Negative pole piece of lithium ion battery, preparation method of negative pole piece, lithium ion battery and electric equipment

Abstract

The invention discloses a negative pole piece of a lithium ion battery, a preparation method of the negative pole piece, the lithium ion battery and electric equipment, and belongs to the technical field of new energy. The negative electrode comprises a current collector and active coatings attached to two opposite surfaces of the current collector, the active coating is a composite active coating; the composite active coating comprises a first active coating and a second active coating; the first active coating is attached to the surface of the current collector, and the second active coating is attached to the surface, away from the current collector, of the first active coating; an active material in the first active coating is a first carbon material; an active material in the second active coating is a second carbon material; the graphitization degree of the first carbon material is G1, the graphitization degree of the second carbon material is G2, and G1 and G2 meet the relational expression I: G1 > G2. The negative pole piece disclosed by the invention has quick charge performance, long cycle performance and high energy density, and the overall comprehensive performance of the battery is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of new energy, in particular to a lithium ion battery negative electrode and a preparation method thereof, a lithium ion battery and an electric device. BACKGROUND

[0002] Lithium ion batteries have been widely used in electric vehicles and energy storage stations due to their high specific energy, green safety and other advantages. However, there are currently fast charging and life anxiety. Improving the fast charging and cycle life of lithium ion batteries has become a hot spot and urgent need for the development of lithium ion batteries.

[0003] Currently, artificial graphite is mainly used as the negative electrode material of lithium ion batteries in the industry. Artificial graphite has approached ideal graphite, and high-graphitized artificial graphite (ideal graphite) has many deficiencies in practical application. For example, the kinetics is poor, the cycle life is short, and the comprehensive performance is not ideal. SUMMARY

[0004] The main purpose of the present application is to provide a lithium ion battery negative electrode and a preparation method thereof, a lithium ion battery and an electric device, to solve the problem that the fast charging performance, cycle performance and energy density of the graphite negative electrode material cannot be considered simultaneously in the prior art.

[0005] In order to achieve the above-mentioned purpose, according to one aspect of the present application, a lithium ion battery negative electrode is provided, the negative electrode includes a current collector and an active coating attached to the two opposite surfaces of the current collector; the active coating is a composite active coating; the composite active coating includes a first active coating and a second active coating; the first active coating is attached to the surface of the current collector, and the second active coating is attached to the surface of the first active coating away from the current collector.

[0006] Among them, the active material in the first active coating includes a first carbon material, and the graphitization degree of the first carbon material is G1; the active material in the second active coating includes a second carbon material, and the graphitization degree of the second carbon material is G2, and G1 and G2 satisfy the relationship formula I: G1 > G2.

[0007] Further, in the relationship formula I, G1-G2=5%~20%.

[0008] Further, in the relationship formula I, G1-G2=8%~12%.

[0009] Further, the numerical range of G1 is: 90%≤G1≤100%.

[0010] Further, the numerical range of G2 is: 80%≤G2<90%.

[0011] Further, the first carbon material is a mixed material of a first carbon material A and a first carbon material B; wherein the graphitization degree of the first carbon material A is G 1A, the graphitization degree of the first carbon material B is G 1B ; and G 1A has a numerical range of 90%≤G 1A ≤95%; G 1B has a numerical range of 95%<G 1B ≤100%.

[0012] Further, the weight ratio of the first carbon material A and the first carbon material B is 1:(1-9).

[0013] Further, the weight ratio of the first carbon material A and the first carbon material B is 1:(3-7).

[0014] Further, the second carbon material is a mixed material of a second carbon material A and a second carbon material B; wherein the graphitization degree of the second carbon material A is G 2A , the graphitization degree of the second carbon material B is G 2B ; and G 2A has a numerical range of 80%≤G 2A ≤85%; G 2B has a numerical range of 85%<G 2B <90%.

[0015] Further, the weight ratio of the second carbon material A and the second carbon material B is 1:(1-9).

[0016] Further, the weight ratio of the second carbon material A and the second carbon material B is 1:(4-8).

[0017] Further, the first carbon material and the second carbon material respectively satisfy at least one of the following conditions: Condition 1: La=40-400nm, La is the average size of the a-axis direction of the crystal grain;

[0018] Condition 2: Lc=10-200nm, Lc is the average size of the c-axis direction of the crystal grain;

[0019] Condition 3: OI=1.5-30, OI is the powder orientation index;

[0020] Condition 4: ID / IG≥0.04, ID / IG is the powder disorder degree;

[0021] Condition 5: D50=0.5-25μm, D50 is the powder volume distribution median particle size;

[0022] Condition 6: K90≤5, K90 is the powder particle size distribution width, K90=(D90-D10) / D50;

[0023] Condition 7: 0.5m 2 / g≤BET≤3m 2 / g, BET is the specific surface area.

[0024] Further, the first carbon material has at least one of conditions 1 to 7; wherein, condition 1: La = 80-300 nm, condition 2: Lc = 40-150 nm, condition 3: OI = 2-10, condition 4: ID / IG≥0.10, condition 5: D50 = 6-15 μm, condition 6: K90≤2, condition 7: 1.0 m 2 / g≤BET≤2.0 m 2 / g.

[0025] Further, the second carbon material has at least one of conditions 1 to 7; wherein, condition 1: La = 40-200 nm, condition 2: Lc = 20-120 nm, condition 3: OI = 5-25, condition 4: ID / IG≥0.15, condition 5: D50 = 5-15 μm, condition 6: K90≤2, condition 7: 1.0 m 2 / g≤BET≤2.5 m 2 / g.

[0026] Further, the first carbon material and the second carbon material are respectively graphite.

[0027] Further, the current collector is a copper foil.

[0028] Further, the negative electrode tab has at least one of conditions 8 to 10; wherein, condition 8: the active coating porosity is 8%-50%; condition 9: the tab area density is 50-300 g / m 2 ; condition 10: the tab full charge expansion rate is≤25%.

[0029] Further, the porosity of the first active coating is 8-50%.

[0030] Further, the porosity of the second active coating is 12-35%.

[0031] Further, the thickness of the first active coating is 30-100 μm.

[0032] Further, the thickness of the second active coating is 20-80 μm.

[0033] Further, the weight percentage content of the first carbon material in the first active coating is 95%-99%.

[0034] Further, the weight percentage content of the second carbon material in the second active coating is 95%-98%.

