Pre-lithium-treated negative electrode, composite negative electrode, method for manufacturing the same, and use

Abstract

This invention relates to a pre-lithiumized anode, a composite anode, a method for manufacturing the same, and its use. The pre-lithiumized anode comprises an anode active material and a cocoon-structured lithium-carbon material, wherein the cocoon-structured lithium-carbon material is distributed between the anode active materials. The cocoon structure comprises a cocoon formed from a structural carbon material and one or more lithium-containing particles contained within the cocoon. The pre-lithiumized anode has a stable structure, the degree of pre-lithiumization is controllable, and when used in combination with a conventional cathode, it can significantly improve initial Coulomb efficiency and cycle life. The manufacturing method is simple and enables large-scale industrial production.

Description

Technical Field

[0001] The present invention relates to the field of lithium battery technology, and specifically relates to a prelithiated negative electrode, a composite negative electrode, a method for manufacturing the same, and use thereof.

Background Art

[0002] Lithium-ion batteries have advantages such as a long cycle life, a high energy density, and no memory effect, and are currently the most widely applied secondary batteries. Conventionally, graphite, silicon-carbon materials, and silicon-oxygen materials are often applied to the negative electrodes of lithium-ion batteries. In the initial charge-discharge process of lithium-ion batteries, a large amount of lithium is consumed in the formation of SEI on the negative electrode surface, resulting in a low initial Coulomb efficiency, a significant decrease in the actual specific energy of the lithium-ion battery, and severely restricting the large-scale commercial application of lithium-ion batteries. Therefore, research on how to improve the initial Coulomb efficiency has become active.

[0003] Prelithiation using metallic lithium powder has made some progress. Tesla's patent (CN108780887B) discloses an electrode film comprising carbon particles, a single-element metal, and a fibrillated binder, wherein the electrode film is self-supporting and free of residual solvent. The carbon particles include graphite particles, and the single-element metal includes single-element lithium metal particles. The manufacturing method includes the steps of forming an electrode film mixture by mixing single-element lithium metal, a plurality of carbon particles, and a fibrillated binder, and forming an electrode film from the electrode film mixture, i.e., prelithiation by mixing metallic lithium powder and graphite. Lithium metallic powder is highly reactive and needs to be stabilized before use. The usual method involves forming a lithium carbonate or lithium fluoride layer on its surface, such as the passivation lithium powder used in FMC. However, the conductivity of the lithium carbonate or lithium fluoride layer is low, and after the lithium metallic powder functions, cavities are formed within the negative electrode, reducing the conductivity of the negative electrode. Furthermore, lithium dendrites may grow in relatively thin areas of the negative electrode, which is detrimental to improving negative electrode performance.

[0004] CN114765254A discloses a method for pre-lithifying a negative electrode sheet, employing a dry process to mix metallic lithium powder into the electrode plate. This effectively improves the battery's energy density by replenishing the lithium consumed during the initial charging process when SEI forms on the negative electrode. However, after the metallic lithium powder is deactivated, the resulting passivation layer has poor conductivity, reducing the utilization rate of the metallic lithium powder. After the metallic lithium powder has functioned, cavities or holes are formed on the negative electrode, resulting in uneven current density and making it easy for lithium dendrites to form during the cycling process. Furthermore, pre-lithification only solves the problem of low initial Coulomb efficiency and cannot improve the negative electrode capacity.

[0005] CN102201565A discloses a high-capacity metallic lithium powder composite anode, a method for manufacturing it, and a multilayer composite electrode. A high-capacity anode is manufactured by mixing metallic lithium powder, a binder such as PVDF, and an anode material such as graphite. The metallic lithium powder reacts with PVDF, causing a decrease in the binding performance of the PVDF and ultimately rendering it ineffective. At the same time, some metallic lithium is lost, and the problems of volume expansion and dendrite growth of metallic lithium during the cycling process cannot be solved.

