%; d) the negative electrode current collector comprises carbon-coated copper foil; e) the dyne value of the negative electrode current collector is >40.

[0014] In another aspect, the present invention provides an electrical device comprising the battery described above.

[0015] In the battery provided by the present invention, by setting a first active material layer and a second active material layer on the negative electrode, and the mass percentage of silicon element in the second active material layer is greater than the mass percentage of silicon element in the first active material layer, and by adding 5%-35% of ethyl butyrate carboxylic acid ester solvent to the electrolyte, the rate performance and cycle performance of the battery can be improved. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the structure of a negative electrode sheet according to an embodiment of the present invention;

[0017] Figure 2 This is a schematic diagram of the projection structure of the negative electrode coating on the negative electrode current collector according to an embodiment of the present invention;

[0018] Figure 3 This is a schematic diagram of the projection structure of the negative electrode coating on the negative electrode current collector according to an embodiment of the present invention;

[0019] Figure 4 This is a schematic cross-sectional view of the negative electrode sheet according to an embodiment of the present invention;

[0020] Explanation of reference numerals in the attached figures: 11 Negative electrode current collector; 12 Negative electrode coating; 121 First active material layer; 122 Second active material layer; 101: First side; 102: Second side; 13: Recess; 130: Recess group; L: Width of the recess; △L: Spacing between two adjacent recesses; h: Depth of the recess; △L1: Distance between the outer edge of the recess closest to the first side of the negative electrode coating and the outer edge of the first side of the negative electrode coating; △L2: Distance between the recess closest to the outer edge of the second side of the negative electrode coating and the outer edge of the second side of the negative electrode coating; w: Distance between the recesses in two adjacent recess groups in the second direction y; x: First direction; y: Second direction; z: Third direction. 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. The specific embodiments listed below are merely descriptions of the principles and features of the present invention, and the examples are only for explaining the present invention and are not intended to limit the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] According to the inventors' research and analysis, during battery charging, lithium ions are released from the positive electrode and inserted into the negative electrode, while electrons flow from the positive electrode to the negative electrode through the external circuit. Typically, the lithium-ion transport rate is lower than the electron transport rate, leading to electrochemical polarization. Furthermore, with increasing cycle count, the negative electrode coating develops cracks due to the continuous expansion and contraction of the silicon-carbon material. The formation and expansion of these cracks cause the active material in the negative electrode coating to detach from the negative electrode current collector, increasing the internal resistance of the electrode, reducing lithium-ion transport efficiency, and making the battery prone to self-discharge and internal short circuits. Electrochemical polarization and the expansion of the silicon-carbon material lead to a deterioration in the battery's rate performance and cycle performance.

[0023] This invention provides a battery comprising a positive electrode, a negative electrode, and an electrolyte. The negative electrode includes a negative current collector 11 and a negative electrode coating 12 on the surface of the negative current collector. The negative electrode coating comprises a silicon-carbon material, which includes porous carbon and silicon particles deposited in the porous carbon channels. The negative electrode coating includes a first active material layer 121 and a second active material layer 122. The first active material layer 121 is located on at least one side surface 11 of the negative current collector, and the second active material layer 122 is located on the side of the first active material layer 121 opposite to the negative current collector 11. The mass percentage of silicon in the second active material layer is greater than the mass percentage of silicon in the first active material layer. The electrolyte comprises a carboxylic acid ester, including ethyl butyrate, and the mass percentage of ethyl butyrate in the electrolyte is 5%-35%.

[0024] This invention improves the rate performance and cycle performance of a battery by setting a first active material layer and a second active material layer on the negative electrode, with the second active material layer having a higher mass percentage of silicon than the first active material layer, and by adding 5%-35% of ethyl butyrate carboxylic ester solvent to the electrolyte. Specifically, 1) the second active material layer can increase battery capacity, and the first active material layer with low silicon content is located on the surface of the negative electrode current collector with higher current density, suppressing the decrease in conductivity and ion conduction ability of the first active material layer caused by excessive silicon content, effectively conducting electrons and lithium ions, reducing electrochemical polarization, and improving the rate performance and cycle performance of the battery; 2) the second active material layer with higher expansion (due to high silicon content) and the first active material layer with lower expansion (due to low silicon content) form a structure that gradually relieves stress. This structure can effectively avoid excessive stress difference during charging and discharging, reduce the generation and propagation of cracks, and improve the rate performance of the battery; Ethyl butyrate has a lower dielectric constant than traditional carbonate solvents (such as ethylene carbonate), but it also has lower viscosity. This characteristic is beneficial for the moderate dissociation of lithium salts and the rapid migration of ions, avoiding localized concentration polarization. Furthermore, ethyl butyrate has a lower surface tension than traditional carboxylic acid esters (such as ethyl propionate), allowing for more thorough wetting of the electrode and ensuring that both active material layers participate deeply in the reaction. Therefore, ethyl butyrate helps balance the electrochemical reactions of different negative electrode active material layers, reduces electrochemical polarization, reduces stress concentration caused by negative electrode coating expansion, and improves the overall stability of the electrode. At the same time, the high oxidation resistance of ethyl butyrate can also improve the rate and cycle performance of the battery by improving the stability of the interface and electrolyte.

[0025] In some embodiments, the mass percentage (n%) of silicon in the second active material layer is 3%-50%, such as 3%, 5%, 10%, 20%, 30%, 40%, or 50%, and the mass percentage (w%) of silicon in the first active material layer is 0%-20%, such as 0%, 5%, 10%, 15%, or 20%, which facilitates better conduction of electrons and lithium ions, reduces electrochemical polarization, and improves the rate performance and cycle performance of the battery. Preferably, n is 5-40 and w is 0-10.

[0026] In some embodiments, the thickness of the first active material layer is x1 μm, the thickness of the second active material layer is x2 μm, x2>x1, and the thickness of the second active material layer is greater than the thickness of the first active material layer. This can increase the silicon content in the negative electrode coating without significantly increasing the volume expansion of the negative electrode coating, thereby improving the energy density of the battery.