[0035] According to a second aspect of the present application, a preparation method of the above lithium ion battery negative electrode is provided, comprising the following steps:

[0036] coating the first active slurry on two opposite surfaces of the current collector respectively to form a first active coating layer;

[0037] coating the second active slurry on the surface of the first active coating layer to form a second active coating layer;

[0038] wherein the first active slurry comprises a first carbon material with a graphitization degree G1; the second active slurry comprises a second carbon material with a graphitization degree G2; G1 and G2 satisfy the relationship I: G1>G2.

[0039] Further, in the relationship I, G1-G2=5%~20%.

[0040] Further, in the relationship I, G1-G2=8%~12%.

[0041] Further, the numerical range of G1 is: 90%≤G1≤100%.

[0042] Further, the numerical range of G2 is: 80%≤G2<90%.

[0043] Further, the first carbon material is a mixed material of a first carbon material A and a first carbon material B; wherein the graphitization degree of the first carbon material A is G 1A , the graphitization degree of the first carbon material B is G 1B ; and the numerical range of G 1A is: 90%≤G 1A ≤95%; the numerical range of G 1B is: 95%<G 1A ≤100%.

[0044] Further, the weight ratio of the first carbon material A and the first carbon material B is 1:(1~9).

[0045] Further, the weight ratio of the first carbon material A and the first carbon material B is 1:(3~7).

[0046] Further, the second carbon material is a mixed material of a second carbon material A and a second carbon material B; wherein the graphitization degree of the second carbon material A is G 2A , the graphitization degree of the second carbon material B is G 2B ; and the numerical range of G 2A is: 80%≤G 2A ≤85%; the numerical range of G 2B is: 85%<G 2A <90%.

[0047] Further, the weight ratio of the second carbon material A and the second carbon material B is 1:(1~9).

[0048] Further, the weight ratio of the second carbon material A and the second carbon material B is 1:(4-8).

[0049] Further, the first active slurry comprises a first carbon material, a first conductive agent and a first binder.

[0050] Further, the weight ratio of the first carbon material, the first conductive agent and the first binder is (95-99):(0.1-5.0):(0.1-6.0).

[0051] Further, the second active slurry comprises a second carbon material, a second conductive agent and a second binder.

[0052] Further, the weight ratio of the second carbon material, the second conductive agent and the second binder is (95-98):(0.1-5.0):(0.1-6.0).

[0053] Further, the viscosity of the first active slurry is 1000-8000 mPa·s.

[0054] Further, the viscosity of the second active slurry is 2000-10000 mPa·s.

[0055] Further, the first carbon material and the second carbon material are both graphite.

[0056] Further, the current collector is a copper foil.

[0057] According to a third aspect of the present application, a lithium ion battery is provided, comprising a positive electrode, a negative electrode, a separator and an electrolyte; the negative electrode is the lithium ion battery negative electrode or the lithium ion battery negative electrode prepared by the preparation method of the lithium ion battery negative electrode.

[0058] According to a fourth aspect of the present application, an electrical equipment is provided, comprising a battery; the battery is the lithium ion battery.

[0059] Compared with the prior art, the present application has the following technical effects:

[0060] The lithium ion battery negative electrode and the preparation method thereof, the lithium ion battery and the electrical equipment provided by the present application have the following advantages: the negative electrode active coating is designed as a double-layer gradient graphitization degree carbon material, and the graphitization degree gradually decreases from the first active coating (high graphitization degree) close to the current collector to the second active coating (low graphitization degree) far from the current collector; the low graphitization degree carbon material on the outside has good stability in the process of deintercalating lithium, can improve the long cycle performance of the battery, has a fast lithium ion diffusion speed, can obviously improve the fast charging performance of the battery, has small expansion in the process of charging and discharging, and can improve the safety; the high graphitization degree carbon material on the inside ensures that the battery has high energy density, and thus both fast charging performance and long cycle performance are considered, and the comprehensive performance of the battery is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] The drawings that constitute part of this application are used to provide a further understanding of this application. The illustrative embodiments of this application and their descriptions are used to explain this application and do not constitute an improper limitation on this application. In the drawings:

[0062] Figure 1 Schematic diagram of the interlayer spacing structure of highly graphitized carbon provided in the embodiment of the present application;

[0063] Figure 2 Schematic diagram of the interlayer spacing structure of low-graphitization carbon provided in the embodiment of the present application;

[0064] Figure 3 Schematic diagram of the negative electrode structure of a lithium-ion battery prepared in an embodiment of the present application.

[0065] Reference numerals:

[0066] 1. Current collector; 2. First active coating; 3. Second active coating; 4. Composite active coating; d002, spacing between adjacent carbon layers. DETAILED DESCRIPTION

[0067] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0068] As mentioned in the background art, existing lithium-ion batteries have defects such as poor dynamics, short cycle life, and inability to simultaneously take into account comprehensive performance such as energy density.

[0069] In order to solve the above problems, according to one aspect of the present application, a lithium-ion battery negative electrode plate is provided, the negative electrode plate comprising a current collector 1 and an active coating attached to two opposite surfaces of the current collector 1; the active coating is a composite active coating 4; the composite active coating 4 comprises a first active coating 2 and a second active coating 3; the first active coating 2 is attached to the surface of the current collector 1, and the second active coating 3 is attached to the surface of the first active coating 2 away from the current collector 1; wherein, the active material in the first active coating 2 comprises a first carbon material; the active material in the second active coating 3 comprises a second carbon material; the degree of graphitization of the first carbon material is G1, the degree of graphitization of the second carbon material is G2, and G1 and G2 satisfy the relationship I: G1>G2.

[0070] The present application designs the negative electrode active coating as a double-layer and gradient graphitized carbon material, and the graphitization degree gradually decreases from the first active coating 2 (containing a high-graphitized carbon material) close to the current collector to the second active coating 3 (containing a low-graphitized carbon material) far away from the current collector; the high-graphitized carbon material has a smaller interlayer spacing, and the carbon layers are closely arranged, such asFigure 1 As shown in d002, the carbon layer structure has an excellent energy density, for example, it can reach 200 to 400Wh / kg. Low graphitization carbon materials have a wide interlayer spacing, such as Figure 2 As shown in d002, it is beneficial to the lithium ion intercalation and deintercalation performance; the design of the above-mentioned double-layer and gradient graphitization carbon material can also make the porosity of the negative electrode increase from the coating close to the current collector to the coating far away from the current collector. The larger the porosity, the more conducive to the transmission and diffusion of lithium ions; the second active coating with low graphitization is set in the outermost layer. Since the porosity of this layer is larger and it is the first to contact with the electrolyte, it makes it easier for lithium ions to enter the negative electrode carbon material for lithium intercalation and deintercalation, and the lithium ion diffusion rate is fast, which can significantly improve the battery fast charging performance, for example, the fast charging time can be less than 20 minutes; improve the long-term cycle performance of the battery, and the capacity decays to 80% and can be cycled 10,000 times; and the battery expands little during charging and discharging, and the material structure has good stability, which can improve safety; through the design of a double-layer and first high and then low gradient graphitization carbon material, it can not only improve the battery fast charging and long cycle performance but also take into account high energy density, thereby improving the overall comprehensive performance of the battery.

