Lithium ion battery

Abstract

The invention provides a lithium ion battery, which comprises a positive plate, a negative plate, a diaphragm and an electrolyte, the negative plate comprises a current collector and a negative active material layer formed on at least one side surface of the current collector; the negative electrode active material layer comprises a negative electrode additive, and the negative electrode additive is selected from one or more of cyclic siloxane and chain siloxane; the electrolyte comprises a carbonic ester solvent, and the carbonic ester solvent comprises a first carbonic ester solvent, dimethyl carbonate and propylene carbonate. According to the lithium ion battery provided by the invention, the negative electrode additive is added into the negative electrode plate, and the proportional relation of the carbonic ester solvent and the negative electrode additive in the electrolyte is regulated and controlled, so that the porosity of the negative electrode plate and the adsorption capacity of the electrolyte are improved, the local electrolyte lithium salt concentration of the negative electrode plate is improved, and meanwhile, the lithium ion battery has strong adsorption on ester electrolyte and is beneficial to improving the lithium ion battery performance. And the desolvation process of lithium ions is accelerated, so that the fast charging performance of the battery cell is improved, and the cycle performance of the lithium ion battery is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and particularly to a lithium-ion battery. Background Art

[0002] With the development trend of the lithium-ion battery industry, lithium-ion batteries with higher energy density have gradually become a research hotspot. Currently, researchers mainly improve the volumetric energy density of lithium-ion batteries by increasing the electrode surface density.

[0003] The solid-phase diffusion coefficient of lithium in the negative electrode of a lithium-ion battery is relatively small, which makes the solid-phase diffusion of lithium in the negative electrode of a lithium-ion battery the control step of the entire electrode reaction. Therefore, with the increase in the thickness of the lithium-ion battery electrode, a series of problems will arise, such as: a decrease in the compaction density of the electrode, a higher tortuosity of the electrode, and a more complex pore structure of the electrode, etc. This will lead to a more complex lithium-ion transport path, thereby hindering the lithium-ion transport and resulting in a decline in the rate performance and cycle performance of the lithium-ion battery; on the other hand, with the increase in the thickness of the lithium-ion electrode, there will also be a phenomenon of insufficient infiltration of the negative electrode in the electrolyte, resulting in a decrease in the transport rate of lithium ions and a slowdown in the desolvation kinetics of lithium ions, causing irreversible lithium loss such as lithium deposition and purple spots in the lithium-ion battery, and further affecting the electrochemical performance of the lithium-ion battery. Summary of the Invention

[0004] The technical problem solved by the present invention is to provide a lithium-ion battery, and the lithium-ion battery provided by the present application can improve the kinetics and fast charge cycle performance of the negative electrode of the lithium-ion battery.

[0005] In view of this, the present application provides a lithium-ion battery, including a positive electrode, a negative electrode, a separator, and an electrolyte. The negative electrode includes a current collector and a negative active material layer formed on at least one surface of the current collector;

[0006] The negative active material layer includes a negative additive, and the negative additive is selected from one or more of a cyclic siloxane represented by formula (I) and a chain siloxane represented by formula (II). The content of the negative additive in the negative active material layer is X, and X is 0.01 wt% to 1.0 wt%;

[0007] The electrolyte includes a carbonate solvent, and the carbonate solvent includes a first carbonate solvent, dimethyl carbonate, and propylene carbonate with a mass ratio of 1:Y:Z. The first carbonate solvent is other carbonate solvents except dimethyl carbonate and propylene carbonate;

[0008] The X, Y, and Z satisfy the following relationship:

[0009] 1 ≤ (5×Y) / (2×Z) ≤ 8;

[0010] 0 < (2×X) / (0.1%×Z) ≤ 5;

[0011]

[0012] Wherein, m and n are independently selected from integers greater than 0.

[0013] In some specific embodiments, the separator includes a ceramic coating on the positive electrode side, and the median particle size Dv50 of the ceramic particles in the ceramic coating is A, 0.05 μm ≤ A ≤ 2 μm, and A and X satisfy 0.5 ≤ A / (100×X) ≤ 8.

[0014] In some specific embodiments, n and m in the cyclic siloxane and the chain siloxane are independently selected from 1 to 10.

[0015] In some specific embodiments, the melting point of the negative electrode additive is 300 - 400 °C;

[0016] And / or, the negative electrode additive is in an amorphous state in the XRD curve, has a characteristic peak between 5° and 25°, and the half-peak width of the characteristic peak is 2° - 20°;

[0017] And / or, in the infrared spectrum curve of the negative electrode additive, there is a stretching vibration peak corresponding to the Si - O - Si bond at a wave number of 900 - 100 cm -1 There is a stretching vibration peak corresponding to the Si - C bond at 600 - 700 cm -1 There is a stretching vibration peak corresponding to the C - H bond at 2800 - 3000 cm -1 There is a stretching vibration peak corresponding to the C - H bond at 2800 - 3000 cm

[0018] In some specific embodiments, the negative electrode active material layer further includes a negative electrode active material, a conductive agent, a binder, and a thickener; the content of the negative electrode active material is 80 - 98 wt%, the content of the conductive agent is 0.1 - 15 wt%, the content of the binder is 0.1 - 15 wt%, and the content of the thickener is 0.1 - 15 wt%.

[0019] In some specific embodiments, the electrolyte further includes a lithium salt and an electrolyte additive, the content of the carbonate solvent is 40 - 90 wt%, the content of the lithium salt is 5 - 30 wt%, and the content of the electrolyte additive is 5 - 30 wt%; the electrolyte additive in the electrolyte includes fluoroethylene carbonate and 1,3 - propane sultone with a mass ratio of (2 - 5):1.

[0020] In some specific embodiments, the first carbonate solvent includes ethylene carbonate; the liquid absorption amount of the carbonate solvent by the negative electrode sheet per unit mass is 1 - 40%;

[0021] and / or, the liquid absorption amount of the negative electrode sheet per unit mass for the ethylene carbonate is 1 to 20%;

[0022] and / or, the liquid absorption amount of the negative electrode sheet per unit mass for the dimethyl carbonate is 1 to 30%;

[0023] and / or, the liquid absorption amount of the negative electrode sheet per unit mass for the propylene carbonate is 5 to 40%.

[0024] In some specific embodiments, the compaction density of the negative electrode sheet is 1.0 to 1.8 g / cm 3 .

[0025] In some specific embodiments, the median particle size Dv50 of the negative electrode additive is 1 to 5 μm, and Dv90 is 8 to 15 μm;

[0026] and / or, the Dv50 of the positive electrode active material of the positive electrode sheet is 0.1 to 30 μm.

[0027] In some specific embodiments, the ceramic particles of the separator are selected from one or more of aluminum oxide, boehmite, silicon dioxide, zirconium dioxide, barium sulfate, magnesium hydroxide, fluorapatite, fluorophlogopite, mullite, aluminum titanate, copper oxide, titanium dioxide, zinc oxide;

[0028] and / or, the thickness of the ceramic coating of the separator is 0.1 to 5 μm.

[0029] The present application provides a lithium-ion battery, which includes a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte. Among them, the negative electrode active material layer in the negative electrode sheet includes a negative electrode additive, and the negative electrode additive is selected from one or more of chain siloxane and cyclic siloxane. The above negative electrode additive can significantly increase the porosity of the negative electrode sheet and increase the contact area between the negative electrode sheet and the electrolyte, thereby improving the fast charging performance of the lithium-ion battery; at the same time, the introduction of the above negative electrode additive makes the negative electrode sheet have a higher electrolyte absorption amount, which can improve the desolvation kinetics of lithium ions in the lithium-ion battery; the present application also defines the proportional relationship between the negative electrode additive and the solvent in the electrolyte, so that the negative electrode sheet can adsorb a large amount of carbonate electrolyte, and at the same time increase the local electrolyte lithium salt concentration of the negative electrode sheet to reduce polarization, accelerate the charge transfer power, and improve the fast charging ability of the battery cell, thereby improving the kinetics and fast charging cycle performance of the negative electrode sheet of the lithium-ion battery.

