Negative active material and negative slurry and preparation method thereof, negative electrode sheet, lithium ion battery and charging method thereof

Abstract

This invention relates to a negative electrode active material and its preparation method, a negative electrode slurry and its preparation method, a negative electrode sheet, and a lithium-ion battery. The negative electrode active material comprises carbon materials and silicon-based materials. The carbon materials include a first carbon material and a second carbon material. The first carbon material includes graphite, and the second carbon material includes hard carbon and / or graphitized soft carbon. The mass ratio of carbon materials to silicon-based materials is carbon material:silicon-based material = 85-97%:3-15%. When the second carbon material includes hard carbon, the mass ratio of graphite to hard carbon is graphite:hard carbon = 91-97%:3-9%; or when the second carbon material includes graphitized soft carbon, the mass ratio of graphite to graphitized soft carbon is graphite:graphitized soft carbon = 92-98%:2-8%. This invention's negative electrode active material improves the high-rate charging capability of the negative electrode; improves the charging capability and cycle performance of the negative electrode; and improves the energy density of fast-charging batteries.

Description

Technical Field

[0001] This invention relates to a negative electrode active material and its preparation method, a negative electrode slurry and its preparation method, a negative electrode sheet, a lithium-ion battery and a charging method for a lithium-ion battery, belonging to the field of lithium-ion power battery production technology. Background Technology

[0002] In recent years, the biggest anxieties of new energy vehicle users have been insufficient driving range and long charging times. Now, significant breakthroughs have been made in high-power charging technology, and the 800V high-voltage supercharging network is rapidly expanding. Supercharging models will be launched in large numbers within one or two years, thereby promoting the development of 4C / 6C fast charging cell technology and increasing the requirements for cell energy density.

[0003] However, considering the current maturity of the preparation of positive and negative electrode materials and electrolytes, the main limitation lies in the negative electrode material system. The following are the previously used lithium-ion battery negative electrode system technical solutions in this field:

[0004] 1. Pure fast-charging graphite system, soft-pack battery energy density 220-240Wh / kg, continuous charging rate of 4C-6C at 20-80% SOC;

[0005] 2. (95-97%) graphite + (3-5%) hard carbon system, soft-pack battery energy density 220-235Wh / kg, continuous charging rate ≥6C at 20-80% SOC;

[0006] 3. (85-97%) graphite + (3-15%) silicon-oxygen anode system, soft-pack battery energy density 250-270Wh / kg, continuous charging rate of 4C-6C with 20-80% SOC.

[0007] However, while fast-charging lithium-ion batteries using pure graphite anode systems or graphite-mixed hard carbon anode systems can achieve the required high-rate charge-discharge performance, their energy density is limited. Fast-charging lithium-ion batteries using graphite-mixed silicon-oxygen anode systems show some improvement in energy density and high-rate charge-discharge capability, but they cannot suppress the expansion and pulverization of the silicon anode during high-rate charge-discharge processes, thus reducing high-rate charge-discharge capability and cycle life. Therefore, developing a novel silicon-mixed anode system for fast-charging lithium-ion batteries is particularly important.

[0008] The main drawbacks of existing technologies are:

[0009] (1) The high-rate charge and discharge performance of fast-charging lithium-ion batteries with pure graphite anode system or graphite mixed with hard carbon anode system can meet the requirements, but the energy density is limited.

[0010] (2) The energy density and high-rate charge and discharge capability of fast-charging lithium-ion batteries with graphite-doped silicon-oxygen anode system have been improved to a certain extent, but the expansion and pulverization of silicon anode during high-rate charge and discharge process cannot be suppressed, thus reducing the high-rate charge and discharge capability and cycle life.

[0011] (3) In addition, the above two negative electrode systems cannot simultaneously meet the performance requirements of high energy density and high charge and discharge rate. Summary of the Invention

[0012] The problem the invention aims to solve

[0013] In order to overcome the shortcomings of the prior art, the present invention aims to provide a silicon-based anode system with better rate capability and cycle performance, so as to improve the energy density and anode charging capability of lithium-ion batteries, or further improve the energy density while ensuring the anode charging capability, and facilitate the application of the new mixed silicon anode system for fast-charging lithium-ion batteries in large-scale production.

[0014] Solution for solving the problem

[0015] In view of this situation, the inventors, through diligent research, have provided the following implementation scheme.

[0016] [1] A negative electrode active material, characterized in that the negative electrode active material comprises a carbon material and a silicon-based material, the carbon material comprises a first carbon material and a second carbon material, the first carbon material comprises graphite, and the second carbon material comprises hard carbon and / or graphitized soft carbon.

[0017] The mass ratio of the carbon material to the silicon-based material is 85-97% to 3-15%.

[0018] And when the second carbon material includes hard carbon, the mass ratio of graphite to hard carbon is graphite:hard carbon = 91-97%:3-9%; or

[0019] When the second carbon material includes graphitized soft carbon, the mass ratio of graphite to graphitized soft carbon is graphite:graphitized soft carbon = 92-98%:2-8%.

[0020] [2] According to the negative electrode active material described in [1], the mass ratio of the carbon material to the silicon-based material is carbon material: silicon-based material = 90-95%: 5-10%;

[0021] The mass ratio of graphite to hard carbon is graphite:hard carbon = 94-97%:3-6%;

[0022] The mass ratio of graphite to graphitized soft carbon is 96-98% : 2-4%.

[0023] [3] The negative electrode active material according to [1] or [2], wherein the silicon-based material comprises at least one of silicon oxide, silicon carbide and silicon nitride;

[0024] Preferably, the carbon matrix in the silicon-carbon compound comprises resin carbon.

[0025] [4] The negative electrode active material according to any one of [1] to [3], wherein the graphite comprises at least one of artificial graphite and natural graphite.

[0026] [5] The negative electrode active material according to any one of [1] to [4], wherein the hard carbon comprises at least one of resin carbon, organic polymer pyrolysis carbon and biomass-based carbon.

[0027] [6] A method for preparing a negative electrode active material, characterized in that...

[0028] The negative electrode active material comprises carbon materials and silicon-based materials. The carbon materials include a first carbon material and a second carbon material. The first carbon material includes graphite, and the second carbon material includes hard carbon and / or graphitized soft carbon.

[0029] The mass ratio of the carbon material to the silicon-based material is 85-97% to 3-15%.

[0030] And when the second carbon material includes hard carbon, the mass ratio of graphite to hard carbon is graphite:hard carbon = 91-97%:3-9%, and the preparation method includes the step of mixing graphite, hard carbon, and silicon-based materials; or

[0031] When the second carbon material includes graphitized soft carbon, the mass ratio of graphite to graphitized soft carbon is 92-98%:2-8%, and the preparation method includes the steps of graphitizing graphite and soft carbon and then adding silicon-based materials for mixing.

[0032] [7] According to the preparation method described in [6], when the first carbon material includes graphite and the second carbon material includes hard carbon, the preparation method includes first ball milling and mixing the graphite and the silicon-based material, and then adding hard carbon and mixing.

[0033] Preferably, the ball milling and mixing of the graphite and the silicon-based material, as well as the mixing process of adding hard carbon, are both dry mixing methods;

[0034] Preferably, the ball milling and mixing of the graphite and the silicon-based material is carried out during the negative electrode homogenization process;

[0035] Preferably, the ball mill operates at a rotation speed of 15.4-25.4 rpm / min for 2-4 hours, and the milling media are steel balls and / or cast iron balls, with a ball-to-material ratio of material to milling media of 15-20:0-1.

[0036] The particle size distribution of the ball-milled graphite and silicon-based material mixture is D10 = 4.5-6.5 μm, D50 = 11.5-13.5 μm, D90 = 22.5-24.5 μm, and D99 = 33.5-35.5 μm.

[0037] [8] According to the preparation method described in [6], when the first carbon material includes graphite and the second carbon material includes graphitized soft carbon, the preparation method includes embedding graphite into the interior of soft carbon by infiltration, coating, granulation and graphitization treatment to obtain a composite material of graphite and graphitized soft carbon, and then adding silicon-based material and ball milling.

[0038] Preferably, the embedding method is implemented by vapor deposition, the coating is implemented by adding a carbon source and carrying out a hydrothermal reaction, and the graphitization treatment temperature is 2500-2800℃;

[0039] Preferably, the ball mill rotates at a speed of 10.4-15.4 rpm / min for 2-4 hours, and the milling media are steel balls and / or cast iron balls, with a ball-to-material ratio of material to milling media of 12-17:0-1.

[0040] Preferably, the particle size distribution of the mixture of ball-milled graphite and graphitized soft carbon composite material with silicon-based material is D10 = 3.5-5.5 μm, D50 = 10.5-12.5 μm, D90 = 20.5-22.5 μm, and D99 = 31.5-33.5 μm.

[0041] [9] The preparation method according to any one of [6] to [8], wherein the hard carbon comprises at least one of resin carbon, organic polymer pyrolysis carbon and biomass-based carbon;

[0042] The soft carbon includes at least one of petroleum coke, needle coke, carbon fiber, and carbon microspheres;

[0043] The mass ratio of graphite to hard carbon is graphite:hard carbon = 94-97%:3-6%;

[0044] The mass ratio of graphite to graphitized soft carbon is 96-98% : 2-4%;

[0045] The mass ratio of the carbon material to the silicon-based material is 90-95% to 5-10%.

[0046]

[10] A negative electrode slurry comprising the negative electrode active material described in any one of [1] to [5], or the negative electrode active material obtained by any one of the preparation methods described in [6] to [9], as well as a binder and a conductive agent.

[0047]

[11] According to the negative electrode slurry of

[10] , wherein the binder comprises at least a first binder and a second binder.

[0048] The first adhesive and the second adhesive may be the same or different.

[0049] The first adhesive and the second adhesive are respectively selected from at least one of carboxymethyl cellulose, styrene-butadiene rubber, ethylene propylene diene monomer rubber, fluororubber, polyacrylonitrile, polyethylene oxide, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoroethylene copolymer, polyvinyl alcohol, and polyvinyl butyral resin.

[0050]

[12] The negative electrode slurry according to

[10] or

[11] , wherein the conductive agent comprises at least one of carbon black, carbon nanotubes or carbon fibers;

[0051] Preferably, the carbon black includes at least one of super conductive carbon black, acetylene black, Ketjen black, channel black, furnace black, and lampblack.

[0052]

[13] A method for preparing a negative electrode slurry according to any one of

[10] to

[12] , comprising the following steps:

[0053] Step S1 involves mixing carbon materials and silicon-based materials to obtain the negative electrode active material.

