CN111384388B

CN111384388B - High-energy-density lithium ion battery

Info

Publication number: CN111384388B
Application number: CN201811638969.6A
Authority: CN
Inventors: 王岑; 张和宝; 李喆; 叶兰
Original assignee: Amprius Nanjing Co ltd
Current assignee: Boselis Hefei Co ltd; Bosellis Nanjing Co ltd
Priority date: 2018-12-29
Filing date: 2018-12-29
Publication date: 2021-09-28
Anticipated expiration: 2038-12-29
Also published as: CN111384388A

Abstract

The invention relates to a high-energy density lithium ion battery, wherein the anode is one or more of the following: LiCoO₂、Li(Ni_xMn_yCo_1‑x‑y)O₂(0≤x≤1,0≤y≤1)、Li(Ni_xCo_yAl_1‑x‑y)O₂(0≤x≤1,0≤y≤1)、Li₂MnO₄、LiNi_0.5Mn_0.5O₂、LiNi_0.5Mn_1.5O₄、LiMPO₄，aLi₂MnO₃·(1‑a)Li(Ni_xMn_yCo_1‑x‑y)O₂(x is more than or equal to 0 and less than or equal to 1, and y is more than or equal to 0 and less than or equal to 1); the negative electrode comprises silicon particles with surface modification, a carbon conductive agent capable of forming a conductive network, an organic polymer binder with high tensile strength and high elastic deformation characteristics and a current collector substrate beneficial to electronic conduction. The invention can improve the energy density of the battery, the multiplying power performance and the low-temperature performance of the battery and has better safety performance.

Description

High-energy-density lithium ion battery

Technical Field

The invention relates to the field of lithium ion batteries, in particular to a high-energy-density lithium ion battery.

Background

In recent years, with the gradual consumption of traditional fossil energy and the increasingly serious global warming problem, the importance of new energy in future society is becoming more and more recognized. In all new energy systems, solar energy, wind energy, water energy, nuclear energy and the like do not have convenient mobility; lithium ion batteries, as a portable energy storage form, have their particular irreplaceability in practical applications, and thus are widely used.

Although fuel-powered engines will continue to exist for some time in the future, the trend that new energy vehicles will become the leading actors is unalterable.

Although the trend of new energy vehicles to become the leading corner is not changed, people are consciously aware that the energy density of the power system (battery, motor, cable harness) of a pure electric vehicle is far from meeting the current demand compared with the power system (engine, gearbox, oil tank, transmission shaft) of a traditional fuel vehicle. It is stated above that the contribution of silicon materials, especially high capacity silicon materials, to the energy density of a battery is very promising.

Silicon anode materials have incomparable high capacity advantage (Li) over other anode materials₂₂Si₅And the theoretical lithium storage capacity at normal temperature is 3600 mAh/g), which is about 10 times of the theoretical capacity of the current commercial graphite cathode material. However, since silicon is a semiconductor and has slightly poor electron conductivity, it is thought that the addition of a small amount of silicon material to the conventional pure graphite negative electrode system improves the capacity without affecting the electron transport properties of the electrode. However, due to the natural characteristics of the electronic state distribution of the graphite and silicon materials, lithium ions are preferentially inserted into the silicon lattice to form a lithium silicon alloy during lithium intercalation (corresponding to the charging process of the battery) and then are inserted into the graphite lattice to form a lithium carbon alloy in the graphite-doped silicon negative electrode system. Therefore, the serious volume effect exists in the process of completely inserting and extracting lithium from silicon, the volume change rate is about 400 percent, electrode material pulverization and electrode material and current collector separation are easily caused, and the silicon material loses electrochemical activity at the early stage of the cycle of the battery, namely most of the silicon material loses electrochemical activity; in addition, silicon is caused by volume effect during charge and dischargeA Solid Electrolyte Interface (SEI) protective layer formed on the surface of the material is continuously broken and fresh silicon surface is repeatedly exposed to the electrolyte, and thus the electrolyte is continuously consumed to generate a new SEI film, which adversely affects the cycle performance of the battery. Although many structures are conceived to be compounded with silicon and carbon materials or graphite materials, the above problems are not well solved. In summary, it is not easy to blend the silicon negative electrode material with the graphite material to increase the energy density and satisfy the commercialization conditions.

Disclosure of Invention

The invention provides a high-energy-density lithium ion battery, which breaks through the conventional main composition taking silicon materials as a negative electrode, completely replaces the traditional graphite material, obtains the high-energy-density lithium ion battery and can be suitable for large-scale commercial production.

In order to achieve the purpose, the technical scheme provided by the invention is as follows:

a high energy density lithium ion battery is provided,

the battery comprises a positive electrode, a negative electrode, electrolyte, a diaphragm and a packaging material;

the positive electrode material is one or more of the following: LiCoO₂、Li(Ni_xMn_yCo_1-x-y)O₂(0≤x≤1,0≤y≤1)、Li(Ni_xCo_yAl_1-x-y)O₂(0≤x≤1,0≤y≤1)、Li₂MnO₄、LiNi_0.5Mn_0.5O₂、LiNi_0.5Mn_1.5O₄、LiMPO₄，aLi₂MnO₃• (1-a)Li(Ni_xMn_yCo_1-x-y)O₂(x is more than or equal to 0 and less than or equal to 1, y is more than or equal to 0 and less than or equal to 1), and M is selected from one or more of Co, Ni and Mn;

the negative electrode comprises silicon particles with surface modification, a carbon conductive agent capable of forming a conductive network, an organic polymer binder with high tensile strength and high elastic deformation characteristics and a current collector substrate beneficial to electronic conduction;

the mass fraction of the silicon particles with surface modification in the electrode is 80-96%, the mass fraction of the carbon conductive agent capable of forming a conductive network in the electrode is 0.8-6%, and the mass fraction of the organic polymer binder with high tensile strength and high elastic deformation characteristics in the electrode is 3-15%;

wherein the porosity of the negative electrode is 35-50%.

Wherein the capacity density of the negative electrode is more than or equal to 780mAh/cm³；

The surface capacity of the negative electrode is 3.0-10.0mAh/cm²。

Further, the silicon particles in the silicon particles with surface modification are monocrystalline silicon particles, polycrystalline silicon particles, amorphous silicon particles, crystalline silicon wires, amorphous silicon wires, crystalline silicon rods, amorphous silicon rods, crystalline silicon tubes, amorphous silicon tubes, crystalline silicon cones, amorphous silicon cones, crystalline porous silicon, amorphous porous silicon, crystalline hollow silicon spheres, amorphous hollow silicon spheres, and one or more combinations of all the above materials processed by lithium pre-intercalation (pre-lithiation).

Preferably, the mass fraction of the silicon particles with surface modification in the electrode is 85% -96%.

Preferably, the mass fraction of the silicon particles with surface modification in the electrode is 90-96%.

Preferably, the mass fraction of the silicon particles with surface modification in the electrode is 92% to 96%.

Further, the silicon particles having surface modification have a median particle diameter D50 of 0.8 to 6.0 μm and a maximum particle diameter D100 of less than or equal to four times the value corresponding to the median particle diameter D50.

Preferably, the silicon particles with surface modification have a median particle diameter D50 of 0.8 to 1.8 microns and a maximum particle diameter D100 of less than or equal to four times the value corresponding to the median particle diameter D50.

Preferably, the silicon particles with surface modification have a median particle diameter D50 of 1.3 to 4.2 microns and a maximum particle diameter D100 of less than or equal to four times the value of the corresponding median particle diameter D50.

Preferably, the silicon particles with surface modification have a median particle diameter D50 of 3.5 to 6.0 microns and a maximum particle diameter D100 of less than or equal to four times the value corresponding to the median particle diameter D50.

Further, the surface of the silicon particle with the surface modification is carbon-coated, and the graphitization degree of the coated carbon is not limited, and the silicon particle can be either amorphous carbon or graphitized carbon;

the mass fraction of the coated carbon in the silicon particles with surface modification is 1-5%.

The precursor modified by carbon coating is a hydrocarbon compound.

Further, the hydrocarbon compound is preferably one or a combination of more of glucose, sucrose, low-temperature coal pitch, medium-temperature coal pitch, high-temperature coal pitch, low-temperature petroleum pitch, medium-temperature petroleum pitch, high-temperature petroleum pitch, dopamine, hydrogel, phenolic resin, polyvinyl alcohol, ethylene, acetylene and propylene.