[0030] Furthermore, the present application also defines the relationship between the ceramic particles in the separator and the negative electrode additive, which can make the negative electrode sheet and the separator form a good synergistic effect, ensure the uniform distribution of the electrolyte between the positive and negative electrodes, enhance the liquid absorption and liquid retention ability of the battery cell, and promote the improvement of the cycle performance of the lithium-ion battery. Description of the Drawings

[0031] Figure 1 It is the particle size distribution curve of the negative electrode additive in the present invention;

[0032] Figure 2 It is the infrared spectrum of the chain siloxane with n = 2 in the present invention;

[0033] Figure 3 It is the XRD pattern of the chain siloxane with n = 2 in the present invention. Detailed implementation manners

[0034] To further understand the present invention, the preferred implementation manners of the present invention will be described below in conjunction with embodiments. However, it should be understood that these descriptions are only for further explaining the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0035] In view of the problems in the prior art that the low porosity of the negative electrode sheet leads to insufficient infiltration in the electrolyte, the low lithium ion desolvation kinetics at low temperatures, and the large solid-phase diffusion resistance of lithium ions in the negative electrode sheet, resulting in lithium deposition and purple spots in the lithium ion battery, thereby affecting the electrochemical performance of the lithium ion battery, the present application provides a lithium ion battery. By adding a negative electrode additive to the negative electrode sheet and regulating the proportional relationship between the carbonate solvent and the negative electrode additive in the electrolyte, the porosity of the negative electrode sheet and the adsorption amount of the electrolyte are increased, the local electrolyte lithium salt concentration of the negative electrode sheet is increased, and at the same time, it has strong adsorption for the ester-based electrolyte, accelerating the lithium ion desolvation process, thereby improving the fast charging performance of the battery cell and the cycle performance of the lithium ion battery. Specifically, the embodiment of the present invention discloses a lithium ion battery, including a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte. The negative electrode sheet includes a current collector and a negative electrode active material layer formed on at least one surface of the current collector;

[0036] The negative electrode active material layer includes a negative electrode additive. The negative electrode additive is selected from one or more of the cyclic siloxanes shown in formula (I) and the chain siloxanes shown in formula (II). The negative electrode additive is selected from one or more of the chain siloxanes and cyclic siloxanes. The content of the negative electrode additive in the negative electrode active material layer is X, and X is 0.01 wt% to 1.0 wt%;

[0037] The electrolyte includes a carbonate solvent. The carbonate solvent includes a first carbonate solvent, dimethyl carbonate, and propylene carbonate with a mass ratio of 1:Y:Z. The first carbonate solvent is other carbonate solvents except propylene carbonate and dimethyl carbonate;

[0038] The X, Y, and Z satisfy the following relationship:

[0039] 1 ≤ (5 × Y) / (2 × Z) ≤ 8;

[0040] 0 < (2×X) / (0.1%×Z) ≤ 5;

[0041]

[0042] Wherein, m and n are independently selected from integers greater than 0.

[0043] In the lithium-ion battery provided by the present application, it includes a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte; wherein, the positive electrode sheet is a positive electrode sheet well-known to those skilled in the art, that is, it includes a positive electrode current collector and a positive electrode active material layer formed on at least one surface of the positive electrode current collector; the present application has no special limitation on the positive electrode current collector, and it can be a positive electrode current collector well-known to those skilled in the art. By way of example, the positive electrode current collector can be selected from aluminum foil; similarly, the present application has no special limitation on the positive electrode active material layer, and it can be a positive electrode active material layer well-known to those skilled in the art, which can include a positive electrode active material, a conductive agent, and a binder; the positive electrode active material is well-known to those skilled in the art. By way of example, the positive electrode active material can be selected from lithium cobaltate; the conductive agent is well-known to those skilled in the art. By way of example, the conductive agent can be selected from carbon black and carbon nanotubes; the binder is well-known to those skilled in the art. By way of example, the binder can be selected from polyvinylidene fluoride. The Dv50 of the positive electrode active material is 0.1 to 30 μm. Specifically, the Dv50 of the positive electrode active material is 0.5 to 25 μm. More specifically, the Dv50 of the positive electrode active material is 1 to 20 μm.

[0044] In the present application, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer formed on at least one side surface of the negative electrode current collector. Specifically, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer formed on one side surface of the negative electrode current collector, or the negative electrode sheet includes a negative electrode current collector and negative electrode active material layers formed on both side surfaces of the negative electrode current collector.

[0045] In the negative electrode sheet, the negative electrode active material includes a negative electrode additive, and the negative electrode additive is selected from one or more of chain siloxanes and cyclic siloxanes. Among them, the chain siloxane is a kind of chain siloxane compound containing Si-O-Si bonds, and its general formula is C3H9SiO(C2H6SiO) m SiC3H9, and the structural formula is shown in formula (Ⅱ):

[0046]

[0047] Wherein, m is selected from integers greater than 0.

[0048] Specifically, m ranges from 1 to 10; more specifically, m is 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 ······; when m is 2, the structural formula of the chain siloxane is as follows:

[0049]

[0050] The cyclic siloxane is a class of cyclic structure compounds containing Si-O-Si bonds, and its general formula is (C2H6SiO) n , and the structural formula is as shown in formula (Ⅰ),

[0051]

[0052] wherein, n is selected from integers greater than 0.

[0053] Specifically, n ranges from 1 to 10; more specifically, n is 1, 2, 3, 4, 5, 6, 7, 8, 9, 10; when n is 2, the structural formula of the cyclic siloxane is as follows:

[0054]

[0055] In this application, the negative electrode additive has the following characteristics: the melting point is 300 - 400 °C, it is in an amorphous state in the XRD curve, has a characteristic peak between 5° and 25°, and the half-peak width of the characteristic peak is 2° - 20°; in the infrared spectrum curve, there is a stretching vibration peak corresponding to the Si-O-Si bond at a wave number of 900 - 100 cm -1 and there is a stretching vibration peak corresponding to the Si-C bond at 600 - 700 cm -1 , and there is a stretching vibration peak corresponding to the C-H bond at 2800 - 3000 cm -1 . The negative electrode additive with the above characteristics can introduce a certain amount of porosity in the negative electrode sheet, synchronously perform surface modification, increase the electrolyte adsorption amount, increase the local electrolyte lithium salt concentration of the electrode sheet to reduce polarization, and at the same time strongly adsorb the carbonate-based electrolyte, accelerate the desolvation process of lithium ions, accelerate the charge transfer kinetics, improve the fast charging performance of the battery cell, and prevent the occurrence of solvent co-intercalation reaction.

[0056] As Figure 2 shown, Figure 2 is the infrared spectrum curve of the chain siloxane when n = 2. As can be seen from Figure 2 , this chain siloxane has a stretching vibration peak corresponding to the Si-O-Si bond at a wave number of 987 cm -1 , a stretching vibration peak corresponding to the Si-C bond at 795 cm -1 , and a stretching vibration peak corresponding to the C-H bond at 2922 cm -1 . AsFigure 3 As described, Figure 3 is the XRD curve pattern of the chain siloxane when n = 2. It can be seen from Figure 3 that the chain siloxane is in an amorphous and undetermined state, and has a characteristic peak located between 10° and 25°. The full width at half maximum of this characteristic peak is 2° to 15°.

[0057] In the negative electrode active material layer, the content of the negative electrode additive is X, where X is 0.01 wt% to 1.0 wt%. Specifically, X is 0.05 wt% to 0.95 wt%. More specifically, X is 0.10 wt% to 0.80 wt%. More specifically, X is 0.25 wt% to 0.70 wt%. More specifically, X is 0.38 wt% to 0.50 wt%.

[0058] Further, the negative electrode active material layer further includes a negative electrode active material, a conductive agent, a binder, and a thickener. Among them, the negative electrode active material includes one or more of a graphite negative electrode material, a silicon oxide negative electrode material, a silicon carbon negative electrode material, and a soft carbon negative electrode material. Specifically, the negative electrode active material is selected from a graphite negative electrode material, a silicon oxide negative electrode material, a silicon carbon negative electrode material, or a soft carbon negative electrode material; in a specific embodiment, the negative electrode active material is selected from artificial graphite. The conductive agent includes one or more of furnace black, acetylene black, Ketjen black, Super P, KS-6, and carbon nanotubes. Specifically, the conductive agent is selected from furnace black, acetylene black, Ketjen black, Super P, KS-6, or carbon nanotubes; in a specific embodiment, the conductive agent is selected from carbon black. The binder includes one or more of styrene-butadiene rubber (SBR) and polyacrylic acid (PAA). Specifically, the binder is selected from styrene-butadiene rubber (SBR) or polyacrylic acid. In a specific embodiment, the binder is selected from styrene-butadiene rubber. The thickener includes one or more of sodium carboxymethyl cellulose (CMC-Na), lithium carboxymethyl cellulose (CMC-Li), polyacrylic acid (PAA), and polyacrylonitrile (PAN). Specifically, the thickener is selected from sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyacrylic acid, or polyacrylonitrile; in a specific embodiment, the thickener is selected from sodium carboxymethyl cellulose. In the negative electrode active material layer, the content of the negative electrode active material is 80-98 wt%, the content of the conductive agent is 0.1-15 wt%, the content of the binder is 0.1-15 wt%, and the content of the thickener is 0.1-15 wt%; the sum of the masses of the negative electrode active material, the conductive agent, the binder, the thickener, and the negative electrode additive is 100%; specifically, the content of the negative electrode active material is 82-95 wt%, the content of the conductive agent is 0.5-12 wt%, the content of the binder is 0.5-12 wt%, and the content of the thickener is 0.5-12 wt%; more specifically, the content of the negative electrode active material is 85-92 wt%, the content of the conductive agent is 1.0-10 wt%, the content of the binder is 1.0-10 wt%, and the content of the thickener is 1.0-10 wt%; more specifically, the content of the negative electrode active material is 88-90 wt%, the content of the conductive agent is 3.0-8.0 wt%, the content of the binder is 3.0-8.0 wt%, and the content of the thickener is 3.0-8.0 wt%. The above contents will affect the performance of the battery, such as electrochemical performances such as rate performance and cycle performance.

[0059] In the negative electrode active material layer, the negative electrode additive is used as a raw material, and its median particle size Dv50 is 1-5 μm, and Dv90 is 8-15 μm; specifically, such as Figure 1As shown. The particle size of the negative electrode additive also affects the liquid retention capacity and the electrolyte adsorption capacity of the negative electrode sheet, thereby affecting the fast charging performance of the battery.