[0027] In some embodiments, 0.1 ≤ x1 / (x1+x2) ≤ 0.49, such as a range consisting of 0.1, 0.2, 0.24, 0.28, 0.32, 0.36, 0.4, 0.49, or any combination thereof, can better increase the silicon content in the negative electrode coating without significantly increasing the volume expansion of the negative electrode coating, thereby further improving the energy density of the battery.

[0028] In some embodiments, 70μm ≤ x1 + x2 ≤ 150μm, such as 70μm, 80μm, 90μm, 100μm, 110μm, 120μm, 130μm, 140μm, 150μm, or any combination thereof, can further improve the energy density of the battery while reducing electrode internal resistance and improving battery rate performance. Preferably, x1 = 20μm-70μm, x2 = 20μm-120μm.

[0029] In some embodiments, the carboxylic acid ester also includes one or more of methyl formate, methyl acetate, propyl acetate, ethyl propionate, propyl propionate, methyl butyrate, ethyl acetate, methyl levulinate, and methyl pyruvate, which gives the electrolyte a more efficient ion transport rate and helps to further improve the cycle performance of the battery.

[0030] In some embodiments, the electrolyte further includes carbonates, which include one or more of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethylene carbonate, and propylene carbonate.

[0031] Carbonates have a high dielectric constant and good solubility. Using carboxylic esters and carbonates together helps to form a stable SEI layer and improve the cycle life of the battery. Compared with most carbonate solvents, carboxylic esters have higher conductivity, lower viscosity and freezing point. When the proportion of carboxylic esters in the electrolyte is greater than that of carbonates, these characteristics make the ion transport in the electrolyte more efficient, which can quickly enter the upper and lower layers of the negative electrode, reduce the impact of the reaction imbalance of the double coating, and further improve the rate and cycle performance of the battery.

[0032] According to the inventors' research, compared to graphite, hard carbon has a larger interlayer spacing, which facilitates the insertion and extraction of lithium ions, provides more lithium active sites, shortens the lithium ion diffusion path, reduces local current density, and improves the rate performance of the battery. In some embodiments, the first active material layer includes hard carbon, which has less volume expansion, reducing the risk of the active material detaching from the current collector due to excessive volume change, thereby improving the cycle performance and safety performance of the battery. Preferably, the mass percentage of hard carbon in the first active material layer is 1% to 10%, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any combination thereof, which is beneficial for further improving the cycle performance of the battery. In some embodiments, the second active material layer includes hard carbon, preferably, the mass percentage of hard carbon in the second active material layer is 1% to 10%, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any combination thereof, which is beneficial for further improving the rate performance of the battery.

[0033] In some embodiments, the electrolyte further includes a lithium salt. Preferably, the concentration of the lithium salt in the electrolyte is 1M to 4M, where M represents mol / L, such as 1M, 1.5M, 2M, 2.5M, 3M, 3.5M, 4M, or any combination thereof. By adjusting the concentration of the lithium salt in the electrolyte, the concentration of Li can be adjusted. + This reduces the diffusion rate, decreases electrochemical polarization, and thus improves the cycle performance of the battery.

[0034] In some embodiments, the lithium salt includes one or more of lithium hexafluorophosphate, lithium difluorophosphate, lithium difluorooxalate borate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium difluorobis(oxalate)phosphate, lithium tetrafluoroborate, lithium bis(oxalate)borate, lithium hexafluoroantimonyate, lithium hexafluoroarsenate, lithium di(pentafluoroethylsulfonyl)imide, and lithium tri(trifluoromethylsulfonyl)methyl. Preferably, the mass percentage of the lithium salt in the electrolyte is 12% to 30%, for example, 12%, 15%, 20%, 25%, 30%, or any combination thereof.

[0035] In some embodiments, the electrolyte further includes a first additive, which comprises one or more of lithium difluorophosphate, vinyl sulfate, and lithium difluorooxalate borate. This first additive can form a stable interface layer (SEI and CEI) on the electrode surface, reducing impedance, decreasing electrochemical polarization, and improving battery cycle and rate performance. Preferably, the mass percentage of the first additive in the electrolyte is 0.01% to 3%, for example, 0.01%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, or any combination thereof, more preferably 0.1% to 2%.

[0036] In some embodiments, the electrolyte further includes a second additive, which includes an unsaturated nitrile additive, including 1,4-dicyano-2-butene. The unsaturated nitrile additive participates in the formation of the positive and negative electrode films, improving the stability and mechanical strength of the CEI and SEI films, preventing contact between the electrolyte and the active materials, reducing side reactions between the electrolyte and the active materials, and improving the cycle performance of the battery. Preferably, the mass percentage of the second additive in the electrolyte is 0.01% to 2%, for example, 0.01%, 0.1%, 0.2%, 0.5%, 1%, 1.5%, 2%, or any combination thereof, more preferably 0.1% to 2%.

[0037] In some embodiments, the surface of the negative electrode coating is provided with recesses (i.e., recessed grooves), which allow the electrolyte to rapidly diffuse from the recessed grooves into the interior of the negative electrode coating, shortening the diffusion path of lithium ions, accelerating the lithium ion conduction rate, and reducing the impedance at each interface, thereby improving the rate performance and cycle performance of the battery. Furthermore, it facilitates electrolyte flow, allowing the electrolyte to more fully wet the cell and increasing the electrolyte storage capacity of the cell. Preferably, the distance between two adjacent recesses is 0.5mm-10mm, for example, 0.5mm, 1mm, 3mm, 5mm, 7mm, 9mm, 10mm, or any combination thereof. Preferably, the depth of the recess is 5μm-60μm, for example, 5μm, 10μm, 15μm, 20μm, 25μm, 30μm, 40μm, 50μm, 60μm, or any combination thereof, which further improves the rate performance and cycle performance of the battery.

[0038] Specifically, the surface of the negative electrode coating may be provided with a recess 13 (i.e., the recess 13 is continuously provided on the surface of the negative electrode coating 12), or, as... Figures 1 to 3 As shown, the surface of the negative electrode coating 12 is provided with at least two recesses 13, and these recesses 13 can be distributed along the first direction x (e.g., Figure 2 As shown), it can be distributed along the second direction y, or some of the recesses 13 can be distributed along the first direction x and some of the recesses 13 can be distributed along the second direction y.

