A super-fast-charging negative electrode sheet and a lithium ion battery comprising the same

Abstract

The application discloses a super-fast-charging negative electrode sheet and a lithium ion battery comprising the same. The negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer, the negative electrode active material layer is arranged on at least one surface of the negative electrode current collector, the negative electrode active material layer comprises an active material layer A and an active material layer B, the active material layer A is arranged between the current collector and the active material layer B, and the active material layer B contains silicon oxide particles. The lithium ion battery of the application can be stably cycled under 5C-10C step charging conditions.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of energy storage, in particular to a super-fast-charging negative electrode sheet and a lithium ion battery comprising the same. BACKGROUND

[0002] In recent years, consumers have increasingly high requirements for the charging speed of electronic products and electric vehicles, and as a result, higher requirements have been put forward for the fast-charging capability of lithium ion batteries as energy carriers.

[0003] Silicon oxide particles have three advantages over graphite: first, under the same capacity area density conditions, the negative electrode sheet containing silicon oxide particles is thinner, thus having a shorter lithium ion diffusion path in the liquid phase; second, the structure of silicon oxide particles is amorphous and is of an alloy type lithium storage mode, thus having more lithium intercalation channels; and third, the lithium intercalation potential of silicon oxide particles is higher than that of graphite, and is less likely to cause lithium precipitation during high-rate charging. By constructing a mixed negative electrode system of silicon oxide particles and graphite, the fast-charging performance of lithium ion batteries can be improved.

[0004] The theory of porous electrodes shows that the polarization potential of the negative electrode sheet is unevenly distributed, and high-rate charging will exacerbate this unevenness, thereby shortening the constant current charging time. According to the lithium intercalation characteristics of active materials, the structure of the negative electrode sheet can be designed to reduce the impact of uneven polarization potential distribution.

[0005] Therefore, how to select appropriate negative electrode active materials and design specific negative electrode sheet structures to achieve the fast-charging performance of lithium ion batteries has become a difficult problem to be solved in the field of negative electrode material development and battery design. SUMMARY

[0006] In order to improve the above technical problems, the present application provides a super-fast-charging negative electrode sheet and a lithium ion battery comprising the same.

[0007] In order to achieve the above-mentioned purpose, the present application realizes the following technical solutions:

[0008] A negative electrode sheet, comprising a negative electrode current collector and a negative electrode active material layer, the negative electrode active material layer being arranged on at least one surface of the negative electrode current collector, the negative electrode active material layer comprising an active material layer A and an active material layer B, the active material layer A being arranged between the current collector and the active material layer B; the active material layer B containing silicon oxide particles, the silicon oxide particles satisfying the following relationship:

[0009] D i ≤ 35 μm (III),

[0010] d i ≤ 25 μm (IV),

[0011] 0.45≤(ΣE j 2 ) / (ΣD i 2 )≤0.75 (V),

[0012] (ΣF k 2 ) / (ΣD i 2 )≥0.37 (VI),

[0013] wherein, Σ represents summing up data, D i represents the circumscribed circle diameter of any silicon oxide particle, d i represents the inscribed circle diameter of any silicon oxide particle, E j represents the circumscribed circle diameter of silicon oxide particle with d i ≥9μm, F k represents the circumscribed circle diameter of silicon oxide particle with d i ≥4μm, i, j, k represent the number of silicon oxide particles, and S represents the cross-sectional area of the active material layer B in the observation area.

[0014] According to the present application, the active material layer A is free of silicon oxide particles.

[0015] It is found that the lithium intercalation potential of silicon oxide particles is higher than that of graphite, and silicon oxide particles can withstand greater polarization potential without lithium deposition. The active material layer B is outside the negative electrode sheet, and the polarization potential during super-high rate charging is much greater than that of the active material layer A. Concentrating silicon oxide particles in the active material layer B can effectively reduce the lithium deposition phenomenon on the surface of the negative electrode sheet.

[0016] According to the present application, the thickness L A of the active material layer A satisfies 20μm≤L A ≤40μm.

[0017] According to the present application, the thickness L B of the active material layer B satisfies 35μm≤L B ≤60μm.

[0018] When the above thickness conditions are met, the uniformity of coating and the overall kinetics of the battery electrode sheet can be ensured. When L A <20μm or L B <35μm, the electrode sheet is prone to have phenomena such as material scraping during coating, and uniform distribution of active material cannot be ensured; and when L A >40μm or L B >60μm, the ohmic resistance of the electrode sheet is large, the polarization is intensified, and the risk of lithium deposition is increased.

[0019] According to the present application, in the active material layer B, the mixed amount of silicon oxide particles satisfies the following formula:

[0020] 0.05≤(ΣF k 2 ) / S≤0.47,

[0021] wherein Σ represents summation processing of data, F k represents the circumscribed circle diameter of silicon oxide particles with d i ≥4μm, k represents the number of silicon oxide particles, and S represents the cross-sectional area of the active material layer B in the observation region.

[0022] According to the present application, in the active material layer B, the specific surface area of silicon oxide particles is less than or equal to 1.2m 2 / g.

[0023] According to the present application, the mass proportion of silicon oxide particles in the active material layer B is about 5wt%-25wt%.

[0024] According to the present application, the silicon oxide particles contain Si element and O element, and the molar ratio x (mol / mol) of O element to Si element satisfies 0.7≤x≤1.4.

[0025] According to the present application, at least a part of the surface of the silicon oxide particles contains a coating layer.

[0026] The present application also provides a silicon oxide particle for the above-mentioned negative electrode sheet, which at least comprises the following features:

[0027] (1)D v max≤35;

[0028] (2)9.0≤D v 50≤13.0;

[0029] (3)BET≤1.2;

[0030] wherein:

[0031] D v max represents the maximum particle size of the silicon oxide particles, with the unit of μm;

[0032] D v 50 represents the median particle size of the silicon oxide particles, with the unit of μm;

[0033] BET represents the specific surface area of the silicon oxide particles, with the unit of m 2 / g.

[0034] The present application also provides a lithium ion battery comprising the above-mentioned negative electrode sheet.

[0035] According to the present application, the lithium ion battery has the following characteristics after 1-5 charge-discharge cycles when the negative electrode sheet is irreversibly expanded:

[0036] (1) The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer, the negative electrode active material layer is provided on at least one surface of the negative electrode current collector, the negative electrode active material layer includes an active material layer A and an active material layer B, the active material layer A is provided between the current collector and the active material layer B;

[0037] The active material layer A does not contain silicon oxide particles, the thickness L A satisfies 21 μm≤L A ≤44 μm;

[0038] The active material layer B contains silicon oxide particles, the thickness L B satisfies 44 μm≤L B ≤75 μm;

[0039] (2) The silicon oxide particles satisfy the following relationship:

[0040] D i ’≤44 μm,

[0041] d i ’≤32 μm,

[0042] 0.45≤(ΣE j ’ 2 ) / (ΣD i ’ 2 )≤0.75,

[0043] (ΣF k ’ 2 ) / (ΣD i ’ 2 )≥0.37,

[0044] 0.06≤(ΣF k ’ 2 ) / S’≤0.53,

[0045] wherein Σ represents summing processing of data, D i ’ represents the diameter of the circumscribed circle of any silicon oxide particle, d i ’ represents the diameter of the inscribed circle of any silicon oxide particle, E j ’ represents the diameter of the circumscribed circle of the silicon oxide particle with D i ’≥11.2 μm, F k ’ represents d ithe circumscribed circle diameter of the silicon oxide particles of ≥ 5.0 μm, i, j, k represent the number of the silicon oxide particles, and S' represents the cross-sectional area of the active material layer B in the observation region.