The invention discloses a high-energy-density lithium ion battery, which comprises silicon particles with surface modification, a carbon conductive agent capable of forming a conductive network, an organic polymer binder with high tensile strength and high elastic deformation characteristics and a current collector substrate beneficial to electronic conduction, wherein the silicon particles are coated with a silicon coating;

the mass fraction of the silicon particles with surface modification in the electrode is 80-96%, the mass fraction of the carbon conductive agent capable of forming a conductive network in the electrode is 0.8-6%, and the mass fraction of the organic polymer binder with high tensile strength and high elastic deformation characteristics in the electrode is 3-15%; therefore, the negative electrode of the present invention is distinct from a negative electrode system in which graphite incorporates a small amount of silicon-containing material, and can be considered as a negative electrode similar to a pure silicon material. In the negative electrode system of the graphite doped with a small amount of silicon-containing material, the silicon material is in a state of nearly completely lithium-inserting during charging and discharging and nearly completely lithium-removing during discharging, which means that for a single silicon particle (or crystal grain), the silicon material repeatedly undergoes a process of expanding to a maximum value and then contracting to a minimum value, and a Solid Electrolyte Interface (SEI) is continuously formed on the surface of the silicon particle (or crystal grain), so that electrolyte and lithium ions are consumed, and the capacity of the battery is rapidly attenuated. The above phenomenon is more remarkable as the doping amount of silicon increases. The negative electrode system can well control the lithium intercalation/deintercalation capacity of the silicon negative electrode, namely the expansion and contraction degree of the negative electrode as long as the voltage window of the negative electrode for deintercalating lithium during circulation is well controlled, so that the SEI material formed on the silicon surface is damaged as little as possible and is reformed again, and the circulation performance of the silicon material can be effectively improved; meanwhile, because a certain margin is still left when the silicon negative electrode is embedded with lithium, the battery does not need to worry about the failure caused by lithium precipitation on the surface like the traditional graphite negative electrode when being overcharged, thereby improving the safety of the battery; secondly, the high silicon content in the negative electrode can still effectively ensure the high capacity (600-2000 mAh/g) of the negative electrode, and compared with a graphite negative electrode, the coating thickness or the surface density of the negative electrode can be greatly reduced, so that the energy density of the battery is improved; thirdly, as the surface density of the cathode is greatly reduced, the dynamic performance of the cathode in the aspect of electron and ion mass transfer can be effectively improved, and the rate capability and the low-temperature performance of the battery are further improved; finally, because the potential of the silicon negative electrode material relative to Li metal is naturally higher than that of the graphite negative electrode material when lithium is embedded, the potential of the silicon negative electrode material is still not close to the Li metal in a high-rate rechargeable battery so as to cause lithium precipitation, and therefore, the safety of the silicon negative electrode material is better than that of the graphite negative electrode when the silicon negative electrode material is subjected to quick charge or low-temperature charge.

The surface capacity of the negative electrode is 3.0-10.0mAh/cm²Under the condition of the surface capacity, the effective capacity of the active substance can be exerted to the maximum extent, and unnecessary mass or volume ratio of inactive substances (such as a diaphragm, a copper foil, an aluminum plastic film, an insulating tape, a lug and the like) is reduced, so that the energy density of the battery is optimized, and the battery is suitable for the requirements of the existing batteries for consumer electronics, power batteries and aerospace in large-scale application. If the area capacity is less than 3.0mAh/cm²The mass or volume ratio of the inactive substances in the battery core is too large, so that the value of practical application is lost, which is also a problem commonly existing in experimental data of most academic articles.

The porosity of the negative electrode is 35-50%, and in the porosity range, the electrolyte can perfectly infiltrate the inside of the negative electrode pole piece, and meanwhile, good electrical contact between negative electrode particles can be ensured, so that the electronic and ionic conduction of the surface of the negative electrode can realize the most optimized balance, and the energy density and the dynamic performance of the battery can also reach a higher balance state.

The silicon particles with surface modification have a median particle diameter D50 of 0.8-6.0 microns and a maximum particle diameter D100 of less than or equal to four times the value of the corresponding median particle diameter D50; since the thickness of the electrode is usually much larger than the size of a single particle, the problem of uneven thickness or uneven stress caused by the expansion of local large particles can be effectively prevented by the limitation of the particle size of the silicon particles.

The surface of the silicon particle with the surface modification is carbon-coated modification, the graphitization degree of the coated carbon is not limited, and the silicon particle can be either amorphous carbon or graphitized carbon, and preferably graphitized carbon. The arrangement of carbon atom layers in the graphitized carbon material is more regular, and the conductivity of the graphitized carbon material is higher than that of an amorphous carbon layer, so that the transmission of electrons during charge and discharge is facilitated; meanwhile, the expansion stress resistance of the graphitized carbon coating material is more outstanding, and the cracking of the carbon shell caused by the huge expansion of the silicon particles during lithium intercalation can be better relieved.

The carbon conductive agent capable of forming a conductive network in the negative electrode can be at least one or a combination of more of conductive carbon black particles, acetylene black, chain carbon black, multi-walled carbon nanotubes, single-walled carbon nanotubes, super-ordered carbon nanotubes, vapor-grown carbon fibers, conductive graphite flakes, multi-layer graphene and single-layer graphene. The zero-dimensional, one-dimensional and two-dimensional conductive agents are organically combined to play a bridging role, so that an electronic conduction network of the cathode is effectively established, and the circulation stability of the electrode in a long circulation process is ensured.

Preferably, the carbon conductive agent capable of forming a conductive network in the negative electrode contains at least one-dimensional conductive agent, such as multi-walled carbon nanotubes, single-walled carbon nanotubes, super-aligned carbon nanotubes, and vapor-grown carbon fibers.

The organic polymer binder in the negative electrode can be at least one or a combination of more of carboxymethyl cellulose, lithium carboxymethyl cellulose, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, lithium polyacrylate, polystyrene acrylic acid copolymer, polyacrylate copolymer, carboxymethyl cellulose-acrylic acid copolymer, polyimide, polyamide imide, polyacrylonitrile acrylic acid copolymer, alginic acid, sodium alginate, lithium alginate, ethylene acrylic acid copolymer, hydrogel, xanthan gum, polyethylene oxide, polyvinyl alcohol and polyacrylic acid-polyvinyl alcohol cross-linked copolymer.

Preferably, the organic polymer binder in the negative electrode contains at least one binder having high tensile strength and high elastic deformation. By combining the organic polymer binders with high tensile strength and high elastic deformation characteristics, the surface of the silicon material is wrapped by the binders, so that on one hand, the expansion of particles can be inhibited to a certain extent, the damage to an SEI (solid electrolyte interphase) film is reduced, on the other hand, the particles can still be tightly connected with the particles and a current collector after the repeated expansion-contraction of the silicon material, the electrical activity of the material is kept, and the cycle performance of the battery is improved.

The current collector substrate which is beneficial to electronic conduction in the negative electrode can be a solid copper foil, a perforated copper foil, a foamed copper foil, a solid copper foil coated with a carbon-containing conducting layer on the surface, a perforated copper foil coated with a carbon-containing conducting layer on the surface, a solid stainless steel foil, a perforated stainless steel foil, a solid stainless steel foil coated with a carbon-containing conducting layer on the surface, a perforated stainless steel foil coated with a carbon-containing conducting layer on the surface, a solid iron foil, a perforated iron foil, a foamed iron foil coated with a carbon-containing conducting layer on the surface, a solid nickel foil, a perforated nickel foil, a foamed nickel foil, a solid nickel foil coated with a carbon-containing conducting layer on the surface, a perforated nickel foil coated with a carbon-containing conducting layer on the surface, and a foamed nickel foil coated with a carbon-containing conducting layer on the surface. The current collector substrate has the main effects of effectively conducting electrons in the electrochemical reaction process and facilitating processing operation in the electrode manufacturing process, and the transmission of the electrons can be effectively promoted by punching, foaming or coating a carbon-containing conducting layer on the surface of the current collector substrate, so that the electrode performance is improved to a certain extent. Preferably, the thickness of the current collector substrate is 4-10 microns.

