A negative electrode sheet and a lithium ion battery including the same

Abstract

The present application discloses a 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; the active material layer A contains silicon oxide particles. The lithium ion battery of the present application has high constant current charge input ratio and cycle capacity retention rate under 1.5C-4.0C charging condition.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of energy storage, in particular to a 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 also been put forward for the fast-charging performance of lithium ion batteries as energy carriers. According to the porous electrode theory, the uniformity of lithium intercalation of active materials in the negative electrode sheet is related to the active materials used and the overall structure of the negative electrode sheet. Therefore, how to select appropriate negative electrode active materials and design specific negative electrode sheet structures to solve the expansion of silicon negative electrodes and cycle stability, so as to realize 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

[0003] In order to improve the above technical problems, the present application provides a negative electrode sheet and a lithium ion battery comprising the same.

[0004] In order to achieve the above-mentioned purpose, the present application realizes the following technical scheme:

[0005] A negative electrode sheet, comprising a negative electrode current collector and a negative electrode active material layer, the negative electrode active material layer being provided 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 provided between the current collector and the active material layer B;

[0006] The active material layer A contains silicon oxide particles, the silicon oxide particles satisfying the following relationship:

[0007] D i ≤ 35 μm (III),

[0008] d i ≤ 25 μm (IV),

[0009] 0.45 ≤ (ΣE j 2 ) / (ΣD i 2 ) ≤ 0.75 (V),

[0010] (ΣF k 2 ) / (ΣD i 2 ) ≥ 0.37 (VI),

[0011] wherein Σ represents summing processing of data, D i represents the circumscribed circle diameter of any silicon oxide particle, d irepresents the diameter of the inscribed circle of any silicon oxide particle, E j represents D i represents the diameter of the circumscribed circle of the silicon oxide particle with a size of ≥9 μm, F k represents d i represents the diameter of the circumscribed circle of the silicon oxide particle with a size of ≥4 μm, i, j, k represent the number of the silicon oxide particle.

[0012] According to the present application, the active material layer B does not contain silicon oxide particles.

[0013] It is found that the lithium intercalation potential of silicon oxide particles is higher than that of graphite, and sufficient lithium intercalation can still be achieved when the polarization potential is small. The polarization potential of the active material layer A is smaller than that of the active material layer B, and the concentration of silicon oxide particles in the active material layer A can effectively reduce the lithium intercalation non-uniformity of the whole electrode.

[0014] According to the present application, the thickness L A of the active material layer A satisfies 35 μm≤L A ≤60 μm.

[0015] According to the present application, the thickness L B of the active material layer B satisfies 20 μm≤L B ≤50 μm.

[0016] When the above thickness conditions are met, the uniformity of coating and the overall kinetics of the battery electrode can be ensured. When L A < 35 μm or L B < 20 μm, the electrode coating is prone to scratching and other phenomena, and the uniform distribution of active materials cannot be ensured; when L A > 60 μm or L B > 50 μm, the ohmic resistance of the electrode is large, the polarization is intensified, and the risk of lithium precipitation is increased.

[0017] According to the present application, in the active material layer A, the mixing amount of silicon oxide particles satisfies the following relationship:

[0018] 0.05≤(ΣF k 2 ) / S≤0.47;

[0019] wherein Σ represents the summation of data, F k represents d i represents the diameter of the circumscribed circle of the silicon oxide particle with a size of ≥4 μm, k represents the number of the silicon oxide particle, and S represents the cross-sectional area of the active material layer A in the observation area.

[0020] According to the present application, in the active material layer A, the specific surface area of the silicon oxide particles is less than or equal to 1.2 m 2 / g.

[0021] According to the present application, the mass ratio of the silicon oxide particles is about 5wt% to 25wt% relative to the active material layer A.

[0022] According to the present application, the silicon oxide particles contain Si element and O element, and the molar ratio x (mol / mol) of the O element to the Si element satisfies 0.7≤x≤1.4.

[0023] According to the present application, at least a part of the surface of the silicon oxide particles contains a coating layer.

[0024] The present application also provides a silicon oxide particle for the above negative electrode sheet, which at least includes the following features:

[0025] (1) D v max≤35;

[0026] (2) 9.0≤D v 50≤13.0;

[0027] (3) BET≤1.2;

[0028] wherein:

[0029] D v max represents the maximum particle size of the silicon oxide particles, and the unit is μm;

[0030] D v 50 represents the median particle size of the silicon oxide particles, and the unit is μm;

[0031] BET represents the specific surface area of the silicon oxide particles, and the unit is m 2 / g.

[0032] The present application also provides a lithium ion battery comprising the above negative electrode sheet.

[0033] According to the present application, after 1 to 5 charge-discharge cycles, the negative electrode sheet is irreversibly expanded, and at this time, the negative electrode sheet has the following features:

[0034] (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, and the active material layer A is arranged between the current collector and the active material layer B.

[0035] The active material layer A contains silicon oxide particles, and the thickness L A satisfies 44 μm≤L A ≤75 μm.

[0036] The active material layer B does not contain silicon oxide particles, and the thickness L B satisfies 21 μm ≤ L B ≤ 55 μm.