[0054] Step S2 involves adding a first binder and a conductive agent to the negative electrode active material and then performing dry mixing to obtain a dry powder mixture.

[0055]

[14] The preparation method according to

[13] further includes step S3 of kneading the dry powder mixture with water, then adding a second binder and mixing to obtain a negative electrode slurry.

[0056]

[15] According to the preparation method described in

[13] or

[14] , wherein the first adhesive and the second adhesive are the same or different,

[0057] The first adhesive and the second adhesive are respectively selected from at least one of carboxymethyl cellulose, styrene-butadiene rubber, ethylene propylene diene monomer rubber, fluororubber, polyacrylonitrile, polyethylene oxide, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoroethylene copolymer, polyvinyl alcohol, and polyvinyl butyral resin.

[0058]

[16] A negative electrode sheet, characterized in that it is obtained by coating a negative electrode slurry as described in any one of

[10] to

[12] or a negative electrode slurry obtained by any one of the preparation methods described in

[13] to

[15] onto a negative electrode current collector.

[0059]

[17] A lithium-ion battery comprising a negative electrode according to

[16] .

[0060]

[18] A method for charging a lithium-ion battery, characterized in that the negative electrode of the lithium-ion battery comprises a negative electrode active material, the negative electrode active material comprises a carbon material and a silicon-based material, the carbon material comprises a first carbon material and a second carbon material, the first carbon material comprises graphite, the second carbon material comprises hard carbon and / or graphitized soft carbon, wherein the mass ratio of the carbon material to the silicon-based material is carbon material: silicon-based material = 85-97%: 3-15%;

[0061] When the first carbon material includes graphite and the second carbon material includes hard carbon, the mass ratio of graphite to hard carbon is graphite:hard carbon = 91-97%:3-9%.

[0062] When the first carbon material includes graphite and the second carbon material includes graphitized soft carbon, the mass ratio of graphite to graphitized soft carbon is graphite:graphitized soft carbon = 92-98%:2-8%.

[0063] The charging method includes:

[0064] When the battery's state of charge (SOC) is within the first range, pre-charge at a rate of 0.5 times or less;

[0065] When the battery's state of charge (SOC) is in the second range, constant current charging is performed at a rate of 0.5 times or higher.

[0066] When the battery's state of charge (SOC) is in the third range, trickle charging is performed at a rate of less than 1.

[0067]

[19] According to the charging method described in

[18] , when the mass ratio of the graphite to the hard carbon is graphite:hard carbon = 94-97%:3-6%, the charging method specifically includes:

[0068] When the first range is within 5%, the battery is pre-charged at a rate of 0-0.5.

[0069] When the second range is more than 5% and less than 80%, the battery is charged at a constant current using a four-stage mode: the first stage at 0.5-1 times the current, the second stage at 1-3 times the current, the third stage at 3-4 times the current, and the fourth stage at 1-2.5 times the current.

[0070] When the third range is above 80% but below 100%, a two-stage trickle charging mode is used for the battery, consisting of a first stage at a rate of 0.5-1x and a second stage at a rate of 0-0.5x; or

[0071] When the mass ratio of graphite to hard carbon is graphite:hard carbon = 91-94%:6-9% and does not include 94%:96%, the charging method specifically includes:

[0072] When the first range is within 5%, the battery is pre-charged at a rate of 0-0.5.

[0073] When the second range is above 5% and below 90%, a four-stage constant current charging mode is used for the battery: stage one (0.5-6x rate), stage two (1-6x rate), stage three (1.5-5x rate), and stage four (1-1.5x rate).

[0074] When the third range is above 90% but below 100%, a two-stage trickle charging mode is used to charge the battery, with the first stage at a rate of 0.5-1 and the second stage at a rate of 0-0.5.

[0075]

[20] According to the charging method described in

[19] , when the mass ratio of the graphite to the hard carbon is graphite:hard carbon = 94-97%:3-6%, the charging method specifically includes:

[0076] When the battery's state of charge (SOC) is in the second range, the charging modes are as follows: first stage 0.5-1 times rate when SOC is 5-10%, second stage 1-3 times rate when SOC is 10-20%, third stage 3-4 times rate when SOC is 20-60%, and fourth stage 1-2.5 times rate when SOC is 60-80%.

[0077] Preferably, in the fourth stage when the SOC is 60-80%, charging is performed at a rate of 2-2.5 times when the SOC is 60-70% and at a rate of 1-2 times when the SOC is 70-80%; or

[0078] When the mass ratio of graphite to hard carbon is graphite:hard carbon = 91-94%:6-9% and does not include 94%:96%, the charging method specifically includes:

[0079] When the battery's state of charge (SOC) is in the second range, the following charging modes are adopted: a first stage with a charging rate of 0.5-6 times when the SOC is 5-10%, a second stage with a charging rate of 1-6 times when the SOC is 10-30%, a third stage with a charging rate of 1.5-5 times when the SOC is 30-70%, and a fourth stage with a charging rate of 1-1.5 times when the SOC is 70-90%.

[0080] Preferably, in the third stage where the SOC is 30-70%, the charging mode is adopted with a rate of 4-5 times when the SOC is 30-50%, a rate of 2.5-4 times when the SOC is 50-60%, and a rate of 1.5-2.5 times when the SOC is 60-70%.

[0081]

[21] According to the charging method described in

[18] , when the mass ratio of the graphite to the graphitized soft carbon is graphite:graphitized soft carbon = 96-98%:2-4%, the charging method specifically includes:

[0082] When the first range is within 10%, a two-stage mode is used to precharge the battery: the first stage is 0-0.5 times the charging rate, and the second stage is 0.5-1 times the charging rate.

[0083] When the second range is above 10% but below 80%, a three-stage constant current charging mode is used for the battery: a first stage at 1-3 times the charging rate, a second stage at 4-5 times the charging rate, and a third stage at 1-2.5 times the charging rate.

[0084] When the third range is above 80% but below 100%, a two-stage trickle charging mode is used for the battery, consisting of a first stage at a rate of 0.5-1x and a second stage at a rate of 0-0.5x; or

[0085] When the mass ratio of graphite to graphitized soft carbon is graphite:graphitized soft carbon = 92-96%:4-8% and does not include 96%:4%, the charging method specifically includes:

[0086] When the first range is within 5%, the battery is pre-charged at a rate of 0-0.5.

[0087] When the second range is above 5% and below 90%, a four-stage constant current charging mode is used for the battery: stage one (0.5-8x rate), stage two (1-8x rate), stage three (1.5-6x rate), and stage four (1-1.5x rate).

[0088] When the third range is above 90% but below 100%, a two-stage trickle charging mode is used to charge the battery, with the first stage at a rate of 0.5-1 and the second stage at a rate of 0-0.5.

[0089]

[22] According to the charging method described in

[21] , when the mass ratio of the graphite to the graphitized soft carbon is graphite:graphitized soft carbon = 96-98%:2-4%, the charging method specifically includes:

[0090] When the battery's state of charge (SOC) is in the second range, a charging mode of 1-3 times rate in the first stage when SOC is 10-20%, 4-5 times rate in the second stage when SOC is 20-60%, and 1-2.5 times rate in the third stage when SOC is 60-80% is adopted.

[0091] Preferably, in the third stage when the SOC is 60-80%, charging is performed at a rate of 2-2.5 times when the SOC is 60-70% and at a rate of 1-2 times when the SOC is 70-80%; or

[0092] When the mass ratio of graphite to graphitized soft carbon is graphite:graphitized soft carbon = 92-96%:4-8% and does not include 96%:4%, the charging method specifically includes:

[0093] When the battery's state of charge (SOC) is in the second range, the following charging modes are adopted: a first stage with a rate of 0.5-8 times when the SOC is 5-10%, a second stage with a rate of 1-8 times when the SOC is 10-30%, a third stage with a rate of 1.5-6 times when the SOC is 30-70%, and a fourth stage with a rate of 1-1.5 times when the SOC is 70-90%.

[0094] Preferably, in the third stage where the SOC is 30-70%, the charging mode is adopted with a rate of 4-6 times when the SOC is 30-50%, a rate of 2.5-4 times when the SOC is 50-60%, and a rate of 1.5-2.5 times when the SOC is 60-70%.

[0095] The effects of the invention

[0096] In the novel silicon-doped anode system for fast-charging lithium-ion batteries of the present invention...

[0097] 1. Graphite & hard carbon (85-97%) + silicon-oxygen anode system (3-15%), where graphite:hard carbon = 91-97%:3-9%, soft-pack battery energy density 260-280Wh / kg, maximum charging rate of 6C at 20-80% SOC, simultaneously improving energy density and anode charging capability; Graphite & hard carbon (85-97%) + silicon-carbon anode system (3-15%), where graphite:hard carbon = 91-97%:3-9%, soft-pack battery energy density ≥285Wh / kg, maximum charging rate of 4C-6C at 20-80% SOC, further improving energy density while ensuring anode charging capability;

[0098] 2. Graphite & graphitized soft carbon (85-97%) + silicon-oxygen anode system (3-15%), wherein the ratio of graphite to graphitized soft carbon is 92-98% to 2-8%, the energy density of the soft-pack battery is 265-285Wh / kg, and the continuous charging rate of 20-80% SOC is aver.5C, which improves both energy density and anode charging capability; Graphite & graphitized soft carbon (85-97%) + silicon-carbon anode system (3-15%), wherein the ratio of graphite to graphitized soft carbon is 92-98% to 2-8%, the energy density of the soft-pack battery is >285Wh / kg, and the continuous charging rate of 20-80% SOC is aver.4C-5C, which further improves energy density while ensuring anode charging capability;

[0099] 3. The negative electrode active material obtained by this invention has a more uniform particle size distribution and better morphological regularity, which is beneficial to improving rate and cycle performance, and can also improve the energy density of the battery.

[0100] Furthermore, the novel silicon-doped anode system for fast-charging lithium-ion batteries of the present invention can achieve the following technical effects:

[0101] First, by controlling the content of hard carbon and graphite, the advantages of hard carbon relative to graphite and silicon-based anodes in terms of isotropy and large interlayer spacing are fully utilized to improve the high-rate charging capability of the anode; at the same time, the advantage of the high hardness of hard carbon itself is utilized to suppress the expansion of silicon anode to a certain extent, thereby improving the charging capability and cycle performance of the anode.