The battery further includes an electrolyte composition; the electrolyte comprises lithium salt, solvent and additive; the lithium salt includes LiN (C)_xF_2x+1SO₂)(C_yF_2y+1SO₂)、LiPF₆、LiBF₄、LiBOB、LiODFB、LiAsF₆、Li(CF₃SO₂)₂N、LiCF₃SO₃、LiFSI、LiTFSI、LiPO₂F₂、LiClO₄Wherein x and y are positive integers; the solvent comprises one or more of Ethylene Carbonate (EC), Propylene Carbonate (PC), Ethyl Methyl Carbonate (EMC), Methyl Propyl Carbonate (MPC), diethyl carbonate (DEC), dimethyl carbonate (DMC), gamma-butyrolactone (GBL), 1, 3-Dioxolane (DOL), Acetonitrile (AN), Methyl Formate (MF), Methyl Acetate (MA), Ethyl Propionate (EP) and Propyl Propionate (PP); the additive is Vinylene Carbonate (VC), ethylene carbonate (VEC), fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), Propylene Sulfite (PS), Ethylene Sulfite (ES), dimethyl sulfite (DMS), diethyl sulfite (DES), Methylene Methanedisulfonate (MMDS), Biphenyl (BP), Fluorobenzene (FB), Cyclohexylbenzene (CHB), 1-propyl cyclic phosphoric anhydride (PPACA), potassium Perfluorobutylsulfonate (PNB), tris (2,2, 2-trifluoroethyl) phosphite (TTFP), Hexamethylphosphazene (HMPN), 1, 3-propylene sulfonic acid lactone (PTS), lithium tetrafluorophenylboronate, phthalic anhydride, hexamethyldisilazane, glutaronitrile (AND), Succinonitrile (SN), ethylene sulfate (DTD), ethylene glycol dipropyl ether (DENE).

The battery further includes a separator composition; the diaphragm comprises polyethylene, polypropylene, polyethylene-polypropylene, aramid diaphragm, polyimide, PET and non-woven fabric; one or two surfaces of the diaphragm can be coated with functional substances, and the functional substances are one or the combination of a plurality of ceramic materials, high molecular polymers and lithium ion fast conductor materials; the ceramic material is Al₂O₃、TiO₂、AlOOH、ZrO₂、SnO₂、SiO₂、MgO、Mg(OH)₂、Al(OH)₃One or more of CaO and ZnO; the high molecular polymer is polyethylene oxide (PEO), polyvinylidene fluoride (PVDF), polyacrylic acid (PAA) or polymethyl methacrylate (PMMA)One or more of methyl acrylate (PMMA), polyvinyl alcohol (PVA) combination; the lithium ion fast conductor material is one or a combination of more of Lithium Lanthanum Zirconium Oxide (LLZO), Lithium Lanthanum Titanium Oxide (LLTO), lithium germanium phosphorus sulfur compound (LGPS) and lithium phosphorus sulfur compound (LPS).

The battery further includes an encapsulant; the packaging material comprises an aluminum-plastic film, a steel shell, an aluminum shell and an aluminum alloy shell; the shape and size of the packaging material are not limited.

The preparation method of the cathode can adopt the processes of homogenizing, coating, drying and rolling which are commonly used when the lithium ion battery is produced in the conventional industrialization, and silicon particles with surface modification, carbon conductive agent capable of forming a conductive network, organic polymer binder with high tensile strength and high elastic deformation characteristics and solvent are subjected to high-speed shearing action to form uniform and stable slurry, and then the uniform and stable slurry is uniformly coated on a current collector substrate to form a slurry wet film with a certain thickness; drying the slurry wet film by an oven to evaporate the solvent to form an electrode with certain thickness and porosity; and applying pressure to the electrode by using a hydraulic double-roll machine to obtain the negative electrode with the required porosity.

The method comprises the following specific steps:

silicon particles with surface modification, a carbon conductive agent capable of forming a conductive network, an organic polymer binder with high tensile strength and high elastic deformation characteristics and a solvent are subjected to high-speed shearing action with the linear speed of 5-25 m/s and the time of 2-12 h to form uniform and stable slurry;

1. uniformly coating a layer of slurry wet film with the thickness of 80-250 micrometers on a current collector substrate by adopting a conventional coating process, such as transfer coating, extrusion coating and other coating modes;

2. the passing temperature of the slurry wet film is 75-140 DEG C^oEvaporating the solvent after the drying oven of C to form an electrode with the thickness of 30-60 microns and the porosity of 50-70%;

3. and applying pressure to the electrodes by using a hydraulic double-roller machine to obtain the negative electrode with the porosity of 35-50%.

The preparation process of the high-energy-density battery is basically the same as that of the traditional lithium ion battery, and the high-energy-density battery can be suitable for button batteries, winding type soft-package batteries, laminated and winding common soft-package batteries, winding type square hard-shell batteries, laminated type square hard-shell batteries, laminating and winding common square hard-shell batteries, winding type cylindrical batteries and the like, wherein the winding type soft-package batteries are taken as an example, but not limited to the following specific steps:

(1) homogenizing: respectively mixing the positive/negative electrode active material with a thickening agent, a conductive agent, a binder and a proper amount of solvent, and forming stable and uniform fluid with certain viscosity through the high-speed shearing action of a stirrer, namely positive/negative electrode slurry;

(2) coating: uniformly coating the positive/negative electrode slurry on coiled aluminum foil/copper foil by a coating machine according to a certain process in an intermittent coating or continuous coating mode, accurately controlling the coating thickness, width and material quality (namely areal density) in unit area by controlling the parameters of the coating machine, and drying the wet film in the middle coating section by baking equipment to store the pole piece in a coiled manner;

(3) rolling: rolling the coiled pole pieces into pole pieces with lower porosity by a double-roller machine, and coiling and storing the pole pieces;

(4) slitting: cutting the rolled pole piece into certain widths according to the model of the finished battery;

(5) tabletting: adhering an insulating adhesive tape and/or a flat adhesive tape for preventing the direct contact of the positive electrode and the negative electrode to the blank foil of the cut pole piece, and welding corresponding pole lug materials in an ultrasonic welding mode;

(6) winding: winding the positive plate/the diaphragm/the negative plate for a plurality of circles by adopting a manual winding or automatic/semi-automatic winding mode to enable the positive plate/the diaphragm/the negative plate to be tightly contacted to form a winding core, then putting the winding core into an aluminum-plastic packaging shell which is punched by a corresponding die, carrying out top sealing and side sealing by using a packaging machine, and carrying out sealing on the other side edge after liquid injection is finished;

(7) baking: because moisture has a certain negative effect on the lithium ion battery, the lithium ion battery needs to be baked at high temperature for a long time before the electrolyte is injected, so that the moisture content in the winding core is reduced to the lowest possible extent;

(8) liquid injection: injecting a proper amount of electrolyte into the aluminum-plastic packaging shell, wherein the electrolyte contains lithium salt, a main solvent and a small amount of additive;

(9) standing in vacuum: air in the winding core is discharged as much as possible in a vacuumizing mode, so that the positive/negative pole pieces and the diaphragm can be completely soaked by electrolyte;

(10) and (3) sealing: packaging the side edge of the aluminum plastic packaging bag by using a sealing machine, wherein a certain distance is reserved between the sealing position and the winding core, so that a small amount of gas (often called as an air bag) generated by the battery after subsequent pre-formation is convenient to store;

(11) aging: aging for 24-48 h at a certain temperature to enable the electrolyte to more fully infiltrate the diaphragm and the pores in the positive and negative pole pieces;

(12) pre-formation: applying a certain current to the battery through an external power supply to charge the battery core, so that a certain protective film is generated between the positive/negative electrode and the electrolyte, and a part of gas byproducts are generated;

(13) degassing: puncturing the air bag by using degassing equipment, then vacuumizing, and completely removing the gas generated in the pre-formation stage;

(14) and (3) sealing: sealing the part close to the winding core again, and cutting off the air bag to form a complete battery core;

(15) aging: standing the sealed battery cell for 24-48 h at a certain temperature to make the positive/negative electrode surface protective film more stable;

(16) capacity grading: and carrying out 1-2 circulating charge and discharge tests on the battery cells through a certain current, and selecting the battery cells with normal capacity for production shipment.