[0071] In some embodiments, in equation I, G1-G2 = 5% to 20%; for example, any value among 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, or any range therebetween; specifically, 8% to 12%, further 9% to 11%, and further still 10%. By sequentially controlling the difference between the high degree of graphitization of the first active coating 2 and the low degree of graphitization of the second active coating 3 within the aforementioned ranges, the battery negative electrode can be gradually improved to simultaneously achieve high energy density, long cycle life, and fast charging performance.

[0072] In some embodiments, the numerical range of G1 is: 90% ≤ G1 ≤ 100%; as a high degree of graphitization, its numerical value is any value among 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, or a range between any two thereof; specifically, 92% to 98%, further 93% to 98%, for example, 96%. The numerical range of G2 is: 80% ≤ G2 < 90%; as a low degree of graphitization, its numerical value is any value among 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, or a range between any two thereof; specifically, 80% to 88%, further 83% to 88%, for example, 86%. By controlling the value ranges of G1 and G2 respectively within the above ranges, it can gradually be more conducive to the battery negative electrode having comprehensive performance such as high energy density, long cycle and fast charging, and the two coated carbon material structures can achieve a good connection and transition, ensuring the performance and structural stability of the battery negative electrode.

[0073] In some embodiments, the first carbon material is a mixed material of the first carbon material A and the first carbon material B; wherein the graphitization degree of the first carbon material A is G 1A , the graphitization degree of the first carbon material B is G 1B ; and the value range of G 1A is 90%≤G 1A ≤95%; for example, any value of 90%, 91%, 92%, 93%, 94%, 95% or a range value between any two of them; the value range of G 1B is 95%<G 1A ≤100%; for example, any value of 95.5%, 96%, 97%, 98%, 99%, 100% or a range value between any two of them. By mixing the carbon materials in two parts according to the graphitization degree of the first carbon material, the continuity and synergy of the carbon material performance from the first active coating to the second active coating are facilitated, and the stability of the battery anode structure and performance is ensured.

[0074] In some embodiments, the weight ratio of the first carbon material A and the first carbon material B is 1:(1-9); specifically, any value of 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9 or a range value between any two of them; for example, 1:(2-8), and further for example, 1:(3-7), and further 1:(4-6). By controlling the amount of the two carbon materials according to the above ratio, the continuity of the anode carbon material structure is further ensured, and the battery anode has good stable energy density, long cycle and fast charging performance.

[0075] In some embodiments, the second carbon material is a mixed material of the second carbon material A and the second carbon material B; wherein the graphitization degree of the second carbon material A is G 2A , the graphitization degree of the second carbon material B is G 2B ; and the value range of G 2A is 80%≤G 2A ≤85%; specifically, any value of 80%, 81%, 82%, 83%, 84%, 85% or a range value between any two of them; the value range of G 2B is 85%<G 2A <90%; specifically, any value of 85.5%, 86%, 87%, 88%, 89% or a range value between any two of them. By mixing the carbon materials in two parts according to the graphitization degree of the second carbon material, the continuity and synergy of the carbon material performance from the second active coating to the first active coating are facilitated, and the stability of the battery anode performance and structure is ensured.

[0076] In some embodiments, the weight ratio of the second carbon material A and the second carbon material B is 1:(1-9); specifically any value or a range value between any two values selected from 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, and 1:9; for example, 1:(2-8), further for example, 1:(3-8), further 1:(4-8), further 1:(4-6). By controlling the amount of the two carbon materials in the above-mentioned ratio, the continuity of the negative electrode carbon material structure is further ensured, which is beneficial to the battery negative electrode having good stable energy density, long cycle, and fast charging performance.

[0077] In some embodiments, the first carbon material and the second carbon material respectively satisfy one of the following conditions:

[0078] Condition 1: La=40-400nm, La is the average size of the a-axis direction of the crystal grain;

[0079] Condition 2: Lc=10-200nm, Lc is the average size of the c-axis direction of the crystal grain;

[0080] Condition 3: OI=1.5-30, OI is the powder orientation index;

[0081] Condition 4: ID / IG≥0.04, ID / IG is the powder disorder degree;

[0082] Condition 5: D50=0.5-25μm, D50 is the powder volume distribution median particle size;

[0083] Condition 6: K90≤5, K90 is the powder particle size distribution width, K90=(D90-D10) / D50;

[0084] Condition 7: 0.5m 2 / g≤BET≤3m 2 / g, BET is the specific surface area.

[0085] The above technical solution includes: the first carbon material has any one or two or more of the above conditions 1 to 7; or, the second carbon material has any one or two or more of the above conditions 1 to 7; or, the first carbon material has all of the conditions 1 to 7; or, the second carbon material has all of the conditions 1 to 7; or, the first carbon material and the second carbon material both have all of the conditions 1 to 7. The above two carbon materials have the above conditions, and the multiple conditions synergistically make the carbon material have good energy density, long cycle, and fast charging performance.

[0086] In some embodiments, the first carbon material has at least one of conditions 1 to 7; condition 1: La = 80-300 nm, condition 2: Lc = 40-150 nm, condition 3: OI = 2-10, condition 4: ID / IG≥0.1, condition 5: D50 = 6-15 μm, condition 6: K90≤2, condition 7: 1.0 m 2 / g≤BET≤2 m 2 / g. By controlling the grain structure parameters or powder conditions of the carbon material at different positions, the above conditions of the carbon material are targeted to play their respective roles; for example, by controlling the grain structure parameters or powder conditions of the first carbon material within the above ranges, it is more conducive to achieve good energy density.