[0046] Advantages of the present application

[0047] According to the porous electrode theory, when the electronic conductivity of the solid phase is much greater than the ionic conductivity of the liquid phase, the polarization of the negative electrode sheet is approximately the same as that of the pure liquid phase. In the actual battery system, the electronic conductivity K s of the solid phase is > 0.1 S / cm, the ionic conductivity K l of the liquid phase is < 0.01 S / cm, and K s is greater than K l by more than one order of magnitude. Therefore, the negative electrode sheet can be analyzed using the pure liquid phase polarization model, and thus the formula for the surface polarization potential η 0 of the negative electrode sheet can be obtained:

[0048] η 0 = I · (p l Z) 1 / 2 / tanh[(p l / Z) 1 / 2 · L], (I)

[0049] wherein I is the total current flowing through the negative electrode sheet, p l is the apparent specific resistance of the electrolyte in the negative electrode sheet, Z is the reaction impedance of the electrode per unit volume, and L is the thickness of the active material layer.

[0050] As can be seen from formula (I), η 0 is proportional to I, that is, the greater the total current flowing through the negative electrode sheet, the greater the surface polarization potential. Under the condition of 5C-10C super-high-rate fast charging, the surface polarization potential of the negative electrode sheet is very large, and for graphite with a balanced lithium intercalation potential of only about 0.05-0.2 V, lithium precipitation is likely to occur. The balanced lithium intercalation potential of the silicon oxide particles is about 0.2-0.6 V, and the silicon oxide particles can withstand a greater polarization potential. Therefore, the silicon oxide particles can be concentrated and distributed near the outer surface of the negative electrode sheet to reduce the risk of lithium precipitation.

[0051] At the same time, the calculation formula of the polarization potential η(x) is:

[0052] η(x) = η 0 cosh[(p l / Z) 1 / 2 · (x-L)] / cosh[(p l / Z) 1 / 2 · L], (II)

[0053] wherein η 0denoted as α, where α is the polarization potential of the outer surface of the negative electrode; x is the distance along the thickness direction of the electrode, with x = 0 μm at the outer surface of the active material layer and the direction towards the current collector as the positive direction.

[0054] From formula (II), it can be seen that in the range x∈[0,L], η(x) decreases monotonically with x, and when x=0μm, η(x) is at its maximum value η. 0 When x = L, η(x) reaches its minimum value of 0V. That is, the polarization is greatest on the outer surface of the active material layer and least on the inner surface in contact with the current collector. Furthermore, according to formula (I), the greater the total current I flowing through the negative electrode, the greater the surface polarization potential η. 0 The larger the thickness, the more uneven the polarization potential distribution of the negative electrode, and the more uneven the degree of lithium intercalation of the active material along the thickness direction. For the above-mentioned system with uneven lithium intercalation distribution, a stepped fast charging mode can be used, that is, as the charging capacity increases, the charging rate is gradually reduced. This can achieve fast charging while reducing the risk of surface lithium plating.

[0055] On the other hand, silicon oxide particles undergo significant volume changes during lithium insertion / extraction cycles, leading to continuous damage and repair of the surface SEI film and ongoing consumption of active lithium. For smooth, micron-sized particles, an increased specific surface area results in more SEI film formation, but also greater damage and repair, accelerating battery cycle capacity decay. Therefore, to minimize electrode deformation due to localized strain, the particle size of silicon oxide particles can be maximized to reduce specific surface area and active lithium consumption. However, simply increasing the particle size is insufficient to guarantee a small specific surface area. Among all three-dimensional geometries, spheres have the smallest specific surface area, while silicon oxide particles are typically formed from fragmented bulk materials, exhibiting various irregular shapes such as rods, plates, and polyhedra, resulting in a large specific surface area. Therefore, controlling the shape of silicon oxide particles can adjust the fast-charging cycle performance of the negative electrode and the lithium-ion battery.

[0056] In view of this, the present invention provides a super-fast charging negative electrode and a lithium-ion battery based on the negative electrode, which can be stably cycled under 5C to 10C stepped charging conditions. Attached Figure Description

[0057] Figure 1 This is a cross-sectional schematic diagram of the negative electrode sheet of the present invention; wherein, 11 represents silicon oxide particles, 12 represents the active material layer, 13 represents the current collector, and L... A L represents the thickness of the active material layer A. B This indicates the thickness of the active material layer B.

[0058] Figure 2 This is a schematic diagram of the circumcircle and incircle of the silicon oxide particles in this invention. Detailed Implementation

[0059] [Negative electrode sheet and preparation thereof]

[0060] As described above, the present application provides a negative electrode sheet including a negative electrode current collector and a negative electrode active material layer provided on at least one surface of the negative electrode current collector, the active material layer including an active material layer A and an active material layer B, the active material layer A being provided between the current collector and the active material layer B;

[0061] The active material layer B contains silicon oxide particles satisfying the following relational expression:

[0062] D i ≤ 35 μm (III),

[0063] d i ≤ 25 μm (IV),

[0064] 0.45 ≤ (ΣE j 2 ) / (ΣD i 2 ) ≤ 0.75 (V),

[0065] (ΣF k 2 ) / (ΣD i 2 ) ≥ 0.37 (VI),

[0066] wherein Σ indicates a summation process for data, D i indicates a circumscribed circle diameter of an arbitrary silicon oxide particle, d i indicates an inscribed circle diameter of an arbitrary silicon oxide particle, E j indicates a circumscribed circle diameter of a silicon oxide particle of D i ≥ 9 μm, F k indicates a circumscribed circle diameter of a silicon oxide particle of d i ≥ 4 μm, i, j, k indicate numbers of silicon oxide particles, and S indicates a cross-sectional area of the active material layer B in an observation region.

[0067] In one embodiment, the active material layer A does not contain silicon oxide particles.

[0068] In one embodiment, the thickness L A of the active material layer A satisfies 20 μm ≤ L A ≤ 40 μm.

[0069] In one embodiment, the thickness L B of the active material layer B satisfies 35 μm ≤ L B ≤ 60 μm.

[0070] The present application limits the particle size of silicon oxide particles in the negative electrode sheet by the relations (III) and (IV). When the above conditions are met, the silicon oxide particles have moderate particle size, and the volume change thereof during cycling does not cause significant deformation of the electrode sheet. When there are silicon oxide particles with D i > 35 μm or d i > 25 μm, the absolute value of the volume change thereof during cycling is large, which can cause excessive stress in local areas, and there is a risk of bulging of the active material layer, thus deteriorating the electrical contact between the active material layer and the current collector, and further accelerating the cycle capacity decay of the battery.

