CN118588871B

CN118588871B - Negative plate and application thereof

Info

Publication number: CN118588871B
Application number: CN202411067897.XA
Authority: CN
Inventors: 许晨光; 鲍春晓; 吴煊伟; 尚彪; 苏瑾昭
Original assignee: BYD Co Ltd
Current assignee: BYD Co Ltd
Priority date: 2024-08-06
Filing date: 2024-08-06
Publication date: 2024-11-15
Anticipated expiration: 2044-08-06
Also published as: CN118588871A

Abstract

The present invention provides a negative electrode sheet and its application. The negative electrode sheet of the present invention comprises a negative electrode current collector and a negative electrode active material layer disposed on at least one side of the negative electrode current collector, wherein the negative electrode active material layer comprises a hard carbon material and a nano-lubricating factor, and the nano-lubricating factor comprises one or more of nano-oxides, nano-carbonates, nano-polymers, nano-carbon materials, nano-boron compounds, nano-sulfides, and nano-metallic elements. The negative electrode sheet has high compaction density, low injection coefficient, and low electrode sheet resistivity by introducing the nano-lubricating factor into the hard carbon negative electrode active material layer.

Description

Negative plate and application thereof

Technical Field

The invention belongs to the technical field of batteries, and relates to a negative plate and application thereof.

Background

Lithium Ion Batteries (LIBs) have been widely used in the fields of power batteries, consumer electronics, energy storage, etc. because of their high energy density, long cycle life and mature industrial manufacturability, but because of low lithium resource reserves and maldistribution, the sustainable development of LIBs is hindered, so that the development of new energy storage technologies is urgently needed to replace the application of LIBs in some fields. Sodium is an alkali metal element adjacent to lithium element in the periodic table, and has similar physical and chemical properties. Thus, sodium Ion Batteries (SIBs) have attracted considerable attention due to their wide availability and low cost as potential alternatives to LIBs.

The current negative electrode materials of sodium ion batteries mainly comprise tin-based materials, antimony-based materials, silicon-based materials, soft carbon materials, sodium ion conductors, hard carbon materials and the like. Among the numerous negative electrode materials, the hard carbon material is considered as the most likely positive electrode material for secondary batteries to be industrialized because of the advantages of low cost, good conductivity, environmental friendliness, abundant sources, and the like.

However, the hard carbon negative electrode material has high mechanical strength and more particle edges and corners, so that the compaction density of the negative electrode plate is lower during rolling, the volume energy density of the negative electrode plate is too low, a high liquid injection coefficient is caused, and the application and development of the sodium ion battery are obviously slowed down.

Disclosure of Invention

The invention provides a negative plate, which is characterized in that a nano lubrication factor is introduced into a hard carbon negative active material layer, so that the negative plate has high compaction density, low liquid injection coefficient and lower plate resistivity.

The invention also provides a battery, which has excellent energy density and high initial efficiency because the battery comprises the negative plate.

The invention also provides an electronic device, which comprises the battery, so that the battery also has excellent energy density and high initial efficiency in the use process.

The invention provides a negative electrode plate, which comprises a negative electrode current collector and a negative electrode active material layer arranged on at least one side surface of the negative electrode current collector, wherein the negative electrode active material layer comprises a hard carbon material and a nano lubrication factor;

The nanometer lubrication factor comprises one or more of nanometer oxide, nanometer carbonate, nanometer macromolecule, nanometer carbon material, nanometer boron compound, nanometer sulfide and nanometer metal simple substance.

The negative plate, wherein the D50 particle size of the nano lubrication factor is 50-800 nm;

and/or the D50 particle size of the hard carbon material is 3-10 mu m.

The negative electrode sheet as described above, wherein the nano-oxide comprises one or more of SiO ₂、Al₂O₃、TiO₂;

And/or, the nano-carbonate comprises one or more of CaCO ₃、MgCO₃、Na₂CO₃;

and/or the nanometer macromolecule comprises one or more of polystyrene and polymethyl methacrylate;

And/or the nano carbon material comprises one or more of fullerene C60, diamond and graphene;

and/or the nano boron compound comprises one or more of calcium borate and magnesium borate;

and/or, the nano-sulfide comprises one or more of ZnS and MoS ₂;

And/or the nano metal simple substance comprises one or more of Cu, al and Zn.

The negative plate comprises the nano lubricating factor and a nano sulfide, wherein the nano lubricating factor comprises a mixture of nano oxides and nano sulfides in a mass ratio of (1-3) to 1.

The negative electrode sheet as described above, wherein the nano-oxide is selected from SiO ₂ and/or Al ₂O₃, and the nano-sulfide is selected from MoS ₂.

The negative plate, wherein the mass ratio of the hard carbon material to the nano lubrication factor is 100: (0.1 to 10).