[0060] In the negative electrode sheet provided by the present application, the tap density of the negative electrode sheet is 1.0-1.8 g / cm 3 , specifically, the tap density of the negative electrode sheet is 1.3-1.7 g / cm 3 , more specifically, the tap density of the negative electrode sheet is 1.5-1.6 g / cm 3 . In the present application, the decrease in the tap density of the negative electrode sheet reflects the improvement of the toughness of the negative electrode sheet from the side.

[0061] In the lithium-ion battery, the electrolyte includes a carbonate solvent. Specifically, the carbonate solvent includes a first carbonate solvent, dimethyl carbonate, and propylene carbonate with a mass ratio of 1:Y:Z. The first carbonate solvent is other carbonate solvents except propylene carbonate and dimethyl carbonate;

[0062] X, Y, and Z satisfy the following relationship: 1≤(5×Y) / (2×Z)≤8; 0<(2×X) / (0.1%×Z)≤5.

[0063] In the lithium-ion battery, the negative electrode additive has different adsorption amounts for different electrolyte solvents. After research by the applicant, the contents of different electrolyte solvents are related to the content of the negative electrode additive so that the negative electrode additive can adsorb a large amount of carbonate electrolyte. When X, Y, and Z satisfy the above relational formula, it is possible to ensure that the electrolyte composition after the cell formation reaches an ideal state, and to maximize the promotion of the transmission of lithium ions between the positive electrode and the negative electrode, and improve the fast charging cycle performance of the cell.

[0064] In the above carbonate solvent, the first carbonate solvent is other carbonate solvents except propylene carbonate and dimethyl carbonate. For example, the first carbonate solvent is selected from ethylene carbonate.

[0065] Further, X, Y, and Z satisfy the following relationship: 2≤(5×Y) / (2×Z)≤6; 0.5≤(2×X) / (0.1%×Z)≤1.5; more specifically, 2.4≤(5×Y) / (2×Z)≤3; 0.8≤(2×X) / (0.1%×Z)≤1.0.

[0066] The electrolyte further includes a lithium salt and an electrolyte additive. The lithium salt is a lithium salt well-known to those skilled in the art, and no special limitation is imposed on this in the present application. In a specific embodiment, the lithium salt is selected from lithium hexafluorophosphate. The electrolyte additive includes one or both of fluoroethylene carbonate (FEC) and 1,3 - propanesultone (PS). Further, the electrolyte additive includes fluoroethylene carbonate and 1,3 - propanesultone in a mass ratio of (2 - 5):1. In the electrolyte, the content of the carbonate solvent is 40 - 90 wt%, the content of the lithium salt is 5 - 30 wt%, and the content of the electrolyte additive is 5 - 30 wt%. The total mass of the carbonate solvent, the lithium salt, and the electrolyte additive in the electrolyte is 100 wt%. Specifically, the content of the carbonate solvent is 43 - 86 wt%, the content of the lithium salt is 8 - 27 wt%, and the content of the electrolyte additive is 7 - 28 wt%. More specifically, the content of the carbonate solvent is 50 - 80 wt%, the content of the lithium salt is 10 - 25 wt%, and the content of the electrolyte additive is 10 - 25 wt%. More specifically, the content of the carbonate solvent is 56 - 72 wt%, the content of the lithium salt is 14 - 20 wt%, and the content of the electrolyte additive is 12 - 22 wt%. More specifically, the content of the carbonate solvent is 60 - 70 wt%, the content of the lithium salt is 16 - 18 wt%, and the content of the electrolyte additive is 16 - 20 wt%. The content of the carbonate solvent affects the adsorption amount of the negative electrode sheet, and the content of the electrolyte additive affects the composition of the negative electrode SEI film, thereby affecting the ion transport rate and thus the fast charging performance of the battery.

[0067] In a lithium-ion battery, the separator is disposed between the positive electrode sheet and the negative electrode sheet, and includes a ceramic coating facing the positive electrode sheet. The median particle size Dv50 of the ceramic particle raw material in the ceramic coating is A, where 0.05 μm ≤ A ≤ 2 μm, and A and X satisfy 0.5 ≤ A / (100×X) ≤ 8. Through research, the applicant has found that when A satisfies the above relationship, the most coordinated synergistic effect exists between the negative electrode sheet and the ceramic separator, which can ensure the uniform distribution of the electrolyte between the positive and negative electrodes, further increase the liquid absorption and retention capacity of the battery cell, and promote the cycle performance of the lithium-ion battery; that is, the particle size of the ceramic particles affects the liquid storage capacity of the ceramic separator. If the above ratio is too small or too large, the liquid storage capacity of the ceramic coating will not match the adsorption rate of the negative electrode to the carbonate solvent. Specifically, 0.05 μm ≤ A ≤ 1 μm, and A and X satisfy 0.5 ≤ A / (100×X) ≤ 4; more specifically, 0.1 μm ≤ A ≤ 0.5 μm, and A and X satisfy 1.2 ≤ A / (100×X) ≤ 2.9; more specifically, 0.2 μm ≤ A ≤ 0.3 μm, and A and X satisfy 2 ≤ A / (100×X) ≤ 2.5. When the above conditions are met, the liquid storage capacity of the ceramic coating matches the adsorption rate of the negative electrode to the carbonate solvent optimally, which is beneficial to improving the cycle performance of the battery at high rates.

[0068] In the present application, the thickness of the ceramic coating is 0.1 - 5 μm; specifically, the thickness of the ceramic coating is 0.5 - 3 μm, more specifically, the thickness of the ceramic coating is 1.2 - 2.6 μm, and more specifically, the thickness of the ceramic coating is 1.5 - 2.0 μm. The ceramic particles are selected from one or more of aluminum oxide, boehmite, silicon dioxide, zirconium dioxide, barium sulfate, magnesium hydroxide, fluorapatite, fluorophlogopite, mullite, aluminum titanate, copper oxide, titanium dioxide, and zinc oxide; specifically, the ceramic particles are selected from aluminum oxide, boehmite, silicon dioxide, zirconium dioxide, barium sulfate, magnesium hydroxide, fluorapatite, fluorophlogopite, mullite, aluminum titanate, copper oxide, titanium dioxide, or zinc oxide. In the separator, the substrate of the separator is a material well-known to those skilled in the art, and no special limitation is imposed in this application. In specific embodiments, the substrate of the separator is selected from PE.

[0069] Based on the particle size ratio relationship of the raw material ceramic particles in the above-mentioned negative electrode additive, electrolyte carbonate solvent, and ceramic coating, the liquid absorption capacity of the negative electrode sheet per unit mass for the carbonate solvent is 1-40%, the liquid absorption capacity of the negative electrode sheet per unit mass for ethylene carbonate is 1-20%, the liquid absorption capacity of the negative electrode sheet per unit mass for dimethyl carbonate is 1-30%, and the liquid absorption capacity of the negative electrode sheet per unit mass for propylene carbonate is 5-40%; specifically, the liquid absorption capacity of the negative electrode sheet per unit mass for the carbonate solvent is 3-30%, the liquid absorption capacity of the negative electrode sheet per unit mass for ethylene carbonate is 3-15%, the liquid absorption capacity of the negative electrode sheet per unit mass for dimethyl carbonate is 5-20%, and the liquid absorption capacity of the negative electrode sheet per unit mass for propylene carbonate is 8-30%; more specifically, the liquid absorption capacity of the negative electrode sheet per unit mass for the carbonate solvent is 8-21%, the liquid absorption capacity of the negative electrode sheet per unit mass for ethylene carbonate is 6-11%, the liquid absorption capacity of the negative electrode sheet per unit mass for dimethyl carbonate is 7-16%, and the liquid absorption capacity of the negative electrode sheet per unit mass for propylene carbonate is 10-21%.

[0070] The preparation method of the lithium-ion battery of the present application is carried out according to the method well-known to those skilled in the art. For example, the preparation method of the negative electrode sheet is specifically as follows:

[0071] Mix the negative electrode active material, conductive agent, binder, and thickener, add a solvent to obtain a negative electrode slurry, form the negative electrode slurry on the surface of the negative electrode current collector, and obtain a negative electrode sheet after drying and rolling;

[0072] The preparation method of the positive electrode sheet is specifically as follows:

[0073] Mix the positive electrode active material, conductive agent, binder, and solvent to obtain a positive electrode slurry, form the positive electrode slurry on the surface of the positive electrode current collector, and obtain a positive electrode sheet after drying and rolling;

[0074] The preparation method of the electrolyte is specifically as follows:

[0075] Mix the lithium salt, electrolyte additive, and carbonate solvent to obtain an electrolyte;

[0076] The preparation method of the separator is specifically as follows:

[0077] Mix the ceramic particles and the solvent to obtain a ceramic coating slurry, form the ceramic coating slurry on the surface of the substrate, and obtain a separator after drying;

[0078] After the preparation of the above-mentioned positive electrode sheet, negative electrode sheet, electrolyte and separator is completed, the positive electrode sheet, separator and negative electrode sheet are stacked in order, and the ceramic coating side of the separator is in contact with the positive electrode sheet, and then the tabs are welded and wound to obtain a bare cell, and finally the bare cell is placed in a membrane shell, and after packaging, liquid injection, formation and other processes, a lithium-ion battery is obtained.