[0071] The present application not only limits the particle size distribution of silicon oxide particles, but also limits the shape of silicon oxide particles by the relations (V) and (VI). The cross section of a sphere is circular, and the diameter of the inscribed circle and the circumscribed circle of the cross section is equal. For irregular geometric bodies, the closer the diameter of the inscribed circle and the circumscribed circle of the cross section shape, the closer the shape is to a circle. For example, when the diameter of the circumscribed circle is 1, the diameter of the inscribed circle of an equilateral triangle is 0.5, the diameter of the inscribed circle of a square is 0.71, the diameter of the inscribed circle of a regular hexagon is 0.87, and the diameter of the inscribed circle of a circle is 1. In view of this, the present application unexpectedly found that, when the size of the circumscribed circle of the cross section shape of silicon oxide particles is constant, the diameter of the inscribed circle must be large enough, in which case the overall shape of the silicon oxide particles is closer to a sphere, thus effectively reducing the side reactions on the surface of the silicon oxide particles. When the relations (III) and (IV) are met, the electrode sheet contains appropriate proportions of silicon oxide particles with D i ≥ 9 μm and sufficient proportions of silicon oxide particles with d i ≥ 4 μm, in which case the specific surface area of the silicon oxide particles is less than or equal to 1.2 m 2 / g (the specific surface area of the silicon oxide particles commonly used in the prior art is generally greater than 2.0 m 2 / g), and the side reactions are less. When (ΣE j 2 ) / (ΣD i 2 ) < 0.45, the overall particle size of the silicon oxide particles is small, the specific surface area is large, and the surface side reactions are more. When (ΣE j 2 ) / (ΣD i 2 ) > 0.75, the overall particle size of the silicon oxide particles is large, which can exacerbate the uneven distribution of stress in the electrode sheet, leading to deformation of the electrode sheet, thus deteriorating the electrical contact between the active material layer and the current collector, and further accelerating the cycle capacity decay of the battery. When (ΣF k 2 ) / (ΣD i2 ) <0.37, the overall shape of the silicon oxide particles deviates too far from the spherical shape, for example, there are more rod-shaped or sheet-shaped particles, at this time the specific surface area of the silicon oxide particles is generally greater than 1.2 m 2 / g, and there are more side reactions.

[0072] In one specific embodiment, in the active material layer B, the mixing amount of the silicon oxide particles satisfies the following formula:

[0073] 0.05 ≤ (ΣF k 2 ) / S ≤ 0.47,

[0074] wherein Σ represents the summation of the data, F k represents the circumscribed circle diameter of the silicon oxide particles with d i ≥ 4 μm, k represents the number of the silicon oxide particles, and S represents the cross-sectional area of the active material layer B in the observation area.

[0075] It is found that when the mixing amount of the silicon oxide particles satisfies the above relationship, the mass ratio of the silicon oxide particles to the active material layer B is about 5wt%-25wt%.

[0076] It is found that when the mass ratio of the silicon oxide particles is about 5wt%-25wt%, the silicon oxide particles can be uniformly dispersed between the graphite particles, and the local stress is small; when (ΣF k 2 ) / S < 0.05, the content of the silicon oxide particles is too low, and it is difficult to ensure that the lithium ion battery has high energy density; when (ΣF k 2 ) / S > 0.47, the content of the silicon oxide particles is too high, and the particle aggregation area is prone to appear, which aggravates the local expansion, the active material electrical contact is poor, and the battery fast charging performance is poor.

[0077] In the present application, the above relationship is based on the cross-sectional photo of the silicon oxide particles, the photo is the cross-sectional photo of the negative electrode sheet, the ion milling equipment can be used to cut perpendicular to the surface of the negative electrode sheet, and the scanning electron microscope (SEM) and the energy dispersive X-ray spectrometer (EDS) are used to observe the cross-section to obtain. The length of the negative electrode sheet in the observation area is ≥ 150 μm.

[0078] In the present application, the circumscribed circle represents the smallest circle that can completely contain the silicon oxide particles. The inscribed circle represents the largest circle that can be completely contained by the silicon oxide particles. The schematic diagram is shown in Figure 2 .

[0079] In one specific embodiment, the molar ratio x of O element to Si element of the silicon oxide particles satisfies 0.7≤x≤1.4, exemplarily 0.7, 0.8, 1.0, 1.2, 1.4 or any value within the range of any two of the aforementioned values. When the relationship is satisfied, the silicon oxide particles have a high specific capacity and a stable structure; when x<0.7, the silicon oxide particles have a small amount of silicate inert matrix formed after lithium intercalation and poor cycle structure stability; when x>1.4, the oxygen element content in the silicon oxide particles is too high, the irreversible reaction increases, the specific capacity of the material decreases, and it is not conducive to achieving a high energy density target.

[0080] Further, at least a part (for example, a coating rate of greater than 0 and less than or equal to 100%) of the surface of the silicon oxide particles in the active material layer B further comprises a coating layer, specifically a carbon coating layer. For example, the material in the carbon coating layer is selected from one or more of graphite, amorphous carbon, graphene, carbon nanotubes.

[0081] Further, the negative electrode active material layer further comprises other negative electrode materials. For example, the other negative electrode materials are selected from one or more of graphite, hard carbon, soft carbon materials.

[0082] Further, the negative electrode active material layer further comprises a conductive agent. For example, the conductive agent is selected from one or more of carbon black (Super P), acetylene black, Ketjen black, carbon fiber, single-walled carbon nanotubes (SWCNTs), and multi-walled carbon nanotubes (MWCNTs).

[0083] Further, the negative electrode active material layer further comprises a binder. For example, the binder is selected from one or more of carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyethylene, polyvinyl alcohol, polyvinyl chloride, polyvinyl fluoride, polyvinyl pyrrolidone, polytetrafluoroethylene, polypropylene, polyacrylic acid, butadiene-styrene rubber (SBR), and epoxy resin.

[0084] Further, the negative electrode current collector is selected from one or more of copper foil, carbon-coated copper foil, and punched copper foil.

[0085] The present application also provides a preparation method of the above negative electrode sheet, comprising:

[0086] mixing the optional other negative electrode materials, the conductive agent, and the binder to obtain a negative electrode slurry A;

[0087] mixing the silicon oxide particles, the optional other negative electrode materials, the conductive agent, and the binder to obtain a negative electrode slurry B;

[0088] The negative electrode slurry A and the negative electrode slurry B are coated on the current collector in a layered form, wherein the negative electrode slurry A is in the inner layer close to the current collector, and the negative electrode slurry B is in the outer layer away from the current collector, then dried and sliced, followed by drying, and finally rolled, cut, to obtain the negative electrode sheet.

[0089] According to the present application, the negative electrode slurry further contains a solvent. For example, the solvent is water.

[0090] According to the present application, the drying temperature is 70-90℃, and exemplary values are 70℃, 80℃, and 90℃.

[0091] According to the present application, the drying temperature is 90-110℃, and exemplary values are 90℃, 100℃, and 110℃; and the drying time is 8-24h, and exemplary values are 8h, 10h, 12h, 24h, or any value within the range of any two of the aforementioned values.

[0092] [Silicon oxide particles and preparation thereof]

[0093] The present application provides a silicon oxide particle for the above-mentioned negative electrode sheet, which at least comprises the following features:

[0094] (1) D v max≤35;

[0095] (2) 9.0≤D v 50≤13.0;

[0096] (3) BET≤1.2.

[0097] Wherein:

[0098] D v max represents the maximum particle size of the silicon oxide particle, in μm;

[0099] D v 50 represents the median particle size of the silicon oxide particle, in μm;

[0100] BET represents the specific surface area of the silicon oxide particle, in m 2 / g.

[0101] In some embodiments, the median particle size Dv50 of the silicon oxide particle satisfies: 9.0≤Dv50≤11.0.

[0102] In some embodiments, the median particle size Dv50 of the silicon oxide particle satisfies: 11.0<Dv50≤13.0.