Compared with the prior art, the invention has the following beneficial effects:

1. the high silicon content in the cathode system can effectively ensure the high capacity of the cathode, namely the coating thickness or the surface density of the cathode can be greatly reduced, thereby being beneficial to improving the energy density of the battery;

2. meanwhile, as the surface density of the cathode is greatly reduced, the dynamic performance of the cathode in the aspect of electron and ion mass transfer can be effectively improved, and the rate capability and the low-temperature performance of the battery are further improved;

3. because the potential of the silicon negative electrode material relative to Li metal is naturally higher than that of the graphite negative electrode material when lithium is embedded, the potential of the silicon negative electrode material is still not close to the Li metal when the silicon negative electrode material is charged with a large multiplying power so as to cause lithium precipitation, and therefore, the safety of the silicon negative electrode material is better than that of the graphite negative electrode when the silicon negative electrode material is charged with the graphite negative electrode material quickly;

4. when the battery is designed, the lithium insertion/removal capacity of the silicon cathode can be well controlled by controlling the surface densities of the cathode and the anode and the cyclic voltage window, namely, the SEI material formed on the silicon surface is damaged as little as possible and is reformed again by controlling the expansion and contraction degrees of the silicon cathode, so that the cyclic performance of the silicon material can be effectively improved; meanwhile, because the silicon negative electrode still has a large margin when lithium is embedded, the battery does not worry about the safety problem of the battery caused by lithium precipitation on the surface like the traditional graphite negative electrode when the battery is overcharged;

5. the preparation process of the electrode is very simple, and the common processes of homogenizing, coating, drying and rolling are adopted when the lithium ion battery is produced industrially.

Drawings

FIG. 1: SEM image of the negative electrode in example 1 at 30 x magnification.

FIG. 2: SEM image of CVD coated polysilicon particles in example 1.

FIG. 3: comparison of cycle retention for example 1 versus comparative examples 3 and 4.

FIG. 4: SEM image of the negative electrode in example 5.

FIG. 5: SEM image of polysilicon particles after coating with carbon in example 6.

FIG. 6: SEM image of polysilicon particles after coating with carbon in example 7.

FIG. 7: SEM image of polysilicon particles after coating with carbon in example 8.

FIG. 8: SEM image of the negative electrode in example 8.

FIG. 9: SEM image of single particles on the surface of the negative electrode in example 8.

FIG. 10: SEM image of single particles on the surface of the negative electrode after 100 charge and discharge cycles in example 8.

Detailed Description

The present invention will be further described with reference to specific examples and comparative examples.

Comparative example 1

Preparing a battery:

(1) homogenizing:

the positive electrode active material lithium cobaltate (LiCoO)₂) With the conductive agent multi-walled carbon nanotubes (MWCNTs) and the thickener/binder polyvinylidene fluoride (PVDF) at 98: 0.8: 1.2, adding a proper amount of solvent N-methyl pyrrolidone (NMP), and forming for 5s by the high-speed shearing action of a planetary stirrer and a high-speed dispersion disc^-1A stable and uniform fluid with the viscosity of 5000mPa & s at the shearing rate is the anode slurry;

the negative active material artificial graphite (median particle diameter D50=18.2 micrometers, maximum particle diameter D100=45.4 micrometers) was mixed with thickener sodium carboxymethyl cellulose (CMCNa) and binder Styrene Butadiene Rubber (SBR) at a ratio of 98.2: 0.8: 1.0, adding a proper amount of deionized water (H)₂O) for 5s by high-speed shearing action with shearing capability such as planetary stirrer and high-speed dispersion plate^-1A stable and uniform fluid with the viscosity of 3000mPa & s at the shearing rate is the negative electrode slurry;

(2) coating:

coating the positive slurry on an aluminum foil of a positive current collector at certain intervals by using special coating equipment, wherein the thickness of the aluminum foil is 8-20 mu m, coating the positive and negative surfaces of the aluminum foil at intervals, and drying the coated pole piece to obtain a positive pole piece;

coating the negative electrode slurry on a copper foil of a negative electrode current collector at certain intervals by using special coating equipment, wherein the thickness of the copper foil is 4-10 mu m, coating the positive and negative surfaces of the aluminum foil at intervals, and drying the coated pole piece to obtain a negative electrode pole piece;

(3) rolling: rolling the coiled pole piece into a pole piece with a certain porosity by a double-roller machine; wherein the porosity of the positive pole piece is 18% (corresponding to the compacted density of 4.182 g/cm)³) The porosity of the negative electrode was 21% (corresponding to a compacted density of 1.738 g/cm)³），Both the two pole pieces are stored in a roll;

(5) tabletting: welding an aluminum lug to the positive electrode according to the designed size to form a leading-out end of the positive electrode, attaching a protective adhesive tape of the positive electrode according to the design requirement after welding the aluminum lug, welding a nickel lug to the negative electrode according to the designed size to form a leading-out end of the negative electrode, and attaching a protective adhesive tape of the negative electrode according to the design requirement after welding the nickel lug;

(6) winding and packaging: winding the positive pole piece/diaphragm/negative pole piece by a plurality of layers in a manual winding or automatic/semi-automatic winding mode to enable the positive pole piece/diaphragm/negative pole piece to be in close contact with each other to form a winding core, then placing the winding core into an aluminum-plastic packaging shell which is punched by a corresponding die, sealing the edge by a sealing machine, and leaving an opening for subsequent liquid injection;

(7) baking: placing the coiled core into a vacuum oven for 120 times^oC. Baking for 24 hours to reduce the water content in the roll core to the minimum;

(8) liquid injection: injecting a proper amount of electrolyte into the aluminum-plastic packaging shell, wherein the electrolyte comprises 1.2M LiPF₆+ ethylene carbonate/ethyl methyl carbonate/diethyl carbonate/vinylene carbonate/fluoroethylene carbonate/a small amount of electrolyte additive;

(9) standing in vacuum: placing the liquid-injected winding core into a vacuum standing box, vacuumizing and keeping the negative pressure for 20min to enable the positive/negative electrode plates and the diaphragm to be capable of completely soaking electrolyte;

(10) and (3) sealing: sealing and welding the last opening of the aluminum-plastic packaging bag by using a sealing machine, wherein a certain distance is reserved between the sealing position and the winding core, so that the storage of a small amount of gas (often called as an air bag) generated by the battery after the subsequent pre-formation is facilitated;

(11) aging: placing the sealed battery at 40^oAging in a standing box for 1-3 days to allow the electrolyte to fully soak all areas again;

(12) pre-formation: charging the battery with a current of 0.01-2C;

(13) degassing: puncturing the air bag by using degassing equipment, vacuumizing, and completely removing gas generated in the pre-formation stage;

(15) aging: the sealed battery cell is arranged at 40^oStanding for 12-72 hours under C to make the surface protective film of the positive/negative electrode more stable;

(16) capacity grading: and carrying out first-cycle charge-discharge activation on the battery cells through a 0.5C charge/0.2C discharge program, and selecting the battery cells with normal capacity for production shipment, wherein the cut-off voltage of the charge activation is 4.4V.

And (3) testing the battery performance: at 25^oUnder the condition of C, the lithium ion battery is charged to the highest charging voltage V by first using a constant current of 0.5C_maxThen charging to a current less than 0.02C at the constant voltage, and discharging the lithium ion battery to the lowest discharge voltage V at a constant current of 0.2C_min. The discharge capacity of this time is recorded as the first cycle discharge capacity, and the discharge energy of this time is divided by the mass of the battery cell to obtain the energy density of the first cycle. Charging the lithium ion battery to the highest charging voltage V at a constant current of 0.5C_maxThen charging to a current less than 0.02C at the constant voltage, and discharging the lithium ion battery to the lowest discharge voltage V at a constant current of 0.5C_min. The discharge capacity of this time is recorded as the second cycle discharge capacity, the lithium ion battery is subjected to n times of 0.5C constant current cycle charge and discharge according to the above mode, and the cycle discharge capacity after the n-th cycle is taken. Capacity retention (%) = [ discharge capacity at n-th cycle/discharge capacity at second cycle)]*100%；。

The full battery is tested to reach 300Wh/kg in first cycle energy density (when the charge-discharge cycle voltage window is 4.4V-2.75V and at the charge-discharge rate of 0.5C) after capacity grading, the first coulombic efficiency is 92.0 percent, and the capacity retention rate after 100 cycles is 97.0 percent.