The negative electrode sheet as described above, wherein the negative electrode active material layer further comprises a conductive agent and/or a binder;

The mass ratio of the hard carbon material to the nano lubrication factor to the conductive agent to the binder is (80-100): (1-5): (0-5): (0.1 to 10).

The negative plate is characterized in that the compaction density of the negative plate is more than or equal to 0.98g/cm ³, the resistivity is 0.2-0.8 mΩ cm, and the porosity is 30% -40%.

The invention also provides a battery, which comprises a positive plate, a negative plate, a diaphragm and electrolyte, wherein the negative plate comprises the negative plate.

The battery comprises, by mass, 5% -20% of NaPF ₆%, 30% -60% of propylene carbonate, 30% -50% of methyl ethyl carbonate, 2% -5% of fluoroethylene carbonate, 0.1% -0.8% of propenyl-1, 3-sultone and 0.2% -0.8% of ethylene sulfate.

The battery is characterized in that the electrolyte injection coefficient is 3-10.

The invention also provides an electronic device comprising a battery as described above.

The implementation of the invention has at least the following beneficial effects:

1) The nanometer lubrication factor is introduced into the hard carbon negative electrode based on the ball acting machinery in the nanometer tribology, can play a role of a miniature ball bearing between hard carbon particles, can be flattened under the action of heavy load, can fill and improve the surface roughness of the hard carbon surface with rugged surface, reduces friction resistance, reduces friction coefficient and improves the compaction density of the negative electrode plate.

2) The nano lubrication factor has high surface energy, can be fully adsorbed and wrapped on the surface of the hard carbon particles, and improves the compressive property of the hard carbon material, so that the hard carbon material is not easy to crack and break under high rolling load.

3) The nano lubricating factor can replace part of the conductive agent, so that the pressure density is improved, the battery energy density is improved, and meanwhile, the contact resistance is reduced due to the fact that hard carbon particles are more tightly contacted, the electron transmission performance is not negatively influenced, and even the stripping strength of the pole piece is improved to a certain extent, and the first-circle coulomb efficiency of the battery and the stripping strength of the pole piece are improved.

Drawings

FIG. 1 is a schematic and partial enlarged view of the distribution of hard carbon materials and nano lubrication factors in a negative plate of the invention;

fig. 2 is an SEM image of a cross section of the negative electrode sheet of example 1;

fig. 3 is an SEM image of a cross section of the negative electrode sheet of example 2;

fig. 4 is an SEM image of a cross section of the negative electrode sheet of example 3;

fig. 5 is an SEM schematic of the cross section of the negative electrode sheet of comparative example 1.

Reference numerals illustrate:

1-hard carbon particles;

2-nano lubrication factor.

Detailed Description

For the purpose of making the objects, technical solutions and advantages of the present invention more apparent, the technical solutions in the embodiments of the present invention will be clearly and completely described in the following in conjunction with the embodiments of the present invention, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.

The hard carbon negative electrode material has high mechanical strength and multiple particle edges and corners, has a microporous structure, is difficult to fully slide and fill micropores among particles in the rolling process of the hard carbon negative electrode, so that the porosity of a negative electrode plate is higher, meanwhile, the disorder degree of the hard carbon material is high, and the stacking and crosslinking effects of carbon layers in a microstructure lead to large elastic strain and large rebound, so that the compaction density is lower during rolling, the volume energy density of a battery is lower, and the liquid injection coefficient is too high.

Based on the above, the invention provides a negative electrode sheet, comprising a negative electrode current collector and a negative electrode active material layer arranged on at least one side surface of the negative electrode current collector, wherein the negative electrode active material layer comprises a hard carbon material and a nano lubrication factor;

In the graph of the distribution schematic and partial enlargement of the hard carbon material and the nano lubrication factor in the negative plate of the invention, as shown in the graph of the graph 1, the nano lubrication factor 2 of the invention is fully adsorbed on the surface of the hard carbon particles 1 and filled in the gaps of the hard carbon particles 1, thereby playing a role in lubrication, reducing the friction coefficient among the hard carbon particles, increasing sliding and rolling friction, fully sliding and filling micropores under the rolling stress, reducing the gaps of particles, increasing the contact area among the particles, reducing the porosity of the negative plate, improving the compaction density of the negative plate, reducing the liquid injection coefficient, and in addition, because the contact among the particles is tighter, the contact resistance is reduced, the electron transmission capacity is not obviously reduced or even improved to some extent, the negative plate has lower resistivity, and the first circle coulomb efficiency of the battery is improved.