[0037] (2) The silicon oxide particles satisfy the following relationship:

[0038] D i ' ≤ 44 μm,

[0039] d i ' ≤ 32 μm,

[0040] 0.45 ≤ (ΣE j ' 2 ) / (ΣD i ' 2 ) ≤ 0.75,

[0041] (ΣF k ' 2 ) / (ΣD i ' 2 ) ≥ 0.37,

[0042] 0.06 ≤ (ΣF k ' 2 ) / S' ≤ 0.53,

[0043] wherein Σ indicates summation of data, D i ' indicates the diameter of the circumscribed circle of any silicon oxide particle, d i ' indicates the diameter of the inscribed circle of any silicon oxide particle, E j ' indicates the diameter of the circumscribed circle of the silicon oxide particle of which D i ' ≥ 11.2 μm, F k ' indicates the diameter of the circumscribed circle of the silicon oxide particle of which d i ' ≥ 5.0 μm, i, j, k indicate the number of the silicon oxide particle, and S' indicates the cross-sectional area of the negative electrode sheet in the observation region.

[0044] Advantages of the present application

[0045] 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 similar to that of the pure liquid phase. In the actual battery system, the electronic conductivity K s of the solid phase is greater than 0.1 S / cm, the ionic conductivity K l of the liquid phase is less than 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 distribution formula of the polarization potential η can be obtained:

[0046] η(x) = η0 cosh[k·(x-L)] / cosh(kL), (I)

[0047] wherein k=(p l / Z) 1 / 2 ;η 0 is the polarization potential of the outer surface of 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 unit volume electrode, L is the thickness of the active material layer of the negative electrode sheet; x is the distance along the thickness direction of the electrode sheet, with the outer surface of the active material layer as x=0 μm and the direction towards the current collector as the positive direction.

[0048] From formula (I), it can be obtained that η(x) monotonically decreases with x in the range of x∈[0, L], η(x) is the maximum value η 0 when x=0 μm, and η(x) is the minimum value 0 V when x=L. That is, the polarization of the outer surface of the active material layer is the maximum, and the polarization of the inner surface in contact with the current collector is the minimum. When the active material layer of the negative electrode sheet is a uniform component, under the condition of large-rate current charging, the lithium intercalation of the outer surface is sufficient while the lithium intercalation of the inner surface is insufficient, and the utilization rate of the whole electrode sheet is low. Therefore, along the thickness direction of the electrode sheet, reasonable component distribution design can improve the uniformity of lithium intercalation of the negative electrode sheet.

[0049] On the other hand, the silicon oxide particles have large volume change in the lithium deintercalation cycle, and the surface SEI film is continuously damaged and repaired, and the active lithium is continuously consumed. For the micron-level particles with smooth surface, the more the specific surface area increases, the more the generated SEI film is, and the more the damage and repair amount is, and then the battery cycle capacity attenuation is accelerated. Therefore, under the premise that the local strain does not cause the deformation of the electrode sheet, the particle size of the silicon oxide particles can be increased as much as possible to reduce the specific surface area of the silicon oxide particles and the consumption amount of the active lithium. However, merely increasing the particle size of the silicon oxide particles is not enough to ensure that the silicon oxide particles have a smaller specific surface area. Among all three-dimensional geometric bodies, the specific surface area of the sphere is the smallest, and the silicon oxide particles are usually formed by crushing bulk bodies, and contain various irregular shapes such as rods, sheets and polyhedrons, which leads to a larger specific surface area. Therefore, controlling the shape of the silicon oxide particles can alleviate the expansion of the silicon negative electrode, thereby further adjusting the cycle performance of the negative electrode sheet and the lithium ion battery.

[0050] Therefore, the present application provides a negative electrode sheet and a lithium ion battery based on the negative electrode sheet, which has high constant current charge input ratio and cycle capacity retention rate under the condition of 1.5C-4.0C charging. BRIEF DESCRIPTION OF DRAWINGS

[0051] Figure 1 is a schematic diagram of the cross section of the negative electrode sheet of the present application. In the figure, 11 represents the silicon oxide particles, 12 represents the active material layer, 13 represents the current collector, and LA L represents the thickness of the active material layer A. B This indicates the thickness of the active material layer B.

[0052] Figure 2 This is a schematic diagram of the circumcircle and incircle of the silicon oxide particles in this invention. Detailed Implementation

[0053] [Negative electrode sheet and its preparation]

[0054] As mentioned above, the present invention provides a negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a negative electrode active material layer, the negative electrode active material layer being disposed 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 disposed between the current collector and the active material layer B;

[0055] The active material layer A contains silicon oxide particles, and the silicon oxide particles satisfy the following relationship:

[0056] D i ≤35μm (III),

[0057] d i ≤25μm (IV),

[0058] 0.45≤(ΣE j 2 ) / (ΣD i 2 )≤0.75 (V),

[0059] (ΣF k 2 ) / (ΣD i 2 )≥0.37 (VI),

[0060] Where Σ represents the summation of the data, and D i d represents the circumcircle diameter of any silicon oxide particle. i E represents the diameter of the inscribed circle of any silicon oxide particle. j D represents i The outer circle diameter of silicon oxide particles ≥9μm, F k d i The outer circle diameter of silicon oxide particles ≥4μm, i, j, k represent the particle numbers of silicon oxide particles, and S represents the cross-sectional area of ​​active material layer A in the observation area.