[0102] Secondly, by utilizing the advantages of graphitized soft carbon, which has a larger specific surface area and larger interlayer spacing compared to graphite and silicon-based anodes, the high-rate charging capability of the anode is improved and the safety potential of the anode is reduced, thereby increasing the lithium storage capacity of the anode. At the same time, by leveraging the advantages of the stable crystal structure and strong electrolyte adaptability of soft carbon itself, the safety performance of the anode is improved.

[0103] Third, the particle size distribution of the negative electrode active material is more uniform and the morphology is more regular, which is conducive to improving rate performance and cycle performance. Attached Figure Description

[0104] Figure 1 This is the preparation process of the negative electrode active material used in this invention. Detailed Implementation

[0105] Various exemplary embodiments, features, and aspects of the present invention will be described in detail below. The term "exemplary" as used herein means "serving as an example, embodiment, or illustration." Any embodiment described herein as "exemplary" is not necessarily to be construed as superior to or better than other embodiments.

[0106] Furthermore, to better illustrate the present invention, numerous specific details are set forth in the following detailed embodiments. Those skilled in the art should understand that the present invention can be practiced without certain specific details. In other instances, methods, means, apparatus, and steps well known to those skilled in the art have not been described in detail in order to highlight the spirit of the present invention.

[0107] Unless otherwise stated, all units used in this specification are international standard units, and all numerical values ​​and ranges appearing in this invention should be understood to include systematic errors that are unavoidable in industrial production.

[0108] In this specification, the word "may" has two meanings: to perform a certain process and not to perform a certain process.

[0109] In this specification, references to "some specific / preferred embodiments," "other specific / preferred embodiments," "implementation," etc., refer to specific elements (e.g., features, structures, properties, and / or characteristics) related to that embodiment, which are included in at least one of the embodiments described herein and may or may not be present in other embodiments. Furthermore, it should be understood that these elements may be combined in any suitable manner in various embodiments.

[0110] In this specification, the range of values ​​referred to as "value A to value B" refers to the range including the endpoint values ​​A and B.

[0111] In this instruction manual, when "room temperature" or "room temperature" is used, the temperature can be between 10-40℃.

[0112] <First Aspect>

[0113] This invention provides a negative electrode active material comprising a carbon material and a silicon-based material. The carbon material comprises a first carbon material and a second carbon material. The first carbon material includes graphite, and the second carbon material includes hard carbon and / or graphitized soft carbon. The mass ratio of the carbon material to the silicon-based material is 85-97%:3-15%. When the second carbon material includes hard carbon, the mass ratio of graphite to hard carbon is 91-97%:3-9%. Or when the second carbon material includes graphitized soft carbon, the mass ratio of graphite to graphitized soft carbon is 92-98%:2-8%.

[0114] By including graphite and hard carbon and / or graphitized soft carbon in the carbon material and keeping its content within the above range, the energy density and high-rate charge / discharge capability of lithium-ion batteries can be improved to a certain extent without degrading the expansion and pulverization of the silicon anode during high-rate charge / discharge processes, thereby improving cycle life.

[0115] The porous structure of hard carbon enables lithium storage. Therefore, by maintaining the hard carbon content within the aforementioned range, hard carbon exhibits advantages over graphite and silicon-based anodes in terms of isotropy and large interlayer spacing, thereby enhancing the high-rate charging capability of the anode. Simultaneously, the high hardness of hard carbon itself helps to suppress silicon anode expansion to some extent, improving the anode's charging capacity and cycle performance. Furthermore, by maintaining the graphite content within the aforementioned range, the problems of insufficient compaction and low specific capacity of hard carbon can be overcome.

[0116] The graphitized soft carbon possesses advantages such as a large specific surface area and wide interlayer spacing. Therefore, by maintaining the soft carbon content within the aforementioned range, graphite can be well embedded within the soft carbon, enhancing the high-rate charging capability of the negative electrode and reducing its safety potential, thereby increasing its lithium storage capacity. Simultaneously, the stable crystal structure and strong electrolyte adaptability of soft carbon itself improve the safety performance of the negative electrode. Furthermore, maintaining the graphite content within the aforementioned range can overcome the problems of high irreversible capacity, low output voltage, and lack of a clear charge / discharge plateau during the initial charge / discharge cycle of soft carbon.

[0117] In one exemplary implementation, from the perspective of further improving the energy density and high-rate charge / discharge capability of lithium-ion batteries and improving cycle life, the mass ratio of carbon material to silicon-based material is carbon material:silicon-based material = 90-95%:5-10%.

[0118] In another exemplary embodiment, from the perspective of further improving the charging capacity and cycle performance of the negative electrode, the mass ratio of graphite to hard carbon is graphite:hard carbon = 94-97%:3-6%; the mass ratio of graphite to graphitized soft carbon is graphite:graphitized soft carbon = 96-98%:2-4%.

[0119] In an exemplary preferred embodiment, the mass ratio of graphite, hard carbon or graphitized soft carbon, and silicon-based material is graphite:hard carbon:silicon-based material = 77.35-94.09%:2.91-7.65%:3-15%, or graphite:graphitized soft carbon:silicon-based material = 78.2-95.06%:1.94-6.8%:3-15%.

[0120] The silicon-based material is not particularly limited, and those commonly used in the art can be used. In one exemplary embodiment, for example, the silicon-based material comprises at least one of silicon oxide, silicon carbide, and silicon nitride. In an exemplary preferred embodiment, the carbon matrix in the silicon carbide comprises resin carbon. Resin carbon has a higher hardness than biomass-based carbon, which can suppress the expansion of silicon in the silicon carbide material; by blending existing resin-based porous carbon matrix silicon-carbon anodes with graphite anodes, the electronic conductivity of porous carbon itself is utilized, and the ionic conductivity is improved during the porous silicon-carbon preparation process, reducing the size of nano-silicon grains and suppressing the expansion of the silicon-carbon anode during high-rate charging and cycling; taking advantage of the high specific capacity of silicon-carbon anodes, the energy density of fast-charging batteries is improved, which is therefore more preferable.

[0121] Graphite is not particularly limited and those commonly used in the art can be used. In one exemplary embodiment, the graphite comprises at least one of synthetic graphite and natural graphite.

[0122] In one exemplary embodiment, hard carbon comprises at least one of resin carbon, organic polymer pyrolysis carbon, and biomass-based carbon.

[0123] In view of this, a specific embodiment of the present invention provides a novel blended silicon anode system for fast-charging lithium-ion batteries. The silicon anode system uses graphite & hard carbon (85-97%) + silicon-oxygen / silicon-carbon anode system (3-15%), wherein the graphite:hard carbon = 91-97%:3-9%. First, the above graphite + silicon-oxygen / silicon-carbon anode is ball-milled and mixed in a ball mill. The morphology of the material is characterized. The particle size distribution of the material is more uniform and the morphology is more regular, which is beneficial to improving the rate and cycle performance, thus obtaining ball-milled graphite + silicon-oxygen / silicon-carbon. Then, hard carbon is mixed with the ball-milled graphite + silicon-oxygen / silicon-carbon according to the above ratio to obtain a silicon-based anode system with better rate and cycle performance, while improving the energy density of the battery.

[0124] Another specific embodiment of the present invention provides a novel blended silicon anode system for fast-charging lithium-ion batteries. The silicon anode system uses graphite and graphitized soft carbon (85-97%) + silicon-oxygen / silicon-carbon anode system (3-15%), wherein the ratio of graphite to graphitized soft carbon is 92-98% to 2-8%. First, the graphite is embedded inside the graphitized soft carbon, and then coated, granulated, and graphitized to obtain a composite material of graphite and graphitized soft carbon. This composite material is then ball-milled and mixed with silicon-based materials in the above ratio. The morphology of the material is characterized, and the particle size distribution is more uniform and the morphology is more regular, which is beneficial to improving the rate and cycle performance, while also increasing the energy density of the battery.

[0125] Furthermore, the present invention provides a method for preparing a negative electrode active material, wherein the negative electrode active material comprises a carbon material and a silicon-based material, the carbon material comprises a first carbon material and a second carbon material, the first carbon material comprises graphite, and the second carbon material comprises hard carbon and / or graphitized soft carbon, the mass ratio of the carbon material to the silicon-based material is carbon material:silicon-based material = 85-97%:3-15%, and when the first carbon material comprises graphite and the second carbon material comprises hard carbon, the mass ratio of the graphite to the hard carbon is graphite:hard carbon = 91-97%:3-9%, the preparation method includes the step of mixing graphite, hard carbon and silicon-based material; or when the first carbon material comprises graphite and the second carbon material comprises graphitized soft carbon, the mass ratio of the graphite to the graphitized soft carbon is graphite:graphitized soft carbon = 92-98%:2-8%, the preparation method includes the step of graphitizing graphite and soft carbon and then adding silicon-based material and mixing.

[0126] In one exemplary embodiment, the preparation method of the present invention includes first ball milling and mixing graphite and silicon-based materials, and then adding hard carbon and mixing. Optionally pretreated raw materials are weighed according to the above molar ratio and mixed and ball-milled in a ball mill jar to obtain a mixture.

[0127] In this invention, the ball milling conditions can be appropriately adjusted according to actual conditions. In an exemplary embodiment, from the perspective of making the mixture uniform and the particle size of the mixture smaller, thereby improving the charging performance of the negative electrode material itself, the ball milling speed in the preparation method of this invention is 15.4-25.4 rpm / min, the time is 2-4 h, the ball milling media are steel balls and / or cast iron balls, and the ball-to-material ratio is material to ball milling media = 15-20: 0-1. In an exemplary embodiment, the particle size distribution of the mixture of graphite and silicon-based materials after ball milling is D10 = 4.5-6.5 μm, D50 = 11.5-13.5 μm, D90 = 22.5-24.5 μm, and D99 = 33.5-35.5 μm.

[0128] In an exemplary preferred embodiment, from the perspective of more uniform particle size distribution and better morphological regularity of the material, which is beneficial to improving the rate of increase and cycle performance, the ball milling and mixing of graphite and silicon-based materials, as well as the mixing process of adding hard carbon, are all dry mixing methods.

[0129] Furthermore, in one exemplary embodiment, from the perspective of making operation more convenient and reducing production costs, the preparation method of the present invention includes dry mixing of graphite and silicon-based materials during a negative electrode homogenization process.

[0130] In one exemplary embodiment, the preparation method of the present invention includes embedding graphite into soft carbon via infiltration, coating, granulating, and graphitizing to obtain a composite material of graphite and graphitized soft carbon, followed by ball milling with a silicon-based material. In a preferred embodiment, the infiltration embedding is carried out by vapor deposition, the coating is carried out by a hydrothermal reaction with a carbon source, and the graphitization temperature is 2500-2800°C. Exemplarily, the carbon source for coating can be hard carbon, and the content of the carbon source can be 0-0.5 wt% of the soft carbon content.