When the particle size of the nano lubrication factor is too large, the nano lubrication factor is not easy to adsorb and fill in the surface and micropores of the hard carbon particles; when the particle size of the nano lubrication factor is too small, the dispersibility of the particles is poor, secondary particles are easy to agglomerate, and the particles are difficult to uniformly disperse and wrap on the surface and in micropores of hard carbon particles, so that the lubrication effect is poor. In a specific embodiment, the D50 particle size of the nano lubrication factor is 50 to 800nm, preferably 200 to 400nm. In the particle size range, the nano lubrication factor is better adsorbed on the surface of the hard carbon particles and filled in micropores of the hard carbon particles, so that the compaction density of the nano lubrication factor is further improved.

Illustratively, the D50 particle size of the nano-lubrication factor may be 50nm, 100nm, 150nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, 500nm, 550 nm, 600nm, 650 nm, 700nm, 750 nm, 800nm, or a range of any two of these.

In one embodiment, the hard carbon material has a D50 particle size of 3 to 10 μm. The hard carbon material with the particle size range can form a synergistic effect of particle accumulation and pore filling with nano lubrication factors which are far smaller than the nano size of pores (micron level), so that the nano lubrication factors are fully filled in the pores among the hard carbon particles to play a role of a miniature ball bearing, and under the condition of heavy load roller pressing, the surface roughness of the hard carbon is filled and improved, the friction resistance is reduced, and the friction coefficient is reduced.

In a specific embodiment, the nano-oxide comprises one or more of SiO ₂、Al₂O₃、TiO₂;

And/or, the nano-sulfide comprises one or more of ZnS and MoS ₂;

and/or the nano metal simple substance comprises one or more of Cu, al and Zn.

The inventor researches find that when the nano lubrication factor comprises a mixture of nano oxide and nano sulfide in a mass ratio of (1-3): 1, and the nano oxide is further selected from SiO ₂ and/or Al ₂O₃, and the nano sulfide is further selected from MoS ₂, the negative electrode sheet has higher compacted density and lower resistivity. The reason is that MoS ₂ is of a lamellar structure, the binding force between molecular layers is weak, and slippage between layers can occur under a small shearing force, so that sliding friction is increased between hard carbons, and friction factors and friction force are reduced; spherical SiO ₂ and/or Al ₂O₃ particles can play a role of a miniature ball bearing, and under the action of heavy load, the nano lubrication factors are flattened, so that the surface roughness of the hard carbon surface roughness can be filled and improved, the friction resistance is reduced, and the friction coefficient is reduced. When the two are mixed within the mass ratio range, besides the lubrication effect of the self on hard carbon, the spherical SiO ₂ and/or Al ₂O₃ particles can promote the sliding between molecular layers of MoS ₂, so that the whole sliding friction is increased, and meanwhile, the rolling friction is increased due to the fact that the spherical SiO ₂ and/or Al ₂O₃ particles have more sliding surfaces with smaller friction coefficients and are brought by MoS ₂, so that the negative electrode plate can have higher compaction density after being combined.

The source of the hard carbon material is not particularly limited, and the hard carbon material can be obtained commercially or prepared by self.

In a specific embodiment, the hard carbon material is obtained by carbonizing one or more of needle coke, asphalt tar, petroleum coke, square coke, starch, coconut shell, walnut shell, olive shell, oil tea shell, tung oil shell, chestnut shell, phenolic resin, epoxy resin, urea-formaldehyde resin, straw and wood.

Further, the carbonization temperature may be 1000-1600 ℃. In order to obtain a particulate hard carbon material, it may also be subjected to a crushing treatment after carbonization.

In a preferred embodiment, the mass ratio of hard carbon material to nano-lubrication factor is 100: (0.1-10), more preferably, the mass ratio of the hard carbon material to the nano lubrication factor is 100: (0.5 to 6). In the mass ratio range, not only can the nano lubrication factor fully play a role in lubrication, but also the reduction of battery energy density caused by the reduction of the amount of active materials in the negative plate due to the excessive addition of the nano lubrication factor can be avoided.

In a specific embodiment, the anode active material layer further includes a conductive agent and/or a binder. Wherein, the mass ratio of the hard carbon material, the nano lubrication factor, the conductive agent and the binder is (80-100): (1-5): (0-5): (0.1 to 10)

The inventors have found that even if the nano-lubrication factor is used in the above range in place of a part of the conductive agent, the electrochemical performance of the battery is not significantly affected. Therefore, the negative electrode plate can also reduce the manufacturing cost of the negative electrode plate.

The kind of the conductive agent is not particularly limited in the present invention, and may be selected from conductive agents conventionally used in the art, including, but not limited to, one or more of acetylene black, super P, super S, carbon fiber, carbon nanotube and ketjen black.

The kind of binder is not particularly limited, and may be selected from binders conventionally used in the art, including, but not limited to, one or more of polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer, polytetrafluoroethylene, polyacrylonitrile, polypropylene carbonate, styrene-butadiene rubber (SBR), nitrile rubber, sodium carboxymethyl cellulose (CMC), polyethylene oxide, and ethylene oxide-propylene oxide copolymer.