[0061] In one specific embodiment, the thickness L of the active material layer A is... A Satisfying 35μm≤L A ≤60μm;

[0062] The active material layer B does not contain silicon oxide particles, and the thickness L B satisfies 20 μm ≤ L B ≤ 50 μm.

[0063] The present application limits the particle size of the silicon oxide particles in the negative electrode sheet by the relations (III) and (IV). When the above conditions are satisfied, the silicon oxide particles have a moderate particle size, and the volume change thereof during the cycle process 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 the cycle process is large, which can cause excessive stress in the local area, and the active material layer has the risk of bulging, thus deteriorating the electrical contact between the active material layer and the current collector, and further accelerating the cycle capacity decay of the battery.

[0064] The present application not only limits the particle size distribution of the silicon oxide particles, but also limits the shape of the 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 thereof 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. Therefore, the present application unexpectedly found that when the size of the circumscribed circle of the cross section shape of the silicon oxide particles is constant, the diameter of the inscribed circle must be large enough, and in this 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 satisfied, 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, and in this 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 conventional silicon oxide is generally greater than 1.2 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 2When (ΣF k 2 ) / (ΣD i 2 < 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 < 2 / g, and there are more side reactions.

[0065] In one specific embodiment, the blending amount of the silicon oxide particles satisfies the following relationship: 0.05≤(ΣF k 2 ) / S≤0.47, wherein Σ, F k , k and S are defined as above.

[0066] It is found that when the blending amount of the silicon oxide particles satisfies the above relationship, the mass ratio of the silicon oxide particles to the active material layer A is about 5wt%-25wt%.

[0067] It is found that when the mass ratio of the silicon oxide particles is about 5wt%-25wt%, the silicon oxide particles can be more uniformly dispersed between the graphite particles, and the local stress is smaller; when (ΣF k 2 ) / S<0.05, the content of the silicon oxide particles is too low 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, which is easy to cause particle aggregation area, aggravate local expansion, and cause poor electrical contact of the active material and fast capacity attenuation of the battery.

[0068] 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 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 ≥150μm.

[0069] 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 in the silicon oxide particles. The schematic diagram is shown as Figure 2

[0070] ​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. Exemplary values are 0.7, 0.8, 1.0, 1.2, 1.4 or any value within the range of any two of the aforementioned values. When this relationship is satisfied, the silicon oxide particles have a high specific capacity and a stable structure; when x<0.7, the silicon oxide particles form a silicate inert matrix after intercalating lithium, and the cycle structure stability is poor; when x>1.4, the oxygen element content in the silicon oxide particles is too high, the irreversible reaction increases, the material specific capacity decreases, and it is not conducive to achieving a high energy density target.

[0071] According to the present application, at least a portion of the surface of the silicon oxide particles (for example, the coating rate is greater than 0 and less than or equal to 100%) in the active material layer A 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.

[0072] According to the present application, 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.

[0073] According to the present application, 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).

[0074] 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, styrene butadiene rubber (SBR), and epoxy resin.

[0075] Further, the negative electrode current collector is selected from one or more of copper foil, carbon-coated copper foil, and punched copper foil.

[0076] The present application also provides a preparation method of the above-mentioned negative electrode sheet, comprising:

[0077] Mixing the silicon oxide particles, the optional other negative electrode materials, the conductive agent, and the binder to obtain a negative electrode slurry A;

[0078] Mixing the optional other negative electrode materials, the conductive agent, and the binder to obtain a negative electrode slurry B;

[0079] 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.

[0080] According to the present application, the negative electrode slurry further contains a solvent.

[0081] According to the present application, the drying temperature is 70-90℃, exemplarily 70℃, 80℃, 90℃.

[0082] According to the present application, the drying temperature is 90-110℃, exemplarily 90℃, 100℃, 110℃; and the drying time is 8-24h, exemplarily 8h, 10h, 12h, 24h or any value within the range of any two of the aforementioned values.

[0083] [Silicon oxide particles and preparation thereof]

[0084] The present application provides a silicon oxide particle for the above-mentioned negative electrode sheet, which at least comprises the following features:

[0085] (1) D v max≤35;

[0086] (2) 9.0≤D v 50≤13.0;

[0087] (3) BET≤1.2.

[0088] Wherein:

[0089] D v max represents the maximum particle size of the silicon oxide particle, in μm;

[0090] D v 50 represents the median particle size of the silicon oxide particle, in μm;

[0091] BET represents the specific surface area of the silicon oxide particle, in m 2 / g.

[0092] In some embodiments, the median particle size Dv50 of the silicon oxide particle satisfies: 9.0≤Dv50≤11.0.

[0093] In some embodiments, the median particle size Dv50 of the silicon oxide particle satisfies: 11.0<Dv50≤13.0.

[0094] According to the present application, the silicon oxide particles contain Si element and O element, the molar ratio x (mol / mol) of the O element and Si element (O / Si) satisfies 0.7≤x≤1.4, exemplarily 0.7, 1.0, 1.1, 1.2, 1.4 or any value within the range consisting of any two of the aforementioned values.