[0079] The lithium ion battery provided by the present invention adds a negative electrode additive to the negative electrode active material layer. The additive can significantly improve the porosity of the negative electrode sheet and increase the contact area between the negative electrode sheet and the electrolyte, thereby improving the fast charging performance of the lithium ion battery. In addition, the additive has a higher electrolyte adsorption capacity, which can improve the desolvation kinetics of lithium ions in the lithium ion battery at low temperatures, and at the same time adapt the proportion of each solvent in the electrolyte. Therefore, while adsorbing a large amount of carbonate electrolyte solvents, the local electrolyte lithium salt concentration of the electrode sheet is increased to reduce polarization, accelerate the charge transfer kinetics, improve the fast charging performance of the battery cell, and prevent the occurrence of solvent co-intercalation reaction, thereby improving the kinetics and cycle performance of the negative electrode sheet of the lithium ion battery at low temperatures. Furthermore, the median particle size Dv50 of the ceramic particles in the diaphragm ceramic coating is A, and 0.05μm≤A<2μm, while satisfying 1≤(5×Y) / (2×Z)≤8, 0<(2×X) / (0.1%×Z)≤5, and 0.5≤A / (100×X)≤8. This can make the negative electrode sheet in the high energy density lithium ion battery have a high porosity characteristic, so that the negative electrode sheet is fully infiltrated in the electrolyte, and the desolvation kinetics of lithium ions are improved, and the diffusion resistance of lithium ions at the solid electrolyte interface (SEI) is reduced, so that the lithium ion battery has a higher energy density and a better fast charging cycle performance.

[0080] In order to further understand the present invention, the battery provided by the present invention is described in detail below in conjunction with the embodiments, and the protection scope of the present invention is not limited by the following embodiments.

[0081] Example 1

[0082] (1) Preparation of negative electrode sheet

[0083] According to the mass ratio of 96.79:0.6:1.3:1.3:0.01, artificial graphite as the negative electrode active material, carbon black as the conductive agent, styrene-butadiene rubber as the binder, sodium carboxymethyl cellulose as the thickener and negative electrode additives were weighed and mixed thoroughly. After adding deionized water, the mixture was stirred thoroughly and vacuum-defoamed to form a uniform negative electrode slurry. The negative electrode slurry was coated on a copper foil (negative electrode current collector) with a thickness of 6 μm, and the coating surface density was 9.89 mg / cm 2 Then it was dried in a 90℃ oven and rolled (the compacted density was 1.60g / cm 3 ), cutting to obtain a negative electrode sheet; wherein the negative electrode additive is selected from octamethylcyclotetrasiloxane;

[0084] (2) Preparation of positive electrode

[0085] The positive electrode active material lithium cobalt oxide (Dv50 particle size is 11.86 μm), the conductive agent carbon black, the carbon nanotubes and the binder polyvinylidene fluoride were weighed according to the mass ratio of 97.0:1:0.5:1.5, and N-methylpyrrolidone was added after being fully mixed. Then, the mixture was fully stirred and vacuum-defoamed to form a uniform positive electrode slurry. The positive electrode slurry was coated on an aluminum foil with a thickness of 9 μm (positive electrode current collector), and the coating surface density was 18.25 mg / cm 2 Then it was dried in an oven at 80℃ and rolled (the compacted density was 4.15g / cm 3 ), cutting to obtain a positive electrode sheet;

[0086] (3) Preparation of electrolyte

[0087] In a glove box filled with argon (H2O < 0.05ppm, O2 < 0.05ppm), ethylene carbonate (EC), dimethyl carbonate (DMC), and propylene carbonate (PC) are mixed in a mass ratio of 1:1.2:1 to obtain an electrolyte solvent with a total mass of 79.5wt% of the electrolyte, and then lithium hexafluorophosphate (LiPF6) is added to the electrolyte solvent at a concentration of 14% based on the total mass of the electrolyte. After dissolution, 6.5wt% of additives based on the total mass of the electrolyte are added, wherein the additives include fluoroethylene carbonate (FEC) and 1,3-propane sultone (PS) with contents of 7% and 3%, respectively. The mixture is stirred evenly, and an electrolyte is obtained after passing the moisture and free acid tests.

[0088] (4) Preparation of diaphragm

[0089] Alumina and PVDF with a Dv50 particle size of 0.05 μm were weighed in a mass ratio of 90:10 and dispersed in N-methylpyrrolidone, and fully stirred to form a ceramic coating slurry. The ceramic coating slurry was coated on one side of a PE diaphragm substrate (the substrate thickness was 7 μm) by a gravure coating process, and a diaphragm was obtained after drying, wherein the thickness of the ceramic coating was 1.5 μm;

[0090] (5) Assembling lithium-ion batteries

[0091] The positive electrode sheet, separator and negative electrode sheet prepared above are stacked in order, with the separator being located between the positive electrode sheet and the negative electrode sheet, and the ceramic coating in the separator facing the positive electrode sheet, and then a bare cell is obtained by ear welding and winding, and the bare cell is placed in a 0.09 mm aluminum-plastic film shell, and a lithium-ion battery is prepared through processes such as packaging, liquid injection, formation, secondary sealing and sorting.

[0092] Example 2

[0093] (1) Preparation of negative electrode sheet

[0094] According to the mass ratio of 96.75:0.6:1.3:1.3:0.05, artificial graphite as the negative electrode active material, carbon black as the conductive agent, styrene-butadiene rubber as the binder, sodium carboxymethyl cellulose as the thickener and negative electrode additives were weighed and mixed thoroughly. After adding deionized water, the mixture was stirred thoroughly and vacuum-defoamed to form a uniform negative electrode slurry. The negative electrode slurry was coated on a copper foil (negative electrode current collector) with a thickness of 6 μm, and the coating surface density was 9.89 mg / cm 2 Then it was dried in a 90℃ oven and rolled (the compacted density was 1.60g / cm 3 ), cutting to obtain a negative electrode sheet; wherein the negative electrode additive is selected from octamethylcyclotetrasiloxane;

[0095] (2) Preparation of positive electrode

[0096] The positive electrode active material lithium cobalt oxide (Dv50 particle size is 11.86 μm), the conductive agent carbon black, the carbon nanotubes and the binder polyvinylidene fluoride were weighed according to the mass ratio of 97.0:1:0.5:1.5, and N-methylpyrrolidone was added after being fully mixed. Then, the mixture was fully stirred and vacuum-defoamed to form a uniform positive electrode slurry. The positive electrode slurry was coated on an aluminum foil with a thickness of 9 μm (positive electrode current collector), and the coating surface density was 18.25 mg / cm 2 Then it was dried in an oven at 80℃ and rolled (the compacted density was 4.15g / cm 3 ), cutting to obtain a positive electrode sheet;

[0097] (3) Preparation of electrolyte

[0098] In a glove box filled with argon (H2O < 0.05ppm, O2 < 0.05ppm), ethylene carbonate (EC), dimethyl carbonate (DMC), and propylene carbonate (PC) are mixed in a mass ratio of 1:2.4:2 to obtain an electrolyte solvent with a total mass of 79.5wt% of the electrolyte, and then lithium hexafluorophosphate (LiPF6) is added to the electrolyte solvent at a concentration of 14% based on the total mass of the electrolyte. After dissolution, 6.5wt% additives based on the total mass of the electrolyte are added, wherein the additives include fluoroethylene carbonate (FEC) and 1,3-propane sultone (PS) with contents of 7% and 3%, respectively. The mixture is stirred evenly, and an electrolyte is obtained after passing the moisture and free acid tests.

[0099] (4) Preparation of diaphragm

[0100] Alumina and PVDF with a Dv50 particle size of 0.2 μm were weighed in a mass ratio of 90:10 and dispersed in N-methylpyrrolidone, and fully stirred to form a ceramic coating slurry. The ceramic coating slurry was coated on one side of a PE diaphragm substrate (the substrate thickness was 7 μm) by a gravure coating process, and a diaphragm was obtained after drying, wherein the thickness of the ceramic coating was 1.5 μm;

[0101] (5) Assembling lithium-ion batteries

[0102] The positive electrode sheet, separator and negative electrode sheet prepared above are stacked in order, with the separator being located between the positive electrode sheet and the negative electrode sheet, and the ceramic coating in the separator facing the positive electrode sheet, and then a bare cell is obtained by ear welding and winding, and the bare cell is placed in a 0.09 mm aluminum-plastic film shell, and a lithium-ion battery is prepared through processes such as packaging, liquid injection, formation, secondary sealing and sorting.