The composition of the negative electrode current collector is not particularly limited in the present invention, and may be selected from negative electrode current collectors conventionally used in the art, for example, copper foil.

Further, by controlling the factors such as the type and the particle size of the nano lubrication factor and the hard carbon material, the mixing proportion of the nano lubrication factor and the hard carbon material, the compaction density of the negative electrode plate is more than or equal to 0.98g/cm ³, the resistivity is 0.2-0.8mΩ & cm, and the porosity is 30% -40%, so that the battery has high energy density, high first efficiency and low liquid injection coefficient.

The negative electrode sheet of the present invention may be prepared with reference to a conventional method, for example, in a specific embodiment, the negative electrode sheet may be prepared with reference to the following method:

And mixing the hard carbon material, the nano lubricating factor, the conductive agent and the binder according to a designed mass ratio to prepare slurry, and then sequentially carrying out coating, drying, rolling and tabletting procedures on the slurry to obtain the negative plate.

Preferably, the viscosity of the slurry is 2000-800 Pa.S.

Preferably, the drying temperature is 60-120 ℃, and the drying time is 20-60 min.

The battery of the invention has the advantages of high energy density, high initial efficiency and low liquid injection coefficient due to the inclusion of the negative electrode plate.

The pair of batteries of the invention can be lithium ion batteries or sodium ion batteries, and are preferably sodium ion batteries.

In a preferred embodiment, the electrolyte comprises, by mass, 5% -20% of NaPF ₆%, 30% -60% of propylene carbonate (PP), 30% -50% of methyl ethyl carbonate (EMC), 2% -5% of fluoroethylene carbonate (FEC), 0.1% -0.8% of propenyl-1, 3-sultone (PST) and 0.2% -0.8% of ethylene sulfate (DTD).

Furthermore, the electrolyte injection coefficient of the electrolyte can reach 3-10 by controlling the composition of the electrolyte and the negative electrode plate.

The composition of the positive electrode sheet is not particularly limited in the present invention, and reference may be made to a positive electrode sheet composition conventional in the art. Specifically, the positive plate comprises a positive current collector and a positive active material layer arranged on at least one side surface of the positive current collector.

The composition of the positive electrode current collector is not particularly limited in the present invention, and may be selected from positive electrode current collectors conventionally used in the art, such as aluminum foil.

In a specific embodiment, the positive electrode active material layer includes a positive electrode active material, a conductive agent, and a binder.

Specifically, the positive electrode active material includes, but is not limited to, one or more of layered metal oxides, polyanionic compounds, prussian blue/white compounds.

The types of the conductive agent and the binder may refer to the selection range of the conductive agent and the binder in the negative electrode sheet, and will not be described herein.

The composition of the separator may also be referred to as a conventional separator composition in the art, and by way of example, the separator may be a PP separator, a PE separator, a PP and PE composite separator, or the like.

The preparation method of the battery is not particularly limited, and it may be prepared by referring to a conventional method in the art.

For example, in one specific embodiment, a battery may be prepared by:

And placing the positive plate, the diaphragm and the negative plate in sequence, then obtaining a battery core assembly through winding or lamination, and then obtaining the battery after the procedures of liquid injection, formation, capacity division and the like.

The invention also provides an electronic device comprising a battery as described above. The invention is not particularly limited to electronic equipment, and can be any electric equipment comprising the battery, including but not limited to mobile phones, portable equipment, notebook computers, electric bicycles, electric automobiles, electric toys, energy storage equipment and the like.

The negative electrode sheet and the application thereof provided by the invention will be specifically described by way of specific examples.

Unless otherwise indicated, reagents, materials and equipment used in the examples below are conventional in the art, conventional materials and conventional equipment, and are commercially available, and the reagents involved can also be obtained synthetically by methods conventional in the art.

Example 1

The embodiment provides a negative electrode sheet and a battery, and the preparation method thereof is as follows:

1. preparation of negative electrode sheet

The hard carbon material with the particle size D50 of 6 mu m, the conductive agent SP, the nano lubrication factor SiO ₂ with the particle size D50 of 300nm, SBR and CMC are mixed according to the mass ratio of 95:1.5:0.5:1.5:1.5 dispersing in solvent water to form anode active slurry with the viscosity of 3000 Pa.s, coating the slurry on the two side surfaces of an aluminum foil with the thickness of 15 mu m of an anode current collector, baking for 2min at 80 ℃, and rolling and tabletting to obtain the anode sheet.

