CN108808006B - Negative pole piece and battery - Google Patents

Abstract

The invention provides a negative pole piece and a battery, wherein the negative pole piece comprises a negative current collector and a negative diaphragm which is arranged on at least one surface of the negative current collector and comprises a negative active material. The powder compacted density P of the negative active material under 3000Kg of pressure_3kAnd average particle diameter D of negative electrode active material_vThe relationship between 50 satisfies: 0.15 is less than or equal to 1/D_v50+0.2/P_3kLess than or equal to 1. The battery provided by the invention has the characteristics of excellent dynamic performance and long cycle life under high-rate quick charging.

Description

Negative pole piece and battery

technical field

The present invention relates to the field of batteries, in particular to a negative pole piece and a battery.

Background technique

Rechargeable batteries have outstanding characteristics such as light weight, high energy density, no pollution, no memory effect, and long service life, so they are widely used in new energy vehicles. However, the long charging time is one of the important factors limiting the rapid popularization of new energy vehicles. In terms of technical principle, the core of battery fast charging technology is to improve the moving speed of ions between positive and negative electrodes through chemical system reconciliation and design optimization. If the negative electrode cannot withstand high current charging, the negative electrode will have metal precipitation during fast charging, and at the same time, a large number of by-products will be produced on the surface of the negative electrode, which will affect the cycle life and safety of the battery. Therefore, the key to fast charging technology lies in the design of negative electrode active materials and negative electrode plates.

SUMMARY OF THE INVENTION

In view of the problems existing in the background art, the purpose of the present invention is to provide a negative electrode plate and a battery, which have the characteristics of excellent kinetic performance and long cycle life under high-rate fast charging.

In order to achieve the above object, in the first aspect of the present invention, the present invention provides a negative electrode sheet, which includes a negative electrode current collector and a negative electrode membrane provided on at least one surface of the negative electrode current collector and comprising a negative electrode active material. The relationship between the powder compaction density P _3k of the negative electrode active material under a pressure of 3000Kg and the average particle size D _v 50 of the negative electrode active material satisfies: 0.15≦1/D _v 50+0.2/P _3k ≦1. The unit of the average particle diameter D _v 50 is μm, and the unit of the powder compaction density P _3k is g/cm ³ .

In a second aspect of the present invention, the present invention provides a battery comprising the negative electrode plate described in the first aspect of the present invention.

Compared with the prior art, the present invention at least includes the following beneficial effects:

By rationally designing the negative electrode active material, the present invention makes the powder compaction density of the negative electrode active material and the average particle size of the negative electrode active material satisfy a certain relationship, and obtains a battery with excellent kinetic performance and long cycle life under high-rate fast charging. Battery.

Detailed ways

The negative electrode sheet and the battery according to the present invention will be described in detail below.

First, the negative electrode sheet according to the first aspect of the present invention is described, which includes a negative electrode current collector and a negative electrode membrane provided on at least one surface of the negative electrode current collector and including a negative electrode active material. The relationship between the powder compaction density P _3k of the negative electrode active material under a pressure of 3000Kg and the average particle size D _v 50 of the negative electrode active material satisfies: 0.15≦1/D _v 50+0.2/P _3k ≦1. The unit of the average particle diameter D _v 50 is μm, and the unit of the powder compaction density P _3k is g/cm ³ .

In the process of battery charging, for the negative electrode, the following three electrochemical processes are required: (1) the active ions (such as lithium ions, sodium ions, etc.) extracted from the positive active material enter the electrolyte, and As the electrolyte enters the pores of the negative electrode membrane, the liquid phase conduction of active ions in the pores is completed, and the liquid phase conduction includes liquid phase diffusion and electromigration; (2) The active ions and electrons complete the charge exchange on the surface of the negative electrode active material; ( 3) Active ions are conducted from the surface of the negative electrode active material to the inside of the negative electrode active material crystal in a solid phase.