[0103] According to the present invention, the silicon oxide particles contain Si and O elements, and the molar ratio x (mol / mol) of the O and Si elements (O / Si) satisfies 0.7 ≤ x ≤ 1.4, exemplarily 0.7, 1.0, 1.1, 1.2, 1.4 or any point within the range of the aforementioned pairwise values.

[0104] In some embodiments, the molar ratio x of O and Si elements in the silicon oxide particles satisfies: 1.0 ≤ x ≤ 1.4, for example, 1.0, 1.1, 1.2, 1.4 or any point within the range of the aforementioned pairwise values.

[0105] In some embodiments, the molar ratio x of O and Si elements in the silicon oxide particles satisfies: 0.7 ≤ x < 1.0. Examples include 0.7, 0.8, 0.9, or any value within the range of the aforementioned pairwise values.

[0106] This invention also provides a method for preparing the above-mentioned silicon oxide particles, the method comprising:

[0107] 1) Mix silicon powder and silica powder at a Si / SiO2 molar ratio of 0.33 to 3.00 to obtain a mixture;

[0108] 2) In 10 -6 ~10 -4 The mixture is reacted for 4 to 10 hours at a pressure of MPa and a temperature of 1000–1200°C to generate gas.

[0109] 3) The gas is condensed to obtain a solid;

[0110] 4) The solid is pulverized to obtain powder A;

[0111] 5) Carbon coating treatment is applied to powder A to obtain powder B;

[0112] 6) Perform particle size classification on powder B to obtain the silicon oxide particles.

[0113] According to the present invention, in step 1), the mixing can be carried out by a horizontal mixer, an air-flow mixer or a horizontal ball mill.

[0114] According to the present application, the pulverization in step 4) includes primary pulverization and secondary pulverization, the primary pulverization aims to grind the solid into powder, and the secondary pulverization aims to round the edges of the powder particles, and make the particle shape tend to be spherical. The primary pulverization can be performed by a horizontal ball mill, and the secondary pulverization can be performed by a vibration ball mill. The container material used in the primary and secondary pulverization is stainless steel, and the ball mill bead material can be stainless steel or zirconia. In the primary and secondary pulverization, the total filling volume of the solid to be pulverized and the ball mill beads is 25% to 40% of the container. In the primary pulverization, the diameter of the ball mill beads is 1 to 2 cm, the mass ratio of the solid to be pulverized to the ball mill beads is 0.05 to 0.15, the container rotation frequency is 200 to 300 rpm, and the ball milling time is 8 to 12 h. In the secondary pulverization, the diameter of the ball mill beads is 0.3 to 1 cm, the mass ratio of the solid to be pulverized to the ball mill beads is 0.3 to 0.5, the container vibration frequency is 400 to 800 rpm, and the ball milling time is 5 to 8 h.

[0115] According to the present application, in step 5), the carbon coating method includes chemical vapor deposition.

[0116] According to the present application, the step of the chemical vapor deposition method includes: performing high-temperature calcination treatment on the powder A in a carbon source gas atmosphere to obtain the powder B.

[0117] Preferably, the carbon source gas can be a mixed gas of argon / acetylene (C2H2). For example, the proportion of acetylene (C2H2) in the mixed gas is 3% to 20%, and exemplary values are 3%, 5%, 8%, 10%, 15%, 20%, or any point value within the range formed by any two of the foregoing values.

[0118] According to the present application, the mass ratio of the carbon source gas flowing per minute to the silicon oxide particles is 0.05% to 0.4%, and exemplary values are 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, or any point value within the range formed by any two of the foregoing values.

[0119] Preferably, the temperature of the high-temperature calcination treatment is 600 to 800°C, and exemplary values are 600°C, 700°C, and 800°C; the time of the high-temperature calcination treatment is 3 to 60 min, and exemplary values are 3 min, 5 min, 8 min, 10 min, 20 min, 30 min, 40 min, 50 min, and 60 min. Further, the temperature rising rate of the high-temperature calcination treatment is 5 to 15°C / min, and exemplary values are 5°C / min, 10°C / min, and 15°C / min.

[0120] Preferably, the high-temperature calcination treatment is performed in an inert gas atmosphere. For example, it is performed in a nitrogen or argon atmosphere.

[0121] According to an exemplary embodiment of the present application, the carbon-coating method comprises the following steps:

[0122] i) heating powder A to 600-800°C under argon protection;

[0123] ii) passing argon / acetylene mixed gas with C2H2 content of 3-20%, reaction time 3-60 min;

[0124] iii) naturally cooling to room temperature under argon protection to obtain powder B.

[0125] According to the present application, in step 6), the purpose of the particle size grading treatment is to obtain D v max and D v 50 satisfying the aforementioned requirements, the method used comprises airflow grading.

[0126] [Li-ion battery]

[0127] The present application also provides a Li-ion battery comprising the above negative electrode sheet.

[0128] According to the present application, after 1-5 charge-discharge cycles, the negative electrode sheet undergoes irreversible expansion, and at this time the negative electrode sheet has the following characteristics:

[0129] (1) the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer, the negative electrode active material layer is arranged on at least one surface of the negative electrode current collector, the negative electrode active material layer comprises an active material layer A and an active material layer B, the active material layer A is arranged between the current collector and the active material layer B;

[0130] the active material layer A does not contain silicon oxide particles, and the thickness L A satisfies 21 μm≤L A ≤44 μm;

[0131] the active material layer B covers the surface of the active material layer A, contains silicon oxide particles, and the thickness L B satisfies 44 μm≤L B ≤75 μm.

[0132] (2) in the cross-sectional photo of the negative electrode sheet, the silicon oxide particles satisfy the following relationship:

[0133] D i ’≤44 μm,

[0134] d i ’≤32 μm,

[0135] 0.45≤(ΣE j ’ 2) / (ΣD i 2 ) ≤ 0.75,

[0136] (ΣF k 2 ) / (ΣD i 2 ) ≥ 0.37,

[0137] 0.06 ≤ (ΣF k 2 ) / S' ≤ 0.53.

[0138] wherein Σ denotes a summation of data, D i ' denotes a circumscribed circle diameter of any silicon oxide particle, d i ' denotes an inscribed circle diameter of any silicon oxide particle, E j ' denotes a circumscribed circle diameter of silicon oxide particles having D i ' ≥ 11.2 μm, F k ' denotes a circumscribed circle diameter of silicon oxide particles having d i ' ≥ 5.0 μm, i, j, k denote the number of silicon oxide particles, and S' denotes a cross-sectional area of the active material layer B in the observation region.

[0139] According to the present application, the lithium ion battery further comprises a cathode sheet.

[0140] According to the present application, the cathode sheet comprises a cathode current collector and a cathode active material layer coated on the surface of the cathode current collector. Preferably, the cathode active material layer comprises a cathode material.

[0141] According to the present application, the current collector is selected from one or more of an aluminum foil, a carbon-coated aluminum foil, and a punched aluminum foil.

[0142] According to the present application, the cathode material is selected from one or more of lithium iron phosphate, lithium manganese phosphate, lithium vanadium phosphate, lithium iron silicate, lithium cobalt oxide (LCO), nickel cobalt manganese ternary material, nickel manganese / cobalt manganese / nickel cobalt binary material, lithium manganese oxide, and lithium-rich manganese-based material.