2. Preparation of positive plate

And (3) mixing and pulping the laminar oxide NFM (NaNi _1/3Fe_1/3Mn_1/3O₂) serving as the anode active material, the conductive agent SP and the PVDF according to the mass ratio of 97:1.5:1.5, coating the mixture on the surfaces of two sides of the 17-mu m carbon-coated aluminum foil serving as the anode current collector, and drying, rolling and tabletting to obtain the anode plate.

3. Battery assembly

Placing the prepared negative electrode sheet, the prepared diaphragm and the prepared positive electrode sheet in sequence, winding to obtain a battery core, placing the battery core in an outer packaging foil, injecting electrolyte, and performing processes such as formation, capacity division and the like to obtain a battery;

Wherein the electrolyte comprises 10% of NaPF ₆, 50% of PP, 35% of EMC, 4% of FEC, 0.4% of PST and 0.6% of DTD according to mass percentage.

Example 2

The present embodiment provides a negative electrode sheet and a battery, the preparation method of which is substantially the same as that of embodiment 1, except that in the preparation of the negative electrode sheet, the mass ratio of hard carbon material, conductive agent SP, nano lubrication factor SiO ₂, SBR and CMC is replaced with 95:1.0:1.0:1.5:1.5.

Example 3

The present embodiment provides a negative electrode sheet and a battery, and the preparation method thereof is basically the same as that of embodiment 1, except that in the preparation of the negative electrode sheet, no conductive agent SP is added, and the mass ratio of the hard carbon material, the nano lubrication factor SiO ₂, the SBR and the CMC is 95:2:1.5:1.5.

Example 4

The present embodiment provides a negative electrode sheet and a battery, the preparation method of which is substantially the same as that of embodiment 2, except that in the preparation of the negative electrode sheet, the nano lubrication factor is replaced with a nano lubrication factor having a mass ratio of 3: siO ₂ and MoS ₂ of 1.

Example 5

This example provides a negative electrode sheet and a battery, the production method of which is substantially the same as that of example 2, except that in the production of the negative electrode sheet, the particle diameter D50 of the used nano lubrication factor is replaced with 100nm.

Example 6

This example provides a negative electrode sheet and a battery, the manufacturing method of which is basically the same as that of example 2, except that in the manufacturing of the negative electrode sheet, the particle diameter D50 of the used nano lubrication factor is replaced with 900nm.

Example 7

This example provides a negative electrode sheet and a battery, the production method of which is substantially the same as that of example 2, except that in the production of the negative electrode sheet, the particle diameter D50 of the hard carbon material used was replaced with 2 μm.

Example 8

The present example provides a negative electrode sheet and a battery, the manufacturing method of which is substantially the same as that of example 2, except that in the preparation of the negative electrode sheet, the nano lubrication factor was replaced with Al ₂O₃.

Example 9

The present example provides a negative electrode sheet and a battery, the preparation method of which is basically the same as that of example 2, except that in the preparation of the negative electrode sheet, the nano lubrication factor is replaced with TiO ₂.

Example 10

The present example provides a negative electrode sheet and a battery, the preparation method of which is basically the same as that of example 2, except that in the preparation of the negative electrode sheet, the nano lubrication factor is replaced with CaCO ₃.

Example 11

The present example provides a negative electrode sheet and a battery, the preparation method of which is substantially the same as that of example 2, except that in the preparation of the negative electrode sheet, the nano lubrication factor is replaced with polystyrene microspheres.

Example 12

The present example provides a negative electrode sheet and a battery, the manufacturing method of which is substantially the same as that of example 2, except that the nano lubrication factor was replaced with fullerene C60 in the preparation of the negative electrode sheet.

Example 13

This example provides a negative electrode sheet and a battery, the preparation method of which is basically the same as that of example 2, except that in the preparation of the negative electrode sheet, the nano lubrication factor is replaced with calcium borate.

Example 14

The present embodiment provides a negative electrode sheet and a battery, the manufacturing method of which is substantially the same as that of embodiment 2, except that in the manufacturing of the negative electrode sheet, the mass ratio of hard carbon material, conductive agent SP, nano lubrication factor SiO ₂, SBR and CMC is replaced with 79:1.0:15:1.5:1.5.

Example 15

The present embodiment provides a negative electrode sheet and a battery, the preparation method of which is substantially the same as that of embodiment 1, except that in the preparation of the negative electrode sheet, the mass ratio of hard carbon material, conductive agent SP, nano lubrication factor SiO ₂, SBR and CMC is replaced with 95:1.95:0.05:1.5:1.5.

Example 16

The present embodiment provides a negative electrode sheet and a battery, the preparation method of which is substantially the same as that of embodiment 2, except that in the preparation of the negative electrode sheet, the nano lubrication factor is replaced with a nano lubrication factor having a mass ratio of 3: al ₂O₃ and MoS ₂ of 1.