[0103] Example 3

[0104] (1) Preparation of negative electrode sheet

[0105] According to the mass ratio of 96.7:0.6:1.3:1.3:0.1, artificial graphite as the negative electrode active material, carbon black as the conductive agent, styrene-butadiene rubber as the binder, sodium carboxymethyl cellulose as the thickener and negative electrode additives were weighed and mixed thoroughly. After adding deionized water, the mixture was stirred thoroughly and vacuum-defoamed to form a uniform negative electrode slurry. The negative electrode slurry was coated on a copper foil (negative electrode current collector) with a thickness of 6 μm, and the coating surface density was 9.89 mg / cm 2 Then it was dried in a 90℃ oven and rolled (the compacted density was 1.60g / cm 3 ), cutting to obtain a negative electrode sheet; wherein the negative electrode additive is selected from octamethylcyclotetrasiloxane;

[0106] (2) Preparation of positive electrode

[0107] The positive electrode active material lithium cobalt oxide (Dv50 particle size is 11.86 μm), the conductive agent carbon black, the carbon nanotubes and the binder polyvinylidene fluoride were weighed according to the mass ratio of 97.0:1:0.5:1.5, and N-methylpyrrolidone was added after being fully mixed. Then, the mixture was fully stirred and vacuum-defoamed to form a uniform positive electrode slurry. The positive electrode slurry was coated on an aluminum foil with a thickness of 9 μm (positive electrode current collector), and the coating surface density was 18.25 mg / cm 2 Then it was dried in an oven at 80℃ and rolled (the compacted density was 4.15g / cm 3 ), cutting to obtain a positive electrode sheet;

[0108] (3) Preparation of electrolyte

[0109] In a glove box filled with argon (H2O < 0.05ppm, O2 < 0.05ppm), ethylene carbonate (EC), dimethyl carbonate (DMC), and propylene carbonate (PC) are mixed in a mass ratio of 1:2.8:2 to obtain an electrolyte solvent with a total mass of 79.5wt% of the electrolyte, and then lithium hexafluorophosphate (LiPF6) is added to the electrolyte solvent at a concentration of 14% based on the total mass of the electrolyte. After dissolution, 6.5wt% additives based on the total mass of the electrolyte are added, wherein the additives include fluoroethylene carbonate (FEC) and 1,3-propane sultone (PS) with contents of 7% and 3%, respectively. The mixture is stirred evenly, and an electrolyte is obtained after passing the moisture and free acid tests.

[0110] (4) Preparation of diaphragm

[0111] Alumina and PVDF with a Dv50 particle size of 0.5 μm were weighed in a mass ratio of 90:10 and dispersed in N-methylpyrrolidone, and fully stirred to form a ceramic coating slurry. The ceramic coating slurry was coated on one side of a PE diaphragm substrate (the substrate thickness was 7 μm) by a gravure coating process, and a diaphragm was obtained after drying, wherein the thickness of the ceramic coating was 1.5 μm;

[0112] (5) Assembling lithium-ion batteries

[0113] The positive electrode sheet, separator and negative electrode sheet prepared above are stacked in order, with the separator being located between the positive electrode sheet and the negative electrode sheet, and the ceramic coating in the separator facing the positive electrode sheet, and then a bare cell is obtained by ear welding and winding, and the bare cell is placed in a 0.09 mm aluminum-plastic film shell, and a lithium-ion battery is prepared through processes such as packaging, liquid injection, formation, secondary sealing and sorting.

[0114] Example 4

[0115] (1) Preparation of negative electrode sheet

[0116] According to the mass ratio of 96.5:0.6:1.3:1.3:0.3, artificial graphite as the negative electrode active material, carbon black as the conductive agent, styrene-butadiene rubber as the binder, sodium carboxymethyl cellulose as the thickener and negative electrode additives were weighed and mixed thoroughly. After adding deionized water, the mixture was stirred thoroughly and vacuum-defoamed to form a uniform negative electrode slurry. The negative electrode slurry was coated on a copper foil (negative electrode current collector) with a thickness of 6 μm, and the coating surface density was 9.89 mg / cm 2 Then it was dried in a 90℃ oven and rolled (the compacted density was 1.60g / cm 3 ), cutting to obtain a negative electrode sheet; wherein the negative electrode additive is selected from octamethylcyclotetrasiloxane;

[0117] (2) Preparation of positive electrode

[0118] The positive electrode active material lithium cobalt oxide (Dv50 particle size is 11.86 μm), the conductive agent carbon black, the carbon nanotubes and the binder polyvinylidene fluoride were weighed according to the mass ratio of 97.0:1:0.5:1.5, and N-methylpyrrolidone was added after being fully mixed. Then, the mixture was fully stirred and vacuum-defoamed to form a uniform positive electrode slurry. The positive electrode slurry was coated on an aluminum foil with a thickness of 9 μm (positive electrode current collector), and the coating surface density was 18.25 mg / cm 2 Then it was dried in an oven at 80℃ and rolled (the compacted density was 4.15g / cm 3 ), cutting to obtain a positive electrode sheet;

[0119] (3) Preparation of electrolyte

[0120] In a glove box filled with argon (H2O < 0.05ppm, O2 < 0.05ppm), ethylene carbonate (EC), dimethyl carbonate (DMC), and propylene carbonate (PC) are mixed in a mass ratio of 1:2.88:1.2 to obtain an electrolyte solvent with a total mass of 79.5wt% of the electrolyte, and then lithium hexafluorophosphate (LiPF6) is added to the electrolyte solvent at a concentration of 14% based on the total mass of the electrolyte. After dissolution, 6.5wt% of additives based on the total mass of the electrolyte are added, wherein the additives include fluoroethylene carbonate (FEC) and 1,3-propane sultone (PS) with contents of 7% and 3%, respectively. The mixture is stirred evenly, and an electrolyte is obtained after passing the moisture and free acid tests.

[0121] (4) Preparation of diaphragm

[0122] Alumina and PVDF with a Dv50 particle size of 0.9 μm were weighed in a mass ratio of 90:10 and dispersed in N-methylpyrrolidone, and fully stirred to form a ceramic coating slurry. The ceramic coating slurry was coated on one side of a PE diaphragm substrate (the substrate thickness was 7 μm) by a gravure coating process, and a diaphragm was obtained after drying, wherein the thickness of the ceramic coating was 1.5 μm;

[0123] (5) Assembling lithium-ion batteries

[0124] The positive electrode sheet, separator and negative electrode sheet prepared above are stacked in order, with the separator being located between the positive electrode sheet and the negative electrode sheet, and the ceramic coating in the separator facing the positive electrode sheet, and then a bare cell is obtained by ear welding and winding, and the bare cell is placed in a 0.09 mm aluminum-plastic film shell, and a lithium-ion battery is prepared through processes such as packaging, liquid injection, formation, secondary sealing and sorting.

[0125] Example 5

[0126] (1) Preparation of negative electrode sheet

[0127] According to the mass ratio of 95.8:0.6:1.3:1.3:1, artificial graphite as the negative electrode active material, carbon black as the conductive agent, styrene-butadiene rubber as the binder, sodium carboxymethyl cellulose as the thickener and negative electrode additives were weighed and mixed thoroughly. After adding deionized water, the mixture was stirred thoroughly and vacuum-defoamed to form a uniform negative electrode slurry. The negative electrode slurry was coated on a copper foil (negative electrode current collector) with a thickness of 6 μm, and the coating surface density was 9.89 mg / cm 2 Then it was dried in a 90℃ oven and rolled (the compacted density was 1.60g / cm 3 ), cutting to obtain a negative electrode sheet; wherein the negative electrode additive is selected from octamethylcyclotetrasiloxane;

[0128] (2) Preparation of positive electrode

[0129] The positive electrode active material lithium cobalt oxide (Dv50 particle size is 11.86 μm), the conductive agent carbon black, the carbon nanotubes and the binder polyvinylidene fluoride were weighed according to the mass ratio of 97.0:1:0.5:1.5, and N-methylpyrrolidone was added after being fully mixed. Then, the mixture was fully stirred and vacuum-defoamed to form a uniform positive electrode slurry. The positive electrode slurry was coated on an aluminum foil with a thickness of 9 μm (positive electrode current collector), and the coating surface density was 18.25 mg / cm 2 Then it was dried in an oven at 80℃ and rolled (the compacted density was 4.15g / cm 3 ), cutting to obtain a positive electrode sheet;

[0130] (3) Preparation of electrolyte

[0131] In a glove box filled with argon (H2O < 0.05ppm, O2 < 0.05ppm), ethylene carbonate (EC), dimethyl carbonate (DMC), and propylene carbonate (PC) are mixed in a mass ratio of 1:4:4 to obtain an electrolyte solvent with a total mass of 79.5wt% of the electrolyte, and then lithium hexafluorophosphate (LiPF6) with a mass of 14% based on the total mass of the electrolyte is added to the electrolyte solvent. After dissolution, 6.5wt% of additives based on the total mass of the electrolyte are added, wherein the additives include fluoroethylene carbonate (FEC) and 1,3-propane sultone (PS) with a content of 7% and 3%, respectively. The mixture is stirred evenly, and an electrolyte is obtained after passing the moisture and free acid tests.

[0132] (4) Preparation of diaphragm

[0133] Alumina and PVDF with a Dv50 particle size of 0.5 μm were weighed in a mass ratio of 90:10 and dispersed in N-methylpyrrolidone, and fully stirred to form a ceramic coating slurry. The ceramic coating slurry was coated on one side of a PE diaphragm substrate (the substrate thickness was 7 μm) by a gravure coating process, and a diaphragm was obtained after drying, wherein the thickness of the ceramic coating was 1.5 μm;

[0134] (5) Assembling lithium-ion batteries

[0135] The positive electrode sheet, separator and negative electrode sheet prepared above are stacked in order, with the separator being located between the positive electrode sheet and the negative electrode sheet, and the ceramic coating in the separator facing the positive electrode sheet, and then a bare cell is obtained by ear welding and winding, and the bare cell is placed in a 0.09 mm aluminum-plastic film shell, and a lithium-ion battery is prepared through processes such as packaging, liquid injection, formation, secondary sealing and sorting.