[0087] In some embodiments, the second carbon material has at least one of conditions 1 to 7; condition 1: La = 40-200 nm, condition 2: Lc = 20-120 nm, condition 3: OI = 5-25, condition 4: ID / IG≥0.15, condition 5: D50 = 5-15 μm, condition 6: K90≤2, condition 7: 1.0 m 2 / g≤BET≤2.5 m 2 / g. By controlling the grain structure parameters or powder conditions of the second carbon material within the above ranges, it is more conducive to achieve good fast charging and long cycle performance.

[0088] In some embodiments, the first carbon material and the second carbon material are graphite; for example, artificial graphite; and the current collector is a copper foil. By selecting this type of graphite, it is easy to control the degree of graphitization, and the material itself has good electrical properties.

[0089] In some embodiments, the negative electrode tab has at least one of conditions 8 to 10; wherein, condition 8: the porosity of the active coating is 8%-50%, further 19-30%; condition 9: the areal density of the tab is 50-300 g / m 2 , further 200-260 g / m 2 ; condition 10: the full charge expansion rate of the tab is ≤25%, and the full charge expansion rate of the tab is: (the thickness of the graphite fully embedded with lithium - the thickness of the tab after rolling) / the thickness of the tab after rolling x 100%. By controlling the physical structure parameters of the negative electrode tab within the above ranges, the negative electrode tab has good electrical conductivity, energy density, long cycle performance, fast charging performance, and structural stability.

[0090] In some embodiments, the porosity of the first active coating is 8-50%; and the porosity of the second active coating is 12-35%. By precisely controlling the porosities of the inner and outer coatings, the overall porosity of the negative electrode coating has continuity, and is conducive to lithium ion diffusion and transmission, ensuring high energy density and structural stability.

[0091] In some embodiments, the thickness of the first active coating is 30-100 μm, for example any value or a range value between any two values of 30, 40, 50, 60, 70, 80, 90, 100 μm; the thickness of the second active coating is 20-80 μm, for example any value or a range value between any two values of 20, 30, 40, 50, 60, 70, 80 μm. By precisely controlling the thickness of the inner and outer coatings, in combination with the porosity of the inner and outer layers, the different conditions of the carbon materials, and the multi-faceted synergy, the overall negative electrode coating has good continuity in microstructure and good continuity in electrochemical performance, which is conducive to improving the high energy density, continuous lithium ion diffusion capacity, structural stability, and the like of the battery negative electrode.

[0092] In some embodiments, the weight percentage content of the first carbon material in the first active coating is 95%-99%; the weight percentage content of the second carbon material in the second active coating is 95%-98%. By precisely controlling the content of the two carbon materials in different coatings, the first active coating and the second active coating can each have respective functions, and the functions of the two layers have good synergy, which promotes the overall electrode negative electrode to have high energy density, fast charging, long cycle performance, and structural stability.

[0093] According to a second aspect of the present application, a preparation method of the above lithium ion battery negative electrode is provided, comprising the following steps:

[0094] The first active slurry is coated on two opposite surfaces of the current collector 1 to form a first active coating 2;

[0095] The second active slurry is coated on the surface of the first active coating 2 to form a second active coating 3;

[0096] The first active slurry comprises a first carbon material, and the graphitization degree of the first carbon material is G1; the second active slurry comprises a second carbon material, and the graphitization degree of the second carbon material is G2; G1 and G2 satisfy the relationship G1>G2.

[0097] The double-layer coating method of the present application can be selected from the prior art; when coating, the first active slurry is first coated on the opposite first surface and second surface of the current collector, then the second active slurry is continuously coated on the surface of the first active coating on the two surfaces, and finally dried to form a negative electrode sheet.

[0098] In some embodiments, G1 is 5% to 20% greater than G2. Controlling the difference in the graphitization degree of the two carbon materials within the above range is conducive to significantly improving the high energy density, long cycle and fast charging performance of the battery anode. Further, the numerical range of G1 is 90%≤G1≤100%. The numerical range of G2 is 80%≤G2<90%. Controlling the graphitization degree of the two carbon materials within the above different ranges; more conducive to the battery anode to balance high energy density, long cycle and fast charging performance.

[0099] In some embodiments, the first carbon material is a mixed material of the first carbon material A and the first carbon material B; wherein the graphitization degree of the first carbon material A is G 1A , the graphitization degree of the first carbon material B is G 1B ; and the numerical range of G 1A is 90%≤G 1A ≤95%; the numerical range of G 1B is 95%<G 1A ≤100%. The second carbon material is a mixed material of the second carbon material A and the second carbon material B; wherein the graphitization degree of the second carbon material A is G 2A , the graphitization degree of the second carbon material B is G 2B ; and the numerical range of G 2A is 80%≤G 2A ≤85%; the numerical range of G 2B is 85%<G 2A <90%. Further, the weight ratio of the first carbon material A and the first carbon material B is 1:(1-9); for example 1:(3-7); further, the weight ratio of the second carbon material A and the second carbon material B is 1:(1-9); for example 1:(4-8). By using the above mixing method, the continuity between the two coatings in structure and performance can be realized, which is conducive to the stability of the anode structure and performance.

[0100] In some embodiments, the first active slurry includes a first carbon material, a first conductive agent and a first binder; the weight ratio of the first carbon material, the first conductive agent and the first binder is (95-99):(0.1-5.0):(0.1-6.0). The second active slurry includes a second carbon material, a second conductive agent and a second binder; the weight ratio of the second carbon material, the second conductive agent and the second binder is (95-98):(0.1-5.0):(0.1-6.0). The weight ratio of the first active slurry and the second active slurry is 1:1. The viscosity of the first active slurry is 1000-8000 mPa·s, and the viscosity of the second active slurry is 2000-10000 mPa·s; by controlling the content of the two carbon materials, the active coating formed respectively has different effects, such as the first active coating mainly has high energy density, and the second active coating mainly has long cycle and fast charging performance.

[0101] According to a third aspect of the present application, a lithium ion battery is provided, comprising a positive electrode, a negative electrode, a separator and an electrolyte; the negative electrode is the lithium ion battery negative electrode or the lithium ion battery negative electrode prepared by the preparation method of the lithium ion battery negative electrode.

[0102] In some embodiments, the active material of the positive electrode is one or a mixture of more than one of lithium iron phosphate, lithium manganese iron phosphate or nickel-cobalt-manganese ternary system; the separator is a separator based on a polyethylene or polypropylene base material; and the electrolyte is composed of a solvent and a lithium salt.