Example 17

The present example provides a negative electrode sheet and a battery, the manufacturing method of which is basically the same as that of example 2, except that in the manufacturing of the negative electrode sheet, the nano lubrication factor is replaced with MoS ₂.

Example 18

The present example provides a negative electrode sheet and a battery, the preparation method of which is substantially the same as that of example 2, except that in the preparation of the negative electrode sheet, the nano lubrication factor is replaced with SiO ₂、Al₂O₃ and MoS ₂ in a mass ratio of 1.5:1.5:1.

Example 19

The present example provides a negative electrode sheet and a battery, the preparation method of which is basically the same as that of example 2, except that in the preparation of the negative electrode sheet, the nano lubrication factor is replaced with TiO ₂ and MoS ₂ in a mass ratio of 3:1.

Example 20

This example provides a negative electrode sheet and a battery, the preparation method of which is basically the same as that of example 2, except that in the preparation of the negative electrode sheet, the nano lubrication factor is replaced with ZnS.

Example 21

The present example provides a negative electrode sheet and a battery, the preparation method of which is substantially the same as that of example 2, except that in the preparation of the negative electrode sheet, the nano lubrication factor was replaced with SiO ₂ and ZnS in a mass ratio of 3:1.

Example 22

The present example provides a negative electrode sheet and a battery, the manufacturing method of which is basically the same as that of example 2, except that in the preparation of the negative electrode sheet, the nano lubrication factor is replaced with SiO ₂ and MoS ₂ in a mass ratio of 1:1.

Example 23

The present example provides a negative electrode sheet and a battery, the manufacturing method of which is basically the same as that of example 2, except that in the preparation of the negative electrode sheet, the nano lubrication factor is replaced with SiO ₂ and MoS ₂ in a mass ratio of 2:1.

Example 24

The present example provides a negative electrode sheet and a battery, the manufacturing method of which is basically the same as that of example 2, except that in the preparation of the negative electrode sheet, the nano lubrication factor is replaced with SiO ₂ and MoS ₂ in a mass ratio of 1:3.

Example 25

This example provides a negative electrode sheet and a battery, the manufacturing method of which is basically the same as that of example 2, except that the nano lubrication factor is replaced with Cu in the manufacturing of the negative electrode sheet.

Example 26

This example provides a negative electrode sheet and a battery, which were basically identical to example 2 in the preparation method, except that the hard carbon material used in the preparation of the negative electrode sheet was replaced with 3 μm in particle diameter D50.

Example 27

This example provides a negative electrode sheet and a battery, which were basically identical to example 2 in the preparation method, except that the hard carbon material used in the preparation of the negative electrode sheet was replaced with 10 μm in particle diameter D50.

Example 28

This example provides a negative electrode sheet and a battery, which were basically identical to example 2 in the preparation method, except that the hard carbon material used in the preparation of the negative electrode sheet was replaced with 12 μm in particle diameter D50.

Example 29

This example provides a negative electrode sheet and a battery, the manufacturing method of which is basically the same as that of example 2, except that in the manufacturing of the negative electrode sheet, the particle diameter D50 of the used nano lubrication factor SiO ₂ is replaced with 600nm.

Example 30

This example provides a negative electrode sheet and a battery, the manufacturing method of which is basically the same as that of example 2, except that the particle diameter D50 of the used nano lubrication factor SiO ₂ was replaced with 30nm in the manufacturing of the negative electrode sheet.

Comparative example 1

This comparative example provides a negative electrode sheet and a battery, the preparation method of which is substantially the same as that of example 1, except that silicon dioxide is not added in the preparation of the negative electrode sheet, and the mass ratio of the hard carbon material, the conductive agent SP, SBR and CMC is 95:2:1.5:1.5.

Test case

1. Cross-section SEM

The testing method comprises the following steps: and acquiring the section morphology photographs of the negative plates of examples 1-3 and comparative example 1 by adopting a scanning electron microscope, and observing the distribution of nano lubrication factors and pores in the negative plates.

Fig. 2 is an SEM image of a cross section of a negative electrode sheet of example 1, fig. 3 is an SEM image of a cross section of a negative electrode sheet of example 2, fig. 4 is an SEM image of a cross section of a negative electrode sheet of example 3, fig. 5 is an SEM image of a cross section of a negative electrode sheet of comparative example 1, and as can be seen from comparison of fig. 2 to 5, pores among hard carbon particles in the negative electrode sheet of comparative example 1 are more and larger, porosity is high, compaction density of the sheet is low, whereas the gaps between the hard carbon particles of the negative electrode sheet become smaller, contact of the particles becomes tighter, and porosity becomes lower as the addition ratio of the nano lubrication factor increases in the negative electrode sheet of examples 1 to 3.