[0136] Example 6

[0137] (1) Preparation of negative electrode sheet

[0138] According to the mass ratio of 96.0:0.6:1.3:1.3:0.8, artificial graphite as the negative electrode active material, carbon black as the conductive agent, styrene-butadiene rubber as the binder, sodium carboxymethyl cellulose as the thickener and negative electrode additives were weighed and mixed thoroughly. After adding deionized water, the mixture was stirred thoroughly and vacuum-defoamed to form a uniform negative electrode slurry. The negative electrode slurry was coated on a copper foil (negative electrode current collector) with a thickness of 6 μm, and the coating surface density was 9.89 mg / cm 2 Then it was dried in a 90℃ oven and rolled (the compacted density was 1.60g / cm 3 ), cutting to obtain a negative electrode sheet; wherein the negative electrode additive is selected from octamethylcyclotetrasiloxane;

[0139] (2) Preparation of positive electrode

[0140] The positive electrode active material lithium cobalt oxide (Dv50 particle size is 11.86 μm), the conductive agent carbon black, the carbon nanotubes and the binder polyvinylidene fluoride were weighed according to the mass ratio of 97.0:1:0.5:1.5, and N-methylpyrrolidone was added after being fully mixed. Then, the mixture was fully stirred and vacuum-defoamed to form a uniform positive electrode slurry. The positive electrode slurry was coated on an aluminum foil with a thickness of 9 μm (positive electrode current collector), and the coating surface density was 18.25 mg / cm 2 Then it was dried in an oven at 80℃ and rolled (the compacted density was 4.15g / cm 3 ), cutting to obtain a positive electrode sheet;

[0141] (3) Preparation of electrolyte

[0142] In a glove box filled with argon (H2O < 0.05ppm, O2 < 0.05ppm), ethylene carbonate (EC), dimethyl carbonate (DMC), and propylene carbonate (PC) are mixed in a mass ratio of 1:3.2:4 to obtain an electrolyte solvent with a total mass of 79.5wt% of the electrolyte, and then lithium hexafluorophosphate (LiPF6) with a mass of 14% based on the total mass of the electrolyte is added to the electrolyte solvent. After dissolution, 6.5wt% of additives based on the total mass of the electrolyte are added, wherein the additives include fluoroethylene carbonate (FEC) and 1,3-propane sultone (PS) with a content of 7% and 3%, respectively. The mixture is stirred evenly, and an electrolyte is obtained after passing the moisture and free acid tests.

[0143] (4) Preparation of diaphragm

[0144] Alumina and PVDF with a Dv50 particle size of 0.96 μm were weighed in a mass ratio of 90:10 and dispersed in N-methylpyrrolidone, and fully stirred to form a ceramic coating slurry. The ceramic coating slurry was coated on one side of a PE diaphragm substrate (the substrate thickness was 7 μm) by a gravure coating process, and a diaphragm was obtained after drying, wherein the thickness of the ceramic coating was 1.5 μm;

[0145] (5) Assembling lithium-ion batteries

[0146] The positive electrode sheet, separator and negative electrode sheet prepared above are stacked in order, with the separator being located between the positive electrode sheet and the negative electrode sheet, and the ceramic coating in the separator facing the positive electrode sheet, and then a bare cell is obtained by ear welding and winding, and the bare cell is placed in a 0.09 mm aluminum-plastic film shell, and a lithium-ion battery is prepared through processes such as packaging, liquid injection, formation, secondary sealing and sorting.

[0147] Example 7

[0148] (1) Preparation of negative electrode sheet

[0149] According to the mass ratio of 96.79:0.6:1.3:1.3:0.01, artificial graphite as the negative electrode active material, carbon black as the conductive agent, styrene-butadiene rubber as the binder, sodium carboxymethyl cellulose as the thickener and negative electrode additives were weighed and mixed thoroughly. After adding deionized water, the mixture was stirred thoroughly and vacuum-defoamed to form a uniform negative electrode slurry. The negative electrode slurry was coated on a copper foil (negative electrode current collector) with a thickness of 6 μm, and the coating surface density was 9.89 mg / cm 2 Then it was dried in a 90℃ oven and rolled (the compacted density was 1.60g / cm 3 ), cutting to obtain a negative electrode sheet; wherein the negative electrode additive is selected from octamethylcyclotetrasiloxane;

[0150] (2) Preparation of positive electrode

[0151] The positive electrode active material lithium cobalt oxide (Dv50 particle size is 11.86 μm), the conductive agent carbon black, the carbon nanotubes and the binder polyvinylidene fluoride were weighed according to the mass ratio of 97.0:1:0.5:1.5, and N-methylpyrrolidone was added after being fully mixed. Then, the mixture was fully stirred and vacuum-defoamed to form a uniform positive electrode slurry. The positive electrode slurry was coated on an aluminum foil with a thickness of 9 μm (positive electrode current collector), and the coating surface density was 18.25 mg / cm 2 Then it was dried in an oven at 80℃ and rolled (the compacted density was 4.15g / cm 3 ), cutting to obtain a positive electrode sheet;

[0152] (3) Preparation of electrolyte

[0153] In a glove box filled with argon (H2O < 0.05ppm, O2 < 0.05ppm), ethylene carbonate (EC), dimethyl carbonate (DMC), and propylene carbonate (PC) are mixed in a mass ratio of 1:0.2:0.16 to obtain an electrolyte solvent with a total mass of 79.5wt% of the electrolyte, and then lithium hexafluorophosphate (LiPF6) is added to the electrolyte solvent at a concentration of 14% based on the total mass of the electrolyte. After dissolution, 6.5wt% of additives based on the total mass of the electrolyte are added, wherein the additives include fluoroethylene carbonate (FEC) and 1,3-propane sultone (PS) with contents of 7% and 3%, respectively. The mixture is stirred evenly, and an electrolyte is obtained after passing the moisture and free acid tests.

[0154] (4) Preparation of diaphragm

[0155] Alumina and PVDF with a Dv50 particle size of 0.05 μm were weighed in a mass ratio of 90:10 and dispersed in N-methylpyrrolidone, and fully stirred to form a ceramic coating slurry. The ceramic coating slurry was coated on one side of a PE diaphragm substrate (the substrate thickness was 7 μm) by a gravure coating process, and a diaphragm was obtained after drying, wherein the thickness of the ceramic coating was 1.5 μm;

[0156] (5) Assembling lithium-ion batteries

[0157] The positive electrode sheet, separator and negative electrode sheet prepared above are stacked in order, with the separator being located between the positive electrode sheet and the negative electrode sheet, and the ceramic coating in the separator facing the positive electrode sheet, and then a bare cell is obtained by ear welding and winding, and the bare cell is placed in a 0.09 mm aluminum-plastic film shell, and a lithium-ion battery is prepared through processes such as packaging, liquid injection, formation, secondary sealing and sorting.

[0158] Example 8

[0159] The preparation method is basically the same as that of Example 7, except that: the content of the negative electrode additive in the negative electrode paste is 0.05 wt%, and the content of the negative electrode active material is adjusted accordingly; the mass ratio of ethylene carbonate, dimethyl carbonate and propylene carbonate is 1:1:0.8.

[0160] Example 9

[0161] The preparation method is basically the same as that of Example 7, except that: the content of the negative electrode additive in the negative electrode paste is 0.1 wt%, and the content of the negative electrode active material is adjusted accordingly; the mass ratio of ethylene carbonate, dimethyl carbonate and propylene carbonate is 1:2:1.6.

[0162] Example 10

[0163] The preparation method is basically the same as that of Example 7, except that: the content of the negative electrode additive in the negative electrode paste is 0.3 wt%, and the content of the negative electrode active material is adjusted accordingly; the mass ratio of ethylene carbonate, dimethyl carbonate and propylene carbonate is 1:6.01:4.8.

[0164] Example 11

[0165] The preparation method is basically the same as that of Example 7, except that: the content of the negative electrode additive in the negative electrode paste is 0.5 wt%, and the content of the negative electrode active material is adjusted accordingly; the mass ratio of ethylene carbonate, dimethyl carbonate and propylene carbonate is 1:10.02:8.

[0166] Example 12

[0167] The preparation method is basically the same as that of Example 7, except that: the content of the negative electrode additive in the negative electrode paste is 0.7 wt%, and the content of the negative electrode active material is adjusted accordingly; the mass ratio of ethylene carbonate, dimethyl carbonate and propylene carbonate is 1:14.02:11.2.

[0168] Example 13

[0169] The preparation method is basically the same as that of Example 9, except that: the mass ratio of ethylene carbonate, dimethyl carbonate and propylene carbonate is 1:1.54:1.6.

[0170] Example 14

[0171] The preparation method is basically the same as that of Example 9, except that: the mass ratio of ethylene carbonate, dimethyl carbonate and propylene carbonate is 1:0.64:1.6.

[0172] Example 15

[0173] The preparation method is basically the same as that of Example 9, except that: the mass ratio of ethylene carbonate, dimethyl carbonate and propylene carbonate is 1:1.92:1.6.

[0174] Example 16

[0175] The preparation method is basically the same as that of Example 9, except that the mass ratio of ethylene carbonate, dimethyl carbonate and propylene carbonate is 1:2.56:1.6.

[0176] Example 17

[0177] The preparation method is basically the same as that of Example 9, except that the mass ratio of ethylene carbonate, dimethyl carbonate and propylene carbonate is 1:3.2:1.6.