[0039] Among them, such as Figures 2 to 4 As shown, at least some of the recesses 13 are distributed along the first direction x, and two adjacent recesses 13 in the first direction x are separated by the negative electrode coating 12. The distance between two adjacent recesses 13 in the first direction x (i.e., the distance between two adjacent recesses 13 in the first direction x) ΔL > 0.

[0040] Specifically, the surface of the negative electrode coating 12 may include at least one set of recesses 130, each set of recesses 130 including at least two recesses 13 distributed along the first direction x. When the number of recesses 130 is at least two (i.e. the surface of the negative electrode coating 12 includes at least two sets of recesses 130), these recesses 130 are distributed along the second direction y.

[0041] For example, such as Figure 2 As shown, the surface of the negative electrode coating 12 includes two sets of recesses 130, which are distributed along the second direction y. In each set of recesses 130, one edge of the recess 13 in the length direction is substantially flush with one edge of the negative electrode coating 12 in the width direction; or, as shown... Figure 3 As shown, the surface of the negative electrode coating 12 has a set of recesses 130, wherein the length of the recesses 13 in the second direction y is substantially equal to the width of the negative electrode coating.

[0042] In some embodiments, in two adjacent recess groups 130, the distance w between the recess 13 in one recess group 130 and the recess 13 in the other recess group 130 in the second direction y is less than or equal to 1 mm (i.e., w ≤ 1 mm), wherein the following relationship is basically satisfied: the width of the negative electrode coating = the length of the recess 13 in one recess group 130 in the second direction y + the length of the recess 13 in the other recess group 130 in the second direction y + w.

[0043] Among the two adjacent recess groups 130, the recess 13 in one recess group 130 and the recess 13 in the other recess group 130 that is closest to the recess 13 can be connected or not connected. When the two recesses 13 are connected, the gap (distance in the second direction y) w between the two recesses 13 is basically equal to 0.

[0044] Continue to refer Figures 2 to 4 The distance between two adjacent recesses 13 in the first direction x is ΔL > 0. The negative electrode coating 12 has a first side 101 and a second side 102 opposite to each other in the first direction x. The distance ΔL1 between the recess 13 closest to the outer edge of the first side 101 of the negative electrode coating 12 and the outer edge of the first side 101 of the negative electrode coating 12 is less than or equal to the distance ΔL between two adjacent recesses 13 (ΔL1 ≤ ΔL). The distance ΔL2 between the recess 13 closest to the outer edge of the second side 102 of the negative electrode coating 12 and the outer edge of the second side 102 of the negative electrode coating 12 is less than or equal to ΔL (ΔL2 ≤ ΔL), so that the recesses 13 are arranged at a distance ΔL on the entire surface of the negative electrode coating 12.

[0045] The distance ΔL between two adjacent recesses 13 in the first direction x refers to the distance between the two adjacent recesses 13 in the first direction x, which is also the distance between two adjacent recesses 13 in each recess group 130.

[0046] Continue to refer Figures 2 to 4 The width direction of the recesses 13 is substantially parallel to the first direction x, and the length direction (extension direction) of these recesses 13 is substantially perpendicular to the first direction x.

[0047] Specifically, the recess 13 can be in the shape of a hole or a groove, and preferably the recess 13 is a linear groove, that is, the projection of the recess 13 on the negative electrode current collector 11 is strip-shaped (e.g., Figure 2 and Figure 3 As shown), specifically it can be a rectangle (such as...). Figure 3 (as shown) or other regular or irregular shapes.

[0048] Continue to refer Figure 2 and Figure 3 When the surface of the negative electrode coating 12 is provided with at least two recesses 13, each recess 13 is a linear groove, and its projection on the negative electrode current collector 11 is basically rectangular. The length direction (extension direction) of these recesses 13 is basically parallel to each other, specifically parallel to the second direction y. The width direction of these recesses 13 is basically parallel, and basically parallel to the first direction x.

[0049] In this embodiment of the invention, a laser can be used to create recesses with preset shapes and parameters such as thickness, width, length and spacing on the surface of the negative electrode coating 2. For example, a recess 13 (linear groove) can be formed on the surface of the negative electrode coating 12 by laser wire drawing. Specifically, the thickness and other parameters of the formed recess 13 can be adjusted by controlling parameters such as laser intensity. These control methods are all conventional operations in the field and will not be described in detail.

[0050] like Figure 3 As shown, the recess 13 can be a complete continuous groove, that is, a laser is used to continuously drill holes on the surface of the negative electrode coating 12 along the extension direction of the preset linear groove to form a continuous groove (at this time, a set of recesses 130 is formed on the surface of the negative electrode coating).

[0051] The inventors discovered through research that when the surface of the negative electrode coating 12 includes at least two sets of recesses 130, it is beneficial to further improve the electrochemical performance and safety performance of the battery. The reason for this is that when the surface of the negative electrode coating 12 includes at least two sets of recesses 130, it is beneficial to conduct electrolyte, allowing the electrolyte to more fully wet the cell, increasing the electrolyte storage capacity of the cell, thereby improving the migration ability of lithium ions, increasing conductivity, reducing voltage drop, and reducing the risk of short circuit.

[0052] In some embodiments, the thickness of the negative electrode current collector is 4μm to 12μm, such as 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, or any combination thereof, which can improve the energy density of the battery while also helping to maintain the mechanical strength of the negative electrode sheet.

[0053] In some embodiments, the tensile strength of the negative electrode current collector is 400 MPa-1000 MPa, for example, 400 MPa, 500 MPa, 600 MPa, 700 MPa, 800 MPa, 900 MPa, 1000 MPa, or any combination thereof.

[0054] In some embodiments, the elongation of the negative electrode current collector is 2%-15%, for example, a range of 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, or any combination thereof.