[0143] According to the present application, the lithium ion battery further comprises a separator. For example, the separator is selected from one or more of a polyethylene separator or a polypropylene separator.

[0144] According to the present application, the lithium ion battery further comprises an electrolyte. Preferably, the electrolyte is a non-aqueous electrolyte, which comprises a solvent and a lithium salt.

[0145] ​​​​For example, the solvent is selected from one or more of ethylene carbonate (EC), propylene carbonate (PC), propyl propionate (PP), diethyl carbonate (DEC), fluoroethylene carbonate (FEC), 1,3 propanesulfonic acid inner ester (PS), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC).

[0146] For example, the lithium salt is selected from one or more of LiPF6, LiBF4, LiSbF6, LiClO4, LiCF3SO3, LiAlO4, LiAlCl4, Li(CF3SO2)2N, LiBOB, and LiDFOB.

[0147] According to the present application, the lithium ion battery further comprises a packaging shell. For example, the packaging shell is selected from one or more of an aluminum plastic film, an aluminum shell, and a steel shell.

[0148] In the present application, the median particle size Dv50 of the silicon oxide particles can be measured by a laser particle size test method. For example, a Malvern particle size tester is used for measurement, and the test procedure is as follows: the silicon oxide particles are dispersed in deionized water containing a dispersant (such as nonylphenol polyoxyethylene ether, content ~ 0.03%wt) to form a mixture, the mixture is ultrasonically treated for 2 minutes, and then placed into the Malvern particle size tester for testing.

[0149] For the specific surface area BET of the silicon oxide particles, a BET (Brunauer-Emmett-Teller) test method can be used. For example, a Tri Star II specific surface analyzer is used for measurement.

[0150] For the molar ratio x of O element to Si element of the silicon oxide particles, an energy spectrum (EDS) analysis method can be used. For example, an Oxford energy spectrometer is used for testing.

[0151] The technical solutions of the present application will be further described in detail below in combination with specific embodiments. It should be understood that the following examples are only illustratively described and explained, and should not be interpreted as limiting the scope of protection of the present application. Any technology realized based on the above description of the present application is covered within the scope of protection intended by the present application.

[0152] Unless otherwise specified, the raw materials and reagents used in the following examples are commercially available or can be prepared by known methods.

[0153] In the following examples and comparative examples of the present application, the electrical performance test methods of the silicon oxide particles, the negative electrode sheet, and the lithium ion battery are as follows:

[0154] 1. Coin cell production and test method:

[0155] Silicon oxide particles, sodium carboxymethyl cellulose (CMC-Na), styrene butadiene rubber (SBR), carbon black (Super P), and single-walled carbon nanotubes (SWCNTs) were mixed in a mass ratio of 85:2:5.5:7:0.5, deionized water was added, and a negative electrode slurry was obtained under the action of a vacuum stirrer. The slurry was coated on a copper foil, dried at 80°C, and then sliced. The slices were then transferred to a vacuum oven at 100°C and dried for 12 h. After rolling in a dry environment, the slices were compacted to about 1.4 g / cm 3 A punching machine was then used to make round slices with a diameter of about 1.2 cm.

[0156] Under an inert atmosphere, 13 wt% of fully dried lithium hexafluorophosphate (LiPF6) and 10 wt% of fluoroethylene carbonate (FEC) were rapidly added to ethylene carbonate (EC), and stirred until uniform to obtain the desired electrolyte.

[0157] In a glove box, a coin-type battery was assembled using a lithium metal sheet as a counter electrode, a polyethylene separator, and the electrolyte.

[0158] A LAND test system was used to discharge at a current of 50 mA / g to 0.005 V, stand for 10 min, and charge at 50 mA / g to 1.5 V. The gram capacity and first efficiency of the negative electrode material were calculated.

[0159] 2. Full cell production and test method

[0160] D v 50 Graphite with a particle size of 15 μm, sodium carboxymethyl cellulose (CMC-Na), styrene butadiene rubber (SBR), and carbon black (Super P) were mixed in a mass ratio of 96.4:1.3:1.7:0.6, deionized water was added, and a negative electrode slurry A was obtained under the action of a vacuum stirrer.

[0161] Silicon oxide particles, D v 50 Graphite with a particle size of 15 μm, sodium carboxymethyl cellulose (CMC-Na), styrene butadiene rubber (SBR), carbon black (Super P), and single-walled carbon nanotubes (SWCNTs) were mixed in a mass ratio of y:(95-y):1.5:2.5:0.85:0.15, deionized water was added, and a negative electrode slurry B was obtained under the action of a vacuum stirrer.

[0162] The negative electrode slurry A was uniformly coated on a copper foil with a thickness of 6 μm, dried at 80°C, the negative electrode slurry B was uniformly coated on the copper foil, dried at 80°C, and then transferred to a vacuum oven at 100°C and dried for 12 h. The negative electrode sheet was then rolled and sliced.

[0163] Lithium cobalt oxide (LCO), polyvinylidene fluoride (PVDF), and carbon black (Super P) are mixed in a mass ratio of 96:2:2, N-methyl pyrrolidone (NMP) is added, and stirring is performed under the action of a vacuum stirrer until a uniform positive electrode slurry is obtained. The positive electrode slurry is uniformly coated on an aluminum foil with a thickness of 12 μm. The coated aluminum foil is baked in an oven and then transferred to an oven at 120°C for drying for 8 h, is rolled at a compaction density of 4.0 g / cm 3 The positive electrode tab is obtained by cutting. The size of the positive electrode tab is smaller than that of the negative electrode tab, so that lithium precipitation at the edge of the negative electrode tab is avoided. The first de-lithiation capacity per unit area of the positive electrode tab is 2% lower than the first lithium intercalation capacity per unit area of the negative electrode tab, so that the negative electrode tab has sufficient lithium storage sites and lithium precipitation of the negative electrode tab is avoided.

[0164] A mixed solution is prepared in an inert atmosphere in a mass ratio of EC:PC:PP:LiPF6:FEC:PS = 13:13:50:15:5:4, and is uniformly stirred to obtain the required electrolyte.

[0165] An 8-μm-thick polyethylene separator is selected.

[0166] A layer of lithium foil is attached to the surface of the negative electrode tab by rolling to obtain a pre-lithiated negative electrode tab. The first efficiency of the pre-lithiated negative electrode tab in the test of a button cell is 91.3% to 92.3%.

[0167] The prepared positive electrode tab, the separator, and the negative electrode tab are stacked in order, with the separator between the positive electrode tab and the negative electrode tab to play a role of isolation, and then a bare cell without electrolyte injection is obtained by winding. The bare cell is placed in an aluminum-plastic-film shell, the prepared electrolyte is injected into the dried bare cell, and the required lithium ion battery is obtained through processes such as vacuum packaging, standing, formation, shaping, and sorting.

[0168] The test steps of the lithium ion battery are as follows:

[0169] (1) A LAND test system is used, and the test temperature is 25°C.

[0170] (2) 2.0C constant-current charging is performed to 4.45V, constant-voltage charging is performed to 0.2C, the cell is allowed to stand for 10 min, 1C discharging is performed to 3.0V, the initial capacity is obtained, and the product of the initial capacity and the average discharging voltage is taken as the energy of the battery.

[0171] 2.0C constant-current charging is performed to 3.82V, constant-voltage charging is performed to 0.02C, the thickness of the battery at this time is measured, and the thickness is taken as the initial thickness of the battery. The product of the initial thickness and the length and width of the battery is taken as the initial volume of the battery, and the energy density of the battery is obtained by dividing the energy of the battery by the initial volume of the battery.