2. Negative plate compaction density

The testing method comprises the following steps: the negative electrode sheets of examples and comparative examples were gradually pressurized under a pressure of 0 to 50t, respectively, rolled, the thickness of the electrode sheet was measured, and then the maximum compaction density achievable by the electrode sheet was determined in combination with the surface state of the electrode sheet, and the values are shown in table 1.

3. Resistivity of negative electrode sheet

The testing method comprises the following steps: the overall resistivity of the negative plates of the above examples and comparative examples, i.e., the sum of the active material layer resistance, the active material layer-to-current collector contact resistance, and the current collector resistance, was measured directly by a BER-series multifunctional plate resistance meter using a biplane controlled voltage disk electrode resistance method, and the values are listed in table 1.

4. First-turn coulombic efficiency of battery

The testing method comprises the following steps: in the constant current charge and discharge mode, the lithium ion batteries of examples and comparative examples were charged to an upper limit voltage of 3.8V at a current density of 0.33C, then constant-voltage charged to a cutoff current of 0.05C at 3.8V, and then discharged to a cutoff voltage of 2.0V at 0.33C, the first-turn charge capacity Q1 and the first-turn discharge capacity Q ₂ of the batteries were recorded, and the first-turn coulomb efficiency of the batteries was calculated from Q ₂/Q₁. The results are shown in Table 1.

5. Coefficient of liquid injection

The testing method comprises the following steps: weighing fresh battery cells, namely weighing the fresh battery cells to be g ₁, and after disassembling the battery cells, weighing the weight g ₂ of the dry pole piece and the weight g ₃ of the structural part to obtain the liquid injection amount g=g ₁-g₂-g₃; and then calculating the liquid injection coefficient by the liquid injection amount/cell capacity to obtain the unit g/Ah. The results are shown in Table 1.

6. Porosity of negative electrode sheet

The testing method comprises the following steps: and measuring the pore size distribution and the porosity of the solid material by referring to GB/T21650.1-2008 mercury porosimetry and gas adsorption method, and adopting the mercury porosimetry to test to obtain the porosity of the negative plate.

TABLE 1

From Table 1, the following conclusions can be analytically drawn:

1) The porosity of the negative electrode plate, the liquid injection coefficient and the compaction density of the negative electrode plate are related, the porosity of the negative electrode plate is low, and the smaller the liquid injection coefficient is, the higher the compaction density of the negative electrode plate is.

2) The resistivity of the negative plate is related to the contents of the conductive agent and the nano lubrication factor, the more the content of the nano lubrication factor is, the greater the compaction density of the negative plate is, the more tightly the hard carbon particles are contacted, the smaller the contact resistance is, and the resistivity of the negative plate is smaller;

As can be seen from the comparison of examples 1 to 3 and examples 14 to 15, when the nano lubrication factor is a non-conductive particle, the decrease in the content of the conductive agent causes a decrease in conductivity with an increase in the content of the nano lubrication factor, which is detrimental to the resistivity of the negative electrode sheet; the content of the conductive agent is fixed, the content of the nano lubrication factor is increased, when the content of the hard carbon material is reduced, the resistivity of the negative plate is increased, and the excessive nano lubrication factor is difficult to disperse in the negative active material layer, so that the dispersion is uneven, the lubrication effect is difficult to play, and the compaction density of the negative plate is obviously reduced;

In summary, a plurality of factors are needed to be considered, so that the addition amount of the non-conductive nano lubrication factor and the conductive agent is balanced so as to ensure that the negative plate has higher compaction density and lower negative plate resistivity;

As can be seen from a comparison of examples 2, 12 and 25, when the nano lubrication factor is conductive fullerene C60 and nano elemental Cu, the lubrication effect of both is weaker than that of silicon dioxide, resulting in a higher porosity and a lower compacted density of the negative electrode sheet, but the negative electrode sheet still has a resistivity comparable to that of example 2 due to the conductive effect of the nano lubrication factor.

3) As can be seen from comparative examples 1,2, 3, and 15, the initial coulombic efficiency of the battery gradually decreases as the content of the conductive agent increases, because the conductive agent has a large number of lithium reactive sites, and active lithium ions are consumed during formation, resulting in a decrease in initial coulombic efficiency; as is clear from comparative examples 2 and 14, when the content of the conductive agent in the anode active material layer is uniform, the content of the nano lubrication factor is excessively increased, and the content of the hard carbon material is reduced, the initial coulombic efficiency of the battery is increased, because the content of the hard carbon material is smaller, and the film-forming active sites are smaller, so that the lithium ion content consumed for forming the SEI film by the initial charge and discharge is smaller, thereby being beneficial to the improvement of the initial coulombic efficiency of the battery.