[0178] Example 18

[0179] The preparation method is basically the same as that of Example 9, except that the mass ratio of ethylene carbonate, dimethyl carbonate and propylene carbonate is 1:0.77:1.6.

[0180] Example 19

[0181] The preparation method is basically the same as that of Example 9, except that the mass ratio of ethylene carbonate, dimethyl carbonate and propylene carbonate is 1:2.5:2.

[0182] Example 20

[0183] The preparation method is basically the same as that of Example 9, except that the mass ratio of ethylene carbonate, dimethyl carbonate and propylene carbonate is 1:5.01:4.

[0184] Example 21

[0185] The preparation method is basically the same as that of Example 9, except that the mass ratio of ethylene carbonate, dimethyl carbonate and propylene carbonate is 1:3.13:2.5.

[0186] Example 22

[0187] The preparation method is basically the same as that of Example 9, except that the mass ratio of ethylene carbonate, dimethyl carbonate and propylene carbonate is 1:1.67:1.33.

[0188] Example 23

[0189] The preparation method is basically the same as that of Example 9, except that the mass ratio of ethylene carbonate, dimethyl carbonate and propylene carbonate is 1:1.25:1.

[0190] Example 24

[0191] The preparation method is basically the same as that of Example 9, except that the mass ratio of ethylene carbonate, dimethyl carbonate and propylene carbonate is 1:0.83:0.67.

[0192] Example 25

[0193] The preparation method is basically the same as that of Example 9, except that: the content of the negative electrode additive in the negative electrode slurry is 0.5 wt%, and the content of the negative electrode active material is adjusted accordingly; the mass ratio of ethylene carbonate, dimethyl carbonate and propylene carbonate is 1:10.02:8, and the Dv50 particle size of alumina is 0.6 μm.

[0194] Example 26

[0195] The preparation method is basically the same as that of Example 9, except that: the content of the negative electrode additive in the negative electrode slurry is 0.4 wt%, and the content of the negative electrode active material is adjusted accordingly; the mass ratio of ethylene carbonate, dimethyl carbonate and propylene carbonate is 1:8.01:6.4, and the Dv50 particle size of alumina is 0.8 μm.

[0196] Example 27

[0197] The preparation method is basically the same as that of Example 9, except that: the content of the negative electrode additive in the negative electrode slurry is 0.14 wt%, and the content of the negative electrode active material is adjusted accordingly; the mass ratio of ethylene carbonate, dimethyl carbonate and propylene carbonate is 1:2.8:2.24, and the Dv50 particle size of alumina is 0.4 μm.

[0198] Example 28

[0199] The preparation method is basically the same as that of Example 9, except that: the content of the negative electrode additive in the negative electrode slurry is 0.1 wt%, and the content of the negative electrode active material is adjusted accordingly; the mass ratio of ethylene carbonate, dimethyl carbonate and propylene carbonate is 1:3.92:3.13, and the Dv50 particle size of alumina is 0.5 μm.

[0200] Example 29

[0201] The preparation method is basically the same as that of Example 9, except that: the content of the negative electrode additive in the negative electrode slurry is 0.25 wt%, and the content of the negative electrode active material is adjusted accordingly; the mass ratio of ethylene carbonate, dimethyl carbonate and propylene carbonate is 1:5.01:4, and the Dv50 particle size of alumina is 2 μm.

[0202] Example 30

[0203] The preparation method is basically the same as that of Example 9, except that: the Dv50 particle size of alumina is 2 μm.

[0204] Example 31

[0205] The preparation method is basically the same as that of Example 1, except that: the negative electrode additive is octamethyltrisiloxane.

[0206] Comparative Example 1

[0207] The preparation method is basically the same as that of Example 4, except that: the content of the negative electrode additive in the negative electrode slurry is 1.2 wt%, and the mass ratio of ethylene carbonate, dimethyl carbonate and propylene carbonate is 1:11.52:4.8.

[0208] Comparative Example 2

[0209] The preparation method is basically the same as that of Example 3, except that: the mass ratio of ethylene carbonate, dimethyl carbonate and propylene carbonate is 1:8:2.

[0210] Comparative Example 3

[0211] The preparation method is basically the same as that of Example 3, except that: the mass ratio of ethylene carbonate, dimethyl carbonate and propylene carbonate is 1:0.64:2.

[0212] Comparative Example 4

[0213] The preparation method is basically the same as that of Example 3, except that: the mass ratio of ethylene carbonate, dimethyl carbonate and propylene carbonate is 1:0.28:0.2.

[0214] Comparative Example 5

[0215] The preparation method is basically the same as that of Example 3, except that: the Dv50 particle size of alumina is 3 μm.

[0216] Comparative Example 6

[0217] The preparation method is basically the same as that of Example 3, except that: the negative electrode additive is selected from dichlorodimethylsiloxane.

[0218] Comparative Example 7

[0219] The preparation method is basically the same as that of Example 3, except that: the negative electrode additive is replaced with deionized water.

[0220] The electrode sheets and batteries prepared in the above examples were respectively subjected to performance tests according to the following methods:

[0221] (1) 48-hour rebound: Lay the negative electrode sheet obtained after rolling flat on a clean tabletop, and measure the thickness H1 of the electrode sheet with a micrometer; then place the electrode sheet in a dry environment for 48 hours, and measure the thickness H2 of the electrode sheet with a micrometer again, and then obtain the 48-hour rebound data according to the formula (H2 - H1) / H1 * 100%;

[0222] (2) Porosity: Let the rolled negative electrode sheet stand in a dry environment for more than 48 hours, then cut it into a certain size, and measure the thickness of the electrode sheet with a micrometer to calculate the volume of the electrode sheet as V1; then put the electrode sheet into the testing equipment, open the gas valve, introduce helium gas, and test the true volume V2 of the electrode sheet; the porosity of the negative electrode sheet is obtained according to the formula (V1 - V2) / V1 * 100%;

[0223] (3) Liquid absorption capacity of the electrolyte: Let the rolled negative electrode sheet stand in a dry environment for more than 48 hours and cut it into a certain size, then place the cut negative electrode sheet in beakers containing a certain amount of EC, PC, and DMC respectively, and let it stand for 24 hours. Then take out the negative electrode sheet, wipe off the excess electrolyte solvent on the surface of the negative electrode sheet with lint-free paper, and then weigh the mass of the negative electrode sheet as M1. Finally, place the negative electrode sheet in an oven at 100 °C to dry it, and weigh the mass of the dried negative electrode sheet as M2. Then the liquid absorption capacity of the negative electrode sheet for different electrolyte solvents is obtained according to the formula (M1 - M2) / M2 * 100%;

[0224] (4) Liquid climbing rate: Let the rolled negative electrode sheet stand in a dry environment for more than 48 hours and cut it into a certain size. Then place one end of the cut negative electrode sheet in the electrolyte and the other end hanging in the glove box. Then record the distance that the electrolyte rises in the negative electrode sheet every 3 hours for 24 consecutive hours. At this time, the rising distance of the electrolyte is H1. Then the liquid climbing rate of the negative electrode sheet is obtained according to the formula H1 / 24;

[0225] (5) Tortuosity: In the glove box, assemble the negative electrode sheet - separator - negative electrode sheet into a symmetric battery, test the EIS, the test frequency is 100000 - 1 HZ, the perturbation voltage is 10 mV, and the ionic resistance of the electrode sheet is obtained by fitting the EIS spectrum. Then the tortuosity of the negative electrode sheet is calculated through the MacMullin number formula;

[0226] (6) Cycling performance test method: Place the lithium-ion battery in an environment of 25 °C. After standing for 0.5 hours, when the battery temperature is 25 ± 2 °C, charge it at a constant current of 1.5C to the upper limit voltage (4.5V), and then charge it at a constant voltage of 4.5V to 0.05C and stand for 5 minutes; then discharge it at a constant current of 0.7C to 3.0V and stand for 5 minutes. This is one charge-discharge cycle, and the charge-discharge cycle is carried out 400 times; record the highest discharge capacity of the first 3 cycles as the initial capacity Q1, and the discharge capacity of the 400th time is Q2. Calculate the capacity retention rate of the battery = Q2 / Q1 × 100%;

[0227] (7) Multi-rate charging: Place the lithium-ion battery in an environment of 25°C, let it stand for 10 min, discharge it at a rate of 0.7C to the lower limit voltage (3.0V), let it stand for 10 min, then charge it to the upper limit voltage (4.5V) at rates of 1C, 2C, and 3C respectively, and perform constant voltage charging until 0.05C, let it stand for 5 min, and record the constant current charging ratio of the lithium-ion battery at different rates.