[0055] In some embodiments, the dyne value of the negative electrode current collector is >40, such as a range of 41, 43, 45, 47, 49, 51, 53, 55, 57, 65, 75, 85, or any combination thereof, which can significantly improve the wettability and spreadability of the electrolyte on the surface of the negative electrode current collector, thereby enhancing the fluidity of the electrolyte. Simultaneously, carboxylic acid esters have lower viscosity and better fluidity compared to most carbonate solvents, which is beneficial for electrolyte wetting. The synergistic use of carboxylic acid esters and negative electrode current collectors with a dyne value >40 can further improve the wettability of the electrolyte on the negative electrode sheet, helping the electrolyte to more uniformly wet the electrode material and more effectively penetrate into the microporous structure of the electrode material, thereby achieving a more uniform current density distribution, forming a stable electrolyte interface film (SEI), reducing the risk of lithium plating on the negative electrode surface, and thus improving battery safety and cycle life.

[0056] In some embodiments, the negative current collector includes a carbon-coated copper foil. The carbon-coated copper foil is typically a copper foil with a carbon layer intermittently coated on its surface. Specifically, carbon coating can be performed on the copper foil surface using conventional equipment and processes in the art, such as gravure rollers or skip coating equipment, to form a carbon-coated copper foil. The embodiments of the present invention do not impose any particular restrictions on the carbon coating process.

[0057] In some embodiments, the first active material layer further includes graphite, a conductive agent, a binder, and a thickener, and the second active material layer further includes graphite, a conductive agent, a binder, and a thickener. Silicon-carbon materials and graphite are collectively referred to as negative electrode active materials.

[0058] In some embodiments, the mass ratio of graphite to silicon carbide is (5-30):1, for example, a range consisting of 5:1, 10:1, 15:1, 20:1, 25:1, 30:1 or any two of these.

[0059] In some embodiments, the sphericity of the silicon-carbon material is greater than or equal to 0.8, for example, a range consisting of 0.8, 0.85, 0.88, 0.9, 0.92, 0.94, 0.96, 0.99, or any two of these.

[0060] In some embodiments, the particle size of the silicon-carbon material is between 5 μm and 15 μm, for example, a range of 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 14 μm, 15 μm or any combination thereof.

[0061] Generally, a positive electrode sheet includes a positive current collector and a positive electrode coating on the surface of the positive current collector. Specifically, a positive electrode coating can be provided on both the positive and negative surfaces of the positive current collector.

[0062] Specifically, the positive electrode coating may include a positive electrode active material layer, which includes a positive electrode active material, a conductive agent, and a binder. The positive electrode active material may include conventional positive electrode active materials in the art, such as lithium-containing positive electrode active materials, including at least one of lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, ternary lithium materials, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadium oxide phosphate, and lithium-rich manganese-based materials. The ternary lithium materials may include lithium nickel cobalt manganese oxide and / or lithium nickel cobalt aluminum oxide, etc.

[0063] Wherein, based on the total mass of the positive electrode active material layer, the mass fraction of the positive electrode active material can be 70% to 99%, for example, 70%, 75%, 80%, 85%, 90%, 95%, 99%, or any combination thereof; the mass fraction of the conductive agent can be 0.5% to 15%, for example, 0.5%, 1%, 3%, 5%, 8%, 10%, 12%, 15%, or any combination thereof; and the mass fraction of the binder can be 0.5% to 15%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 5%, 7%, 9%, 11%, 13%, 15%, or any combination thereof, but is not limited to these.

[0064] In this embodiment of the invention, the battery further includes a separator.

[0065] Generally, a separator includes a base membrane and an adhesive layer disposed on both the front and back surfaces of the base membrane. The separator is bonded to the positive and negative electrode plates through the adhesive layer on its surface. A ceramic layer, such as an alumina layer, may also be disposed between the base membrane and the adhesive layer, but it is not limited to this.

[0066] In practice, parameters such as the tensile strength of the diaphragm can be controlled by adjusting the production process and material of the base membrane. These are all standard practices in the field and will not be elaborated further.

[0067] For example, the base membrane can be a polypropylene (PP) membrane, a polyethylene (PE) membrane, a polypropylene / polyethylene (PP / PE) bilayer composite membrane, a polyimide (PI) electrospun membrane, a polypropylene / polyethylene / polypropylene (PP / PE / PP) trilayer composite membrane, or a cellulose nonwoven membrane, or other conventional membrane materials in the field.

[0068] In this embodiment of the invention, the binder in the positive electrode coating and the negative electrode coating can be a conventional adhesive material in the art, such as one or more of polyvinylidene fluoride (PVDF), a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile (PAN), polyacrylate, polyacrylic acid (PAA), polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, polyhexafluoropropylene and styrene-butadiene rubber (SBR), and polyacrylate may include lithium polyacrylate and / or sodium polyacrylate, etc.

[0069] In addition, the negative electrode coating may also include a thickener, which may include carboxymethyl cellulose (CMC) thickeners, such as carboxymethyl cellulose and / or carboxymethyl cellulose salts, such as lithium carboxymethyl cellulose (CMC-Li) and / or sodium carboxymethyl cellulose (CMC-Na).

[0070] In this embodiment of the invention, the conductive agent in the positive electrode coating and the negative electrode coating can be a conventional conductive agent in the art, such as one or more of carbon nanotubes (carbon tubes), carbon black (SP), acetylene black, graphene, and conductive graphite.

[0071] Based on the total mass of the first active material layer, the mass fraction of the negative electrode active material can be 70% to 99%, for example, 70%, 75%, 80%, 85%, 90%, 95%, 99%, or any combination thereof; the mass fraction of the conductive agent can be 0.3% to 12%, for example, 0.3%, 0.5%, 1%, 3%, 5%, 8%, 10%, 12%, or any combination thereof; and the mass fraction of the binder can be 0% to 1%. The mass fraction of the thickener may be 5%, for example, 0%, 0.2%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 7%, 9%, 10%, 12%, 15%, or any two of these, but is not limited to this range.