[0103] In some embodiments, the lithium ion battery further comprises a structural assembly which can be matched according to the battery structure; for example, the square battery is an aluminum shell + cover plate structure, the cylindrical battery is an aluminum shell or steel shell structure, and the soft package battery is an aluminum plastic film structure.

[0104] According to a fourth aspect of the present application, a power consuming device is provided, comprising a battery; the battery is the lithium ion battery.

[0105] In some embodiments, the power consuming device comprises an electric vehicle, a communication device, an energy storage base station, etc.

[0106] The present application will be further described in detail below in combination with specific embodiments, which cannot be understood as limiting the scope of the present application.

[0107] The preparation method of the graphite in the embodiments of the present application is as follows: the graphite powder is filled into a graphite crucible and the powder is compacted; the graphite crucible is placed in a medium frequency induction furnace, argon gas is introduced, and the gas flow is 50 mL / min; after the gas is introduced for 5 h, the temperature rising rate of the medium frequency furnace is set to 10 ℃ / min, and the highest temperature is set to 3000 ℃; when the temperature reaches 3000 ℃, constant temperature is started, and natural cooling to room temperature is performed after the constant temperature ends, i.e. the preparation of the graphite is completed; wherein the constant temperature time is different for different graphitization degrees of the graphite.

[0108] The graphitization degree and constant temperature time of the graphite material used in the embodiments of the present application correspond to: graphitization degree 100%: 60 h; graphitization degree 98%: 50 h; graphitization degree 96%: 40 h; graphitization degree 95%: 37 h; graphitization degree 93%: 34 h; graphitization degree 90%: 30 h; graphitization degree 89%: 28 h; graphitization degree 87%: 26 h; graphitization degree 86%: 23 h; graphitization degree 85%: 20 h; graphitization degree 83%: 17 h; graphitization degree 80%: 15 h; and graphitization degree 70%: constant temperature time 10 h.

[0109] The X-ray diffractometer (XRD) is used to detect the graphitization degree G, La, Lc and OI of the graphite; the Raman spectrometer is used to detect the ID / IG of the graphite; the Malvern 3000 laser particle size analyzer is used to detect the D50 and K90 of the graphite; and the Micromeritics surface area tester is used to detect the BET of the graphite.

[0110] Example 1

[0111] Step S1: Mix graphite 1A (G 1A = 93%) and graphite 1B (G 1B = 98%) in a weight ratio of 1:5 to form mixed graphite I;

[0112] wherein the graphite 1A and the graphite 1B have the following conditions: La(A) = 220 nm, La(B) = 280 nm, Lc(A) = 110 nm, Lc(B) = 140 nm, OI(A) = 5.0, OI(B) = 8.0, ID / IG(A) = 0.13, ID / IG(B) = 0.17, D50(A) = 12 μm, D50(B) = 10 μm, K90(A) = 1.4, K90(B) = 1.6, BET(A) = 1.7, and BET(B) = 1.9.

[0113] Step S2: Mix the mixed graphite I of step S1, carbon black, SBR (butadiene-styrene copolymer) and CMC (carboxymethyl cellulose) in water in a weight ratio of 97:2:0.5:0.5 to form a first active slurry, and the viscosity is 5400 mPa·s.

[0114] Step S3: Mix graphite A2 (G 2A = 83%) and graphite B2 (G 2B = 87%) in a weight ratio of 1:5 to form mixed graphite II;

[0115] wherein the graphite A2 and the graphite B2 have the following conditions: La(A) = 140 nm, La(B) = 180 nm, Lc(A) = 90 nm, Lc(B) = 100 nm, OI(A) = 12.0, OI(B) = 18.0, ID / IG(A) = 0.25, ID / IG(B) = 0.36, D50(A) = 13 μm, D50(B) = 8 μm, K90(A) = 1.4, K90(B) = 1.7, BET(A) = 1.7, and BET(B) = 1.9.

[0116] Step S4: Mix the mixed graphite II of step S3, carbon black, SBR (butadiene-styrene copolymer) and CMC (carboxymethyl cellulose) in water in a weight ratio of 97:2:0.5:0.5 to form a second active slurry, and the viscosity is 6700 mPa·s.

[0117] Step S5: The first active slurry is coated on the opposite first surface and second surface of the current collector 1 (copper foil) respectively to form the first active coating layer 2 with a thickness of 38 μm; and then the second active slurry is further coated on the surface of the first active coating layer 2 on both sides to form the second active coating layer 3 with a thickness of 26 μm; the first active coating layer 2 and the second active coating layer 3 form the composite active coating layer 4; and finally dried to form the negative electrode sheet, the structure of which is shown in Figure 3 .

[0118] Example 2

[0119] Step S1: The graphite A1 (G 1A = 90%) and the graphite B1 (G 1B = 96%) are mixed in a weight ratio of 1:1 to form the mixed graphite I;

[0120] wherein the graphite A1 and the graphite B1 have the following conditions: La(A) = 270 nm, La(B) = 210 nm, Lc(A) = 145 nm, Lc(B) = 104 nm, OI(A) = 3.0, OI(B) = 9.0, ID / IG(A) = 0.18, ID / IG(B) = 0.19, D50(A) = 12 μm, D50(B) = 10 μm, K90(A) = 1.4, K90(B) = 1.6, BET(A) = 1.4, BET(B) = 2.0;

[0121] Step S2: The mixed graphite I of Step S1, carbon black, SBR (butadiene-styrene copolymer) and CMC (carboxymethyl cellulose) are mixed in a weight ratio of 97:2:0.5:0.5 in water to form the first active slurry with a viscosity of 5200 mPa·s;

[0122] Step S3: The graphite A2 (G 2A = 80%) and the graphite B2 (G 2B = 86%) are mixed in a weight ratio of 1:1 to form the mixed graphite II;

[0123] wherein the graphite A2 and the graphite B2 have the following physical properties: La(A) = 170 nm, La(B) = 145 nm, Lc(A) = 107 nm, Lc(B) = 96 nm, OI(A) = 10.0, OI(B) = 17.0, ID / IG(A) = 0.28, ID / IG(B) = 0.33, D50(A) = 13 μm, D50(B) = 8 μm, K90(A) = 1.3, K90(B) = 1.9, BET(A) = 1.4, BET(B) = 1.7;