Comparative example 2

Replacing the formula of the cathode electrode with: the mass ratio of the negative electrode active material artificial graphite (median particle diameter D50=14.0 micrometers, maximum particle diameter D100=39.8 micrometers), SiO with carbon coated on the surface (median particle diameter D50=5.2 micrometers, maximum particle diameter D100=13.5 micrometers), and the conductive agent Vapor Grown Carbon Fiber (VGCF), the thickener lithium polyacrylate (PAANa), and the binder polyacrylate copolymer was 92: 5: 1: 1: 1; the electrode porosity was 21%. Wherein, SiO carries out surface carbon coating by a chemical vapor deposition method: placing SiO powder in the center of a tube furnace, introducing ethylene as a precursor of a carbon coating layer, and heating at 900 ℃ for 3 hours to obtain the SiO with carbon coated on the surface.

The full battery is tested to reach 306 Wh/kg after capacity grading in the first cycle energy density (when the charge-discharge cycle voltage window is 4.4V-2.75V and at the charge-discharge rate of 0.5C), the first coulombic efficiency is 91.2%, and the capacity retention rate after 100 cycles is 92.1%.

Comparative example 3

Replacing the formula of the cathode electrode with: the mass ratio of carbon-coated silicon particles (median particle diameter D50=1.3 micrometers, maximum particle diameter D100=3.9 micrometers) to the conductive agent super-aligned carbon nanotubes, the thickener carboxymethylcellulose sodium (CMCNa), and the binder Styrene Butadiene Rubber (SBR) on the surface of the negative active material was 85: 2: 3: 10; the electrode porosity was 28%. Wherein, the preparation method of the silicon particles coated with carbon on the surface comprises the following steps: 1. uniformly mixing the silicon particles with high-temperature petroleum asphalt; 2. heating and stirring the mixed powder in the step 1 in a coating kettle, and keeping the temperature at 500 ℃ for 2 hours to achieve uniform coating of the asphalt on the surfaces of the silicon particles; 3. and (3) carbonizing the silicon particles coated with the asphalt in the step (2) at 800-1100 ℃ in an inert atmosphere to obtain the silicon particles coated with carbon on the surfaces.

The full battery is tested to reach 327Wh/kg in the first cycle energy density (when the charge-discharge cycle voltage window is 4.4V-2.75V and at the charge-discharge rate of 0.5C) after capacity grading, the first coulombic efficiency is 86.6 percent, and the capacity retention rate after 100 cycles is 61.3 percent.

Comparative example 4

Replacing the formula of the cathode electrode with: the mass ratio of the negative electrode active material polycrystalline silicon particles (median particle diameter D50=1.3 microns, maximum particle diameter D100=3.9 microns) to the conductive carbon black (SuperP) as the conductive agent, the sodium carboxymethyl cellulose (CMCNa) as the thickening agent, the Styrene Butadiene Rubber (SBR) as the binder, and the lithium alginate is 80: 7: 3: 10; the electrode porosity was 35%.

The full battery is tested to reach 328 Wh/kg in first cycle energy density (when the charge-discharge cycle voltage window is 4.4V-2.75V and at the charge-discharge rate of 0.5C) after capacity grading, the first coulombic efficiency is 84.9 percent, and the capacity retention rate after 100 cycles is 66.0 percent.

Example 1

Replacing the formula of the cathode electrode with: the mass ratio of the polycrystalline silicon particles (median particle diameter D50=0.8 micron, maximum particle diameter D100=2.5 micron) coated with carbon, the conductive agent multi-arm carbon nano tube, the conductive graphite, the thickener sodium carboxymethyl cellulose (CMCNa), the sodium polyacrylate (PAANa), the binder Styrene Butadiene Rubber (SBR) and the polystyrene acrylic acid copolymer is 80: 2: 3: 3: 4: 5: 3; the electrode porosity was 35%. Wherein, the powder obtained by crushing the polysilicon is subjected to surface carbon coating by a chemical vapor deposition method: and placing the polycrystalline silicon powder in the center of a tubular furnace, introducing acetylene as a precursor of the carbon coating layer, and heating at 940 ℃ for 2.5 hours to obtain the polycrystalline silicon powder with the carbon coated on the surface. The amount of carbon coated on the surface of the silicon particles was 4.5%.

FIG. 1 is an SEM image of the negative electrode at 30 times magnification, from which it can be seen that the electrode surface is very flat before rolling, which also means that the whole system is relatively uniformly dispersed. Fig. 2 is an SEM image of a polysilicon particle coated with carbon by cvd, which shows that a carbon layer is uniformly deposited on the surface of the particle.

The full battery is tested to reach 340 Wh/kg in the first cycle energy density (when the charge-discharge cycle voltage window is 4.4V-2.75V and at the charge-discharge rate of 0.5C) after capacity grading, the first coulombic efficiency is 86.5 percent, and the capacity retention rate after 100 cycles is 77.8 percent.

Fig. 3 is a comparison curve of cycle retention rates of the full cells of example 1, comparative examples 3 and 4, and it can be seen that the high-content silicon system after carbon coating treatment not only improves the energy density of the cell, but also has better cycle performance.

Example 2

The full battery is tested to reach 346Wh/kg in the first cycle energy density (when the charge-discharge cycle voltage window is 4.4V-2.75V and at the charge-discharge rate of 0.5C) after capacity grading, the first coulombic efficiency is 87.2%, and the capacity retention rate after 100 cycles is 83.5%.

Example 3

The full battery is tested to reach 354Wh/kg after capacity grading in the first cycle energy density (when the charge-discharge cycle voltage window is 4.4V-2.75V and at the charge-discharge rate of 0.5C), the first coulombic efficiency is 87.8 percent, and the capacity retention rate after 100 cycles is 93.2 percent.

Example 4

The positive electrode formula is replaced by: nickel-cobalt-manganese ternary material (Li (Ni)) as positive electrode active material_0.5Mn_0.3Co_0.2)O₂) The mass ratio of the conductive agent multi-layer graphene (MWCNT) to the thickener/binder polyvinylidene fluoride (PVDF) is 98.2: 0.6: 1.2, the electrode porosity is 25%.

Replacing the formula of the cathode electrode with: the mass ratio of the amorphous silicon wire (median particle diameter D50=6.0 microns, maximum particle diameter D100=15.5 microns) coated with glucose as a carbon precursor to the conductive carbon black of the conductive agent, the single-wall carbon nanotube, the carboxymethyl cellulose sodium (CMCNa) of the thickener, the lithium Polyacrylate (PAALi), the Styrene Butadiene Rubber (SBR) of the binder, and the lithium Alginate (Alginate-Li) is 96: 0.5:0.5: 0.5:0.5: 1: 1; the electrode porosity was 40.9%. The preparation method of the amorphous silicon wire with the carbon-coated surface comprises the following steps: 1. dissolving glucose in water to obtain a glucose aqueous solution; 2. adding amorphous silicon nanowires into the glucose aqueous solution obtained in the step (1), and fully stirring and dispersing; 3. drying the amorphous silicon nanowire/glucose syrup material in the step 2 to obtain an amorphous silicon nanowire coated by glucose; 4. and (4) heating and carbonizing the material obtained in the step (3) in an inert atmosphere to obtain the amorphous silicon nanowire with the surface coated with carbon. The amount of carbon coated on the surface of the silicon particles was 3.0%.

The full battery is tested to reach 332Wh/kg after capacity grading in the first cycle energy density (when the charge-discharge cycle voltage window is 4.4V-2.75V and at the charge-discharge rate of 0.5C), the first coulombic efficiency is 87.3 percent, and the capacity retention rate after 100 cycles is 94.0 percent.