[0072] Based on the total mass of the second active material layer, the mass fraction of the negative electrode active material can be 70% to 99%, for example, 70%, 75%, 80%, 85%, 90%, 95%, 99%, or any combination thereof; the mass fraction of the conductive agent can be 0.3% to 12%, for example, 0.3%, 0.5%, 1%, 3%, 5%, 8%, 10%, 12%, or any combination thereof; and the mass fraction of the binder can be 0% to 1%. The mass fraction of the thickener may be 5%, for example, 0%, 0.2%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 7%, 9%, 10%, 12%, 15%, or any two of these, but is not limited to this range.

[0073] In this embodiment of the invention, the positive electrode sheet can be prepared by conventional methods in the art, such as coating. For example, the preparation process of the positive electrode sheet may include: placing materials such as positive electrode active material, conductive agent and binder in a solvent to prepare a positive electrode slurry, the solvent of which includes, for example, N-methylpyrrolidone (NMP), then coating the positive electrode slurry onto the surface of the positive electrode current collector, and after drying, rolling and other processes, forming a positive electrode active material layer on the surface of the positive electrode current collector to obtain the positive electrode sheet.

[0074] In this embodiment of the invention, a negative electrode coating can be formed on the surface of the negative electrode current collector using conventional methods in the art, such as coating, and then a negative electrode sheet can be obtained by laser drilling on the surface of the negative electrode coating. For example, the process of obtaining the negative electrode sheet may include: placing materials such as negative electrode active material, conductive agent and binder in a solvent to prepare a negative electrode slurry, the solvent of which includes, for example, water; applying the negative electrode slurry to the surface of the negative electrode current collector; and forming a negative electrode coating on the surface of the negative electrode current collector after drying, rolling and other processes; and then forming a recess 13 in a predetermined area on the surface of the negative electrode coating by laser drilling to obtain the negative electrode sheet.

[0075] In this embodiment of the invention, the battery can be a lithium-ion battery.

[0076] In this embodiment of the invention, the battery can be manufactured according to conventional methods in the art. For example, the positive electrode, separator, and negative electrode are stacked in sequence and hot-pressed together, then wound to form a core, and then packaged with a package body. After liquid injection (injecting electrolyte into the package body), formation, capacity testing, and OCV (open circuit voltage test), the battery is obtained. These steps / processes are all conventional operations in the art, and the present invention does not impose any special limitations on them and will not elaborate further.

[0077] The present invention also provides an electrical device that has advantages corresponding to the above-mentioned battery, which will not be described in detail here.

[0078] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0079] Example 1

[0080] The battery in this embodiment is prepared by a method including the following steps:

[0081] 1. Preparation of positive electrode sheet

[0082] The positive electrode active material (lithium cobalt oxide), conductive agent Super-P, and binder polyvinylidene fluoride are dispersed in N-methylpyrrolidone (NMP) and stirred evenly to obtain a positive electrode active slurry. The positive electrode active slurry is uniformly coated on two functional surfaces of an aluminum foil. The aluminum foil coated with the positive electrode active slurry is dried at 100°C for 8 hours. After rolling, cutting, cleaning, and attaching tab adhesive, a positive electrode sheet is obtained.

[0083] The mass ratio of the positive electrode active material, conductive agent, and binder is 98:1.2:0.8.

[0084] 2. Preparation of negative electrode sheet

[0085] 1) Graphite and silicon carbide materials are mixed evenly at a mass ratio of 100:0 to obtain the first active material;

[0086] Graphite and silicon carbide materials were stirred evenly at a mass ratio of 80:20 to obtain the second active material; the sphericity of the silicon carbide material was 0.95 and the particle size was 9μm.

[0087] 2) The first active material obtained in step 1) and the conductive agent Super P, the binder styrene-butadiene rubber (SBR) and the thickener sodium carboxymethyl cellulose (CMC) are dispersed in deionized water at a mass ratio of 97:1:1.5:0.5 and stirred evenly to obtain the first negative electrode slurry;

[0088] 3) Disperse the second active material obtained in step 1), the conductive agent Super P, the binder styrene-butadiene rubber (SBR), and the thickener sodium carboxymethyl cellulose (CMC) in deionized water at a weight ratio of 97:1:1.5:0.5, and stir evenly to obtain the second negative electrode slurry;

[0089] 4) A double-layer coating method is used, where the first negative electrode slurry and the second negative electrode slurry are simultaneously coated on both sides of a 4μm thick carbon-coated copper foil (during coating, the extrusion head for coating the second negative electrode slurry is positioned above the extrusion head for coating the first negative electrode slurry, so that the paste formed by the first negative electrode slurry is located between the carbon-coated copper foil and the paste formed by the second negative electrode slurry). After baking and rolling, a negative electrode coating is formed on both sides of the carbon-coated copper foil (the negative electrode coating includes a first active material layer formed by the first negative electrode slurry and a second active material layer formed by the second negative electrode slurry, with the first active material layer located between the carbon-coated copper foil and the second active material layer). After cutting, cleaning, and attaching tab adhesive, a negative electrode sheet is obtained; wherein the silicon content of the second active material layer is 12.5%.

[0090] The carbon-coated copper foil has a tensile strength of 400 MPa, an elongation of 10%, a dyne value of 50, a first active material layer thickness of 30 μm, and a second active material layer thickness of 70 μm.

[0091] 3. Preparation of electrolyte

[0092] In a glove box (H2O < 0.01 ppm, O2 < 0.01 ppm, Ar atmosphere), ethylene carbonate (EC), propylene carbonate (PC), and ethyl propionate (EP) were mixed evenly in a mass ratio of 1:1:3. Then, ethyl butyrate (15% by mass, based on electrolyte mass) was added, followed by fluoroethylene carbonate (10% by mass) and LiPF6 (15% by mass, based on electrolyte mass). The mixture was stirred evenly, and after passing the moisture and free acid tests, the electrolyte was obtained.

[0093] 4. Battery assembly

[0094] The positive and negative electrode sheets are cut according to a preset shape and size. Then, the positive electrode sheet, separator and negative electrode sheet are stacked in sequence and wound into a core and hot-pressed together. Then, the core is sealed with aluminum-plastic film and then successively baked, injected with electrolyte, formed, sealed again, sorted and OCV and other processes to obtain a lithium-ion battery.