[0124] Step S4: mixing the mixed graphite II, carbon black, SBR (butadiene-styrene copolymer) and CMC (carboxymethyl cellulose) in water according to a weight ratio of 97:2:0.5:05 of step S3 to form a second active slurry, and the viscosity is 7100 mPa·s;

[0125] Step S5: coating the first active slurry on the first surface and the second surface of the current collector 1 (copper foil) respectively to form a first active coating layer 2 with a thickness of 50 μm; then coating the second active slurry on the surface of the first active coating layer 2 on both sides to form a second active coating layer 3 with a thickness of 50 μm; the first active coating layer 2 and the second active coating layer 3 form a composite active coating layer 4; finally, drying to form a negative electrode sheet, and the structure is as shown in Figure 3

[0126] Example 3

[0127] Step S1: mixing graphite A1 (G 1A = 95%) and graphite B1 (G 1B = 100%) according to a weight ratio of 1:9 to form mixed graphite I;

[0128] wherein graphite A1 and graphite B1 have the following conditions: La(A) = 230 nm, La(B) = 290 nm, Lc(A) = 109 nm, Lc(B) = 147 nm, OI(A) = 4.1, OI(B) = 9.5, ID / IG(A) = 0.12, ID / IG(B) = 0.14, D50(A) = 12 μm, D50(B) = 10 μm, K90(A) = 1.4, K90(B) = 1.6, BET(A) = 1.4, BET(B) = 2.0;

[0129] Step S2: mixing the mixed graphite I of step S1, carbon black, SBR (butadiene-styrene copolymer) and CMC (carboxymethyl cellulose) in water according to a weight ratio of 97:2:0.5:05 to form a first active slurry, and the viscosity is 5900;

[0130] Step S3: mixing graphite A2 (G 2A = 85%) and graphite B2 (G 2B = 89%) according to a weight ratio of 1:9 to form mixed graphite II;

[0131] ​Wherein, the graphite A2 and the graphite B2 have the following physical conditions: La(A)=177 nm, La(B)=190 nm, Lc(A)=109 nm, Lc(B)=115 nm, OI(A)=13.0, OI(B)=21.0, ID / IG(A)=0.29, ID / IG(B)=0.35, D50(A)=13 μm, D50(B)=8 μm, K90(A)=1.3, K90(B)=1.9, BET(A)=1.4, BET(B)=1.7;

[0132] Step S4: mixing the mixed graphite II, carbon black, SBR (butadiene-styrene copolymer) and CMC (carboxymethyl cellulose) in water according to the weight ratio of 97:2:0.5:05 in step S3 to form a second active slurry, and the viscosity is 7500 mPa·s;

[0133] The first active slurry is coated on the first surface and the second surface of the current collector 1 (copper foil) respectively to form a first active coating layer 2 with a thickness of 100 μm; then the second active slurry is further coated on the surface of the first active coating layer 2 on both sides to form a second active coating layer 3 with a thickness of 80 μm; the first active coating layer 2 and the second active coating layer 3 form a composite active coating layer 4; finally, drying forms a negative electrode sheet, and the structure is as shown in Figure 3 .

[0134] Example 4

[0135] The difference between Example 4 and Example 1 is that the weight ratio of the graphite A1 (G 1A =93%) and the graphite B1 (G 1B =98%) in step S1 is 1:3.

[0136] Example 5

[0137] The difference between Example 4 and Example 1 is that the weight ratio of the graphite A1 (G 1A =93%) and the graphite B1 (G 1B =98%) in step S1 is 1:7.

[0138] Example 6

[0139] The difference between Example 6 and Example 1 is that the weight ratio of the graphite A2 (G 2A =83%) and the graphite B2 (G 2B =87%) in step S3 is 1:4.

[0140] Example 7

[0141] The difference between Example 7 and Example 1 is that the weight ratio of the graphite A2 (G 2A= 83%) and graphite B2 (G 2B = 87%) in a weight ratio of 1 :8.

[0142] Example 8

[0143] Example 8 differs from Example 1 in that the graphite Al in step S1 has G 1A = 90%, the graphite Bl has G 1B = 100%.

[0144] Example 9

[0145] Example 9 differs from Example 1 in that the graphite Al in step S1 has G 1A = 95%, the graphite Bl has G 1B = 96%.

[0146] Example 10

[0147] Example 10 differs from Example 1 in that the graphite A2 in step S3 has G 2A = 80%, the graphite B2 has G 2B = 89%.

[0148] Example 11

[0149] Example 11 differs from Example 1 in that the graphite A2 in step S3 has G 2A = 85%, the graphite B2 has G 2B = 86%.

[0150] Example 12

[0151] Example 12 differs from Example 1 in that the mixed graphite I in step S1 is replaced by one graphite, Gl = 90%; the mixed graphite II in step S3 is replaced by one graphite, G2 = 80%.

[0152] Example 13

[0153] Example 13 differs from Example 1 in that the mixed graphite I in step S1 is replaced by one graphite, Gl = 95%; the mixed graphite II in step S3 is replaced by one graphite, G2 = 89%.

[0154] Example 14

[0155] Example 14 differs from Example 1 in that the mixed graphite I in step S1 is replaced by one graphite, Gl = 98%; the mixed graphite II in step S3 is replaced by one graphite, G2 = 80%.

[0156] Example 15

[0157] Example 15 and Example 13 differ in that the graphite in step S1 is replaced by G1 = 80%; the graphite in step S3 is replaced by G2 = 70%.

[0158] Example 16

[0159] Example 16 and Example 13 differ in that the graphite in step S1 is replaced by G1 = 96%; the graphite in step S3 is replaced by G2 = 70%.

[0160] Example 17

[0161] Example 17 and Example 13 differ in that the graphite in step S1 is replaced by G1 = 90%; the graphite in step S3 is replaced by G2 = 89%.

[0162] Comparative Example 1

[0163] Comparative Example 1 and Example 1 differ in that only the first active slurry is coated on the opposite first and second surfaces of the current collector 1, forming a single layer of high graphitization degree active coating; the second active slurry is not coated; drying forms the negative electrode sheet.

[0164] Comparative Example 2

[0165] Comparative Example 2 and Example 1 differ in that only the second active slurry is coated on the opposite first and second surfaces of the current collector 1, forming a single layer of low graphitization degree active coating; the first active slurry is not coated; drying forms the negative electrode sheet.