4) As can be seen from comparative examples 2,4, 8-13, 16-25, compared with the nano lubrication factor selected from the group consisting of TiO ₂、CaCO₃, polystyrene microsphere, fullerene C60, calcium borate, moS ₂, znS, and other compounds, the nano oxides of both silica and Al ₂O₃ exhibit better nano lubrication, so that the negative electrode sheet has higher density; surprisingly, however, although it is difficult to obtain a higher compacted density of the negative electrode sheet using nano sulfides such as ZnS and MoS ₂ alone, when a mixture of nano oxides and nano sulfides is used as the nano lubrication factor, the negative electrode sheet has a higher compacted density, neither of which is lower than 1.03 g/cm ³, and especially the nano lubrication factor is selected from a mixture of SiO ₂ and MoS ₂ or a mixture of Al ₂O₃ and MoS ₂, and the mixing mass ratio of both is 3:1, the compaction density of the negative plate is highest, and the negative plate has lower resistivity and higher initial circle coulomb efficiency of the battery.

5) As can be seen from comparative examples 2, 5 to 6 and 29 to 30, the D50 particle size of the nano lubrication factor also affects the compacted density of the negative electrode sheet, wherein the compacted density of the negative electrode sheet is highest when the D50 particle size of the nano lubrication factor is 300nm, and gradually decreases as the D50 particle size decreases to 100nm and 30nm, and gradually decreases as the D50 particle size increases to 600nm and 900nm, respectively.

6) As is clear from comparative examples 2, 7, 26 to 28, the D50 particle size of the hard carbon material also affects the compaction density of the negative electrode sheet, wherein the compaction density of the negative electrode sheet is highest when the D50 particle size of the hard carbon material is 6 μm, the compaction density of the negative electrode sheet gradually decreases with the decrease of the particle size when the D50 particle size of the hard carbon material is reduced to 3 μm and 2 μm, and the compaction density of the negative electrode sheet gradually decreases with the increase of the particle size when the D50 particle size is increased to 10 μm and 12 μm, respectively, and accordingly the resistivity of the negative electrode sheet also increases.

7) As is apparent from comparative examples 1 and 1, when the nano lubrication factor is not added, the porosity of the negative electrode sheet is significantly increased and the resistivity of the negative electrode sheet is significantly increased, and the compacted density of the negative electrode sheet is significantly reduced.

The above embodiments are only for illustrating the technical solution of the present invention, and not for limiting the same; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some or all of the technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit of the invention.

Claims

1. A negative electrode sheet, characterized in that it comprises a negative electrode current collector and a negative electrode active material layer disposed on at least one side of the negative electrode current collector, wherein the negative electrode active material layer comprises a hard carbon material and a nano-lubricating factor;

The nano-lubricating factor comprises a mixture of nano-oxide and nano-sulfide in a mass ratio of (1-3):1;

The nano oxide is selected from SiO ₂ and/or Al ₂ O ₃ , and the nano sulfide is selected from MoS ₂ .

2. The negative electrode sheet according to claim 1, characterized in that the D50 particle size of the nano-lubricating factor is 50-800 nm;

And/or, the D50 particle size of the hard carbon material is 3-10 μm.

3 . The negative electrode sheet according to claim 1 , wherein the mass ratio of the hard carbon material to the nano-lubricating factor is 100:(0.1-10).

4. The negative electrode sheet according to claim 1, characterized in that the negative electrode active material layer further comprises a conductive agent and/or a binder;

The mass ratio of the hard carbon material, the nano-lubricating factor, the conductive agent and the binder is (80-100): (1-5): (0-5): (0.1-10).

5 . The negative electrode sheet according to claim 1 , wherein the negative electrode sheet has a compaction density of ≥0.98 g/cm ³ , a resistivity of 0.2-0.8 mΩ·cm, and a porosity of 30%-40%.

6. A battery comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the negative electrode sheet comprises the negative electrode sheet according to any one of claims 1 to 5.

7. The battery according to claim 6, characterized in that the electrolyte comprises, by mass percentage, 5% to 20% of NaPF ₆ , 30% to 60% of propylene carbonate, 30% to 50% of ethyl methyl carbonate, 2% to 5% of fluoroethylene carbonate, 0.1% to 0.8% of propenyl-1,3-sultone, and 0.2% to 0.8% of vinyl sulfate.

8. The battery according to claim 6 or 7, characterized in that the injection coefficient of the electrolyte is 3-10 g/Ah;

The test method of the injection coefficient is as follows: weigh the fresh battery cell as the total weight g ₁ , disassemble the battery cell, weigh the weight of the dry electrode g ₂ , the weight of the structural part g ₃ , and obtain the injection volume g=g ₁ -g ₂ -g ₃ ; then calculate the injection coefficient by injection volume/battery cell capacity, in units of g/Ah.

9. An electronic device, characterized by comprising the battery according to any one of claims 6 to 8.