[0095] Examples 2 to 16 differ from Example 1 in that the content of silicon-carbon materials in each layer or other parameters are adjusted. The mass percentage of silicon in the first active material layer (w), the mass percentage of silicon in the second active material layer (n), the thickness of the first active material layer (x1), the thickness of the second active material layer (x2), and the ratio of the thickness of the first active material layer to the thickness of the negative electrode coating (x1 / (x1+x2)) are different. For details, please refer to Tables 1 and 2. Except for the differences shown in Tables 1 and 2, the other steps and conditions are the same as in Example 1.

[0096] Examples 17 to 19

[0097] The difference from Example 1 is that the tensile strength T, elongation E, dyne value D, and thickness d of the carbon-coated copper foil are different. For details, please refer to Table 1. Except for the differences shown in Table 1, the other steps and conditions are the same as in Example 1.

[0098] Example 20

[0099] The difference from Example 1 is that, in the preparation of the electrolyte, LiPF6 was added to ethyl butyrate in a glove box (H2O < 0.01 ppm, O2 < 0.01 ppm, Ar atmosphere), and after dissolution, the first additive lithium difluorophosphate was added, stirred evenly, and after passing the tests for moisture and free acid, the electrolyte was obtained.

[0100] The electrolyte contains 15% LiPF6 by mass and 0.2% of the first additive by mass.

[0101] Examples 21-22

[0102] The difference from Example 20 is that the mass percentage of the first additive in the electrolyte is different, as shown in Table 2. Except for the differences shown in Table 2, the other steps and conditions are the same as in Example 20.

[0103] Example 23

[0104] The difference from Example 1 is that, in the preparation of the electrolyte, ethylene carbonate, propylene carbonate (PC), and ethyl propionate (EP) were mixed uniformly in a glove box (H2O < 0.01 ppm, O2 < 0.01 ppm, Ar atmosphere) at a mass ratio of 1:1:3. Then, ethyl butyrate (15% by mass, based on electrolyte mass) was added, followed by fluoroethylene carbonate (10% by mass) and LiPF6 (15% by mass, based on electrolyte mass). After dissolution, lithium difluorophosphate (first additive) and 1,4-dicyano-2-butene (second additive) were added and stirred until homogeneous. After passing moisture and free acid tests, the electrolyte was obtained. The mass percentage of the first additive in the electrolyte was 3%, and the mass percentage of the second additive was 2%.

[0105] Examples 24-25

[0106] The difference from Example 23 is that the mass percentage of the second additive in the electrolyte is different, as shown in Table 2. Except for the differences shown in Table 2, the other steps and conditions are the same as in Example 23.

[0107] Example 26

[0108] The difference from Example 23 is that the type of the second additive in the electrolyte is different, and 1,4-dicyano-2-butene is replaced with succinate in equal amounts. The other steps and conditions are the same as in Example 23.

[0109] Example 27

[0110] The difference from Example 23 is that after obtaining the negative electrode sheet in step 4), a laser wire bonding device (set to 28% power) is used to create linear grooves (i.e. recesses, which do not penetrate the negative electrode coating) on ​​the surface of the negative electrode coating on each side. The spacing between the recesses is ΔL = 0.5 mm, and the depth of the recess is h = 5 μm, thus obtaining a negative electrode sheet with recesses on the surface of the negative electrode coating.

[0111] Examples 28 to 30

[0112] The difference from Example 27 is that the recess spacing ΔL and the recess depth h are different. For details, please refer to Table 2. Except for the differences shown in Table 2, the other steps and conditions are the same as in Example 27.

[0113] Example 31

[0114] The difference from Example 1 is that, in the preparation process of the negative electrode, hard carbon, graphite and silicon carbide materials are stirred evenly in a mass ratio of 1:99 to obtain the first active material; hard carbon and graphite are stirred evenly in a mass ratio of 1:79:20 to obtain the second active material; see Table 2 for details. Except for the differences shown in Table 2, the other steps and conditions are the same as in Example 1.

[0115] Examples 32 to 34

[0116] The difference from Example 31 is that the mass percentage of hard carbon in the first active material layer W1 and the mass percentage of hard carbon in the second active material layer W2 are different during the preparation of the negative electrode sheet. For details, please refer to Table 2. Except for the differences shown in Table 2, the other steps and conditions are the same as in Example 31.

[0117] Example 35

[0118] The difference from Example 1 lies in the preparation process of the negative electrode and electrolyte, as detailed in Tables 1 and 2. Except for the differences shown in Tables 1 and 2, the other steps and conditions are the same as in Example 1. The preparation of the negative electrode and electrolyte includes the following steps:

[0119] Preparation of negative electrode

[0120] 1) Hard carbon, graphite, and silicon carbide materials are mixed evenly at a mass ratio of 3:97 to obtain the first active material;

[0121] Hard carbon, graphite, and silicon carbide materials were mixed evenly in a mass ratio of 3:77:20 to obtain the second active material.

[0122] 2) The first active material obtained in step 1) and the conductive agent Super P, the binder styrene-butadiene rubber (SBR) and the thickener sodium carboxymethyl cellulose (CMC) are dispersed in deionized water at a mass ratio of 97:1:1.5:0.5 and stirred evenly to obtain the first negative electrode slurry;

[0123] 3) Disperse the second active material obtained in step 1), the conductive agent Super P, the binder styrene-butadiene rubber (SBR), and the thickener sodium carboxymethyl cellulose (CMC) in deionized water at a weight ratio of 97:1:1.5:0.5, and stir evenly to obtain the second negative electrode slurry;

[0124] 4) A double-layer coating method is adopted, in which the first negative electrode slurry and the second negative electrode slurry are coated on both sides of the carbon-coated copper foil with a thickness of 4μm at the same time (during coating, the extrusion head for coating the second negative electrode slurry is located above the extrusion head for coating the first negative electrode slurry, so that the paste formed by the first negative electrode slurry is located between the carbon-coated copper foil and the paste formed by the second negative electrode slurry). After baking and rolling, a negative electrode coating is formed on both sides of the carbon-coated copper foil (the negative electrode coating includes a first active material layer formed by the first negative electrode slurry and a second active material layer formed by the second negative electrode slurry, with the first active material layer located between the carbon-coated copper foil and the second active material layer). After cutting, cleaning and attaching tab adhesive, the negative electrode sheet is obtained.