[0166] Comparative Example 3

[0167] Comparative Example 3 and Example 1 differ in that the first active slurry and the second active slurry are mixed in a weight ratio of 1:1 to form a mixed slurry; the mixed slurry is coated on the opposite first and second surfaces of the current collector, forming a single layer of mixed graphitization degree active coating; drying forms the negative electrode sheet.

[0168] Comparative Example 4

[0169] Comparative Example 4 and Example 13 differ in that the second active slurry (containing low graphitization degree carbon material, G1 = 80%) is coated on the opposite first and second surfaces of the current collector 1, forming a low graphitization degree active coating; the first active slurry (containing high graphitization degree carbon material, G1 = 90%) is coated on the surface of the first active coating 2, forming a high graphitization degree active coating; drying forms the negative electrode sheet (low graphitization degree on the inside + high graphitization degree on the outside).

[0170] Performance Test

[0171] (1) The surface density test method: a standard size coated pole piece is used, the area is recorded as S㎡, the standard size coated pole piece is weighed by an electronic balance, the weight is recorded as M1g, the standard size copper foil is weighed by a Tianzi balance, the weight is recorded as M2g, and the surface density is (M1-M2) / S.

[0172] (2) The coating porosity test method: a certain amount of pole piece is baked in a vacuum drying oven for 8h, the baking temperature is 70℃, the baked pole piece is placed in a mercury porosimeter, the pressure is set to 200MPa, the porosity is calculated by the pore volume under different external pressures.

[0173] (3) The pole piece full charge expansion rate is (the thickness of the graphite fully embedded with lithium-the thickness of the pole piece after rolling) / the thickness of the pole piece after rolling x 100%,

[0174] The surface density, coating porosity, and pole piece expansion rate of the negative pole pieces prepared in Examples 1-17 and Comparative Examples 1-4 were tested by the above detection methods, and the results are shown in Table 1.

[0175] The negative pole pieces, positive pole pieces (lithium iron phosphate: carbon black: SBR: CMC = 96:2:0.5:0.5), PP separators, and electrolyte (electrolyte, solvent) prepared in Examples 1-17 and Comparative Examples 1-4 were assembled into battery packs.

[0176] The initial efficiency calculation method: the first discharge capacity / total charge capacity during formation x 100%.

[0177] 25℃ 5C charge constant current ratio: at 25℃, using 5C current, constant current constant voltage charging to 3.65V, recording the constant current charging capacity as Q1, the constant current constant voltage charging capacity as Q2, and the 25℃ 5C charge constant current ratio = Q1 / Q2 x 100%.

[0178] 25℃ 3C cycle 1000 times capacity retention rate: at 25℃, using 3C current for charge and discharge cycle for 1000 times, recording the initial capacity Q3 and the 1000th week discharge capacity Q4, and the 25℃ 3C cycle 1000 times capacity retention rate = Q4 / Q3 x 100%.

[0179] The electrochemical performance of the negative electrode assembled batteries of Examples 1-17 and Comparative Examples 1-4 was tested by the above test methods, and the results are shown in Table 2.

[0180] Table 1

[0181]

[0182]

[0183] Table 2

[0184]

[0185]

[0186] From the detection data of Table 1 and Table 2, it can be seen that the battery assembled by the negative electrode plate prepared in Examples 1-17 has a constant current charging ratio of more than 90% and a maximum of 94.2%, indicating that the battery has excellent fast charging performance; the capacity retention rate after 1000 cycles is more than 90% and a maximum of 93.4%, indicating that the battery has excellent long cycle performance; the initial efficiency is mostly between 94% and 95%, indicating that the battery has excellent energy density. From the above detection results, it can be seen that the negative electrode plate prepared in the present application has a double-layer and gradient graphitization degree active coating, which has high energy density, good long cycle performance, excellent fast charging performance, stable structure and safe use.

[0187] Comparative Examples 1-4 respectively use single-layer high-graphitization-degree active coating, single-layer low-graphitization-degree active coating, single-layer high-low mixed graphitization degree coating, and inner low and outer high graphitization degree coating; the batteries assembled therefrom have low energy density, low constant current charging ratio, poor fast charging effect, or poor long cycle performance; obviously, the negative electrode plate prepared by the coating methods of the comparative examples has poor comprehensive performance such as fast charging performance, long cycle performance and energy density, which is not as good as the examples 1-17 of the present application.

[0188] Further, by designing the negative electrode active coating as a double-layer gradient graphitization degree carbon material, and gradually reducing the graphitization degree from the first active coating (high graphitization degree) close to the current collector to the second active coating (low graphitization degree) away from the current collector, the low graphitization degree carbon material on the outside has good stability in the structure during the lithium extraction process, which can improve the long cycle performance of the battery, the lithium ion diffusion speed is fast, which can significantly improve the fast charging performance of the battery, the expansion is small during the charging and discharging process of the battery, which can improve the safety; the high graphitization degree carbon material on the inside ensures that the battery has high energy density, thereby achieving both fast charging performance and long cycle performance, and taking into account high energy density, which improves the comprehensive performance of the battery.

[0189] It should be noted that the terms "first", "second", and the like in the specification and claims of the present application are used to distinguish similar objects, and do not necessarily have to describe a specific order or sequence. It should be understood that the terms used in this way can be interchanged under appropriate circumstances, so that the embodiments of the present application described herein can be implemented in an order other than those described herein.

[0190] The above descriptions are only the preferred embodiments of the present application, and are not intended to limit the present application. The present application can have various modifications and changes for those skilled in the art. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A negative electrode plate for a lithium-ion battery, comprising a current collector and an active coating attached to two opposite surfaces of the current collector; characterized in that: The active coating is a composite active coating (4); the composite active coating (4) comprises a first active coating (2) and a second active coating (3); the first active coating (2) is attached to the surface of the current collector (1), and the second active coating (3) is attached to the surface of the first active coating (2) away from the current collector (1); The active material in the first active coating (2) includes a first carbon material, the graphitization degree of which is G1; the active material in the second active coating (3) includes a second carbon material, the graphitization degree of which is G2, and G1 and G2 satisfy the relationship I:G1>G2.

2. The negative electrode plate of a lithium-ion battery according to claim 1, characterized in that: In the relationship formula I, G1-G2=5% to 20%; preferably, G1-G2=8% to 12%; And / or, the numerical range of G1 is: 90%≤G1≤100%; And / or, the numerical range of G2 is: 80%≤G2<90%.