[0131] In one exemplary embodiment, from the perspective of achieving uniform mixing and a small particle size, the ball milling speed in the preparation method of the present invention is 10.4-15.4 rpm / min, the time is 2-4 h, the ball milling media are steel balls and / or cast iron balls, and the ball-to-material ratio is material to ball milling media = 12-17:0-1. In one exemplary embodiment, the particle size distribution of the ball-milled graphite and graphitized soft carbon composite material mixed with silicon-based material is D10 = 3.5-5.5 μm, D50 = 10.5-12.5 μm, D90 = 20.5-22.5 μm, and D99 = 31.5-33.5 μm.

[0132] In one exemplary embodiment, in the preparation method of the present invention, the mass ratio of graphite to hard carbon is graphite:hard carbon = 94-97%:3-6%; the mass ratio of graphite to graphitized soft carbon is graphite:graphitized soft carbon = 96-98%:2-4%. In another exemplary embodiment, in the preparation method of the present invention, the mass ratio of carbon material to silicon-based material is carbon material:silicon-based material = 90-95%:5-10%.

[0133] In an exemplary preferred embodiment, in the preparation method of the present invention, the mass ratio of graphite, hard carbon or graphitized soft carbon, and silicon-based material is graphite:hard carbon:silicon-based material = 77.35-94.09%:2.91-7.65%:3-15%, or graphite:graphitized soft carbon:silicon-based material = 78.2-95.06%:1.94-6.8%:3-15%.

[0134] Figure 1 This is the preparation process of the novel silicon-doped anode system (the second carbon material includes hard carbon) used in this invention. The various parts of the above-mentioned preparation process flow chart of the novel silicon-doped anode system include:

[0135] (1) Graphite + silicon oxide / silicon carbon anode are ball-milled and mixed in a ball mill ①;

[0136] (2) Hard carbon and graphite are mixed with silicon-oxygen / silicon-carbon doped anode materials ②;

[0137] (3) Add binder CMC and conductive agent SP to the negative electrode dry powder mixture and mix the dry powder ③;

[0138] (4) Add deionized water to the above dry powder mixture and knead it, then add binder SBR④ to obtain a new type of silicon-blended anode slurry;

[0139] After the battery cell is prepared and tested, it may also include:

[0140] (5) Electrode fabrication and cell assembly;

[0141] (6) Cell testing and evaluation.

[0142] Now refer to the appendix Figure 1 The preparation method of the present invention will be described in detail.

[0143] In a particularly specific embodiment, the present invention provides a novel blended silicon anode system for fast-charging lithium-ion batteries. The silicon anode system of the present invention adopts a graphite & hard carbon (85-97%) + silicon-oxygen / silicon-carbon anode system (3-15%), wherein the graphite:hard carbon = 91-97%:3-9%.

[0144] The preparation method of this invention includes: ball milling and mixing graphite and silicon-oxygen / silicon-carbon anode materials in a ball mill ① to obtain a graphite and silicon-oxygen / silicon-carbon blended anode material; then, in the anode slurry process, using a dry slurry process, dry powder premixing of hard carbon and graphite with the silicon-oxygen / silicon-carbon blended anode material ② to obtain a dry powder mixture of graphite, hard carbon, and silicon-oxygen / silicon-carbon blended anode materials; continuing to add binder CMC and conductive agent SP to the dry powder mixture for dry powder mixing ③ to obtain a dry powder mixture of anode active material, conductive agent, and binder; then adding deionized water to the above dry powder mixture for kneading, and then adding binder SBR ④ to obtain a novel blended silicon anode slurry; preparing the above slurry into an electrode sheet, assembling it into a battery cell, and conducting rate and cycle performance tests.

[0145] The step described above involves ball milling and mixing graphite and silicon oxide / silicon carbon anode materials in a ball mill to obtain a graphite and silicon oxide / silicon carbon blended anode material, and then characterizing the material structure.

[0146] The step described above involves mixing hard carbon and graphite with silicon-oxygen / silicon-carbon blended anode material ②. In the anode homogenization process, a dry homogenization process is used to premix hard carbon and graphite with silicon-oxygen / silicon-carbon blended anode material to obtain a mixture of graphite, hard carbon, and silicon-oxygen / silicon-carbon blended anode dry powder.

[0147] The step involves adding binder CMC and conductive agent SP to the negative electrode dry powder mixture for dry powder mixing ③, to obtain a dry powder mixture of negative electrode active material, conductive agent, and binder;

[0148] The step involves adding deionized water to the above dry powder mixture for kneading, and then adding binder SBR④ to obtain a novel blended silicon anode slurry.

[0149] The electrode sheet fabrication and cell assembly step ⑤ involves fabricating the above-mentioned negative electrode slurry into electrode sheets and assembling them into a cell for electrical performance testing.

[0150] Step ⑥, cell testing and evaluation, involves conducting rate and cycle performance tests on the assembled cells to evaluate the improvement effect of the novel doped silicon anode system on the anode charging capability and cycle performance.

[0151] In summary, compared with existing technologies, the novel silicon-doped anode system for fast-charging lithium-ion batteries provided by this invention enhances the high-rate charging capability of the anode; at the same time, it suppresses silicon anode expansion to a certain extent, thereby improving the charging capability and cycle performance of the anode; it utilizes the high specific capacity of silicon-carbon anodes to improve the energy density of fast-charging batteries; and it makes the particle size distribution of the silicon-doped anode system more uniform and the morphology more regular, which is beneficial to improving rate and cycle performance.

[0152] <Second aspect>

[0153] The present invention provides a negative electrode slurry, which includes the negative electrode active material described above, or the negative electrode active material obtained by the preparation method described above, as well as a binder and a conductive agent.

[0154] The negative electrode active material is as described above, and its description is omitted here.

[0155] In one exemplary embodiment, the binder comprises at least a first binder and a second binder, which may be the same or different. The binder is not particularly limited in this invention, and commonly used binders in the art can be used as the first and second binders, respectively. Relative to 100% of the total solid content of the negative electrode slurry, the first binder comprises 1.2-1.5%, and the second binder comprises 2.0-2.3%. In some embodiments of this invention, the first and second binders are selected from at least one of carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), ethylene propylene diene monomer (EPDM), fluororubber, polyacrylonitrile, polyethylene oxide, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoroethylene copolymer, polyvinyl alcohol, and polyvinyl butyral resin.

[0156] In an exemplary preferred embodiment, the first adhesive and the second adhesive are different. Any combination of the first adhesive and the second adhesive can be chosen. For example, the first adhesive can be carboxymethyl cellulose (CMC) and the second adhesive can be styrene-butadiene rubber (SBR). Alternatively, the first adhesive can be styrene-butadiene rubber (SBR) and the second adhesive can be carboxymethyl cellulose (CMC).

[0157] The conductive agent is not particularly limited in this invention, and commonly used conductive agents in the art can be used. For example, conductive agents include carbon black, carbon nanotubes, or carbon fibers. In some embodiments of this invention, the carbon black includes at least one of superconducting carbon black, acetylene black, Ketjen black, channel black, furnace black, and lampblack. The amount of conductive agent used is also not particularly limited; for example, it can be 0.9-1.1%, preferably 1.0%, relative to 100% of the total solid content of the negative electrode slurry.

[0158] Furthermore, the present invention also provides a method for preparing the negative electrode slurry according to the above description, which includes step S1 of mixing carbon material and silicon-based material to obtain a negative electrode active material, step S2 of adding a first binder and a conductive agent to the negative electrode active material and performing dry mixing to obtain a dry powder mixture.

[0159] In one exemplary embodiment, step S1 can be carried out by dry mixing using ball milling. The ball milling conditions are the same as in the above-described method for preparing the negative electrode active material, and can be appropriately adjusted according to the actual situation in this step.

[0160] Specifically, when the carbon material includes graphite and hard carbon, the preparation method of the negative electrode slurry includes first ball milling and mixing graphite and silicon-based materials, and then adding hard carbon for mixing; preferably, the ball milling and mixing of graphite and silicon-based materials and the addition of hard carbon are both dry mixing processes. When the carbon material includes graphite and graphitized soft carbon, the preparation method of the negative electrode slurry includes embedding graphite into the soft carbon by infiltration, performing coating, granulation and graphitization treatment to obtain a composite material of graphite and graphitized soft carbon, and then adding silicon-based materials for ball milling; preferably, the infiltration embedding is carried out by vapor deposition, the coating is carried out by adding a carbon source for hydrothermal reaction, and the graphitization treatment temperature is 2500-2800℃.

[0161] In one exemplary embodiment, in step S2, dry mixing can also be performed using a ball mill. The ball milling conditions are the same as in the above-described method for preparing the negative electrode active material, and can be appropriately adjusted according to the actual situation in this step.

[0162] Furthermore, the first binder and conductive agent are the same as those in the negative electrode slurry described above. In some embodiments of the present invention, examples of the first binder and conductive agent are as described above. In some embodiments of the present invention, relative to 100% of the total solid content of the negative electrode slurry, the amounts of the first binder and conductive agent used are 1.2-1.5% and 0.9-1.1%, respectively.

[0163] The preparation method of the present invention further includes step S3, which involves kneading the dry powder mixture with water, then adding a second binder, and mixing to obtain a negative electrode slurry.

[0164] In one exemplary embodiment, in step S3, the dry powder mixture and water are stirred once in a homogenizing tank, and then a second binder is added and stirred a second time to obtain the negative electrode slurry. The stirring conditions are not particularly limited and those commonly used in the art can be used. For example, during the first stirring, the stirring speed is 500-1000 rpm / min and the stirring time is 60-90 min; during the second stirring, the stirring speed is 300-500 rpm / min and the stirring time is 40-60 min.

[0165] In one exemplary embodiment, the amount of water added is 56-58% relative to the total amount of the negative electrode slurry, and the amount of the second binder added is 2.0-2.3%. Adjusting the amount of water added controls the solid content of the negative electrode slurry to be 42-44%, thereby facilitating subsequent electrode drying and simplifying the operation.

[0166] In one exemplary embodiment, in the preparation method of the present invention, the first adhesive and the second adhesive may be the same or different. The first adhesive and the second adhesive are each selected from at least one of carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), ethylene propylene diene monomer (EPDM), fluororubber, polyacrylonitrile, polyethylene oxide, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoroethylene copolymer, polyvinyl alcohol, and polyvinyl butyral resin, and may be used in combination as appropriate. Preferably, the first adhesive and the second adhesive are different.