[0006] The urgent challenges at this stage are how to precisely control the amount of lithium replenished, ensure a stable structure after pre-lithification, maintain conductivity without degradation, and suppress dendrite growth in a pre-lithified anode; and how to develop a high-capacity composite anode that simultaneously combines specific capacity, cycle performance, and rate characteristics by fully utilizing metallic lithium powder during the cycling process to solve the problems of metallic lithium volume expansion and dendrite growth. [Overview of the Initiative]

[0007] In view of the problems existing in the prior art, the present invention provides a pre-lithified anode, a composite anode, a method for manufacturing the same, and its use. In the pre-lithified anode, the initial Coulomb efficiency of the lithium-ion battery is significantly improved by using a cocoon-structured lithium-carbon material as a lithium replenisher. The cocoon-structured lithium-carbon material contains a carbon material with good conductivity and a certain rigid structure, improving the utilization rate of the lithium-containing core, improving the conductivity and structural stability of the pre-lithified anode, and enabling accurate lithium replenishment. Furthermore, by constructing a structural carbon material on the surface of lithium-containing particles such as metallic lithium powder and / or lithium alloy powder to form a cocoon-structured lithium-carbon material, when a large amount of the above-mentioned cocoon-structured lithium-carbon material is used in the anode active material layer, the structural carbon materials intersect and entangle with each other to form a stable porous skeleton, effectively solving the problems of metallic lithium volume expansion and lithium dendrite growth during the cycle process, while improving the utilization rate of lithium-containing particles.

[0008] To achieve this objective, the present invention employs the following technical solutions.

[0009] A negative electrode for a lithium-ion battery, wherein the negative electrode active material layer of the negative electrode contains a negative electrode active material and a cocoon-structured lithium-carbon material, the cocoon-structured lithium-carbon material is distributed between the negative electrode active materials, and the cocoon-structured lithium-carbon material includes a cocoon body formed of a structural carbon material and one or more lithium-containing particles contained within the cocoon body.

[0010] The negative electrode of the lithium-ion battery of the present invention can be divided into two types, depending on the content of the lithium-carbon material in the cocoon structure: a pre-lithified negative electrode (which has a relatively low lithium-carbon material content and is mainly used for pre-lithification) and a composite negative electrode (which has a relatively high lithium-carbon material content, and in which the structural carbon material forms a porous framework in the negative electrode active material layer).

[0011] According to the first aspect, the negative electrode of the lithium-ion battery of the present invention is a pre-lithified negative electrode, the pre-lithified negative electrode comprises a negative electrode active material and a cocoon-structured lithium-carbon material, the cocoon-structured lithium-carbon material is distributed between the negative electrode active materials, The mass ratio of the negative electrode active material to the cocoon-structured lithium-carbon material is 1g:(1~300)mg. The mass ratio of the structural carbon material to the lithium-containing particles is 1:(1~1000).

[0012] In the present invention, a mayu-structured lithium-carbon material is adopted for lithium replenishment. The lithium-containing particles, as a lithium source, accurately replenish lithium to the negative electrode. The mayu body structure formed of the structural carbon material has a certain rigidity, has good contact with the negative electrode active material, constructs an electron path while playing a supporting role, and does not form obvious cavities even after the lithium-containing particles are consumed, does not increase the internal resistance of the negative electrode, and also has a good lithium ion path, improves the ionic conductivity of the pre-lithiated negative electrode, can meet the needs of high-rate charge and discharge, and the structural carbon material mayu body structure further absorbs and holds the electrolyte, enables the lithium-containing particles to fully exert their capacity, and can overcome the drawbacks of lithium replenishment with metallic lithium powder. The pre-lithiated negative electrode has advantages such as high structural stability, long cycle life, and good rate performance.

[0013] Optionally, the negative electrode active material includes any one or at least a combination of two or more of graphite, tin-based materials, hard carbon, soft carbon, activated carbon, mesocarbon microbeads, silicon-carbon (Si / C) materials or silicon-oxygen (SiO x (0 < x ≦ 2)) materials.