The fast charging capability of the battery is closely related to the particle size of the negative electrode active material and the pore structure of the negative electrode membrane. Generally, the larger the negative electrode active material particles, the greater the solid-phase conduction resistance of active ions in it, and the poorer the fast charging capability of the battery. The better the charging capacity. The more developed the pore structure of the negative membrane, the smaller the liquid phase conduction resistance of active ions, the better the kinetic performance of the battery, and the faster the charging speed. The pore structure of the negative electrode membrane can be measured by the powder compaction density of the negative electrode active material under a pressure of 3000Kg. The smaller the powder compaction density is, the smaller the powder compaction density is, the more negative electrode slurry is made by dispersing into the solvent. After coating, drying and compacting The more developed the pore structure of the negative electrode membrane obtained after the other processes, and the stronger the ability to maintain the pore structure of the negative electrode membrane during the charging and discharging process.

In the design of the negative electrode pole piece of the present invention, the powder compaction density P _3k of the negative electrode active material and the average particle size D _v 50 of the negative electrode active material are _considered together. When the relationship between the average particle size D _v 50 of the negative electrode active material satisfies 0.15≤1/D _v 50+0.2/P _3k ≤1, a battery with excellent kinetic performance and long cycle life under high-rate fast charge can be obtained.

When the average particle size D _v 50 of the negative electrode active material is too small or the powder compaction density P _3k of the negative electrode active material is too small, so that the upper limit of 1/D _v 50+0.2/P _3k exceeds 1, the comprehensive performance of the battery is poor. This is due to the fact that the average particle size _Dv50 of the negative electrode active material is too small, the adhesive force of the negative electrode pole piece is small, and the powder is easy to fall off, and then the electronic conductance of the negative electrode pole piece is greatly affected, and the dynamic performance cannot meet the demand and cannot withstand high pressure. Fast charging speed; the powder compaction density P _3k of the negative electrode active material is too small, and the pore structure of the negative electrode membrane is very developed, but the contact surface between the negative electrode active material and the electrolyte is large, resulting in side reactions between the negative electrode and the electrolyte The cycle performance of the battery is greatly negatively affected, especially the cycle performance of the battery in a high temperature environment is very poor.

When the average particle size D _v 50 of the negative electrode active material is too large or the powder compaction density P _3k of the negative electrode active material is too large, so that the lower limit of 1/D _v 50+0.2/P _3k is lower than 0.15, the overall performance of the battery is also higher. Difference. This is because the average particle size D _v 50 of the negative electrode active material is too large, the solid-phase conduction of active ions in it is difficult, and the kinetic performance of the battery is poor, which cannot meet the needs of the battery for a faster charging speed; The powder compaction density P _3k is too large, the pore structure of the negative membrane is not developed enough, and the ability to maintain the pore structure during cycling is poor, the liquid phase conduction resistance of active ions is large, and the kinetic performance of the battery is poor, which cannot be tolerated. Faster charging speed.

Preferably, the relationship between the powder compaction density P _3k of the negative electrode active material and the average particle size D _v 50 of the negative electrode active material satisfies 0.15≦1/D _v 50+0.2/P _3k ≦0.5.

In the negative electrode sheet according to the first aspect of the present invention, preferably, the average particle diameter D _v 50 of the negative electrode active material is 1.2 μm˜25 μm, and further preferably, the average particle diameter D _v 50 of the negative electrode active material is 3.5 μm˜21 μm , and more preferably, the average particle size D _v 50 of the negative electrode active material is 5 μm˜15 μm.

In the negative electrode sheet according to the first aspect of the present invention, preferably, the powder compaction density P _3k of the negative electrode active material under a pressure of 3000Kg is 0.2g/cm ³ to 2.1g/cm ³ , further preferably, the negative electrode active material The powder compaction density P _3k under the pressure of 3000Kg is 0.5g/cm ³ to 1.9g/cm ³ , and more preferably, the powder compact density P _3k of the negative electrode active material under the pressure of 3000Kg is 1.3g/cm ³ to 1.7g/cm ³ .