[0095] In some embodiments, the molar ratio x of the O element and Si element of the silicon oxide particles satisfies: 1.0≤x≤1.4, exemplarily 1.0, 1.1, 1.2, 1.4 or any value within the range consisting of any two of the aforementioned values.

[0096] In some embodiments, the molar ratio x of the O element and Si element of the silicon oxide particles satisfies: 0.7≤x<1.0. Exemplarily 0.7, 0.8, 0.9 or any value within the range consisting of any two of the aforementioned values.

[0097] The present application also provides a preparation method of the above-mentioned silicon oxide particles, the method comprising:

[0098] 1) mixing silicon powder and silicon dioxide powder at a Si / SiO2 molar ratio of 0.33-3.00 to obtain a mixture;

[0099] 2) reacting the mixture at a gas pressure of 10 -6 ~10 -4 MPa and a temperature of 1000-1200℃ for 4-10h to generate a gas;

[0100] 3) condensing the gas to obtain a solid;

[0101] 4) crushing the solid to obtain a powder A;

[0102] 5) performing carbon coating treatment on the powder A to obtain a powder B;

[0103] 6) performing particle size grading treatment on the powder B to obtain the silicon oxide particles.

[0104] According to the present application, in step 1), the mixing can be performed by a horizontal stirrer, an air flow mixer or a horizontal ball mill.

[0105] 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 particles 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 material of the container used in the primary and secondary pulverization is stainless steel, and the material of the ball milling beads 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 milling beads is 25% to 40% of the container. In the primary pulverization, the diameter of the ball milling beads is 1 to 2 cm, the mass ratio of the solid to be pulverized to the ball milling beads is 0.05 to 0.15, the rotation frequency of the container is 200 to 300 rpm, and the ball milling time is 8 to 12 hours. In the secondary pulverization, the diameter of the ball milling beads is 0.3 to 1 cm, the mass ratio of the solid to be pulverized to the ball milling beads is 0.3 to 0.5, the vibration frequency of the container is 400 to 800 rpm, and the ball milling time is 5 to 8 hours.

[0106] According to the present application, in step 5), the carbon coating method includes chemical vapor deposition.

[0107] According to the present application, the steps of the chemical vapor deposition method include: performing high-temperature calcination treatment on the powder A in a carbon source gas atmosphere to obtain the powder B.

[0108] 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.

[0109] 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.

[0110] 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 minutes, and exemplary values are 3 minutes, 5 minutes, 8 minutes, 10 minutes, 20 minutes, 30 minutes, 40 minutes, 50 minutes, and 60 minutes. Further, the heating 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.

[0111] Preferably, the high-temperature calcination treatment is performed in an inert gas atmosphere. For example, it is performed in a nitrogen or argon atmosphere.

[0112] According to an exemplary embodiment of the present application, the carbon-coating method comprises the following steps:

[0113] i) heating powder A to 600-800°C under argon protection;

[0114] ii) introducing argon / acetylene mixed gas with C2H2 content of 3-20%, and the reaction time is 3-60 min;

[0115] iii) naturally cooling to room temperature under argon protection to obtain powder B.

[0116] According to the present application, in step 6), the purpose of the particle size grading treatment is to obtain D v maxand D v 50 satisfying the aforementioned requirements, and the method used comprises airflow grading.

[0117] [lithium ion battery]

[0118] The present application also provides a lithium ion battery comprising the above negative electrode sheet.

[0119] 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:

[0120] (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, and the active material layer A is arranged between the current collector and the active material layer B;

[0121] the active material layer A contains silicon oxide particles, and the thickness L A satisfies 44 μm≤L A ≤75 μm;

[0122] the active material layer B does not contain silicon oxide particles, and the thickness L B satisfies 21 μm≤L B ≤55 μm.

[0123] (2) the silicon oxide particles satisfy the following relationship:

[0124] D i ’≤44 μm,

[0125] d i ’≤32 μm,

[0126] 0.45≤(ΣE j ’ 2 ) / (ΣD i ’2 )≤0.75,

[0127] (ΣF k ’ 2 ) / (ΣD i ’ 2 )≥0.37,

[0128] 0.06≤(ΣF k ’ 2 ) / S’≤0.53.

[0129] wherein ∑ denotes a summation over the data, D i ’ denotes the diameter of the circumscribed circle of an arbitrary silicon oxide particle, d i ’ denotes the diameter of the inscribed circle of an arbitrary silicon oxide particle, E j ’ denotes the diameter of the circumscribed circle of a silicon oxide particle having a diameter d i ’ ≥ 11.2 pm, F k ’ denotes the diameter of the circumscribed circle of a silicon oxide particle having a diameter d i ’ ≥ 5.0 pm, i, j, k denote the number of the silicon oxide particles, and S’ denotes the cross-sectional area of the active material layer A in the observation region.

[0130] According to the present application, the lithium-ion battery further comprises a positive electrode sheet.

[0131] According to the present application, the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer coated on the surface of the positive electrode current collector. Preferably, the positive electrode active material layer comprises a positive electrode material.

[0132] 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.

[0133] According to the present application, the positive electrode 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.

[0134] 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.

[0135] 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.

[0136] 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).

[0137] 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.

[0138] 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.