Example 5

Replacing the formula of the cathode electrode with: the mass ratio of single crystal silicon particles (median particle diameter D50=1.7 microns, maximum particle diameter D100=4.3 microns) coated with high-temperature coal pitch as a carbon precursor to Vapor Grown Carbon Fibers (VGCF) as a conductive agent, chain carbon black (ECP), carboxymethylcellulose sodium (CMCNa) as a thickener, sodium polyacrylate (PAANa), Styrene Butadiene Rubber (SBR) as a binder, and polyacrylic acrylonitrile copolymer (PAA-PAN) is 90: 2: 2: 1: 1: 2: 2; the electrode porosity was 45%. The preparation method of the high-temperature coal pitch used as the carbon precursor to coat the broken monocrystalline silicon particles comprises the following steps: 1. uniformly mixing the crushed monocrystalline silicon particles with high-temperature coal pitch; 2. heating and stirring the mixed powder in the step 1 in a VC mixer, and keeping the temperature at 400 ℃ for 2 hours to achieve uniform coating of the asphalt on the surfaces of the silicon particles; 3. and (3) heating and carbonizing the silicon particles coated with the asphalt in the step (2) in an inert atmosphere to obtain the silicon particles coated with carbon on the surfaces. The amount of carbon coated on the surface of the silicon particles was 2.6%.

Fig. 4 is an SEM image of the negative electrode when not rolled, from which it can be seen that the active particles and the conductive agent are dispersed relatively uniformly.

The full battery is tested to reach 341 Wh/kg after capacity grading in the first cycle energy density (when the charge-discharge cycle voltage window is 4.4V-2.75V and at the charge-discharge rate of 0.5C), the first coulombic efficiency is 88.1 percent, and the capacity retention rate after 100 cycles is 92.2 percent.

Example 6

The positive electrode formula is replaced by: nickel-cobalt-manganese ternary material (Li (Ni)) as positive electrode active material_0.8Mn_0.1Co_0.1)O₂) The mass ratio of the conductive agent single-walled carbon nanotube (SWCNT) to the thickener/binder polyvinylidene fluoride (PVDF) is 98.8:0.2:1.0, the electrode porosity is 30%.

Replacing the formula of the cathode electrode with: the mass ratio of polycrystalline silicon particles (median particle diameter D50=4.2 micrometers, maximum particle diameter D100=9.8 micrometers) coated with sucrose as a carbon precursor to single-walled carbon nanotubes (SWCNT) as a conductive agent, sodium carboxymethyl cellulose (CMCNa) as a thickening agent, lithium Polyacrylate (PAALi), Styrene Butadiene Rubber (SBR) as a binder, and lithium Alginate (Alginate-Li) was 93: 0.8: 1: 2: 1.6: 1.6; the electrode porosity was 38%. The preparation method of the monocrystalline silicon broken particles coated with the sucrose as the carbon precursor comprises the following steps: 1. dissolving sucrose in water to obtain a sucrose aqueous solution; 2. adding the crushed particles of the monocrystalline silicon into the sucrose aqueous solution obtained in the step (1), and fully stirring and dispersing; 3. drying the silicon particles/sucrose slurry obtained in the step 2 to obtain sucrose-coated monocrystalline silicon crushed particles; 4. and (4) heating and carbonizing the material obtained in the step (3) in an inert atmosphere to obtain the monocrystalline silicon crushed particles with the carbon-coated surfaces. The amount of carbon coated on the surface of the silicon particles was 1.0%.

Fig. 5 is an SEM image of the negative electrode active particles, and the carbon film thickness is thinner when the amount of carbon coated on the surface of the silicon particles is relatively small.

The full battery is tested to reach 354Wh/kg after capacity grading in the first cycle energy density (when the charge-discharge cycle voltage window is 4.2V-2.5V and at the charge-discharge rate of 0.5C), the first coulombic efficiency is 89.2%, and the capacity retention rate after 100 cycles is 92.2%.

Example 7

Replacing the formula of the cathode electrode with: the mass ratio of polycrystalline silicon particles (median particle diameter D50=4.2 micrometers, maximum particle diameter D100=9.8 micrometers) coated with sucrose as a carbon precursor to single-walled carbon nanotubes (SWCNT) as a conductive agent, sodium carboxymethyl cellulose (CMCNa) as a thickening agent, lithium Polyacrylate (PAALi), Styrene Butadiene Rubber (SBR) as a binder, and lithium Alginate (Alginate-Li) was 93: 0.8: 1: 2: 1.6: 1.6; the electrode porosity was 38%. The preparation method of the monocrystalline silicon broken particles coated with the sucrose as the carbon precursor comprises the following steps: 1. dissolving sucrose in water to obtain a sucrose aqueous solution; 2. adding the crushed particles of the monocrystalline silicon into the sucrose aqueous solution obtained in the step (1), and fully stirring and dispersing; 3. drying the silicon particles/sucrose slurry obtained in the step 2 to obtain sucrose-coated monocrystalline silicon crushed particles; 4. and (4) heating and carbonizing the material obtained in the step (3) in an inert atmosphere to obtain the monocrystalline silicon crushed particles with the carbon-coated surfaces. The amount of carbon coated on the surface of the silicon particles was 3.0%.

Fig. 6 is an SEM image of the negative active particles, and when the amount of carbon coated on the surface of the silicon particles is increased, the thickness of the carbon film is increased and the coating uniformity is relatively better.

The full battery is tested to reach 351Wh/kg in first cycle energy density (when the charge-discharge cycle voltage window is 4.2V-2.5V and at the charge-discharge rate of 0.5C) after capacity grading, the first coulombic efficiency is 88.8 percent, and the capacity retention rate after 100 cycles is 92.4 percent.

Example 8

Replacing the formula of the cathode electrode with: the mass ratio of polycrystalline silicon particles (median particle diameter D50=4.2 micrometers, maximum particle diameter D100=9.8 micrometers) coated with sucrose as a carbon precursor to single-walled carbon nanotubes (SWCNT) as a conductive agent, sodium carboxymethyl cellulose (CMCNa) as a thickening agent, lithium Polyacrylate (PAALi), Styrene Butadiene Rubber (SBR) as a binder, and lithium Alginate (Alginate-Li) was 93: 0.8: 1: 2: 1.6: 1.6; the electrode porosity was 38%. The preparation method of the monocrystalline silicon broken particles coated with the sucrose as the carbon precursor comprises the following steps: 1. dissolving sucrose in water to obtain a sucrose aqueous solution; 2. adding the crushed particles of the monocrystalline silicon into the sucrose aqueous solution obtained in the step (1), and fully stirring and dispersing; 3. drying the silicon particles/sucrose slurry obtained in the step 2 to obtain sucrose-coated monocrystalline silicon crushed particles; 4. and (4) heating and carbonizing the material obtained in the step (3) in an inert atmosphere to obtain the monocrystalline silicon crushed particles with the carbon-coated surfaces. The amount of carbon coated on the surface of the silicon particles was 5.0%.

Fig. 7 is an SEM image of the negative active particle, and as the amount of carbon coated on the surface of the silicon particle increases to 5%, the thickness of the carbon film continues to increase, the coating uniformity is relatively best, and the carbon film completely covers the entire surface of the silicon particle. Fig. 8 is an SEM image of the negative electrode, from which it can be seen that the active particles and the conductive agent are dispersed relatively uniformly. Fig. 9 is an SEM of individual particles on the surface of the negative electrode after the negative electrode is formed, from which it is clearly seen that the uniform distribution of the conductive agent single-walled carbon nanotubes on the surface of the particles and the presence of the binder between the particles and the neighboring particles (black contrast area in the upper right corner).

The first cycle energy density (when the charge-discharge cycle voltage window is 4.2V-2.5V and at the charge-discharge rate of 0.5C) of the full battery reaches 350Wh/kg after capacity grading, the first coulombic efficiency is 88.5%, and the capacity retention rate after 100 cycles is 93.0%.

Fig. 10 is an SEM image of surface particles observed after the cycle of the negative electrode, and from the area marked in the white oval frame in the figure, it can be observed that after the particles are expanded and contracted many times and caused to break, the one-dimensional conductive agent capable of forming a highly efficient conductive network and the organic polymer binder having high tensile strength and high elastic deformation characteristics can still effectively cooperate to ensure the electrical conduction between the particles and ensure that the particles always have electrochemical activity.

Example 9

The positive electrode formula is replaced by: nickel-cobalt-manganese ternary material (Li (Ni)) as positive electrode active material_0.6Mn_0.2Co_0.2)O₂) The mass ratio of the conductive carbon black (SuperP) and the thickening agent/binder polyvinylidene fluoride (PVDF) to the conductive agent is 98.0: 0.8: 1.2, the electrode porosity is 27%.