In the negative electrode pole piece of the first aspect of the present invention, the specific type of the negative electrode active material is not specifically limited, and can be selected according to actual needs. Preferably, the negative electrode active material can be selected from one or more of graphite, soft carbon, hard carbon, carbon fiber, mesocarbon microspheres, silicon-based materials, tin-based materials, and lithium titanate. Wherein, the graphite can be selected from one or more of artificial graphite and natural graphite. The silicon-based material may be selected from one or more of elemental silicon, silicon-oxygen compound, silicon-carbon composite, and silicon alloy. The tin-based material can be selected from one or more of elemental tin, tin oxide compounds, and tin alloys.

In the negative electrode sheet of the first aspect of the present invention, the negative electrode film further includes a conductive agent and a binder. The types and contents of the conductive agent and the binder are not specifically limited and can be selected according to actual needs.

In the negative electrode piece of the first aspect of the present invention, the type of negative electrode current collector is not specifically limited, and can be selected according to actual needs, and copper foil is preferably used.

In the negative pole piece of the first aspect of the present invention, the particle diameter D _v 50 of the negative electrode active material can be measured using a laser diffraction particle size distribution measuring instrument (Mastersizer 3000). The powder compaction density P _3k of the negative active material can be obtained by using an electronic pressure testing machine (UTM7305) under a pressure of 3000Kg.

Next, the battery according to the second aspect of the present invention is described, which includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator, wherein the negative electrode sheet is the negative electrode sheet according to the first aspect of the present invention.

In order to ensure the safety of the battery, the number of active ion vacancies that can be accepted by the negative electrode is usually greater than the number of active ions that can be removed by the positive electrode during battery design. low, the energy density of the battery will decrease.

At the same time, the energy density of the battery is also closely related to the particle size of the anode active material. Generally, the larger the negative electrode active material particles, the more sites on the surface of the negative electrode active material for active ions to intercalate, and the higher the gram capacity of the negative electrode active material. The battery design requires only a smaller amount of negative electrode active material to achieve the capacity target. The larger the negative electrode active material particles, the more conducive to the improvement of the energy density of the battery.

In the battery of the second aspect of the present invention, the average particle size D _v 50 of the negative electrode active material is considered in combination with the excess capacity coefficient CB of the battery, when the relationship between the two satisfies: 5≤D _v 50+6/CB When ≤30, the dynamic performance of the battery and the cycle life under high-rate fast charging can be further improved, and at the same time, a higher energy density can be taken into account. Among them, the capacity excess coefficient CB of the battery is the ratio of the negative electrode capacity to the positive electrode capacity under the same area.

When the average particle size D _v 50 of the negative electrode active material is too large or the capacity excess coefficient CB of the battery is too small, so that the upper limit of D _v 50+6/CB exceeds 30, the overall performance of the battery is poor. This is because the average particle size D _v 50 of the negative electrode active material is too large, the negative electrode slurry is easy to settle, the bumps are easy to appear during coating, the product quality rate of the negative electrode pole piece is low, and the cycle performance of the battery will also deteriorate; When the capacity excess coefficient CB is too small, the negative electrode is in an excessively high SOC state when fully charged, and the negative electrode potential caused by polarization is low during high-rate charging, which is easy to lead to the reduction and precipitation of active ions in the negative electrode, and there is a high safety hazard.

When the average particle size D _v 50 of the negative electrode active material is too small or the capacity excess coefficient CB of the battery is too large, so that the lower limit of D _v 50+6/CB is lower than 5, the overall performance of the battery is also poor. This is because the average particle size D _v 50 of the negative electrode active material is too small, and its surface has fewer sites for active ions to intercalate, and the gram capacity is low, and a large amount of negative electrode active material is required in battery design to achieve the expected capacity target. , and then the energy density of the battery is low; if the excess capacity coefficient CB of the battery is too large, the utilization rate of the negative electrode acceptable active ion vacancies during charging will become lower, which will also lead to a decrease in the energy density of the battery.