[0228] (8) Multi-rate discharging: Place the lithium-ion battery in an environment of 25°C, let it stand for 10 min, discharge it at a rate of 0.7C to the lower limit voltage (3.0V), let it stand for 10 min, charge it at a constant current of 0.7C to the upper limit voltage (4.5V), and perform constant voltage charging until 0.05C, then discharge it to the lower limit voltage (3.0V) at rates of 1C, 2C, and 3C respectively, and record the capacity retention rate of the lithium-ion battery at different rates;

[0229] Based on the above test methods, the test results of the negative electrode sheets and battery performance prepared in the examples are shown in Tables 1, 2, and 3:

[0230] Table 1 Data table of the rebound, porosity, adsorption amount of electrolyte solvent, electrolyte creeping rate, and tortuosity of the negative electrode sheets prepared in the examples

[0231]

[0232]

[0233] Table 2 Data table of the electrochemical performance of the lithium-ion batteries prepared in the examples

[0234]

[0235]

[0236]

[0237]

[0238] Table 3 Data table of the fast charging performance of the lithium-ion batteries prepared in the examples

[0239]

[0240]

[0241] In the above Examples 1 to 29, by introducing a negative electrode additive into the negative electrode active material layer, the porosity of the negative electrode sheet is increased, and the porosity reaches more than 35%; at the same time, after introducing the negative electrode additive, the adsorption amount of the negative electrode sheet to the ester-based electrolyte solvent is also increased, among which the adsorption amount to the PC solvent is the highest, reaching 11%, and at the same time, the liquid creeping rate is increased and the tortuosity is reduced; and the residual liquid coefficient of the lithium-ion battery is increased, the room temperature DCIR and the low temperature DCIR are both reduced, and the surface state after room temperature cycling in the negative electrode sheet is improved, and there is no abnormality at the interface.

[0242] In the above Examples 7 to 12, although the values of the negative electrode additive are all in the range of 0.01 to 1.0 wt%, when the value of the negative electrode additive is 0.1 to 0.5 wt% compared with other values, the porosity of the negative electrode sheet, the liquid absorption ratio of the electrolyte solvent and the liquid creeping rate are improved, the tortuosity is reduced, and the lithium-ion residual liquid coefficient is also increased, the room temperature DCIR and the low temperature DCIR are also reduced, and the cycling performance is more excellent.

[0243] In the above Examples 13 to 18, although the relationship between Y and Z all satisfies 1 ≤ (5×Y) / (2×Z) ≤ 8, when the value of (5×Y) / (2×Z) is 1 to 3.5 compared with other values, the room temperature DCIR and the low temperature DCIR of the lithium-ion battery are both reduced, and the cycling retention rate is more excellent.

[0244] In the above Examples 19 to 24, although the relationship between X and Z all satisfies 0 < (2×X) / (0.1%×Z) ≤ 5, when 0 < (2×X) / (0.1%×Z) ≤ 1.5 compared with other values, the room temperature DCIR and the low temperature DCIR of the lithium-ion battery are both reduced, and the cycling retention rate is more excellent.

[0245] In the above Examples 25 to 29, although the relationship between A and X all satisfies 0.5 ≤ A / (100×X) ≤ 8, when 0.5 ≤ A / (100×X) ≤ 3 compared with other values, the room temperature DCIR and the low temperature DCIR of the lithium-ion battery are both reduced, and the cycling retention rate is more excellent.

[0246] In the above Example 30, the relationship between A and X does not satisfy 0.5 ≤ A / (100×X) ≤ 8, the room temperature DCIR and the low temperature DCIR of the lithium-ion battery are affected, and the cycling retention rate also decreases.

[0247] In the above Example 31, the negative electrode additive is changed to chain-like siloxane octamethyltrisiloxane, and the battery performance is basically the same as that of octamethylcyclotetrasiloxane.

[0248] In the above Comparative Example 1, X is not in the range of 0.01 to 1.0 wt%. Although the porosity of the negative electrode sheet is slightly increased, the room temperature DICR and the low temperature DICR of the lithium-ion battery are affected, and the cycling retention rate is also affected.

[0249] In the above Comparative Example 2, (5×Y) / (2×Z) = 10, the normal-temperature DICR and low-temperature DICR of the lithium-ion battery are affected, and the cycle retention rate is slightly reduced.

[0250] In the above Comparative Example 3, (5×Y) / (2×Z) = 0.8, the residual liquid coefficient slightly increases, the normal-temperature DICR and low-temperature DICR of the lithium-ion battery are affected, and the cycle retention rate is also slightly reduced.

[0251] In the above Comparative Example 4, (2×X) / (0.1%×Z) = 10, the normal-temperature DICR and low-temperature DICR of the lithium-ion battery are affected, and the cycle retention rate is also slightly reduced.

[0252] In the above Comparative Example 5, the Dv50 particle size of alumina is not within the range of 0.05 μm to 2 μm, and A / (100×X) = 30, the normal-temperature DICR and low-temperature DICR of the lithium-ion battery are affected, and the cycle retention rate is also slightly reduced.

[0253] In the above Comparative Example 6, the porosity of the negative electrode sheet is greatly reduced, the liquid absorption capacity for the electrolyte is reduced, the liquid creeping rate is reduced, the normal-temperature DICR and low-temperature DICR of the lithium-ion battery are affected, and slight purple spots appear at the top and bottom of the electrode sheet after 400T normal-temperature cycles.

[0254] In the above Comparative Example 7, the porosity of the negative electrode sheet is greatly reduced, the liquid absorption capacity for the electrolyte is reduced, the liquid creeping rate is reduced, the normal-temperature DICR and low-temperature DICR of the lithium-ion battery are affected, and slight purple spots appear at the top and bottom of the electrode sheet after 400T normal-temperature cycles.

[0255] The description of the above embodiments is only used to help understand the method and its core idea of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0256] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A lithium ion battery, comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the negative electrode sheet comprises a current collector and a negative electrode active material layer formed on at least one side surface of the current collector; The negative electrode active material layer includes a negative electrode additive, wherein the negative electrode additive is selected from one or more of a cyclic siloxane as shown in formula (I) and a chain siloxane as shown in formula (II), and the content of the negative electrode additive in the negative electrode active material layer is X, and X is 0.01wt% to 1.0wt%; The electrolyte includes a carbonate solvent, wherein the carbonate solvent includes a first carbonate solvent, dimethyl carbonate and propylene carbonate in a mass ratio of 1:Y:Z, and the first carbonate solvent is another carbonate solvent except the dimethyl carbonate and propylene carbonate; The X, Y, and Z satisfy the following relationship: 1≤(5×Y) / (2×Z)≤8; 0<(2×X) / (0.1%×Z)≤5; in, m and n are independently selected from integers greater than 0.

2. The lithium-ion battery according to claim 1, characterized in that The separator includes a ceramic coating on the positive electrode side, the median particle size Dv50 of the ceramic particles in the ceramic coating is A, 0.05 μm≤A≤2 μm, and A and X satisfy 0.5≤A / (100×X)≤8.

3. The lithium-ion battery according to claim 1, characterized in that In the cyclic siloxane and the chain siloxane, n and m are independently selected from 1 to 10.

4. The lithium-ion battery according to claim 1, characterized in that: The melting point of the negative electrode additive is 300-400°C; And / or, the negative electrode additive is in an amorphous state in the XRD curve, has a characteristic peak between 5° and 25°, and the half-peak width of the characteristic peak is 2° to 20°; And / or, in the infrared spectrum curve of the negative electrode additive, at a wave number of 900 to 100 cm -1 There is a stretching vibration peak corresponding to the Si-O-Si bond at 600-700 cm -1 There is a stretching vibration peak corresponding to the Si-C bond at 2800-3000cm -1 There is a stretching vibration peak corresponding to the CH bond.

5. The lithium-ion battery according to claim 1, characterized in that: The negative electrode active material layer also includes a negative electrode active material, a conductive agent, a binder and a thickener; the content of the negative electrode active material is 80-98wt%, the content of the conductive agent is 0.1-15wt%, the content of the binder is 0.1-15wt%, and the content of the thickener is 0.1-15wt%.

6. The lithium-ion battery according to claim 1, characterized in that The electrolyte also includes a lithium salt and an electrolyte additive, wherein the content of the carbonate solvent is 40 to 90 wt%, the content of the lithium salt is 5 to 30 wt%, and the content of the electrolyte additive is 5 to 30 wt%; the electrolyte additive in the electrolyte includes fluoroethylene carbonate and 1,3-propane sultone in a mass ratio of (2 to 5):

1.

7. The lithium-ion battery according to claim 1, characterized in that: The first carbonate solvent includes ethylene carbonate; the liquid absorption amount of the carbonate solvent per unit mass of the negative electrode sheet is 1 to 40%; And / or, the liquid absorption of the ethylene carbonate per unit mass of the negative electrode sheet is 1 to 20%; And / or, the liquid absorption amount of the dimethyl carbonate per unit mass of the negative electrode sheet is 1 to 30%; And / or, the liquid absorption amount of the propylene carbonate by the negative electrode sheet per unit mass is 5 to 40%.

8. The lithium ion battery according to any one of claims 1 to 7, characterized in that: The compaction density of the negative electrode sheet is 1.0 to 1.8 g / cm 3 .

9. The lithium ion battery according to any one of claims 1 to 7, characterized in that: The median particle size Dv50 of the negative electrode additive is 1 to 5 μm, and Dv90 is 8 to 15 μm; And / or, the Dv50 of the positive electrode active material of the positive electrode sheet is 0.1 to 30 μm.

10. The lithium ion battery according to any one of claims 1 to 7, characterized in that: The ceramic particles of the diaphragm are selected from one or more of aluminum oxide, boehmite, silicon dioxide, zirconium dioxide, barium sulfate, magnesium hydroxide, fluoroapatite, fluorophlogopite, mullite, aluminum titanate, copper oxide, titanium dioxide, and zinc oxide; And / or, the thickness of the ceramic coating of the diaphragm is 0.1-5 μm.

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