[0014] Optionally, the structural carbon material includes any one or at least a combination of two or more of particulate, linear or sheet-like nanocarbon materials. Preferably, it is any one or at least a combination of two or more of acetylene black, ketjen black, Cabot BP2000, Super P, single-walled carbon nanotubes, few-walled carbon nanotubes, multi-walled carbon nanotubes, doped carbon nanotubes, graphene, doped graphene, carbon nanofibers or doped carbon nanofibers. Preferably, it is any one or at least a combination of two or more of single-walled carbon nanotubes, few-walled carbon nanotubes, multi-walled carbon nanotubes, doped carbon nanotubes, graphene or doped graphene.

[0015] Selectively, the doping elements in the doped carbon nanotubes, doped graphene, or doped carbon nanofibers independently include one or at least two of the following elements: fluorine, nitrogen, oxygen, phosphorus, silver, silicon, tin, or zinc.

[0016] Selectively, the lithium-containing particles include metallic lithium particles and / or metallic lithium alloy particles, preferably metallic lithium alloy particles, which remain in small amounts after lithium replenishment, forming a framework and combining with structural carbon material to prevent the formation of large cavities in the negative electrode, prevent an increase in the internal resistance of the negative electrode, and regulate the deposition of metallic lithium, thereby improving the cycle performance of the negative electrode while achieving lithium replenishment.

[0017] Selectively, the mass content of metallic lithium in the metallic lithium alloy particles is 70% or more, and may be, for example, 70%, 72%, 75%, 80%, 83%, 85%, 88%, 90%, 93%, 95%, 97%, or 99%, including but not limited to the values ​​listed above. If the mass content is too low, a large amount of inactive lithium material is introduced, affecting the energy density of the negative electrode. Preferably, it is 85% or more.

[0018] Selectively, the average particle size of the lithium-containing particles is 1 to 100 μm, and may be, for example, 1 μm, 3 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, or 100 μm, and includes, but is not limited to, the values ​​listed above, and is preferably 5 to 30 μm.

[0019] Selectively, the metallic lithium alloy particles include a binary lithium alloy and / or a ternary lithium alloy, the binary lithium alloy powder includes one or at least two of the following: lithium-magnesium alloy, lithium-boron alloy, lithium-silver alloy, lithium-indium alloy, lithium-silicon alloy, lithium-aluminum alloy, or lithium-tin alloy, and the ternary lithium alloy powder includes one or at least two of the following: lithium-tin-silver alloy, lithium-silver-silicon alloy, or lithium-boron-zinc alloy.

[0020] Selectively, the mass ratio of the structural carbon material to the lithium-containing particles is 1:(1~1000), and may be, for example, 1:1, 1:5, 1:10, 1:20, 1:50, 1:55, 1:60, 1:80, 1:90, 1:100, 1:120, 1:150, 1:200, 1:300, 1:400, 1:450, 1:480, 1:500, 1:550, 1:600, 1:700, 1:800, 1:900, 1:950 or 1:1000, and includes, but is not limited to, the above values, and is preferably 1:(10~500).

[0021] Selectively, an organic transmission layer is provided between the lithium-containing particles and the structural carbon material, and the organic transmission layer comprises an organic lithium ion transmission agent and a conductive agent. The organic transmission layer is favorable for the diffusion of lithium ions and further improves the ionic conductivity of the pre-lithiumated negative electrode.

[0022] The conductive agent comprises at least one of carbon nanotubes, carbon black, graphene, and acetylene black. The organolithium ion transport agent comprises polyethylene oxide, polyethylene glycol, polysiloxane, polytrimethylene carbonate, polycarbonate, polyethylene carbonate, polypropylene carbonate, polyvinyylene carbonate, polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, poly(vinylidene fluoride-hexafluoropropylene), polyphenylene sulfide, p-benzoquinone, and at least two copolymers or mixtures of the above polymers.

[0023] The mass ratio of the lithium-containing particles, the organic lithium ion transport agent, and the conductive agent is (80-95):(1-10):(0.1-10), preferably (90-95):(5-10):(0.5-5).