[0167] <Third aspect>

[0168] In addition, the present invention provides a negative electrode sheet, which is obtained by coating the negative electrode slurry described above or the negative electrode slurry obtained by the preparation method described above onto a negative electrode current collector.

[0169] The above-mentioned negative electrode slurry contains the novel silicon-doped negative electrode system prepared in this invention. The silicon-doped negative electrode system has a more uniform particle size distribution and better morphological regularity, which is beneficial to improving rate performance and cycle performance.

[0170] In addition, the present invention provides a lithium-ion battery comprising the negative electrode sheet described above.

[0171] The lithium-ion battery of the present invention improves the high-rate charging capability of the negative electrode by using the negative electrode sheet prepared in the present invention; at the same time, it suppresses the expansion of silicon negative electrode to a certain extent, thereby improving the charging capability and cycle performance of the negative electrode; and by taking advantage of the high specific capacity of silicon-carbon negative electrode, it improves the energy density of fast-charging battery.

[0172] <Fourth Aspect>

[0173] Furthermore, the present invention provides a charging method for a lithium-ion battery, wherein the negative electrode of the lithium-ion battery comprises a negative electrode active material, the negative electrode active material comprising a carbon material and a silicon-based material, the carbon material comprising a first carbon material and a second carbon material, the first carbon material comprising graphite, and the second carbon material comprising hard carbon and / or graphitized soft carbon, wherein the mass ratio of the carbon material to the silicon-based material is carbon material:silicon-based material = 85-97%:3-15%; when the first carbon material comprises graphite and the second carbon material comprises hard carbon, the mass ratio of the graphite to the hard carbon is graphite:hard carbon = 91-97%:3-9%; when the first carbon material comprises graphite and the second carbon material comprises graphitized soft carbon, the mass ratio of the graphite to the graphitized soft carbon is graphite:graphitized soft carbon = 92-98%:2-8%, wherein the charging method includes:

[0174] When the battery's state of charge (SOC) is within the first range, pre-charge at a rate of 0.5 times or less;

[0175] When the battery's state of charge (SOC) is within the second range, constant current charging is performed at a rate of 0.5 times or higher; and

[0176] When the battery's state of charge (SOC) is in the third range, trickle charging is performed at a rate of less than 1.

[0177] This invention employs a stepped charging strategy, prioritizing the use of the middle SOC range (20-80%) for fast charging based on different material systems, while using low-current charging at both ends of the SOC range to ensure battery lifespan.

[0178] Compared to using conventional negative electrode active materials, the charging method of the present invention, combined with a specific charging strategy, can improve the charging rate in the middle SOC range and appropriately expand the SOC range for fast charging.

[0179] In one exemplary embodiment, when the mass ratio of graphite to hard carbon is graphite:hard carbon = 94-97%:3-6%, the charging method specifically includes:

[0180] When the first range is within 5%, the battery is pre-charged at a rate of 0-0.5.

[0181] When the second range is above 5% and below 80%, a four-stage constant current charging mode is used for the battery: stage one (0.5-1x rate), stage two (1-3x rate), stage three (3-4x rate), and stage four (1-2.5x rate).

[0182] When the third range is above 80% but below 100%, a two-stage trickle charge mode is used to charge the battery, with the first stage at a rate of 0.5-1 and the second stage at a rate of 0-0.5.

[0183] Furthermore, in an exemplary embodiment, when the mass ratio of graphite to hard carbon is graphite:hard carbon = 91-94%:6-9% and does not include 94%:6%, the charging method specifically includes:

[0184] When the first range is within 5%, the battery is pre-charged at a rate of 0-0.5.

[0185] When the second range is above 5% and below 90%, a four-stage constant current charging mode is used for the battery: stage one (0.5-6x rate), stage two (1-6x rate), stage three (1.5-5x rate), and stage four (1-1.5x rate).

[0186] When the third range is above 90% but below 100%, a two-stage trickle charging mode is used to charge the battery, with the first stage at a rate of 0.5-1 and the second stage at a rate of 0-0.5.

[0187] In an exemplary embodiment, when the mass ratio of graphite to hard carbon is graphite:hard carbon = 94-97%:3-6%, the charging method specifically includes: when the battery's state of charge (SOC) is in a second range, a charging mode is adopted with a first stage of 0.5-1 times the charging rate when the SOC is 5-10%, a second stage of 1-3 times the charging rate when the SOC is 10-20%, a third stage of 3-4 times the charging rate when the SOC is 20-60%, and a fourth stage of 1-2.5 times the charging rate when the SOC is 60-80%. In a preferred embodiment, in the fourth stage when the SOC is 60-80%, a charging mode is adopted with a charging rate of 2-2.5 times when the SOC is 60-70% and a charging rate of 1-2 times when the SOC is 70-80%.

[0188] Furthermore, in an exemplary embodiment, when the mass ratio of graphite to hard carbon is graphite:hard carbon = 91-94%:6-9% and does not include 94%:6%, the charging method specifically includes: when the battery's state of charge (SOC) is in a second range, employing a charging mode of 0.5-6 times rate in the first stage when the SOC is 5-10%, 1-6 times rate in the second stage when the SOC is 10-30%, 1.5-5 times rate in the third stage when the SOC is 30-70%, and 1-1.5 times rate in the fourth stage when the SOC is 70-90%. In a preferred embodiment, in the second stage when the SOC is 30-70%, charging is performed at a rate of 4-5 times when the SOC is 30-50%, at a rate of 2.5-4 times when the SOC is 50-60%, and at a rate of 1.5-2.5 times when the SOC is 60-70%.

[0189] In a specific embodiment of the present invention, when the mass ratio of graphite to hard carbon is graphite:hard carbon = 91-94%:6-9% and does not include 94%:6%, the charging method specifically includes the following modes: 0-0.5 times rate when the battery state of charge (SOC) is below 5%, 0.5-6 times rate when the battery SOC is between 5-10%, 1-6 times rate when the battery SOC is between 10-30%, and... Charge the battery at a rate of 4-5 times when the battery's state of charge (SOC) is -50%; at a rate of 2.5-4 times when the SOC is 50-60%; at a rate of 1.5-2.5 times when the SOC is 60-70%; at a rate of 1-1.5 times when the SOC is 70-90%; at a rate of 0.5-1 times when the SOC is 90-95%; and at a rate of 0-0.5 times when the SOC is 95-100%. In another specific embodiment of the present invention, when the mass ratio of graphite to hard carbon is graphite:hard carbon = 94-97%:3-6%, the charging method specifically includes charging the battery in the following modes: at a rate of 0-0.5 times when the battery's state of charge (SOC) is below 5%, at a rate of 0.5-1 times when the battery's SOC is 5-10%, at a rate of 1-3 times when the battery's SOC is 10-20%, at a rate of 3-4 times when the battery's SOC is 20-60%, at a rate of 2-2.5 times when the battery's SOC is 60-70%, at a rate of 1-2 times when the battery's SOC is 70-80%, at a rate of 0.5-1 times when the battery's SOC is 80-90%, and at a rate of 0-0.5 times when the battery's SOC is 90-100%.

[0190] In one exemplary embodiment, when the mass ratio of graphite to graphitized soft carbon is graphite:graphitized soft carbon = 96-98%:2-4%, the charging method specifically includes:

[0191] When the first range is within 10%, a two-stage mode is used to precharge the battery: the first stage is 0-0.5 times the charging rate, and the second stage is 0.5-1 times the charging rate.

[0192] When the second range is above 10% but below 80%, a three-stage constant current charging mode is used for the battery: a first stage at 1-3 times the charging rate, a second stage at 4-5 times the charging rate, and a third stage at 1-2.5 times the charging rate.

[0193] When the third range is above 80% but below 100%, a two-stage trickle charge mode is used to charge the battery, with the first stage at a rate of 0.5-1 and the second stage at a rate of 0-0.5.

[0194] Furthermore, in an exemplary embodiment, when the mass ratio of graphite to graphitized soft carbon is graphite:graphitized soft carbon = 92-96%:4-8% and does not include 96%:4%, the charging method specifically includes:

[0195] When the first range is within 5%, the battery is pre-charged at a rate of 0-0.5.

[0196] When the second range is above 5% and below 90%, a four-stage constant current charging mode is used for the battery: stage one (0.5-8x rate), stage two (1-8x rate), stage three (1.5-6x rate), and stage four (1-1.5x rate).

[0197] When the third range is above 90% but below 100%, a two-stage trickle charging mode is used to charge the battery, with the first stage at a rate of 0.5-1 and the second stage at a rate of 0-0.5.

[0198] In an exemplary embodiment, when the mass ratio of graphite to graphitized soft carbon is 96-98% : 2-4% (graphite:graphitized soft carbon = 2-4%), the charging method specifically includes: when the battery's state of charge (SOC) is in a second range, a charging mode of 1-3 times rate in the first stage when the SOC is 10-20%, 4-5 times rate in the second stage when the SOC is 20-60%, and 1-2.5 times rate in the third stage when the SOC is 60-80%. In a preferred embodiment, in the third stage when the SOC is 60-80%, charging is performed at a rate of 2-2.5 times when the SOC is 60-70%, and at a rate of 1-2 times when the SOC is 70-80%.

[0199] Furthermore, in an exemplary embodiment, when the mass ratio of graphite to graphitized soft carbon is graphite:graphitized soft carbon = 92-96%:4-8% and does not include 96%:4%, the charging method specifically includes: when the battery's state of charge (SOC) is in a second range, employing a charging mode of 0.5-8 times rate in the first stage when the SOC is 5-10%, 1-8 times rate in the second stage when the SOC is 10-30%, 1.5-6 times rate in the third stage when the SOC is 30-70%, and 1-1.5 times rate in the fourth stage when the SOC is 70-90%. In a preferred embodiment, in the third stage when the SOC is 30-70%, charging is performed at a rate of 4-6 times when the SOC is 30-50%, at a rate of 2.5-4 times when the SOC is 50-60%, and at a rate of 1.5-2.5 times when the SOC is 60-70%.