Preferably, the relationship between the average particle size D _v 50 of the negative electrode active material and the excess capacity coefficient CB of the battery satisfies 6≤D _v 50+6/CB≤27, further preferably, the average particle size D _v of the negative electrode active material The relationship between 50 and the capacity excess coefficient CB of the battery satisfies 10≤D _v 50+6/CB≤20.

In the battery of the second aspect of the present invention, preferably, the excess capacity factor CB of the battery is 0.8-2.5, and more preferably, the excess capacity factor CB of the battery is 1.0-1.8.

In the battery of the second aspect of the present invention, the types and compositions of the positive electrode plates are not specifically limited, and can be selected according to actual needs.

In the battery of the second aspect of the present invention, the type of the separator is not particularly limited, and can be any separator material used in existing batteries, such as polyethylene, polypropylene, polyvinylidene fluoride and their Multilayer composite films, but not limited to these.

In the battery of the second aspect of the present invention, the specific type and composition of the electrolyte are not specifically limited, and can be selected according to actual needs.

It should be noted that the battery according to the second aspect of the present application can be a lithium-ion battery, a sodium-ion battery, or any other battery using the negative electrode plate of the first aspect of the present invention.

When the battery is a lithium-ion battery:

The positive electrode active material can be selected from lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, olivine structure lithium-containing phosphate, etc. , but the present application is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials for lithium ion batteries can also be used. These positive electrode active materials may be used alone or in combination of two or more. Preferably, the positive electrode active material may be selected from LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (NCM333), LiNi _0.5 Co _0.2 Mn _0.3 O ₂ ( One or more of LiNi _0.6 Co _0.2 Mn _0.2 O ₂ (NCM622), LiNi _0.8 Co _0.1 Mn _0.1 O ₂ (NCM811), LiNi _0.85 Co _0.15 Al _0.05 O ₂ , LiFePO ₄ , and LiMnPO ₄ .

When the battery is a sodium-ion battery:

The positive electrode active material can be selected from transition metal oxide Na _x MO ₂ (M is a transition metal, preferably one or more selected from Mn, Fe, Ni, Co, V, Cu, Cr, 0<x≤1) , polyanion materials (phosphates, fluorophosphates, pyrophosphates, sulfates), Prussian blue materials, etc., but this application is not limited to these materials, this application can also use other materials that can be used as positive electrodes for sodium ion batteries Materials are conventionally known materials. These positive electrode active materials may be used alone or in combination of two or more. Preferably, the positive active material can be selected from NaFeO ₂ , NaCoO ₂ , NaCrO ₂ , NaMnO ₂ , NaNiO ₂ , NaNi _1/2 Ti _1/2 O ₂ , NaNi _1/2 Mn _1/2 O ₂ , Na _2/3 Fe _1/3 Mn _2/3 O ₂ , NaNi _1/3 Co _1/3 Mn _1/3 O ₂ , NaFePO ₄ , NaMnPO ₄ , NaCoPO ₄ , Prussian blue material, the general formula is A _a M _b (PO ₄ ) _c O _x Y _3-x material (wherein A is selected from one or more of H ⁺ , Li ⁺ , Na ⁺ , K ⁺ , NH ⁴⁺ , M is a transition metal cation, preferably selected from V, Ti, One or more of Mn, Fe, Co, Ni, Cu, Zn, Y is a halogen anion, preferably one or more of F, Cl, Br, 0<a≤4, 0<b≤ 2, one or more of 1≤c≤3, 0≤x≤2).

The present application will be further described below by taking a lithium-ion battery as an example and in conjunction with specific embodiments. It should be understood that these examples are only used to illustrate the present application and not to limit the scope of the present application.

The batteries of Examples 1-40 and Comparative Examples 1-9 were prepared according to the following methods.