[0139] In the present application, for the median particle size Dv50 of the silicon oxide particles, a laser particle size testing method can be used. For example, a Malvern particle size tester is used for measurement, and the testing 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.

[0140] For the specific surface area BET of the silicon oxide particles, a BET (Brunauer-Emmett-Teller) testing method can be used. For example, a Tri Star II specific surface analyzer is used for measurement.

[0141] 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.

[0142] 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.

[0143] Unless otherwise specified, the raw materials and reagents used in the following examples are commercially available or can be prepared by known methods.

[0144] In the following examples and comparative examples of the present application, the electrical performance testing methods of the silicon oxide particles, the negative electrode sheet, and the lithium ion battery are as follows:

[0145] 1. Coin cell production and testing method:

[0146] 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 100°C vacuum oven for drying 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.

[0147] Under an inert atmosphere, 13 wt% of fully dried lithium hexafluorophosphate (LiPF6) and 10 wt% of fluoroethylene carbonate (FEC) were quickly added to ethylene carbonate (EC), and stirred until uniform to obtain the required electrolyte.

[0148] 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.

[0149] 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.

[0150] 2. Full battery production and test method

[0151] Silicon oxide particles, D v 50, 15 μm 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 y:(95-y):1.5:2.5:0.85:0.15, deionized water was added, and a negative electrode slurry A was obtained under the action of a vacuum stirrer.

[0152] D v 50, 15 μm graphite, 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 B was obtained under the action of a vacuum stirrer.

[0153] 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, dried at 80°C, and then transferred to a 100°C vacuum oven for drying for 12 h. The negative electrode sheet was then rolled and cut.

[0154] 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 , and is then cut to obtain the desired positive electrode tab. 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 of the negative electrode tab, and sufficient lithium storage sites are ensured for the negative electrode tab to avoid lithium precipitation.

[0155] 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 desired electrolyte.

[0156] An 8-μm-thick polyethylene separator is selected.

[0157] 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, and the first efficiency of the pre-lithiated negative electrode tab in the coin cell test is 91.5% to 92.3%.

[0158] The prepared positive electrode tab, separator, and 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 desired lithium ion battery is obtained through processes such as vacuum packaging, standing, formation, shaping, and sorting.

[0159] The test steps of the lithium ion battery are as follows:

[0160] (1) A LAND test system is used, and the test temperature is 25°C.

[0161] (2) 3.0C constant-current charging is performed to 4.45V to obtain a constant-current charging capacity Q C1 , constant-voltage charging is performed to 0.2C to obtain a constant-voltage capacity Q C2 , standing is performed for 10 min, 1C discharging is performed to 3.0V to obtain an initial capacity, the initial constant-current charge ratio is Q C1 / (Q C1 + Q C2 ), and the product of the initial capacity and the average discharging voltage is the energy of the battery.

[0162] Charged at 3.0C constant current to 3.82V, charged at constant voltage to 0.02C, measured the thickness of the battery at this time, which is the initial thickness of the battery. The initial volume of the battery is the product of the initial thickness and length, width of the battery, and the energy density of the battery is the energy of the battery divided by the initial volume of the battery.

[0163] (3) Charged at 3.0C constant current to 4.45V, charged at constant voltage to 0.2C, rested for 10min, discharged at 1C to 3.0V, rested for 10min, cycled for 500 times with this charge and discharge steps, and the capacity retention rate is the discharge capacity of the 500th cycle divided by the initial capacity.

[0164] (4) Charged at 3.0C constant current to 4.45V, obtained the constant current section charge capacity Q C3 , charged at constant voltage to 0.2C, obtained the constant voltage section capacity Q C4 , rested for 10min, discharged at 1C to 3.0V, and the final constant current charge ratio is Q C3 / (Q C3 +Q C4 ).

[0165] Example

[0166] 1. Preparation and physicochemical parameters of silicon oxide particles

[0167] The following exemplary preparation method of silicon oxide particles is given:

[0168] 1) Mix silicon powder and silicon dioxide powder with Si / SiO2 molar ratio of 0.33-3.00 to obtain a mixture;

[0169] 2) React the mixture under a gas pressure of 2x10 -5 MPa and a temperature of 1050℃ for 6h to generate a gas;

[0170] 3) Condense the gas to obtain a solid;

[0171] 4) Crush the solid to obtain a powder A;

[0172] 5) Carbon-coated treatment is performed on the powder A to obtain a powder B;

[0173] 6) Particle size grading treatment is performed on the powder B to obtain the silicon oxide particles.

[0174] Wherein:

[0175] 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 10 h; 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 6 h.

[0176] 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°C, and the calcination time is 15 min.

[0177] 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 of step 4). Table 1-1 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 efficiency.

[0178] 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.

[0179] Table 1

[0180]

[0181] The silicon oxide particles of examples 1-3 all meet the limitations of the present application, wherein:

[0182] Example 1 is the reference group; the difference between example 2 and example 1 is 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; the difference between example 3 and example 1 is the particle size, the D v 50 of example 1 is within the range of 9.0-11.0 μm, and the D v 50 of example 3 is within the range of 11.0-13.0 μm.