3. The negative electrode plate of a lithium-ion battery according to claim 1 or 2, characterized in that: The first carbon material is a mixed material of a first carbon material A and a first carbon material B; wherein the graphitization degree of the first carbon material A is G 1A , the graphitization degree of the first carbon material B is G 1B ;and The G 1A Numerical range: 90% ≤ G 1A ≤95%; The G 1B Numerical range: 95%<G 1B ≤100%; Preferably, the weight ratio of the first carbon material A to the first carbon material B is 1:(1-9); more preferably, it is 1:(3-7).

4. The negative electrode plate for a lithium-ion battery according to any one of claims 1 to 3, characterized in that: The second carbon material is a mixed material of a second carbon material A and a second carbon material B; wherein the graphitization degree of the second carbon material A is G 2A , the graphitization degree of the second carbon material B is G 2B ;and The G 2A Numerical range: 80% ≤ G 2A ≤85%; The G 2B Numerical range: 85%<G 2B <90%; Preferably, the weight ratio of the second carbon material A to the second carbon material B is 1:(1-9); more preferably, it is 1:(4-8).

5. The negative electrode plate for a lithium-ion battery according to any one of claims 1 to 4, characterized in that: The first carbon material and the second carbon material each satisfy at least one of the following conditions: Condition 1: La = 40-400 nm, where La is the average size of the grains along the a-axis. Condition 2: Lc = 10-200 nm, where Lc is the average size of the grains along the c-axis. Condition 3: OI = 1.5-30, OI is the powder orientation index; Condition 4: ID / IG ≥ 0.04, ID / IG is the powder disorder; Condition 5: D50 = 0.5-25 μm, where D50 is the median particle size of the powder volume distribution; Condition 6: K90 ≤ 5, K90 is the width of the powder particle size distribution, K90 = (D90 - D10) / D50; Condition 7: 0.5m 2 / g≤BET≤3m 2 / g, BET is specific surface area; Preferably, the first carbon material has at least one of the conditions 1 to 7; wherein, the condition 1: La = 80 ~ 300nm, the condition 2: Lc = 40 ~ 150nm, the condition 3: OI = 2 ~ 10, the condition 4: ID / IG ≥ 0.10, the condition 5: D50 = 6 ~ 15μm, the condition 6: K90 ≤ 2, the condition 7: 1.0m 2 / g≤BET≤2.0m 2 / g; Preferably, the second carbon material has at least one of the conditions 1 to 7; wherein, the condition 1: La = 40 to 200 nm, the condition 2: Lc = 20 to 120 nm, the condition 3: OI = 5 to 25, the condition 4: ID / IG ≥ 0.15, the condition 5: D50 = 5 to 15 μm, the condition 6: K90 ≤ 2, the condition 7: 1.0 m 2 / g≤BET≤2.5m 2 / g; and / or, the first carbon material and the second carbon material are graphite respectively; And / or, the current collector is copper foil.

6. The negative electrode plate for a lithium-ion battery according to any one of claims 1 to 5, characterized in that: The negative electrode sheet meets at least one of conditions 8 to 10; Condition 8: The porosity of the active coating is 8% to 50%; Condition 9: The electrode surface density is 50-300g / m 2 ; Condition 10: The expansion rate of the electrode when fully charged is ≤ 25%; and / or, the porosity of the first active coating (2) is 8 to 50%; and / or, the porosity of the second active coating (3) is 12 to 35%; and / or, the thickness of the first active coating (2) is 30 to 100 μm; and / or, the thickness of the second active coating (3) is 20 to 80 μm; And / or, the weight percentage of the first carbon material in the first active coating layer is 95% to 99%; And / or, the weight percentage of the second carbon material in the second active coating layer is 95% to 98%.

7. A method for preparing a negative electrode sheet for a lithium-ion battery according to any one of claims 1 to 6, characterized in that: The preparation method comprises the following steps: Coating the first active slurry on two opposite surfaces of the current collector (1) to form a first active coating (2); Applying a second active slurry on the surface of the first active coating (2) to form a second active coating (3); The first active slurry includes a first carbon material with a graphitization degree of G1; the second active slurry includes a second carbon material with a graphitization degree of G2; and G1 and G2 satisfy a relationship I: G1>G2.

8. The method for preparing a negative electrode sheet for a lithium-ion battery according to claim 7, wherein: In the relationship formula I, G1-G2=5% to 20%; preferably, G1-G2=8% to 12%; And / or, the numerical range of G1 is: 90%≤G1≤100%; And / or, the numerical range of G2 is: 80%≤G2<90%; And / or, the first carbon material is a mixed material of a first carbon material A and a first carbon material B; wherein the graphitization degree of the first carbon material A is G 1A , the graphitization degree of the first carbon material B is G 1B ; and said G 1A Numerical range: 90% ≤ G 1A ≤95%; the G 1B Numerical range: 95%<G 1A ≤100%; Preferably, the weight ratio of the first carbon material A to the first carbon material B is 1: (1-9); more preferably 1: (3-7); And / or, the second carbon material is a mixed material of a second carbon material A and a second carbon material B; wherein the graphitization degree of the second carbon material A is G 2A , the graphitization degree of the second carbon material B is G 2B ; and said G 2A Numerical range: 80% ≤ G 2A ≤85%; the G 2B Numerical range: 85%<G 2A <90%; Preferably, the weight ratio of the second carbon material A to the second carbon material B is 1: (1-9); more preferably 1: (4-8); And / or, the first active slurry includes the first carbon material, a first conductive agent and a first binder; preferably, the weight ratio of the first carbon material, the first conductive agent and the first binder is (95-99):(0.1-5.0):(0.1-6.0); And / or, the second active slurry includes the second carbon material, a second conductive agent and a second binder; preferably, the weight ratio of the second carbon material, the second conductive agent and the second binder is (95-98):(0.1-5.0):(0.1-6.0); and / or, the viscosity of the first active slurry is 1000 to 8000 mPa·s; and / or, the viscosity of the second active slurry is 2000 to 10000 mPa·s; and / or, the first carbon material and the second carbon material are graphite respectively; And / or, the current collector is copper foil.

9. A lithium-ion battery comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte; characterized in that: The negative electrode plate is the negative electrode plate of the lithium ion battery according to any one of claims 1 to 6 or the negative electrode plate of the lithium ion battery prepared by the preparation method according to claim 7 or 8.

10. An electrical device comprising a battery; characterized in that: The battery is the lithium-ion battery according to claim 9.

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