(1) Preparation of positive electrode sheet

The positive electrode active material NCM523, the conductive agent acetylene black, and the binder PVDF are mixed in a mass ratio of 96:2:2, the solvent NMP is added, and the system is stirred under the action of a vacuum mixer until the system is uniform to obtain a positive electrode slurry; The material is evenly coated on the aluminum foil of the positive current collector, dried at room temperature and then transferred to an oven for further drying, and then cold-pressed and cut to obtain a positive electrode piece.

(2) Preparation of negative pole piece

After the negative electrode active material shown in Table 1, the conductive agent acetylene black, the thickener CMC, and the binder SBR are mixed in a mass ratio of 96.4:1:1.2:1.4, the solvent deionized water is added, and the mixture is stirred under the action of a vacuum mixer until The system is uniform to obtain the negative electrode slurry; the negative electrode slurry is uniformly coated on the negative electrode current collector copper foil, dried at room temperature and then transferred to an oven for further drying, and then cold pressed and slitted to obtain a negative electrode pole piece.

(3) Preparation of electrolyte

Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent, and then the fully dried lithium salt LiPF ₆ was dissolved in the mixture. In the latter organic solvent, an electrolyte solution with a concentration of 1 mol/L is prepared.

(4) Preparation of separator

Polyethylene films are selected as separators.

(5) Preparation of lithium ion battery

Stack the above-mentioned positive pole piece, separator film, and negative pole piece in order, so that the separator film is placed between the positive pole piece and the negative pole piece to play a role of isolation, and then roll to obtain a bare cell; place the bare cell in the outer package In the shell, after drying, the electrolyte is injected, and the lithium ion battery is obtained through the processes of vacuum packaging, standing, forming, and shaping.

Next, the performance test of the lithium-ion battery will be described.

(1) Dynamic performance test: At 25°C, the lithium-ion batteries prepared in the examples and comparative examples were fully charged at 4C and fully discharged at 1C for 10 times, and then the lithium-ion batteries were fully charged at 4C, and then The negative pole piece was disassembled and the lithium precipitation on the surface of the negative pole piece was observed. Among them, if the area of the negative electrode surface area of lithium precipitation is less than 5%, it is considered to be slight lithium precipitation, if the area of the negative electrode surface area of lithium precipitation area is 5% to 40%, it is considered to be moderate lithium precipitation, and if the area of the negative electrode surface area of lithium precipitation area is more than 40%, it is considered to be serious lithium precipitation. .

(2) Cyclic performance test: At 25°C, the lithium-ion batteries prepared in the examples and comparative examples were charged at a rate of 3C and discharged at a rate of 1C, and a full-charge-discharge cycle test was performed until the capacity of the lithium-ion battery attenuated to the initial rate. 80% of capacity, record the number of laps.

(3) Actual energy density test: at 25°C, the lithium-ion batteries prepared in the examples and comparative examples were fully charged at a rate of 1C and fully discharged at a rate of 1C, and the actual discharge energy at this time was recorded; at 25°C, Use an electronic balance to weigh the lithium-ion battery; the ratio of the actual discharge energy of the lithium-ion battery 1C to the weight of the lithium-ion battery is the actual energy density of the lithium-ion battery.

Among them, when the actual energy density is less than 80% of the target energy density, the actual energy density of the battery is considered to be very low; when the actual energy density is greater than or equal to 80% of the target energy density and less than 95% of the target energy density, the actual energy density of the battery is considered to be low. ; When the actual energy density is greater than or equal to 95% of the target energy density and less than 105% of the target energy density, the actual energy density of the battery is considered to be moderate; when the actual energy density is greater than or equal to 105% of the target energy density and less than 120% of the target energy density, The actual energy density of the battery is considered to be high; when the actual energy density is more than 120% of the target energy density, the actual energy density of the battery is considered to be very high.