[0183] 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 v50 more than 13.0 μm; in Comparative Examples 4 and 5, the vibration frequency of the container was too high and the crushing strength was too great in the secondary crushing, so the D v 50 less than 9.0 μm, and because the particle size was reduced, the specific surface area was increased, and the BET was more than 1.2 m 2 / g; in Comparative Example 6, the rotation frequency of the container was increased in the primary crushing, and the secondary crushing step was omitted, so the silicon oxide particles retained more corners, and the BET was more than 1.2 m 2 / g.

[0184] As can be seen from Table 1:

[0185] The O / Si molar ratios of the silicon oxide particles of Example 1, Example 3, and Comparative Examples 3 to 6 were all 1.12, and their gravimetric capacities and initial efficiencies were similar, at 1570 to 1610 mAh / g and 74% to 75%, respectively.

[0186] The O / Si molar ratios of Comparative Example 1, Example 1, Example 2, and Comparative Example 2 were 1.55, 1.12, 0.91, and 0.66, respectively, and the gravimetric capacities and initial efficiencies also increased in that order, and the reason for this phenomenon was that the lower the oxygen content, the fewer irreversible reactions involving oxygen.

[0187] 2. Preparation of the negative electrode sheet and physical property parameters

[0188] The following gives the preparation method of the negative electrode sheet of Example 4 to 6 and Comparative Examples 7 to 14:

[0189] The 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 A was obtained under the action of a vacuum stirrer.

[0190] The 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 B was obtained under the action of a vacuum stirrer.

[0191] A copper foil with a thickness of 6 μm was uniformly coated with the negative electrode slurry A at a surface density of 5 mg / cm 2 and dried at 80°C, and a negative electrode slurry B was uniformly coated on a copper foil with a thickness of 6 μm at a surface density of 5 mg / cm 2of 1.6 g / cm2, and then cut into pieces to obtain the negative electrode sheet. 3

[0192] Comparative Examples 15 and 16 were also prepared by the above method, except that in Comparative Example 15, the areal density of the active material layer A was 8.5 mg / cm2 2 ; and in Comparative Example 16, the areal density of the active material layer B was 8 mg / cm2 2 .

[0193] The active material layer of Comparative Example 17 was a uniform composition, and was prepared as follows:

[0194] Silicon oxide particles, D v 50 graphite having 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 9.5:85.5:1.5:2.5:0.85:0.15, and deionized water was added to obtain a negative electrode slurry under the action of a vacuum stirrer.

[0195] A negative electrode slurry was uniformly coated on a copper foil having a thickness of 6 μm at an areal density of 1.6 g / cm2 2 , dried at 80°C, and then transferred to a vacuum oven at 100°C for 12 h, rolled at a compaction of 1.6 g / cm2 3 , and then cut into pieces to obtain the negative electrode sheet.

[0196] Table 2 shows the preparation conditions of the negative electrode sheets of Examples 4 to 6 and Comparative Examples 7 to 17, including the silicon oxide particles used and the amount of the silicon oxide particles mixed in the active material layer A, wherein the amount of the silicon oxide particles mixed in is obtained by the formula y / 95. Table 2 also shows the physical properties 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 ), and (ΣF k 2 ) / S.

[0197] Table 2

[0198] ​

[0199] The negative electrode sheet of each of Examples 4 to 6 satisfies the limitation of the present application, wherein:

[0200] Example 4 is the reference group; Example 5 differs from Example 4 only in that the silicon oxide particles used therein have a lower O / Si molar ratio; and Example 6 differs from Example 4 in that the silicon oxide particles used therein have a lower secondary vibration frequency in the synthesis, and thus D v maxand D v 50are larger, and the proportion of large-particle-size particles is also higher, and thus the corresponding (ΣE j 2 ) / (ΣD i 2 ) and (ΣF k 2 ) / (ΣD i 2 ) are larger.

[0201] The negative electrode sheet of each of Comparative Examples 7 to 17 does not completely satisfy the limitation of the present application (these characteristics are indicated in Table 2 in bold italics), wherein: the O / Si molar ratio of the silicon oxide particles used in Comparative Example 7 is greater than 1.4; the O / Si molar ratio of the silicon oxide particles used in Comparative Example 8 is less than 0.7; the D i maxof the negative electrode sheet in Comparative Example 9 is greater than 35 μm, the d i maxis greater than 25 μm, (ΣE j 2 ) / (ΣD i 2 ) is greater than 0.75, (ΣF k 2 ) / (ΣD i 2 ) is less than 0.37, and comparative analysis shows that the silicon oxide particles used in the negative electrode sheet have a too low vibration frequency in the secondary pulverization process, and the corners of the particles have not been sufficiently ground off, and thus exhibit a large circumscribed circle diameter, and also cause the (ΣF k 2 ) / (ΣD i 2 ) value to relatively decrease; the (ΣE j 2 ) / (ΣD i 2 ) of the negative electrode sheet in Comparative Example 10 is less than 0.45, the (ΣF k 2 ) / (ΣD i 2The vibration frequency of the silicon oxide particles used in the negative electrode is too high during the secondary crushing process, and the particle size is further refined, so that the relevant parameters of the circumscribed circle and the inscribed circle cannot meet the requirements; the (ΣE) of the negative electrode in Comparative Example 11 is less than 0.37. j 2 ) / (ΣD i 2 ), (ΣF k 2 ) / (ΣD i 2 The difference in particle size between the negative electrode and Comparative Example 10 is lower because the silicon oxide particles used in this negative electrode undergo a higher vibration frequency during the secondary crushing process, resulting in smaller particle size. The negative electrode in Comparative Example 12 has a lower (ΣF) particle size. k 2 ) / (ΣD i 2 The value is less than 0.37 because the silicon oxide particles used in this negative electrode were only fined by single-stage grinding, and the rotation frequency of the container during grinding was too high, resulting in the particles retaining more sharp edges; in Comparative Example 13, the negative electrode (ΣF) k 2 The ΣF / S ratio is too low, indicating insufficient silicon oxide particle doping; in Comparative Example 14, the negative electrode's (ΣF) ratio is too low. k 2 The ratio of ) / S is too high, indicating an excessive amount of silicon oxide particles mixed in; in Comparative Example 15, the thickness of active material layer A is greater than 60 μm; in Comparative Example 16, the thickness of active material layer B is greater than 50 μm; and in Comparative Example 17, the thickness of active material layer B is less than 20 μm.