[0200] In a specific embodiment of the present invention, when the mass ratio of graphite to graphitized soft carbon is graphite:graphitized soft carbon = 92-96%:4-8% and does not include 96%:4%, the charging method specifically includes the following modes: 0-0.5 times rate when the battery state of charge (SOC) is below 5%, 0.5-8 times rate when the battery SOC is between 5-10%, 1-8 times rate when the battery SOC is between 10-30%, and... Charge the battery at a rate of 4-6 times when C is 30-50%, at a rate of 2.5-4 times when SOC is 50-60%, at a rate of 1.5-2.5 times when SOC is 60-70%, at a rate of 1-1.5 times when SOC is 70-90%, at a rate of 0.5-1 times when SOC is 90-95%, and at a rate of 0-0.5 times when SOC is 95-100%. In another specific embodiment of the present invention, when the mass ratio of graphite to graphitized soft carbon is 96-98% : 2-4% (graphite : graphitized soft carbon = 2-4%), the charging method specifically includes charging the battery at the following rates: 0-0.5 times when the battery's state of charge (SOC) is below 5%; 0.5-1 times when the SOC is 5-10%; 1-3 times when the SOC is 10-20%; 4-5 times when the SOC is 20-60%; 2-2.5 times when the SOC is 60-70%; 1-2 times when the SOC is 70-80%; 0.5-1 times when the SOC is 80-90%; and 0-0.5 times when the SOC is 90-100%.

[0201] In a specific embodiment of the present invention, when the graphite:hard carbon ratio is 91-97%:3-9%, the charging method is as shown in Table 1:

[0202] Table 1

[0203]

[0204] In a specific embodiment of the present invention, when the ratio of graphite to graphitized soft carbon is 92-98% to 2-8%, the charging method is as shown in Table 2:

[0205] Table 2

[0206]

[0207] Example

[0208] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0209] Example 1

[0210] See Figure 1 The design process of the negative electrode active material in this embodiment includes carbon materials and silicon-based materials. The silicon-based material is a silicon-carbon composite material, and the carbon material is graphite and hard carbon. The mass ratio of silicon-carbon composite material, graphite, and hard carbon is 15%:82.45%:2.55%. First, the graphite and silicon-carbon composite material are ball-milled and mixed. During the negative electrode slurry preparation process, the hard carbon, graphite, and silicon-carbon mixed negative electrode material are premixed into dry powder to obtain the mixed negative electrode active material. The specific preparation process of the negative electrode active material, negative electrode slurry, and lithium-ion battery is as follows:

[0211] (1) Ball milling of graphite and silicon carbide composite material: Graphite and silicon carbide composite material were ball milled in a ball mill at a speed of 20 rpm / min for 3 h. The ball milling media were steel balls and the ball-to-material ratio was 18:1. A mixture of graphite and silicon carbide composite material was obtained and the material structure was characterized. The particle size distribution of the mixture of graphite and silicon carbide composite material was D10 = 5.68 μm, D50 = 13.47 μm, D90 = 23.68 μm, and D99 = 35.17 μm.

[0212] (2) Mixing of hard carbon with graphite and silicon carbon composite material: In the negative electrode homogenization process, a dry homogenization process is used to premix the mixture of hard carbon and graphite with silicon carbon composite material into dry powder to obtain a dry powder mixture of graphite, hard carbon and silicon carbon composite material.

[0213] (3) Add binder CMC (dry powder mass ratio 1.4%, relative to the total weight of solid components in the negative electrode slurry) and conductive agent SP (dry powder mass ratio 1.0%, relative to the total weight of solid components in the negative electrode slurry) to the dry powder mixture in step (2) and mix them to obtain a dry powder mixture of negative electrode active material, conductive agent and binder.

[0214] (4) Add deionized water to the dry powder mixture obtained in step (3) and knead it. Then add binder SBR (2.2% of dry powder mass, relative to the total weight of solid components in the negative electrode slurry) to obtain a negative electrode slurry containing negative electrode active material.

[0215] (5) Negative electrode sheet fabrication and lithium-ion battery assembly: The above negative electrode slurry is made into electrode sheets and assembled into lithium-ion batteries.

[0216] Referring to national standards 31484 and 31486, the lithium-ion battery prepared in this embodiment was subjected to rate and cycle performance tests.

[0217] Example 2

[0218] The negative electrode active material in this embodiment includes carbon material and silicon-based material. The silicon-based material is a silicon-oxygen composite material, and the carbon material is graphite and hard carbon. The mass ratio of silicon-oxygen composite material, graphite and hard carbon is 15%:77.35%:7.65%.

[0219] The specific preparation process of the negative electrode active material, negative electrode slurry, and lithium-ion battery is as follows:

[0220] (1) Ball milling and mixing of graphite + silicon oxide composite material: graphite and silicon oxide composite material were ball milled and mixed in a ball mill at a speed of 20 rpm / min for 3 h. The ball milling media were steel balls and the ball-to-material ratio was 18:1. A mixture of graphite and silicon oxide composite material was obtained and the material structure was characterized in the same manner as in Example 1.

[0221] (2) Mixing of hard carbon with graphite and silicon oxide composite material: In the negative electrode homogenization process, a dry homogenization process is used to premix the mixture of hard carbon and graphite with silicon oxide composite material into dry powder to obtain a dry powder mixture of graphite, hard carbon and silicon oxide composite material.

[0222] (3) Add binder CMC (dry powder mass ratio 1.4%, relative to the total weight of solid components in the negative electrode slurry) and conductive agent SP (dry powder mass ratio 1.0%, relative to the total weight of solid components in the negative electrode slurry) to the dry powder mixture in step (2) and mix them to obtain a dry powder mixture of negative electrode active material, conductive agent and binder.

[0223] (4) Add deionized water to the dry powder mixture obtained in step (3) and knead it. Then add binder SBR (2.2% of dry powder mass, relative to the total weight of solid components in the negative electrode slurry) to obtain a negative electrode slurry containing negative electrode active material.

[0224] (5) Negative electrode sheet fabrication and lithium-ion battery assembly: The above negative electrode slurry is made into electrode sheets and assembled into lithium-ion batteries.

[0225] Referring to national standards 31484 and 31486, the lithium-ion battery prepared in this example was subjected to rate and cycle performance tests in the same manner as in Example 1.

[0226] Example 3

[0227] The negative electrode active material in this embodiment includes carbon material and silicon-based material. The silicon-based material is a silicon-oxygen composite material, and the carbon material is graphite and hard carbon. The mass ratio of silicon-oxygen composite material, graphite and hard carbon is 15%:77.35%:7.65%.

[0228] The specific preparation process of the negative electrode active material, negative electrode slurry, and lithium-ion battery is as follows:

[0229] (1) Ball milling of graphite + silicon oxide composite material: graphite and silicon oxide composite material were ball milled in a ball mill at a speed of 25.5 rpm / min for 3 h. The ball milling media were steel balls and the ball-to-material ratio was 18:1. A mixture of graphite and silicon oxide / silicon carbon composite material was obtained and the material structure was characterized in the same manner as in Example 1.

[0230] (2) Mixing of hard carbon with graphite and silicon oxide composite material: In the negative electrode homogenization process, a dry homogenization process is used to premix the mixture of hard carbon and graphite with silicon oxide composite material into dry powder to obtain a dry powder mixture of graphite, hard carbon and silicon oxide composite material.

[0231] (3) Add binder CMC (dry powder mass ratio 1.4%, relative to the total weight of solid components in the negative electrode slurry) and conductive agent SP (dry powder mass ratio 1.0%, relative to the total weight of solid components in the negative electrode slurry) to the dry powder mixture in step (2) and mix them to obtain a dry powder mixture of negative electrode active material, conductive agent and binder.

[0232] (4) Add deionized water to the dry powder mixture obtained in step (3) and knead it. Then add binder SBR (2.2% of dry powder mass, relative to the total weight of solid components in the negative electrode slurry) to obtain a negative electrode slurry containing negative electrode active material.

[0233] (5) Negative electrode sheet fabrication and lithium-ion battery assembly: The above negative electrode slurry is made into electrode sheets and assembled into lithium-ion batteries.

[0234] Referring to national standards 31484 and 31486, the lithium-ion battery prepared in this example was tested for rate and cycle performance in the same manner as in Example 1.

[0235] Example 4

[0236] The negative electrode active material in this embodiment includes carbon material and silicon-based material. The silicon-based material is a silicon-oxygen composite material, and the carbon material is graphite and hard carbon. The mass ratio of silicon-oxygen composite material, graphite and hard carbon is 15%:77.35%:7.65%.

[0237] The specific preparation process of the negative electrode active material, negative electrode slurry, and lithium-ion battery is as follows:

[0238] (1) Ball milling and mixing of graphite + silicon oxide composite material: graphite and silicon oxide composite material were ball milled and mixed in a ball mill at a speed of 15 rpm / min for 3 h. The ball milling media were steel balls and the ball-to-material ratio was 18:1. A mixture of graphite and silicon oxide / silicon carbon composite material was obtained and the material structure was characterized in the same manner as in Example 1.

[0239] (2) Mixing of hard carbon with graphite and silicon oxide composite material: In the negative electrode homogenization process, a dry homogenization process is used to premix the mixture of hard carbon and graphite with silicon oxide composite material into dry powder to obtain a dry powder mixture of graphite, hard carbon and silicon oxide composite material.

[0240] (3) Add binder CMC (dry powder mass ratio 1.4%, relative to the total weight of solid components in the negative electrode slurry) and conductive agent SP (dry powder mass ratio 1.0%, relative to the total weight of solid components in the negative electrode slurry) to the dry powder mixture in step (2) and mix them to obtain a dry powder mixture of negative electrode active material, conductive agent and binder.

[0241] (4) Add deionized water to the dry powder mixture obtained in step (3) and knead it. Then add binder SBR (2.2% of dry powder mass, relative to the total weight of solid components in the negative electrode slurry) to obtain a negative electrode slurry containing negative electrode active material.

[0242] (5) Negative electrode sheet fabrication and lithium-ion battery assembly: The above negative electrode slurry is made into electrode sheets and assembled into lithium-ion batteries.

[0243] Referring to national standards 31484 and 31486, the lithium-ion battery prepared in this example was tested for rate and cycle performance in the same manner as in Example 1.

[0244] Example 5

[0245] This embodiment provides a negative electrode active material, including carbon materials and silicon-based materials. The carbon materials include graphite and graphitized soft carbon, and the silicon-based materials include silicon-oxygen composite materials. The mass ratio of silicon-oxygen composite materials, graphite and graphitized soft carbon is 10%:87.3%:2.7%.