Replacing the formula of the cathode electrode with: the mass ratio of amorphous porous silicon particles (median particle diameter D50=3.5 micrometers, maximum particle diameter D100=8.9 micrometers) coated with hydrogel as a carbon precursor to multilayer graphene (MLG) as a conductive agent, conductive carbon black (SuperP), lithium carboxymethyl cellulose (CMCLi) as a thickener, polyacrylic acid (PAA), polystyrene-acrylic acid copolymer as a binder, and polyvinyl alcohol (PVA) is 90.1: 1.4: 1.5: 1: 0.5: 3: 2.5; the electrode porosity was 42%. The preparation method for coating by using hydrogel as a carbon precursor comprises the following steps: 1. uniformly mixing pyrrole monomers with water-soluble phytic acid and isopropanol to obtain a solution A; 2. dissolving ammonium persulfate in water to obtain solution B; 3. mixing the amorphous porous silicon particles with the solution A and the solution B, and then carrying out ultrasonic treatment for 5 minutes to obtain a colloidal substance; 4. drying the colloidal substance obtained in the step (3), washing the dried colloidal substance with water for multiple times to remove residual unreacted substances, and drying the dried colloidal substance again; 5. and (4) heating and carbonizing the material obtained in the step (4) in an inert atmosphere to obtain the amorphous porous silicon particles coated with hydrogel serving as a carbon precursor. The amount of carbon coated on the surface of the silicon particles was 4.2%.

The full battery is tested to reach 345Wh/kg in first cycle energy density (when the charge-discharge cycle voltage window is 4.3V-2.5V and at the charge-discharge rate of 0.5C) after capacity grading, the first coulombic efficiency is 88.7 percent, and the capacity retention rate after 100 cycles is 90.9 percent.

Example 10

The positive electrode formula is replaced by: nickel-cobalt-manganese ternary material (Li (Ni)) as positive electrode active material_0.8Mn_0.1Co_0.1)O₂)、Li(Ni_0.6Mn_0.2Co_0.2)O₂The mass ratio of the Conductive Graphite (CG) and the chain carbon black (ECP) to the conductive agent and the thickening agent/binder polyvinylidene fluoride (PVDF) is 60: 36: 2: 0.5: 1.5, the electrode porosity was 28%.

Replacing the formula of the cathode electrode with: the mass ratio of amorphous silicon rods (median particle diameter D50=2.4 micrometers, maximum particle diameter D100=6.5 micrometers) coated with high-temperature petroleum pitch as a carbon precursor to Conductive Graphite (CG), chain carbon black (ECP), multilayer graphene (MLG), lithium Polyacrylate (PAALi) as a thickener, polyacrylic acrylonitrile copolymer (PAA-PAN) as a binder, polyethylene oxide (PEO), and ethylene acrylic acid copolymer (EAA) was 85.1: 3.2: 1.2: 1.5: 2: 2: 2; the electrode porosity was 44%. The preparation method of the amorphous silicon rod coated by the high-temperature petroleum pitch serving as the carbon precursor comprises the following steps: adding amorphous silicon rod particles and high-temperature petroleum asphalt into a mechanical fusion machine; 2. setting the rotating speed of a high-temperature fusion machine to be 1500rpm, and carrying out high-speed treatment for 30min to obtain silicon particles with the surfaces coated with asphalt; 3. and (3) carbonizing the silicon particles coated with the asphalt in the step (2) in an inert atmosphere to obtain the silicon particles coated with carbon on the surfaces. The amount of carbon coated on the surface of the silicon particles was 3.2%.

The first cycle energy density (when the charge-discharge cycle voltage window is 4.3V-2.5V and at the charge-discharge rate of 0.5C) of the full battery reaches 360Wh/kg after capacity grading, the first coulombic efficiency is 88.0 percent, and the capacity retention rate after 100 cycles is 91.1 percent.

Example 11

The positive electrode formula is replaced by: lithium cobaltate (LiCoO) as positive electrode active material₂) Lithium-rich nickel manganese layered compound (0).2Li₂MnO₃∙0.8LiNi_0.5Mn_0.5O₂) The mass ratio of the Conductive Graphite (CG) and the chain carbon black (ECP) to the conductive agent and the polyvinylidene fluoride (PVDF) as the thickening agent/binder is 86: 10: 2: 0.6: 1.4, the electrode porosity is 30%.

Replacing the formula of the cathode electrode with: the mass ratio of crystalline hollow silicon spheres (median particle diameter D50=0.8 micron, maximum particle diameter D100=1.5 micron) coated by chemical vapor deposition to conductive carbon black (SuperP), single-walled carbon nanotubes (SWCNT), super-aligned carbon nanotubes (SACNT), sodium polyacrylate (PAANa) as a thickener, lithium Polyacrylate (PAALi), and lithium Alginate (Alginate-Li) as a binder, carboxymethyl cellulose acrylic copolymer (CMC-PAA), polymethyl methacrylate (PMMA) was 83: 4: 0.5: 1.5: 2: 2: 3: 2: 2; the electrode porosity was 50%. Wherein, the crystalline hollow silicon ball is coated with a carbon layer by a chemical vapor deposition method: firstly, crystalline hollow silicon ball powder is placed in the center of a tubular furnace, then acetylene is introduced to be used as a carbon precursor, and the carbon-coated crystalline hollow silicon ball is obtained by heating for 2 hours at 950 ℃. The amount of carbon coated on the surface of the silicon particles was 5.0%.

The first cycle energy density (when the charge-discharge cycle voltage window is 4.4V-2.75V and at the charge-discharge rate of 0.5C) of the full battery reaches 358Wh/kg after capacity grading, the first coulombic efficiency is 85.8 percent, and the capacity retention ratio after 100 cycles is 96.0 percent.

Example 12

The positive electrode formula is replaced by: nickel-cobalt-aluminum ternary material (Li (Ni)) as positive electrode active material_0.8Co_0.15Al_0.05)O₂) The mass ratio of the conductive agent single-walled carbon nanotube (SWCNT) to the thickening agent/binder polyvinylidene fluoride (PVDF) is 98.8:0.2:1.0, and the electrode porosity is 29%.

Replacing the formula of the cathode electrode with: the mass ratio of the negative active material crystalline silicon cone (median particle diameter D50=1.8 microns, maximum particle diameter D100=5.4 microns) to the conductive agent single-layer graphene (SLG), single-wall carbon nanotube (SWCNT), vapor-grown carbon fiber (VGCF), thickener carboxymethyl cellulose (CMC), polyacrylic acid (PAA), and binder aqueous Polyimide (PI), aqueous polyamide imide (PAI) is 91.3: 0.8: 0.8: 1.8: 0.8: 0.5: 2: 2; the electrode porosity was 44%. Wherein, the crystalline silicon cone which is coated by using low-temperature coal pitch as a carbon precursor: 1. uniformly mixing the crystalline silicon cone with the low-temperature coal tar pitch particles; 2. adding the mixed powder obtained in the step 1 into a VC mixer, simultaneously adding one half of methylformamide in the mass of the powder, heating and stirring the material under inert atmosphere, keeping the temperature constant at 150 ℃ for 2 hours, and then heating to 200 ℃ to evaporate the methylformamide to dryness to obtain the crystalline silicon cone coated with the asphalt; 3. and (3) carbonizing the material obtained in the step (2) in an inert atmosphere to obtain silicon particles with carbon-coated surfaces. The amount of carbon coated on the surface of the silicon particles was 1.4%.

The full battery is tested to reach 357Wh/kg in first cycle energy density (when the charge-discharge cycle voltage window is 4.2V-2.5V and at the charge-discharge rate of 0.5C) after capacity grading, the first coulombic efficiency is 89.2%, and the capacity retention rate after 100 cycles is 92.7%.