[0202] 3. Preparation and physical properties of lithium-ion batteries

[0203] The lithium-ion battery was obtained according to the aforementioned preparation method.

[0204] In the preparation of the pre-lithiated negative electrode, a 5μm thick striped lithium foil was used, i.e., lithium foil segments and blank segments were alternately and repeatedly distributed. The widths of the lithium foil segments and blank segments in each example and comparative example are as follows: Example 7, Example 9, Comparative Examples 20-23 and Comparative Example 28, lithium foil segment width 0.25cm, blank segment width 0.75cm; Example 8 and Comparative Example 27, lithium foil segment width 0.2cm, blank segment width 0.8cm; Comparative Example 18, lithium foil segment width 0.33cm, blank segment width 0.67cm; Comparative Example 19, lithium foil segment width 0.15cm, blank segment width 0.85cm; Comparative Example 24, no lithium replenishment; Comparative Example 25, lithium foil segment width 0.4cm, blank segment width 0.6cm; Comparative Example 26, lithium foil segment width 0.45cm, blank segment width 0.55cm.

[0205] According to the aforementioned cycle system, the battery was disassembled to obtain the negative electrode sheet after 2 charge-discharge cycles.

[0206] Table 3 shows the physical property parameters of the negative electrode sheet of the lithium ion battery after 2 cycles of Examples 7-9 and Comparative Examples 18-28, including the thickness L of the active material layer A A , the thickness L of the active material layer B B , the maximum value of the diameter D of the circumscribed circle i , the maximum value of the diameter d of the inscribed circle i , (ΣE j / 2 ) / (ΣD i / 2 ), (ΣF k / 2 ) / (ΣD i / 2 ), (ΣF k / 2 ) / S.

[0207] Table 3

[0208]

[0209] The data in Table 3 has similar conclusions as Table 2, which will not be repeated here.

[0210] 4. Performance of lithium ion battery

[0211] Table 4 shows the energy density, initial constant current charge ratio, capacity retention rate and final constant current charge ratio of the lithium ion battery of Examples 7-9 and Comparative Examples 18-28.

[0212] Table 4

[0213]

[0214] As can be seen from Table 4, the negative electrode of Examples 4-6 and the corresponding lithium ion battery of Examples 7-9 meet the characteristics described in the present application, the battery energy density is greater than 700 Wh / L, the initial constant current charge ratio is greater than 60%, the cycle capacity retention rate is greater than 80%, and the final constant current charge ratio is greater than 30%; 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, and the battery energy density is less than 700 Wh / L; 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 final constant current charge ratio is less than 30%; the D i , d i , (ΣE j 2 ) / (ΣD i2 ), (ΣF k 2 ) / (ΣD i 2 ) and Comparative Example 20's lithium-ion battery D i '、d i '、(ΣE j ' 2 ) / (ΣD i ' 2 ), (ΣF k ' 2 ) / (ΣD i ' 2 None of these meet the limitations of this invention: the cycle capacity retention rate is less than 80%, and the final constant current charge ratio is less than 30%; the negative electrode of Comparative Example 10 (ΣE) j 2 ) / (ΣD i 2 ), (ΣF k 2 ) / (ΣD i 2 ) and Comparative Example 21's lithium-ion battery (ΣE) j ' 2 ) / (ΣD i ' 2 ), (ΣF k ' 2 ) / (ΣD i ' 2 None of these meet the limitations of this invention: the cycle capacity retention rate is less than 80%, and the final constant current charge ratio is less than 30%; the negative electrode of Comparative Example 11 (ΣE) j 2 ) / (ΣD i 2 ), (ΣF k 2 ) / (ΣD i 2 ), (ΣF k 2 (ΣE) / S and Comparative Example 22's lithium-ion battery j ' 2 ) / (ΣD i ' 2 ), (ΣF k ' 2 ) / (ΣD i ' 2 ), (ΣF k ' 2 Neither (ΣF) nor S meets the limitations of this invention; the cycle capacity retention rate is less than 80%, and the final constant current charge ratio is less than 30%; the negative electrode of Comparative Example 12 has (ΣF) k2 ) / (ΣD i 2 ) and the lithium ion battery of Comparative Example 23 (ΣF k ’ 2 ) / (ΣD i ’ 2 ) does not satisfy the limitation of the present application, the cycle capacity retention rate is less than 80%, and the final constant current charge ratio is less than 30%; (ΣF k 2 ) / S of the negative electrode sheet of Comparative Example 13 and (ΣF k ’ 2 ) / S of the lithium ion battery of Comparative Example 24 do not satisfy the limitation of the present application, the battery energy density is lower than 700 Wh / L, the initial constant current charge ratio is less than 60%, the cycle capacity retention rate is less than 80%, and the final constant current charge ratio is less than 30%; (ΣF k 2 ) / S of the negative electrode sheet of Comparative Example 14 and (ΣF k ’ 2 ) / S of the lithium ion battery of Comparative Example 25 do not satisfy the limitation of the present application, the cycle capacity retention rate is less than 80%, and the final constant current charge ratio is less than 30%; L A of the negative electrode sheet of Comparative Example 15 and L A ’ of the lithium ion battery of Comparative Example 26 do 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 final constant current charge ratio is less than 30%; L B of the negative electrode sheet of Comparative Example 16 and L B ’ of the lithium ion battery of Comparative Example 27 do 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 final constant current charge ratio is less than 30%; the silicon oxide particles of the negative electrode sheets of Comparative Example 17 and Comparative Example 28 are uniformly distributed in the active material layer, do not satisfy the limitation of the present application, the battery energy density is lower than 700 Wh / L, the initial constant current charge ratio is less than 60%, the cycle capacity retention rate is less than 80%, and the final constant current charge ratio is less than 30%.