[0246] The preparation method of the above-mentioned negative electrode active material includes:

[0247] (1) Graphite and soft carbon were subjected to CVD vapor deposition, so that the graphite was embedded into the soft carbon by infiltration. The CVD-deposited graphite and soft carbon were mixed at a mass ratio of 87.3%:2.7%, and hard carbon was added at 220℃ for hydrothermal reaction for 1.5h to complete the hard carbon coating (the hard carbon coating here accounts for 0.1% of the soft carbon content). Then, the mixture was granulated and graphitized at 2500℃ to obtain a composite material of graphite and graphitized soft carbon.

[0248] (2) The composite material of graphite and graphitized soft carbon was mixed with 10% silicon-oxygen composite material and ball-milled at a speed of 13 rpm / min for 3 hours. The ball milling media were steel balls, and the ball-to-material ratio was 15:1.

[0249] 1. The particle size distribution of the mixture of ball-milled graphite and graphitized soft carbon composite material with silicon-oxygen composite material is D10 = 4.65 μm, D50 = 11.43 μm, D90 = 23.66 μm, and D99 = 32.1 μm, thus obtaining the negative electrode active material.

[0250] The negative electrode active material of this embodiment is used to prepare negative electrode slurry, negative electrode sheet and lithium-ion battery. The preparation method is the same as steps (3)-(5) in Example 1.

[0251] Example 6

[0252] Except for the mass ratio of silicon-oxygen composite material, graphite, and graphitized soft carbon being 10%:84.6%:5.4%, everything else was the same as in Example 5.

[0253] Example 7

[0254] Except for step (1), which is replaced by direct mixing without ball milling, all other steps are the same as in Example 1;

[0255] Step (1) is as follows:

[0256] (1) Direct mixing of graphite and silicon-carbon composite materials: Graphite and silicon-oxygen / silicon-carbon composite materials were mixed in a mixer for 3 hours to obtain a mixture of graphite and silicon-oxygen / silicon-carbon composite materials. The material structure was characterized, and the particle size distribution of the mixture of graphite and silicon-carbon composite materials was D10 = 6.7 μm.

[0257] D50=14μm, D90=26.5μm, D99=37.8μm.

[0258] Comparative Example 1

[0259] The following fast-charging lithium-ion battery anode system adopts a common graphite and silicon-oxygen mixed anode system, with 85% graphite and 15% silicon-oxygen mixed silicon anode system, which is directly made into anode slurry and assembled into a soft-pack battery. The energy density of the soft-pack battery is 250-270Wh / kg.

[0260] Negative electrode slurry preparation ①: 85% graphite and 15% silicon oxide dry powder are premixed to obtain a negative electrode dry powder mixture;

[0261] The step involves adding binder CMC and conductive agent SP to the negative electrode dry powder mixture for dry powder mixing ②, to obtain a dry powder mixture of negative electrode active material, conductive agent, and binder;

[0262] The step involves adding deionized water to the above dry powder mixture for kneading, and then adding binder SBR③ to obtain a conventional blended silicon anode slurry.

[0263] The electrode sheet fabrication and cell assembly step ④ involves fabricating the above negative electrode slurry into electrode sheets and assembling them into a cell for the following electrical performance tests.

[0264] Step ⑤, cell testing and evaluation, involves testing the assembled cells for rate and cycle performance in the same manner as in Example 1.

[0265] Comparative Example 2

[0266] The following fast-charging lithium-ion battery anode system adopts a common graphite and silicon-oxygen mixed anode system, a 70% graphite and 30% silicon-oxygen mixed silicon anode system, which is directly made into anode slurry and assembled into a soft-pack battery. The energy density of the soft-pack battery is 300-320Wh / kg.

[0267] Negative electrode slurry preparation ①: 70% graphite and 30% silicon oxide dry powder are premixed to obtain a negative electrode dry powder mixture;

[0268] The step involves adding binder CMC and conductive agent SP to the negative electrode dry powder mixture for dry powder mixing ②, to obtain a dry powder mixture of negative electrode active material, conductive agent, and binder;

[0269] The step involves adding deionized water to the above dry powder mixture for kneading, and then adding binder SBR③ to obtain a conventional blended silicon anode slurry.

[0270] The electrode sheet fabrication and cell assembly step ④ involves fabricating the above-mentioned negative electrode slurry into electrode sheets and assembling them into a cell for electrical performance testing.

[0271] Step ⑤, cell testing and evaluation, involves testing the assembled cells for rate and cycle performance in the same manner as in Example 1.

[0272] Comparative Example 3

[0273] Except for the mass ratio of silicon oxide / silicon carbon composite material, graphite and hard carbon being 16%:75.6%:8.4%, everything else was the same as in Example 1.

[0274] Comparative Example 4

[0275] Except for the silicon-oxygen / silicon-carbon composite material, graphite, and hard carbon in a mass ratio of 2%:95.55%:2.45%,

[0276] Everything else is the same as in Example 1.

[0277] Comparative Example 5

[0278] Except for the mass ratio of silicon oxide / silicon carbon composite material, graphite and graphitized soft carbon being 16%:76.44%:7.56%, everything else was the same as in Example 5.

[0279] Comparative Example 6

[0280] Except for the mass ratio of silicon oxide / silicon carbon composite material, graphite and graphitized soft carbon being 2%:96.53%:1.47%, everything else was the same as in Example 1.

[0281] The capacity retention rates at room temperature rate charging and at room temperature and high temperature cycling were compared between the batteries of Examples 1-7 and Comparative Example-6, respectively. The specific results are shown in Table 3.

[0282] Table 3 Comparison of Electrical Performance Data

[0283]

[0284] As can be seen from the data in Table 3, the novel silicon-doped fast-charging lithium-ion battery anode systems of Examples 1-7 show significant improvements in rate charging capability and cycle performance compared to conventional graphite-doped silicon anode systems.

[0285] Application Example 1

[0286] This application example uses the lithium-ion battery from Example 1 for charging, and the charging method is shown in Table 4.

[0287] Application Example 2

[0288] This application example uses the lithium-ion battery from Example 2 for charging, and the charging method is shown in Table 4.

[0289] Application Example 3

[0290] This application example uses the lithium-ion battery from Example 5 for charging, and the charging method is shown in Table 4.

[0291] Application Example 4

[0292] This application example uses the lithium-ion battery from Example 6 for charging, and the charging method is shown in Table 4.

[0293] Table 4

[0294]

[0295] Table 5

[0296] project Maximum charging rate (C) Charging time (min) Application Example 1 3.5 65 Application Example 2 4.5 50 Application Example 3 4.5 66 Application Example 4 5 51

[0297] As can be seen from Tables 4 and 5, fast charging is achieved by employing a stepped charging strategy, utilizing the intermediate SOC range (20-80%). Furthermore, using the negative electrode active material of this invention can improve the charging rate in the intermediate SOC range, appropriately expanding the SOC range for fast charging.

[0298] Therefore, based on the rate and cycle performance results of the battery of this invention, the battery prepared using the novel silicon-doped fast-charging lithium-ion battery system provided in this invention has the following advantages: First, it leverages the advantages of hard carbon relative to graphite and silicon-based anodes in terms of isotropy and large interlayer spacing to enhance the high-rate charging capability of the anode; simultaneously, the high hardness of hard carbon itself inhibits the expansion of the silicon anode to a certain extent, thereby improving the charging capability and cycle performance of the anode. Second, it leverages the advantages of graphitized soft carbon relative to graphite and silicon-based anodes in terms of large specific surface area and large interlayer spacing to enhance the high-rate charging capability of the anode and control voltage changes; simultaneously, it leverages the advantages of soft carbon itself in terms of stable crystal structure and strong electrolyte adaptability to enhance the safety performance of the anode. Third, the particle size distribution of the anode active material is more uniform and the morphology is more regular, which is beneficial to improving rate and cycle performance.

[0299] The novel silicon-doped anode system of this invention is beneficial for the application of silicon anode systems in the design of fast-charging cell systems and has significant practical significance in production.

[0300] It should be noted that although the technical solution of the present invention has been described with specific examples, those skilled in the art will understand that the present invention should not be limited thereto.

[0301] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or technical improvements to the embodiments in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A negative electrode active material, characterized in that, The negative electrode active material comprises carbon materials and silicon-based materials. The carbon materials include a first carbon material and a second carbon material. The first carbon material includes graphite, and the second carbon material includes hard carbon and / or graphitized soft carbon. The silicon-based material includes at least one of silicon oxide compounds and silicon carbide compounds. The mass ratio of the carbon material to the silicon-based material is 85-97%: 3-15%; And when the second carbon material includes hard carbon, the mass ratio of graphite to hard carbon is graphite:hard carbon = 91-97%:3-9%; or When the second carbon material includes graphitized soft carbon, the mass ratio of graphite to graphitized soft carbon is graphite:graphitized soft carbon = 92-98%:2-8%.

2. The negative electrode active material according to claim 1, wherein the mass ratio of the carbon material to the silicon-based material is carbon material:silicon-based material = 90-95%:5-10%; The mass ratio of graphite to hard carbon is graphite:hard carbon = 94-97%:3-6%; The mass ratio of graphite to graphitized soft carbon is 96-98%:2-4%.

3. The negative electrode active material according to claim 1 or 2, wherein the carbon matrix in the silicon-carbon compound comprises resin carbon.

4. The negative electrode active material according to claim 1 or 2, wherein the graphite comprises at least one of artificial graphite and natural graphite.

5. The negative electrode active material according to claim 1 or 2, wherein the hard carbon comprises at least one of resin carbon, organic polymer pyrolysis carbon, and biomass-based carbon.

6. A method for preparing a negative electrode active material, characterized in that, The negative electrode active material comprises carbon materials and silicon-based materials. The carbon materials include a first carbon material and a second carbon material. The first carbon material includes graphite, and the second carbon material includes hard carbon and / or graphitized soft carbon. The silicon-based material includes at least one of silicon oxides and silicon carbide compounds. The mass ratio of the carbon material to the silicon-based material is 85-97%: 3-15%. And when the second carbon material includes hard carbon, the mass ratio of graphite to hard carbon is graphite:hard carbon = 91-97%:3-9%, and the preparation method includes the step of mixing graphite, hard carbon, and silicon-based materials; or When the second carbon material includes graphitized soft carbon, the mass ratio of graphite to graphitized soft carbon is 92-98%:2-8%, and the preparation method includes the steps of graphitizing graphite and soft carbon and then adding silicon-based materials for mixing.

7. The preparation method according to claim 6, wherein when the first carbon material comprises graphite and the second carbon material comprises hard carbon, the preparation method comprises first ball milling and mixing the graphite and the silicon-based material, and then adding hard carbon and mixing.