[0172] (3) 8.0C constant current charging for 2 min, standing for 10 min, 5.0C constant current charging for 3 min, standing for 10 min, 2.0C constant current charging for 5 min, standing for 10 min, 1C discharging to 3.0V, standing for 10 min, and repeating the above charging and discharging steps for 300 cycles, and taking the discharge capacity of the 300th cycle divided by the initial capacity as the capacity retention rate.

[0173] (4) 8.0C constant current charging for 2 min, standing for 10 min, 5.0C constant current charging for 3 min, standing for 10 min, 2.0C constant current charging for 5 min, disassembling the battery, and observing the degree of lithium precipitation on the surface of the negative electrode sheet.

[0174] Example

[0175] 1. Preparation and physicochemical parameters of silicon oxide particles

[0176] The preparation method of the silicon oxide particles is exemplarily given as follows:

[0177] 1) mixing silicon powder and silicon dioxide powder at a Si / SiO2 molar ratio of 0.33-3.00 to obtain a mixture;

[0178] 2) reacting the mixture at a gas pressure of 2x10 -5 MPa and a temperature of 1050℃ for 6h to generate a gas;

[0179] 3) condensing the gas to obtain a solid;

[0180] 4) crushing the solid to obtain powder A;

[0181] 5) performing carbon coating treatment on the powder A to obtain powder B;

[0182] 6) performing particle size grading treatment on the powder B to obtain the silicon oxide particles.

[0183] Wherein:

[0184] The crushing of step 4) includes primary crushing and secondary crushing. In the primary crushing, the total filling volume of the material to be crushed and the ball milling beads is 30% of the container, the diameter of the ball milling beads is 1.5 cm, the mass ratio of the material to be crushed to the ball milling beads is 0.1, and the ball milling time is 10h; in the secondary crushing, the total filling volume of the material to be crushed and the ball milling beads is 30% of the container, the diameter of the ball milling beads is 0.5 cm, the mass ratio of the material to be crushed to the ball milling beads is 0.4, and the ball milling time is 6h.

[0185] In step 5), the proportion of acetylene (C2H2) in the mixed gas is 5%, the mass ratio of the carbon source gas flowing per minute to the silicon oxide particles is 0.2%, the calcination treatment temperature is 700℃, and the calcination time is 15 min.

[0186] Table 1 gives the preparation parameters of each example and comparative example, including the Si / SiO2 molar ratio in step 1) and the vibration frequency of the ball mill in the secondary crushing in step 4). Table 1 also gives the physicochemical parameters of the silicon oxide particles of each example and comparative example, including the O / Si molar ratio x, the maximum particle size D v max, the median particle size D v 50, the specific surface area BET, the gram capacity of the silicon oxide particles and the initial activity.

[0187] In the primary crushing of examples 1-3 and comparative examples 1-5, the container rotation frequency is 250 rpm; in the primary crushing of comparative example 6, the container rotation frequency is 500 rpm.

[0188] Table 1

[0189]

[0190] The silicon oxide particles of examples 1-3 all meet the limitations of the present application, wherein:

[0191] Example 1 is the reference group; example 2 differs from example 1 in the O / Si molar ratio, example 1 is within the range of 1.0-1.4, and example 2 is within the range of 0.7-1.0; example 3 differs from example 1 in the particle size, D v 50 of example 1 is within the range of 9.0-11.0 μm, and D v 50 of example 3 is within the range of 11.0-13.0 μm.

[0192] The silicon oxide particles of comparative examples 1-6 do not completely meet the limitations of the present application, and these characteristics are indicated in the table in bold italics, wherein: the O / Si molar ratio of comparative example 1 is greater than 1.4; the O / Si molar ratio of comparative example 2 is less than 0.7; in comparative example 3, the vibration frequency of the container in the secondary crushing is too low, the crushing effect is poor, and the D v 50 of the silicon oxide particles is greater than 13.0 μm; in comparative examples 4 and 5, the vibration frequency of the container in the secondary crushing is too high, the crushing intensity is too great, and the D v 50 of the silicon oxide particles is less than 9.0 μm, and because the particle size decreases, the specific surface area increases, and the BET is greater than 1.2 m 2 / g; in comparative example 6, the rotation frequency of the container in the primary crushing is increased, and the secondary crushing step is omitted, at which time the silicon oxide particles retain more corners, and the BET is greater than 1.2 m 2 / g.

[0193] As can be seen from Table 1:

[0194] The O / Si molar ratio of the silicon oxide particles of Example 1, Example 3, Comparative Examples 3-6 is 1.12, and their gravimetric capacity and initial efficiency are similar, being 1570-1610 mAh / g and 74-75%, respectively;

[0195] The O / Si molar ratio of Comparative Example 1, Example 1, Example 2 and Comparative Example 2 decreases in turn, being 1.55, 1.12, 0.91 and 0.66, respectively, and the corresponding gravimetric capacity and initial efficiency also increase in turn, and the reason for this phenomenon is that the lower the oxygen content, the less irreversible reaction involving oxygen.

[0196] 2. Preparation of negative electrode sheet and physical property parameters

[0197] The preparation method of the negative electrode sheet of Example 4-6 and Comparative Examples 7-14 is as follows:

[0198] The silicon oxide particles, D v 50 are mixed with carboxymethyl cellulose sodium (CMC-Na), styrene-butadiene rubber (SBR) and carbon black (Super P) in a mass ratio of 96.4:1.3:1.7:0.6, deionized water is added, and a negative electrode slurry A is obtained under the action of a vacuum stirrer.

[0199] The silicon oxide particles, D v 50 are mixed with carboxymethyl cellulose sodium (CMC-Na), styrene-butadiene rubber (SBR), carbon black (Super P) and single-walled carbon nanotubes (SWCNTs) in a mass ratio of y:(95-y):1.5:2.5:0.85:0.15, deionized water is added, and a negative electrode slurry B is obtained under the action of a vacuum stirrer.

[0200] A copper foil with a thickness of 6 μm is uniformly coated with the negative electrode slurry A at a surface density of 3 mg / cm 2 , dried at 80°C, uniformly coated with the negative electrode slurry B at a surface density of 5 mg / cm 2 , dried at 80°C, then transferred to a 100°C vacuum oven for drying for 12 h, and then rolled at a compaction of 1.6 g / cm 3 , and then cut to obtain a negative electrode sheet.

[0201] Comparative Examples 15 and 16 also use the above method, with the difference being that in Comparative Example 15, the surface density of the active material layer A is 6 mg / cm 2 , and in Comparative Example 16, the surface density of the active material layer B is 8 mg / cm 2 .

[0202] The active material layer of Comparative Example 17 is a uniform composition, and the preparation method is as follows:

[0203] Silicon oxide particles, D v 50 graphite, sodium carboxymethyl cellulose (CMC-Na), styrene butadiene rubber (SBR), carbon black (Super P) and single-walled carbon nanotubes (SWCNTs) were mixed in a mass ratio of 9.5:85.5:1.5:2.5:0.85:0.15, deionized water was added, and a negative electrode slurry was obtained under the action of a vacuum stirrer.