Table 1: Parameters and test results of Examples 1-40 and Comparative Examples 1-9

Examples 1-8 and 9-15 give the test results that the powder compaction density P _3k of the negative electrode active material is 1.8g/cm ³ and 1.2g/cm ³ , and the capacity excess coefficient CB of the battery is fixed at 1.2. , under the same conditions as the powder compaction density P _3k of the negative active material and the capacity excess coefficient CB of the battery, the effect of the average particle size D _v 50 of the negative active material on the battery performance was observed. When the average particle size D _v 50 of the negative electrode active material is relatively too small and does not match the powder compaction density P _3k of the negative electrode active material, resulting in 1/D _v 50+0.2/P _3k >1, the negative electrode pole piece is bonded The force is small, and it is easy to drop powder, and then due to the insufficient electronic conductivity of the negative pole piece, the kinetic performance of the battery is poor, and lithium is seriously precipitated during fast charging at a large rate, and it is easy to cycle diving. Comparative Example 1 and Comparative Example 2 cycled for 430 and 850 laps, respectively, after the capacity diving. When the average particle size D _v 50 of the negative electrode active material is relatively too large and does not match the powder compaction density P _3k of the negative electrode active material, resulting in 1/D _v 50+0.2/P _3k <0.15, lithium ions are active in the negative electrode. The solid-phase conduction resistance inside the material is too large, resulting in poor kinetic performance of the battery. The negative electrode is severely lithium-deposited during fast charging at high rates, and it is easy to cycle diving; in addition, the average particle size of the negative electrode active material D _v 50 is relatively If it is too large, the negative electrode slurry is easy to settle, and it is easy to cause serious bumps on the surface of the negative electrode membrane, which further affects the cycle life of the battery. Comparative Example 3: Volume diving after 300 laps.

Examples 18-22 and 23-28 respectively give the test results that the average particle diameter D _v 50 of the negative electrode active material is 20 μm and 18 μm, and the capacity excess coefficient CB of the battery is fixed at 1.2. The average particle diameter of the negative electrode active material Under the same conditions as D _v 50 and the capacity excess coefficient CB of the battery, the effect of the powder compaction density P _3k of the negative active material on the battery performance was observed. When the powder compaction density P _3k of the negative electrode active material is relatively too small and does not match the average particle size D _v 50 of the negative electrode active material, resulting in 1/D _v 50+0.2/P _3k >1, the pores of the negative electrode membrane The structure is very developed, and the kinetic performance of the battery is good. The negative electrode will not precipitate lithium during high-rate fast charging. However, due to the excessive contact surface between the negative electrode active material and the electrolyte, there are too many side reactions between the negative electrode and the electrolyte. , and then the capacity decays rapidly during the battery cycle, which is detrimental to the cycle life of the battery. The capacity diving after 1100 laps in the comparative example 4, and the capacity diving after 1200 laps in the comparative example 6. When the powder compaction density P _3k of the negative electrode active material is relatively too large and does not match the average particle size Dv50 of the negative electrode active material, resulting in 1/D _v 50+0.2/P _3k <0.15, the pore structure of the negative electrode membrane is insufficient. It is developed, the pore structure maintenance ability during cycling is poor, and the liquid phase conduction resistance of lithium ions is too large, resulting in poor kinetic performance of the battery, and the negative electrode is seriously precipitated during high-rate fast charging, and it is easy to cycle diving. Comparative example 5 has a capacity diving after 460 laps, and comparative example 7 has a capacity diving after 640 laps.

When the relationship between the average particle size D _v 50 of the negative electrode active material and the powder compaction density P _3k of the negative electrode active material is adjusted reasonably, the two are matched and 1/D _v 50+0.2/P _3k is between 0.15 and 1 The battery also has the characteristics of excellent kinetic performance and long cycle life under high-rate fast charging. And preferably, 1/D _v 50+0.2/P _3k is between 0.15 and 0.5.