8. In the preparation method according to claim 7, the ball milling and mixing of the graphite and the silicon-based material, as well as the mixing process of adding hard carbon, are both dry mixing processes.

9. The preparation method according to claim 7, wherein the ball milling and mixing of the graphite and the silicon-based material is carried out during the negative electrode homogenization process.

10. The preparation method according to claim 7, wherein the ball milling speed is 15.4-25.4 rpm, the time is 2-4 h, the ball milling media are steel balls and / or cast iron balls, and the ball-to-material ratio is material to ball milling media = 15-20: 0-1.

11. According to the preparation method of claim 7, the particle size distribution of the mixture of ball-milled graphite and silicon-based material is D10=4.5-6.5μm, D50=11.5-13.5μm, D90=22.5-24.5μm, and D99=33.5-35.5μm.

12. The preparation method according to claim 6, wherein when the first carbon material comprises graphite and the second carbon material comprises graphitized soft carbon, the preparation method comprises embedding graphite into the interior of the soft carbon by infiltration, performing coating, granulation and graphitization treatment to obtain a composite material of graphite and graphitized soft carbon, and then adding silicon-based material and ball milling.

13. The preparation method according to claim 12, wherein the infiltration embedding is carried out by vapor phase deposition, the coating is carried out by adding a carbon source and performing a hydrothermal reaction, and the graphitization treatment temperature is 2500-2800℃.

14. The preparation method according to claim 12, wherein the ball milling speed is 10.4-15.4 rpm, the time is 2-4 h, the ball milling media are steel balls and / or cast iron balls, and the ball-to-material ratio is material to ball milling media = 12-17: 0-1.

15. According to the preparation method of claim 12, the particle size distribution of the mixture of ball-milled graphite and graphitized soft carbon composite material with silicon-based material is D10=3.5-5.5μm, D50=10.5-12.5μm, D90=20.5-22.5μm, and D99=31.5-33.5μm.

16. The preparation method according to claim 6, wherein the hard carbon comprises at least one of resin carbon, organic polymer pyrolysis carbon, and biomass-based carbon; The soft carbon includes at least one of petroleum coke, needle coke, carbon fiber, and carbon microspheres; The mass ratio of graphite to hard carbon is graphite:hard carbon = 94-97%:3-6%; The mass ratio of graphite to graphitized soft carbon is 96-98% : 2-4%; The mass ratio of the carbon material to the silicon-based material is 90-95%: 5-10%.

17. A negative electrode slurry comprising the negative electrode active material according to any one of claims 1 to 5, or the negative electrode active material obtained by the preparation method according to any one of claims 6 to 16, as well as a binder and a conductive agent.

18. The negative electrode slurry according to claim 17, wherein the binder comprises at least a first binder and a second binder. The first adhesive and the second adhesive may be the same or different. The first adhesive and the second adhesive are respectively selected from at least one of carboxymethyl cellulose, styrene-butadiene rubber, ethylene propylene diene monomer rubber, fluororubber, polyacrylonitrile, polyethylene oxide, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoroethylene copolymer, polyvinyl alcohol, and polyvinyl butyral resin.

19. The negative electrode slurry according to claim 17 or 18, wherein the conductive agent comprises at least one of carbon black, carbon nanotubes or carbon fibers.

20. The negative electrode slurry according to claim 19, wherein the carbon black comprises at least one of super conductive carbon black, acetylene black, Ketjen black, channel black, furnace black, and lampblack.

21. A method for preparing the negative electrode slurry according to claim 18, comprising the following steps: Step S1 involves mixing carbon materials and silicon-based materials to obtain the negative electrode active material. Step S2 involves adding a first binder and a conductive agent to the negative electrode active material and then performing dry mixing to obtain a dry powder mixture.

22. The preparation method according to claim 21, further comprising step S3 of kneading the dry powder mixture with water, then adding a second binder, and mixing to obtain a negative electrode slurry.

23. The preparation method according to claim 22, wherein the first adhesive and the second adhesive may be the same or different. The first adhesive and the second adhesive are respectively selected from at least one of carboxymethyl cellulose, styrene-butadiene rubber, ethylene propylene diene monomer rubber, fluororubber, polyacrylonitrile, polyethylene oxide, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoroethylene copolymer, polyvinyl alcohol, and polyvinyl butyral resin.

24. A negative electrode sheet, characterized in that, It is obtained by coating the negative electrode slurry according to any one of claims 17 to 20, or the negative electrode slurry obtained by the preparation method according to any one of claims 21 to 23, onto the negative electrode current collector.

25. A lithium-ion battery comprising the negative electrode sheet according to claim 24.

26. A method for charging a lithium-ion battery, characterized in that, The negative electrode of the lithium-ion battery includes a negative electrode active material, which comprises a carbon material and a silicon-based material. The carbon material comprises a first carbon material and a second carbon material. The first carbon material includes graphite, and the second carbon material includes hard carbon and / or graphitized soft carbon. The silicon-based material comprises at least one of silicon oxide and silicon carbide. The mass ratio of the carbon material to the silicon-based material is 85-97% carbon material: 3-15% silicon-based material. When the first carbon material includes graphite and the second carbon material includes hard carbon, the mass ratio of graphite to hard carbon is graphite:hard carbon = 91-97%:3-9%; When the first carbon material includes graphite and the second carbon material includes graphitized soft carbon, the mass ratio of graphite to graphitized soft carbon is 92-98% : 2-8%. The charging method includes: When the battery's state of charge (SOC) is within the first range, pre-charge at a rate of 0.5 times or less; When the battery's state of charge (SOC) is in the second range, constant current charging is performed at a rate of 0.5 times or higher. When the battery's state of charge (SOC) is in the third range, trickle charging is performed at a rate of less than 1%. When the mass ratio of graphite to hard carbon is graphite:hard carbon = 94-97%:3-6%, the charging method specifically includes: When the first range is within 5%, the battery is pre-charged at a rate of 0-0.

5. When the SOC is above 5% and below 80%, the battery is charged at a constant current using a four-stage mode: a first stage of 0.5-1 times rate when the SOC is 5-10%, a second stage of 1-3 times rate when the SOC is 10-20%, a third stage of 3-4 times rate when the SOC is 20-60%, and a fourth stage of 1-2.5 times rate when the SOC is 60-80%. When the SOC is above 80% but below 100%, a two-stage trickle charging mode is used to charge the battery, with a first stage at 0.5-1 times the rate when the SOC is between 80-90% and a second stage at 0-0.5 times the rate when the SOC is between 90-100%. When the mass ratio of graphite to hard carbon is graphite:hard carbon = 91-94%:6-9% and does not include 94%:96%, the charging method specifically includes: When the first range is within 5%, the battery is pre-charged at a rate of 0-0.

5. When the SOC is above 5% but below 90%, a four-stage constant current charging mode is used for the battery: a first stage of 0.5-6 times rate for SOC between 5-10%, a second stage of 1-6 times rate for SOC between 10-30%, a third stage of 1.5-5 times rate for SOC between 30-70%, and a fourth stage of 1-1.5 times rate for SOC between 70-90%. When the SOC is above 90% but below 100%, a two-stage trickle charging mode is used for the battery: a first stage at 0.5-1 times the rate when the SOC is 90-95%, and a second stage at 0-0.5 times the rate when the SOC is 95-100%. When the mass ratio of graphite to graphitized soft carbon is 96-98% : 2-4% (graphite : graphitized soft carbon = 2-4%), the charging method specifically includes: When the first range is within 10%, the battery is pre-charged using a two-stage mode: a first stage with a SOC of 0-5% and a second stage with a SOC of 5-10% and a first stage with a SOC of 0.5-1%. When the SOC is above 10% but below 80%, a three-stage constant current charging mode is used for the battery: a first stage of 1-3 times rate for SOC between 10-20%, a second stage of 4-5 times rate for SOC between 20-60%, and a third stage of 1-2.5 times rate for SOC between 60-80%. When the SOC is above 80% but below 100%, a two-stage trickle charging mode is used to charge the battery, with a first stage at 0.5-1 times the rate when the SOC is between 80-90% and a second stage at 0-0.5 times the rate when the SOC is between 90-100%. When the mass ratio of graphite to graphitized soft carbon is 92-96% : 4-8% (graphite : graphitized soft carbon) but does not include 96% : 4%, the charging method specifically includes: When the first range is within 5%, the battery is pre-charged at a rate of 0-0.

5. When the SOC is above 5% but below 90%, a four-stage constant current charging mode is used for the battery: a first stage of 0.5-8 times rate for SOC between 5-10%, a second stage of 1-8 times rate for SOC between 10-30%, a third stage of 1.5-6 times rate for SOC between 30-70%, and a fourth stage of 1-1.5 times rate for SOC between 70-90%. When the third range is above 90% but below 100%, a two-stage trickle charging mode is adopted for the battery, with the first stage at a rate of 0.5-1 times when the SOC is 90-95% and the second stage at a rate of 0-0.5 times when the SOC is 95-100%.

27. The charging method according to claim 26, wherein when the mass ratio of graphite to hard carbon is graphite:hard carbon = 94-97%:3-6%, the charging method specifically includes: When the battery's State of Charge (SOC) is in the second range, in the fourth stage where the SOC is 60-80%, charging is performed at a rate of 2-2.5 times when the SOC is 60-70% and at a rate of 1-2 times when the SOC is 70-80%; or When the mass ratio of graphite to hard carbon is graphite:hard carbon = 91-94%:6-9% and does not include 94%:96%, the charging method specifically includes: When the battery's state of charge (SOC) is in the second range, in the third stage where the SOC is 30-70%, the charging mode is 4-5 times when the SOC is 30-50%, 2.5-4 times when the SOC is 50-60%, and 1.5-2.5 times when the SOC is 60-70%.

28. The charging method according to claim 26, wherein when the mass ratio of graphite to graphitized soft carbon is graphite:graphitized soft carbon = 96-98%:2-4%, the charging method specifically includes: When the battery's State of Charge (SOC) is in the second range, in the third stage where the SOC is 60-80%, charging is performed at a rate of 2-2.5 times when the SOC is 60-70% and at a rate of 1-2 times when the SOC is 70-80%; or When the mass ratio of graphite to graphitized soft carbon is 92-96% : 4-8% (graphite : graphitized soft carbon) but does not include 96% : 4%, the charging method specifically includes: When the battery's state of charge (SOC) is in the second range, in the third stage where the SOC is 30-70%, the charging mode is 4-6 times when the SOC is 30-50%, 2.5-4 times when the SOC is 50-60%, and 1.5-2.5 times when the SOC is 60-70%.

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