[0125] The carbon-coated copper foil has a tensile strength of 400 MPa, an elongation of 10%, a dyne value of 50, a thickness of 30 μm for the first active material layer, and a thickness of 70 μm for the second active material layer.

[0126] 5) Using a laser wire bonding device (set to 28% power), linear grooves (i.e. recesses, which do not penetrate the negative electrode coating) are formed on the surface of the negative electrode coating on each side. The spacing between the recesses is ΔL = 5mm and the depth of the recess is h = 30μm, thus producing the negative electrode sheet.

[0127] Preparation of electrolyte

[0128] In a glove box (H2O < 0.01 ppm, O2 < 0.01 ppm, Ar atmosphere), ethylene carbonate (EC), propylene carbonate (PC), and ethyl propionate (EP) were mixed evenly in a mass ratio of 1:1:3. Then, ethyl butyrate (15% by mass, based on electrolyte mass) was added, along with LiPF6. After dissolving, lithium difluorophosphate (first additive), 1,4-dicyano-2-butene (second additive), and fluoroethylene carbonate (10% by mass, based on electrolyte mass) were added. The mixture was stirred evenly, and after passing the tests for moisture and free acid, the electrolyte was obtained.

[0129] The electrolyte contains 15% LiPF6 by mass, 3% of the first additive by mass, and 2% of the second additive by mass.

[0130] Comparative Example 1

[0131] The difference from Example 1 is that, in the preparation of the electrolyte, ethyl butyrate is replaced with propyl propionate in an equal amount, as shown in Tables 1 and 2. Except for the differences shown in Tables 1 and 2, the other steps and conditions are the same as in Example 1.

[0132] Comparative Example 2

[0133] The difference from Example 1 is that, in the preparation process of the negative electrode, the silicon content of the first active material layer (12.5%) is greater than that of the second active material layer (0%). For details, please refer to Tables 1 and 2. Except for the differences shown in Tables 1 and 2, the other steps and conditions are the same as in Example 1.

[0134] Comparative Example 3

[0135] The difference from Example 1 is that, in the preparation process of the negative electrode sheet, the negative electrode coating only includes the first active material layer, as detailed in Tables 1 and 2. Except for the differences shown in Tables 1 and 2, the other steps and conditions are the same as in Example 1. The specific steps are as follows:

[0136] 1) Mix graphite and silicon carbide materials at a mass ratio of 85:15 to obtain the active material;

[0137] 2) Disperse the active material obtained in step 1) with the conductive agent Super P, the binder styrene-butadiene rubber (SBR), and the thickener sodium carboxymethyl cellulose (CMC) in deionized water at a mass ratio of 97:1:1.5:0.5, and stir evenly to obtain the negative electrode slurry;

[0138] 3) The negative electrode slurry is coated on both sides of the carbon-coated copper foil with a thickness of 4μm. After baking and rolling, a negative electrode coating is formed on both sides of the carbon-coated copper foil.

[0139] The carbon-coated copper foil has a tensile strength of 400 MPa, an elongation of 10%, a dyne value of 50, and a negative electrode coating thickness of 70 μm.

[0140] 4) Using a laser drilling device (set to 28% power), linear grooves (i.e. recesses, which do not penetrate the negative electrode coating) are drilled on the surface of the negative electrode coating on each side. The spacing between the recesses is ΔL = 1.2 mm, the width of the recess is L = 80 μm, and the depth of the recess is h = 15 μm, thus producing the negative electrode sheet.

[0141] Comparative Example 4

[0142] The difference from Example 1 is that the mass percentage of ethyl butyrate in the electrolyte is 0.5% during the preparation of the electrolyte, as shown in Tables 1 and 2. Except for the differences shown in Tables 1 and 2, the other steps and conditions are the same as in Example 1.

[0143] Comparative Example 5

[0144] The difference from Example 1 is that the mass percentage of ethyl butyrate in the electrolyte is 60% during the preparation process, as shown in Tables 1 and 2. Except for the differences shown in Tables 1 and 2, the other steps and conditions are the same as in Example 1.

[0145] The following parameters are summarized in Tables 1 and 2: the mass percentage of silicon in the first active material layer (w), the mass percentage of silicon in the second active material layer (n), the thickness of the first active material layer (x1), the thickness of the second active material layer (x2), the ratio of the thickness of the first active material layer to the thickness of the negative electrode coating (x1 / (x1+x2)), the mass percentage of ethyl butyrate in the electrolyte (c), the tensile strength (T) of the carbon-coated copper foil, the elongation (E) of the carbon-coated copper foil, the dyne value (D) of the carbon-coated copper foil, the thickness (d) of the carbon-coated copper foil, the mass percentage of hard carbon in the first active material layer (W1), the mass percentage of hard carbon in the second active material layer (W2), the type of the first additive, the mass percentage of the first additive in the electrolyte (W3), the type of the second additive, the mass percentage of the second additive in the electrolyte (W4), the depth of the recess (h), and the spacing between the recesses (ΔL). Except for the differences shown in Tables 1 and 2, the other conditions are basically the same.

[0146] The following tests were conducted: 1) The dyne value D of the carbon-coated copper foil was tested using a dyne pen; 2) The tensile strength T of the carbon-coated copper foil was tested by cutting the carbon-coated copper foil into samples with a width of 15 mm and a length exceeding 50 mm using a knife; a WD-D3 electronic universal testing machine (accuracy grade 0.5, accuracy ±1% of the indicated value) was used, with a gauge length of 50 mm and a speed of 100 mm / min, to perform a tensile test on the sample and measure the tensile strength T of the carbon-coated copper foil; 3) The elongation E of the carbon-coated copper foil was tested by cutting the carbon-coated copper foil into samples with a width of 15 mm and a length exceeding 50 mm using a knife; a WD-D3 electronic universal testing machine (accuracy grade 0.5, accuracy ±1% of the indicated value) was used, with a gauge length of 50 mm and a speed of 50 mm / min, to perform a tensile test on the sample and measure the elongation E of the carbon-coated copper foil.