The preferred range of the average particle diameter D _v 50 of the negative electrode active material is 1.2 μm to 25 μm, and the preferred range of the powder compaction density P _3k of the negative electrode active material is 0.22 g/cm ³ to 2.1 g/cm ³ . And the applicant needs to explain that when one or both of the average particle diameter of the negative electrode active material D _v 50 and the powder compaction density P _3k of the negative electrode active material do not fall into the above preferred range, but satisfy 1/D _v When 50+0.2/P _3k is between 0.15 and 1, the battery still has the characteristics of excellent kinetic performance and long cycle life under high-rate fast charging, such as Example 16 and Example 17, although the negative electrode active material has a larger The average particle size D _v 50, but with a suitable powder compaction density P _3k , when 1/D _v 50+0.2/P _3k is between 0.15 and 1, the battery can still have good kinetic performance and cycle performance. performance. In Comparative Example 8 and Comparative Example 9, although the average particle size D _v 50 of the negative active material and the powder compaction density P _3k all fall within the preferred range, the sizes of the two do not match, 1/D _v 50+0.2/P The value of _3k fails to fall between 0.15 and 1, and the kinetic performance and cycle performance of the battery are both poor.

Examples 29-33 give the test results that the average particle size D _v 50 of the negative electrode active material is fixed at 1.2 μm and the powder compaction density P3k is fixed at 1.6 g/cm ³ , at this time 1/D _v 50+0.2/P _3k is fixed at 0.958, the battery will not be seriously precipitated during high-rate fast charging, and the battery has excellent dynamic performance, which can meet the design requirements of fast charging of the battery. At this time, adjusting the excess capacity factor CB of the battery can further improve the performance of the battery. However, when the capacity excess coefficient CB of the battery is relatively large, and D _v 50+6/CB<5, the actual energy density of the battery is low.

Examples 34-37 give the test results that the average particle diameter D _v 50 of the negative electrode active material is fixed at 25 μm, and the powder compaction density P _3k is fixed at 1.2 g/cm ³ , at this time 1/D _v 50+0.2/P _3k is fixed at 0.207. At this time, adjusting the excess capacity factor CB of the battery can further improve the performance of the battery. However, when the excess capacity factor CB of the battery is relatively too small, and D _v 50+6/CB>30, although the energy density of the battery is relatively low. However, the negative electrode is in an excessively high SOC state when fully charged, and the negative electrode potential caused by polarization during high-rate charging is low, which easily leads to the reduction and precipitation of lithium ions in the negative electrode, and the kinetic performance and cycle performance of the battery are relatively poor.

Claims (4)

1. a battery, comprising a positive pole piece, a negative pole piece, an electrolyte and a separator, and the negative pole piece includes a negative electrode current collector and is arranged on at least one surface of the negative electrode current collector and comprises the negative electrode diaphragm of negative active material; It is characterized in that, The negative electrode active material is selected from graphite; The relationship between the powder compaction density P _3k of the negative electrode active material under a pressure of 3000Kg and the average particle size D _v 50 of the negative electrode active material satisfies: 0.15≤1/D _v 50+0.2/P _3k ≤0.211 ; The average particle size D _v 50 of the negative electrode active material is 10 μm˜21 μm; The powder compaction density P _3k of the negative electrode active material under the pressure of 3000Kg is 1.8g/cm ³ to 2.1g/cm ³ , in, The unit of average particle size D _v 50 is μm; The unit of powder compaction density P _3k is g/cm ³ . 2. The battery according to claim 1, wherein the graphite is selected from one or more of artificial graphite and natural graphite. 3. The battery according to claim 1, wherein the relationship between the excess capacity coefficient CB of the battery and the average particle size D _v 50 of the negative electrode active material satisfies: 10≤D _v 50+6/CB≤ 20; wherein, the excess capacity coefficient CB of the battery is the ratio of the negative electrode capacity to the positive electrode capacity under the same area. 4 . The battery according to claim 3 , wherein the excess capacity factor CB of the battery is 1.0 to 1.8. 5 .