[0204] The negative electrode slurry was uniformly coated on a copper foil with a thickness of 6 μm at a surface density of 8 mg / cm 2 , dried at 80 °C, then transferred to a vacuum oven at 100 °C for 12 h, and rolled at a compaction of 1.6 g / cm 3 , then cut to obtain negative electrode sheets.

[0205] Table 2 gives the preparation conditions of the negative electrode sheets of Examples 4-6 and Comparative Examples 7-17, including the silicon oxide particles used and their blending amount in the active material layer B, wherein the blending amount of the silicon oxide particles is obtained by the formula y / 95. Table 2 also gives the physical parameters of the negative electrode sheets, including the thickness L A of the active material layer A, the thickness L B of the active material layer B, the maximum value of the diameter D i of the circumscribed circle, the maximum value of the diameter d i of the inscribed circle, (ΣE j 2 ) / (ΣD i 2 ), (ΣF k 2 ) / (ΣD i 2 ), (ΣF k 2 ) / S.

[0206] Table 2

[0207]

[0208] The negative electrode sheets of Examples 4-6 all meet the limitations of the present application, wherein:

[0209] Example 4 is the reference group; Example 5 differs from Example 4 only in that the silicon oxide particles used have a lower O / Si molar ratio; Example 6 differs from Example 4 in that the silicon oxide particles used have a lower secondary vibration frequency in synthesis, so that D v max and D v 50 are larger, and the proportion of large particle size particles is also higher, so that the corresponding (ΣE j 2 ) / (ΣD i2 ) and (∑F k 2 ) / (∑D i 2 ) is greater.

[0210] The negative electrode sheet of Comparative Examples 7-17 cannot fully satisfy the limitations of the present application, and these characteristics are indicated in the table in bold italics. In Comparative Example 7, the O / Si molar ratio of the silicon oxide particles used is greater than 1.4; in Comparative Example 8, the O / Si molar ratio of the silicon oxide particles used is less than 0.7; in Comparative Example 9, the D i maximum value is greater than 35 pm, the d i maximum value is greater than 25 pm, (∑E j 2 ) / (∑D i 2 ) is greater than 0.75, (∑F k 2 ) / (∑D i 2 ) is less than 0.37, and comparative analysis shows that the silicon oxide particles used in this negative electrode sheet have a too low vibration frequency during the secondary crushing process, and the corners of the particles are not sufficiently ground off, thus exhibiting a large circumscribed circle diameter, and also causing the (∑F k 2 ) / (∑D i 2 ) value to relatively decrease; in Comparative Example 10, (∑E j 2 ) / (∑D i 2 ) is less than 0.45, (∑F k 2 ) / (∑D i 2 ) is less than 0.37, and the silicon oxide particles used in this negative electrode sheet have a too high vibration frequency during the secondary crushing process, and the particle size is further refined, so that the circumscribed circle and the inscribed circle related parameters cannot meet the requirements; in Comparative Example 11, (∑E j 2 ) / (∑D i 2 ), (∑F k 2 ) / (∑D i 2 ) are lower than in Comparative Example 10, which is because the silicon oxide particles used in this negative electrode sheet have a higher container vibration frequency during the secondary crushing process, and thus the silicon oxide particle size is smaller; in Comparative Example 12, (∑F k 2 ) / (∑D i 2less than 0.37 due to the fact that the silicon oxide particles used in the negative electrode sheet were subjected to particle size refinement by a single pulverization and the container rotation frequency was too high during the pulverization, and the particles retained more corners; the (ΣF k 2 ) of the negative electrode sheet in Comparative Example 13 was too low and the amount of silicon oxide particles blended was too small; the (ΣF k 2 ) of the negative electrode sheet in Comparative Example 14 was too high and the amount of silicon oxide particles blended was too much; the thickness of the active material layer A in Comparative Example 15 was greater than 40 μm; the thickness of the active material layer B in Comparative Example 16 was greater than 60 μm; and the thickness of the active material layer A in Comparative Example 17 was less than 20 μm.

[0211] 3. Preparation and physical property parameters of lithium ion batteries

[0212] The lithium ion batteries were prepared according to the aforementioned preparation method.

[0213] In the preparation of the pre-lithiated negative electrode sheet, a 5 μm thick stripe lithium foil was used, i.e. the lithium foil segments and blank segments were alternately and repeatedly distributed, and the width of the lithium foil segments and the blank segments in each example and comparative example was as follows: in Examples 7, 9, Comparative Examples 20-23 and Comparative Example 26, the width of the lithium foil segment was 0.25 cm and the width of the blank segment was 0.75 cm; in Example 8 and Comparative Example 28, the width of the lithium foil segment was 0.2 cm and the width of the blank segment was 0.8 cm; in Example 18, the width of the lithium foil segment was 0.33 cm and the width of the blank segment was 0.67 cm; in Comparative Example 19, the width of the lithium foil segment was 0.15 cm and the width of the blank segment was 0.85 cm; in Comparative Example 24, no lithium was supplemented; and in Comparative Examples 25 and 27, the width of the lithium foil segment was 0.4 cm and the width of the blank segment was 0.6 cm.

[0214] The batteries were disassembled after 2 cycles of charge and discharge according to the aforementioned cycle system to obtain the negative electrode sheet.

[0215] Table 3 shows the physical property parameters of the negative electrode sheet of the lithium ion batteries after 2 cycles in Examples 7-9 and Comparative Examples 18-28, including the thickness L A ' of the active material layer A, the thickness L B ' of the active material layer B, the maximum value of the diameter D i ' of the circumscribed circle, the maximum value of the diameter d i ' of the inscribed circle, (ΣE j ' 2 ) / (ΣD i ' 2 ), (ΣF k ' 2 ) / (ΣD i ' 2 ), and (ΣF k ' 2 ) / S.

[0216] Table 3

[0217]

[0218] The data given in Table 3 has similar conclusions as Table 2, which will not be repeated here.

[0219] 4. Performance of lithium ion batteries

[0220] Table 4 gives the energy density, capacity retention rate and lithium precipitation severity of lithium ion batteries of Examples 7-9 and Comparative Examples 18-28. When the area of lithium precipitation on the surface of the negative electrode sheet accounts for less than 5% of the total area of the negative electrode sheet, the lithium precipitation severity is low; when the area of lithium precipitation on the surface of the negative electrode sheet accounts for 5%-20% of the total area of the negative electrode sheet, the lithium precipitation severity is medium; and when the area of lithium precipitation on the surface of the negative electrode sheet accounts for more than 20% of the total area of the negative electrode sheet, the lithium precipitation severity is high.