Example 13

The positive electrode formula is replaced by: the positive active material is a lithium iron phosphate material (LiFePO) with a carbon film coated on the surface₄) The mass ratio of the conductive agent single-walled carbon nanotube (SWCNT), the single-layer graphene (SLG) and the thickener/binder lithium Polyacrylate (PAALi) is 96.0:0.5:0.5: 3.0; adding proper amount of deionized water (H)₂O) for 5s by high-speed shearing action with shearing capability such as planetary stirrer and high-speed dispersion plate^-1And the stable and uniform fluid with the viscosity of 3000mPa & s at the shearing rate is the anode slurry. The porosity of the electrode after coating and drying is 38%.

Replacing the formula of the cathode electrode with: the mass ratio of crystalline silicon tube (median particle diameter D50=6.0 microns, maximum particle diameter D100=20.2 microns) coated with dopamine serving as a carbon precursor as a negative electrode active material to super-aligned carbon nano tube (SACNT) serving as a conductive agent, single-layer graphene (SLG), lithium Polyacrylate (PAALi) serving as a thickening agent, aqueous polyamide imide (PAI) serving as a binder and Styrene Butadiene Rubber (SBR) is 92: 1: 1: 2: 2: 2; the electrode porosity was 46%. Wherein, the crystalline silicon tube is coated with a carbon layer by the following method: 1. dispersing a crystalline silicon tube in a weak alkaline solution with pH =9, adding dopamine hydrochloride powder which is one third of the mass of the crystalline silicon tube while stirring, and continuously stirring for 24 hours; 2. filtering the slurry obtained in the step (1), and drying the obtained filter cake at 120 ℃ in vacuum to obtain a poly-dopamine-coated crystalline silicon tube; 3. and (3) carbonizing the material obtained in the step (2) in an inert atmosphere to obtain the crystalline silicon tube with the surface coated with carbon. The amount of carbon coated on the surface of the silicon particles was 3.5%.

The first cycle energy density (when the charge-discharge cycle voltage window is 3.6V-2.0V and at the charge-discharge rate of 0.5C) of the full battery reaches 256Wh/kg after capacity grading, the first coulombic efficiency is 90.1%, and the capacity retention rate after 100 cycles is 96.7%.

The above description is only a preferred embodiment of the present invention, and should not be taken as limiting the invention in any way, and any person skilled in the art can make any simple modification, equivalent replacement, and improvement on the above embodiment without departing from the technical spirit of the present invention, and still fall within the protection scope of the technical solution of the present invention.

Claims

1. A high energy density lithium ion battery, the battery includes positive pole, negative pole, electrolyte, diaphragm, packaging material, its characterized in that:

the porosity of the negative electrode is 35% -50%;

the surface of the silicon particles with surface modification in the negative electrode is carbon-coated modification, and the graphitization degree of the coated carbon is not limited and is amorphous carbon or graphitized carbon.

2. The high energy density lithium ion battery of claim 1, wherein:

the capacity density of the negative electrode is more than or equal to 780mAh/cm³；

The surface capacity of the negative electrode is 3.0-10.0mAh/cm²。

3. The high energy density lithium ion battery of claim 1, wherein:

the silicon particles in the silicon particles with surface modification in the negative electrode are monocrystalline silicon particles, polycrystalline silicon particles, amorphous silicon particles, crystalline silicon wires, amorphous silicon wires, crystalline silicon rods, amorphous silicon rods, crystalline silicon tubes, amorphous silicon tubes, crystalline silicon cones, amorphous silicon cones, crystalline porous silicon, amorphous porous silicon, crystalline hollow silicon spheres, amorphous hollow silicon spheres and one or more combinations of the materials subjected to lithium pre-intercalation treatment.

4. The high energy density lithium ion battery of claim 1, wherein:

5. The high energy density lithium ion battery of claim 4, wherein:

the precursor modified by carbon coating is a hydrocarbon compound.

6. The high energy density lithium ion battery of claim 1, wherein:

the silicon particles having surface modification in the negative electrode have a median particle diameter D50 of 0.8 to 6.0 μm and a maximum particle diameter D100 of less than or equal to four times the value corresponding to the median particle diameter D50.

7. The high energy density lithium ion battery of claim 1, wherein:

the carbon conductive agent capable of forming a conductive network in the negative electrode is at least one or a combination of more of conductive carbon black particles, acetylene black, chain carbon black, multi-walled carbon nanotubes, single-walled carbon nanotubes, super-ordered carbon nanotubes, vapor-grown carbon fibers, conductive graphite flakes, multi-layer graphene and single-layer graphene.

8. The high energy density lithium ion battery of claim 1, wherein:

the organic polymer binder in the negative electrode is at least one or a combination of more of carboxymethyl cellulose, lithium carboxymethyl cellulose, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, lithium polyacrylate, polystyrene acrylic acid copolymer, polyacrylate copolymer, carboxymethyl cellulose-acrylic acid copolymer, polyimide, polyamide imide, polyacrylonitrile acrylic acid copolymer, alginic acid, sodium alginate, lithium alginate, ethylene acrylic acid copolymer, hydrogel, xanthan gum, polyethylene oxide, polyvinyl alcohol and polyacrylic acid-polyvinyl alcohol cross-linked copolymer.

9. The high energy density lithium ion battery of claim 1, wherein:

the current collector substrate which is beneficial to electronic conduction in the negative electrode is a solid copper foil, a perforated copper foil, a foamed copper foil, a solid copper foil coated with a carbon-containing conducting layer on the surface, a perforated copper foil coated with a carbon-containing conducting layer on the surface, a solid stainless steel foil, a perforated stainless steel foil, a solid stainless steel foil coated with a carbon-containing conducting layer on the surface, a perforated stainless steel foil coated with a carbon-containing conducting layer on the surface, a solid iron foil, a perforated iron foil, a foamed iron foil coated with a carbon-containing conducting layer on the surface, a solid nickel foil, a perforated nickel foil, a foamed nickel foil, a solid nickel foil coated with a carbon-containing conducting layer on the surface, a perforated nickel foil coated with a carbon-containing conducting layer on the surface, or a foamed nickel foil coated with a carbon-containing conducting layer on the surface; the current collector substrate thickness is 4-10 microns.

10. The high energy density lithium ion battery of claim 1, wherein:

the battery further includes an electrolyte composition; the electrolyte comprises lithium salt, solvent and additive; the lithium salt includes LiN (C)_xF_2x+1SO₂)(C_yF_2y+1SO₂)、LiPF₆、LiBF₄、LiBOB、LiODFB、LiAsF₆、Li(CF₃SO₂)₂N、LiCF₃SO₃、LiFSI、LiTFSI、LiPO₂F₂、LiClO₄Wherein x and y are positive integers; the solvent comprises one or more of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, methyl propyl carbonate, diethyl carbonate, dimethyl carbonate, gamma-butyrolactone, 1, 3-dioxolane, acetonitrile, methyl formate, methyl acetate, ethyl propionate and propyl propionate; the additive is one or a combination of more of vinylene carbonate, ethylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, propylene sulfite, ethylene sulfite, dimethyl sulfite, diethyl sulfite, methylene methanedisulfonate, biphenyl, fluorobenzene, cyclohexylbenzene, 1-propyl cyclic phosphoric anhydride, potassium perfluorobutylsulfonate, tris (2,2, 2-trifluoroethyl) phosphite, hexamethylphosphazene, 1, 3-propylene sultone, lithium tetrafluorophenylboronate, phthalic anhydride, hexamethyldisilazane, glutaronitrile, succinonitrile, ethylene sulfate and ethylene glycol dipropyl ether;

the battery further includes a separator composition; the membrane compositionComprises polyethylene, polypropylene, polyethylene-polypropylene, aramid fiber membrane, polyimide, PET and non-woven fabrics; one or two surfaces of the diaphragm can be coated with functional substances, and the functional substances are one or the combination of a plurality of ceramic materials, high molecular polymers and lithium ion fast conductor materials; the ceramic material is Al₂O₃、TiO₂、AlOOH、ZrO₂、SnO₂、SiO₂、MgO、Mg(OH)₂、Al(OH)₃One or more of CaO and ZnO; the high molecular polymer is one or a combination of polyethylene oxide, polyvinylidene fluoride, polyacrylic acid, polymethyl methacrylate and polyvinyl alcohol; the lithium ion fast conductor material is one or a combination of more of a lithium lanthanum zirconium oxide compound, a lithium lanthanum titanium oxide compound, a lithium germanium phosphorus sulfur compound and a lithium phosphorus sulfur compound;