[0215] The above describes 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 made within the spirit and principle of the present application should be included in the scope of protection of the present application.

Claims

1. A negative electrode sheet, characterized in that, The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer. The negative electrode active material layer is disposed 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 disposed between the current collector and the active material layer B. The active material layer A contains silicon oxide particles, and the silicon oxide particles satisfy the following relationship: D i ≤35μm (III), d i ≤25μm (IV), 0.45≤(ΣE j 2 ) / (ΣD i 2 )≤0.75 (V), (ΣF k 2 ) / (ΣD i 2 )≥0.37 (VI), Where Σ represents the summation of the data, and D i d represents the circumcircle diameter of any silicon oxide particle. i E represents the diameter of the inscribed circle of any silicon oxide particle. j D represents i The outer circle diameter of silicon oxide particles ≥9μm, F k d i The outer circle diameter of silicon oxide particles ≥4μm, where i, j, and k represent the particle number. The thickness L of the active material layer A A Satisfying 35μm≤L A ≤60μm; The active material layer B does not contain silicon oxide particles; The thickness L of the active material layer B B Satisfying 20μm≤L B ≤50μm; In the active material layer A, the amount of silicon oxide particles mixed satisfies the following relationship: 0.05≤(ΣF k 2 ) / S≤0.47; Where Σ represents the summation of the data, F k d i The circumscribed circle diameter of silicon oxide particles ≥4 μm, k represents the particle number, and S represents the cross-sectional area of ​​active material layer A in the observation region; the specific surface area of ​​silicon oxide particles in active material layer A is less than or equal to 1.2 m². 2 / g; The silicon oxide particles contain Si and O elements, and the molar ratio x (mol / mol) of O to Si elements satisfies 0.7 ≤ x ≤ 1.

4.

2. The negative electrode sheet according to claim 1, characterized in that, The mass percentage of silicon oxide particles relative to the active material layer A is 5wt%~25wt%.

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

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

5. A lithium-ion battery, characterized in that, The lithium-ion battery includes the negative electrode sheet as described in any one of claims 1-4.

6. The lithium-ion battery according to claim 5, characterized in that, After 1 to 5 charge-discharge cycles, the negative electrode of the lithium-ion battery has the following characteristics: (1) The negative electrode sheet includes a negative current collector and a negative active material layer. The negative active material layer is disposed on at least one surface of the negative current collector. The negative active material layer includes an active material layer A and an active material layer B. The active material layer A is disposed between the current collector and the active material layer B. The active material layer A contains silicon oxide particles and has a thickness of L. A 'Satisfies 44μm≤L A ≤75μm; The active material layer B contains no silicon oxide particles and has a thickness of L. B 'Satisfies 21μm≤L B ≤55μm; (2) The silicon oxide particles satisfy the following relationship: D i ’≤44μm, d i ’≤32μm, 0.45≤(ΣE j ' 2 ) / (ΣD i ' 2 )≤0.75, (S.F. k ' 2 ) / (ΣD i ' 2 )≥0.37, 0.06≤(ΣF k ' 2 ) / S'≤0.53, Where Σ represents the summation of the data, and D i ' represents the circumcircle diameter of any silicon oxide particle, d i ' represents the diameter of the inscribed circle of any silicon oxide particle, E j ' indicates D i 'The circumcircle diameter of silicon oxide particles ≥11.2μm, F k ' indicates d i 'The circumscribed circle diameter of silicon oxide particles ≥5.0μm, i, j, k represent the particle numbers of silicon oxide particles, and S' represents the cross-sectional area of ​​the active material layer A in the observation region.

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