[0221] Table 4

[0222]

[0223] As can be seen from Table 4, the negative electrodes of Examples 4-6 and the corresponding lithium ion batteries of Examples 7-9 meet the various features described in the present application, the battery energy density is greater than 600 Wh / L, the cycle capacity retention rate is greater than 80%, and the lithium precipitation severity is low; the O / Si molar ratio of the silicon oxide particles used in the negative electrode sheet of Comparative Example 7 and the lithium ion battery of Comparative Example 18 is too high, the battery energy density is less than 600 Wh / L, the cycle capacity retention rate is less than 80%, and the lithium precipitation severity is medium; the O / Si molar ratio of the silicon oxide particles used in the negative electrode sheet of Comparative Example 8 and the lithium ion battery of Comparative Example 19 is too low, the cycle capacity retention rate is less than 80%, and the lithium precipitation severity is high; the D i , d i , (ΣE j 2 ) / (ΣD i 2 ), (ΣF k 2 ) / (ΣD i 2 ) and the D i ’, d i ’, (ΣE j ’ 2 ) / (ΣD i ’ 2 ), (ΣF k ’ 2 ) / (ΣD i ’ 2) do not satisfy the limitation of the present application, the cycle capacity retention rate is less than 80%, and the lithium precipitation severity is high; the (ΣE j 2 ) / (ΣD i 2 ), (ΣF k 2 ) / (ΣD i 2 ) of the lithium ion battery of Comparative Example 21 (ΣE j ’ 2 ) / (ΣD i ’ 2 ), (ΣF k ’ 2 ) / (ΣD i ’ 2 ) do not satisfy the limitation of the present application, the cycle capacity retention rate is less than 80%, and the lithium precipitation severity is high; the (ΣE j 2 ) / (ΣD i 2 ), (ΣF k 2 ) / (ΣD i 2 ), (ΣF k 2 ) / S of the negative electrode sheet of Comparative Example 11 and the (ΣE j ’ 2 ) / (ΣD i ’ 2 ), (ΣF k ’ 2 ) / (ΣD i ’ 2 ), (ΣF k ’ 2 ) / S of the lithium ion battery of Comparative Example 22 do not satisfy the limitation of the present application, the cycle capacity retention rate is less than 80%, and the lithium precipitation severity is high; the (ΣF k 2 ) / (ΣD i 2 ) of the negative electrode sheet of Comparative Example 12 and the (ΣF k ’ 2 ) / (ΣD i ’ 2 ) of the lithium ion battery of Comparative Example 23 do not satisfy the limitation of the present application, the cycle capacity retention rate is less than 80%, and the lithium precipitation severity is medium; the (ΣF k 2 ) / S of the negative electrode sheet of Comparative Example 13 and the (ΣF k ’ 2does not satisfy the limitation of the present application, the cycle capacity retention rate is less than 80%, and the lithium precipitation severity is high; the L of the negative electrode sheet of Comparative Example 14 k 2 does not satisfy the limitation of the present application, the cycle capacity retention rate is less than 80%, and the lithium precipitation severity is high; the L of the negative electrode sheet of Comparative Example 14 k ’ 2 does not satisfy the limitation of the present application, the cycle capacity retention rate is less than 80%, and the lithium precipitation severity is high; the L of the negative electrode sheet of Comparative Example 14 A and the L of the lithium ion battery of Comparative Example 26 A does not satisfy the limitation of the present application, the initial constant current charge ratio is less than 60%, the cycle capacity retention rate is less than 80%, and the lithium precipitation severity is high; the L of the negative electrode sheet of Comparative Example 16 B and the L of the lithium ion battery of Comparative Example 27 B does not satisfy the limitation of the present application, the cycle capacity retention rate is less than 80%, and the lithium precipitation severity is high; the L of the negative electrode sheet of Comparative Example 14

[0224] The above describes the embodiments of the present application. However, the present application is not limited to the above-described embodiments. Any modification, equivalent replacement, improvement, and the like within the spirit and principle of the present application should be included in the scope of the present application.

Claims

1. A negative electrode sheet characterized by comprising: The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer, the negative electrode active material layer is arranged on at least one surface of the negative electrode current collector, the negative electrode active material layer includes an active material layer A and an active material layer B, the active material layer A is arranged between the current collector and the active material layer B; The active material layer B contains silicon oxide particles, the silicon oxide particles satisfy the following relationship: D i ≤ 35 μm (III), d i ≤ 25 μm (IV), 0.45 ≤ (ΣE j 2 ) / (ΣD i 2 ) ≤ 0.75 (V), (∑F k 2 ) / (∑D i 2 )≥0.37 (VI), wherein ∑ indicates a summation operation on the data, D i represents the diameter of the circumscribed circle of an arbitrary silicon oxide particle, d i represents the diameter of the inscribed circle of an arbitrary silicon oxide particle, E j represents D i represents the diameter of the circumscribed circle of a silicon oxide particle having a size of ≥ 9 μm, F k represents d i represents the diameter of the circumscribed circle of a silicon oxide particle having a size of ≥ 4 μm, i, j, k represent the number of the silicon oxide particles; The active material layer A does not contain silicon oxide particles; The thickness L of the active material layer A A satisfies 20 μm ≤ L A ≤ 40 μm; The thickness L of the active material layer B B satisfies 35 μm ≤ L B ≤ 60 μm; In the active material layer B, the mixed amount of silicon oxide particles satisfies the following relationship: 0.05 < (ΣF k 2 ) / S < 0.47; wherein ∑ indicates a summation process on data, F k represents a circumscribed circle diameter of a silicon oxide particle having a size of d i ≥ 4 μm, k indicates a number of the silicon oxide particles, and S indicates a cross-sectional area of the active material layer B in the observation region; The specific surface area of the silicon oxide particles in the active material layer B is less than or equal to 1.2 m2 / g 2 / g; The silicon oxide particles contain Si elements and O elements, the molar ratio x (mol / mol) of O elements to Si elements satisfies 0.7≤x≤1.

4.

2. The negative electrode sheet according to claim 1, characterized by The mass proportion of silicon oxide particles relative to the active material layer B is 5wt%-25wt%.

3. The negative electrode sheet according to any one of claims 1-2, characterized by, At least a part of the surface of the silicon oxide particles contains a coating layer.

4. The negative electrode sheet according to claim 3, characterized by The coating layer is a carbon coating layer, the material in the carbon coating layer is selected from one or more of graphite, amorphous carbon, graphene and carbon nanotube.

5. A lithium-ion battery, characterized by The lithium ion battery includes the negative electrode sheet according to any one of claims 1-4.

6. The lithium-ion battery of claim 5, wherein, After 1-5 charge-discharge cycles, the negative electrode sheet has the following characteristics: (1) The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer, the negative electrode active material layer is arranged on at least one surface of the negative electrode current collector, the negative electrode active material layer includes an active material layer A and an active material layer B, the active material layer A is arranged between the current collector and the active material layer B; The active material layer A does not contain silicon oxide particles, and has a thickness L A ’ satisfies 21 μm ≤ L A ’ ≤ 44 μm; The active material layer B contains silicon oxide particles, thickness L B ’ satisfies 44 μm ≤ L B ’ ≤ 75 μm; (2) The silicon oxide particles satisfy the following relationship: D i ≤ 44 μm, d i ≤ 32 μm, 0.45 < (ΣE j ’ / (ΣD 2 ) < 0.75, and i ’ / (ΣD 2 ) < 0.

75. (∑F k 2 ) / (∑D i 2 )≥0.37,​​ 0.06 ≤ (ΣF k ’ 2 ) / S’ ≤ 0.53, wherein ∑ indicates a summation of the data, D i ' indicates the diameter of the circumscribed circle of the arbitrary silicon oxide particle, d i ' indicates the diameter of the inscribed circle of the arbitrary silicon oxide particle, E j ' indicates the diameter of the circumscribed circle of the arbitrary silicon oxide particle, D i ' indicates the diameter of the circumscribed circle of the arbitrary silicon oxide particle, D k ' indicates the diameter of the inscribed circle of the arbitrary silicon oxide particle, E i ' indicates the diameter of the circumscribed circle of the arbitrary silicon oxide particle, D i, j, k indicate the number of the silicon oxide particle, and S' indicates the cross-sectional area of the active material layer B in the observation region.

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