[0147] Table 1

[0148]

[0149]

[0150] Table 2

[0151]

[0152]

[0153] The negative electrode sheets and batteries of each embodiment and comparative example were tested using the following methods, and the results are shown in Table 3:

[0154] 1. The capacity retention rate test method for 1C / 2C batteries is as follows: Place the battery in an environment of (25±3)℃, charge the battery to 4.5V at constant current and constant voltage according to 1C / 2C, then charge it to the cutoff current of 0.05C at constant voltage of 4.5V, and then discharge it at 0.5C. Record the initial capacity Q0. Repeat the above steps for 500 cycles. Use the discharge capacity of 1000 cycles as the capacity Q1 of the battery. Calculate the 1C / 2C constant current capacity retention rate (%) of the battery according to the following formula.

[0155] Capacity retention rate (%) = Q1 / Q0 × 100%.

[0156] 2. The method for testing the thickness change rate of 1C / 2C cells is as follows: Test the thickness D0 of a fully charged cell. Place the battery in an environment of (25±3)℃. Charge the battery to 4.5V at a constant current and constant voltage of 1C / 2C. Then charge it to the cutoff current of 0.05C at a constant voltage of 4.5V. Then discharge it at 0.5C and record the initial capacity Q0. Repeat the above steps for 1000 cycles. Then fully charge the battery. After removing the cell, test the thickness D1 of the fully charged cell at this time. Calculate the thickness change rate of the cell according to the following formula.

[0157] Thickness change rate (%) = (D1-D0) / D0 × 100%.

[0158] Table 3

[0159]

[0160]

[0161] As can be seen from Tables 1 to 3, compared with Comparative Examples 1 to 5, Examples 1 to 19, by setting a first active material layer and a second active material layer on the negative electrode, and the mass percentage of silicon in the second active material layer being greater than the mass percentage of silicon in the first active material layer, and by adding 5%-35% of ethyl butyrate carboxylic acid ester solvent to the electrolyte, can simultaneously improve the rate performance and cycle performance of the battery.

[0162] Furthermore, Examples 20-22 added a first additive to the electrolyte, Examples 23-25 ​​added a second additive to the electrolyte based on Examples 20-22, Examples 27-30 provided a recess on the surface of the negative electrode coating based on Examples 23-25, and Examples 31-34 added hard carbon to the first active material layer and the second active material layer based on Examples 27-30, further improving the rate performance and cycle performance of the battery.

[0163] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features.

[0164] However, these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the various aspects of this invention.

[0165] The scope of the technical solutions in the embodiments.

Claims

1. A battery, characterized in that, Includes positive electrode, negative electrode, and electrolyte; The negative electrode sheet includes a negative electrode current collector and a negative electrode coating located on the surface of the negative electrode current collector. The negative electrode coating includes a silicon-carbon material, which includes porous carbon and silicon particles deposited in the porous carbon channels. The negative electrode coating includes a first active material layer and a second active material layer; the first active material layer is located on at least one side surface of the negative electrode current collector, and the second active material layer is located on the side of the first active material layer opposite to the negative electrode current collector; the mass percentage content of silicon in the second active material layer is greater than the mass percentage content of silicon in the first active material layer. The electrolyte comprises a carboxylic acid ester, which includes ethyl butyrate, and the mass percentage of ethyl butyrate in the electrolyte is 5%-35%.

2. The battery according to claim 1, characterized in that, The mass percentage (n%) of silicon in the second active material layer is 3%-50%; And / or, the mass percentage (w%) of silicon in the first active material layer is 0%-20%; Preferably, n is 5-40 and w is 0-10.

3. The battery according to claim 1, characterized in that, The thickness of the first active material layer is x1μm, and the thickness of the second active material layer is x2μm, where x2>x1; Preferably, 0.1 ≤ x1 / (x1+x2) ≤ 0.49; Preferably, 70μm≤x1+x2≤150μm.

4. The battery according to claim 1, characterized in that, The carboxylic acid esters also include one or more of methyl formate, methyl acetate, propyl acetate, ethyl propionate, propyl propionate, methyl butyrate, ethyl acetate, methyl levulinate, methyl pyruvate, and ethyl difluoroacetate; And / or, the electrolyte further includes carbonates, which include one or more of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethylene carbonate, and propylene carbonate.

5. The battery according to claim 1, characterized in that, The first active material layer comprises hard carbon; preferably, the mass percentage of hard carbon in the first active material layer is 1% to 10%. And / or, the second active material layer comprises hard carbon; preferably, the mass percentage of hard carbon in the second active material layer is 1% to 10%.

6. The battery according to claim 1, characterized in that, The electrolyte further includes a first additive, which includes one or more of lithium difluorophosphate, vinyl sulfate, and lithium difluorooxalate borate. Preferably, the mass percentage of the first additive in the electrolyte is 0.01%-3%, more preferably 0.1%-2%.

7. The battery according to claim 1, characterized in that, The electrolyte further includes a second additive, which includes an unsaturated nitrile additive, specifically 1,4-dicyano-2-butene. Preferably, the mass percentage of the second additive in the electrolyte is 0.01%-2%.

8. The battery according to claim 1, characterized in that, The surface of the negative electrode coating is provided with a recess; Preferably, the distance between two adjacent recesses is 0.5mm-10mm; Preferably, the depth of the recess is 5μm-60μm.

9. The battery according to claim 1, characterized in that, The negative electrode current collector satisfies at least one of the following conditions: a) The thickness of the negative electrode current collector is 4μm to 12μm; b) The tensile strength of the negative electrode current collector is 400MPa-1000MPa; c) The elongation of the negative electrode current collector is 2%-15%; d) The negative electrode current collector includes carbon-coated copper foil; e) The dyne value of the negative electrode current collector is >40.

10. An electrical appliance, characterized in that, The electrical equipment includes the battery as described in any one of claims 1-9.

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