[0024] Selectively, the mass ratio of the negative electrode active material to the cocoon-structured lithium-carbon material includes, but is not limited to, 1g:(1~300)mg, for example, 1g:1mg, 1g:3mg, 1g:5mg, 1g:10mg, 1g:15mg, 1g:20mg, 1g:30mg, 1g:50mg, 1g:100mg, 1g:120mg, 1g:150mg, 1g:180mg, 1g:200mg, 1g:240mg, or 1g:300mg, etc. While the above values ​​are often included, they are not limited to these. The above mass ratio may be selected based on the type of negative electrode active material, the type of lithium-carbon material with a cocoon structure, the initial Coulomb efficiency, and the actual requirements. Generally, the initial Coulomb efficiency of graphite negative electrode materials is higher than that of silicon-containing negative electrode materials, and the actual required amount of graphite negative electrode material is small for the same type of lithium-carbon material with a cocoon structure, preferably 1g:(10~200)mg. If the above mass ratio is too small, that is, if the mass of the lithium-carbon material with a cocoon structure is large, the pre-lithified negative electrode not only has the effect of pre-lithification but also plays a role in storing the lithium source, exhibiting the characteristics of a composite negative electrode, allowing for continuous replenishment of the lithium source during the battery cycle process, and further improving the cycle performance and energy density of the pre-lithified negative electrode.

[0025] According to a second aspect, the present invention provides a method for manufacturing a pre-lithified negative electrode as described in the first aspect, the method comprising the following steps.

[0026] (1) A step of mixing a structural carbon material, lithium-containing particles, and an organic solvent, and then spraying and drying the mixture, or stirring it at a rotational speed of 5000 rpm or more, to obtain a lithium-carbon material with a cocoon structure, and (2) A process of mixing a negative electrode active material, a conductive agent, and a first binder, then forming the binder into fibers to obtain a first mixture, then mixing the first mixture with a cocoon-structured lithium-carbon material to obtain a second mixture, hot pressing the second mixture to form a negative electrode active material layer, and then combining it with a current collector to obtain the pre-lithified negative electrode, or Mixing a negative electrode active material, a conductive agent, a second binder, a lithium-carbon material having a whisker structure, and an organic solvent to produce a negative electrode slurry, and applying the negative electrode slurry onto the surface of a current collector to obtain the pre-lithiated negative electrode described above.

[0027] In the present invention, whether a dry method (without using an organic solvent) or a wet method (using an organic solvent) is adopted, the lithium-carbon material having a whisker structure can be used as a lithium source, and it can be mixed into the electrode system during the mixing process to directly produce a pre-lithiated negative electrode. Preferably, the pre-lithiated negative electrode is produced by a dry method. The dry method can produce a negative electrode with a high energy density and can more perfectly maintain the morphology of the lithium-carbon material having a whisker structure.

[0028] Optionally, step (1) further includes the following operations. (a) Mixing lithium-containing particles, an organic lithium ion transport agent, and a conductive agent to form particles composed of lithium-containing particles and an organic transport layer covering the surface thereof, and (b) Uniformly mixing the obtained particles with a structural carbon material in an organic solvent, and spray-drying or stirring at a high speed to obtain a lithium-carbon material having a whisker structure. The above operations construct an organic ion transport layer on the surface of the lithium-containing particles, which is advantageous for the diffusion of lithium ions and further improves the ionic conductivity of the pre-lithiated negative electrode.

[0029] Optionally, the mixing of the lithium-containing particles, the organic lithium ion transport agent, and the conductive agent is carried out in the presence of an organic solvent, and the solvent may be removed. The organic solvent may include N-methylpyrrolidone (NMP), ethanol, n-hexane, liquid paraffin, tetrahydrofuran, p-xylene, etc.

[0030] Optionally, in step (1), the organic solvent is any one or at least a combination of two of N-methylpyrrolidone, a liquid alkane having 5 to 10 carbon atoms, benzene, p-xylene, or petroleum ether.

[0031] Selectively, in step (1), the spray drying conditions are: intake air temperature of 180-240°C, for example 180°C, 185°C, 190°C, 195°C, 200°C, 205°C, 215°C, or 220°C, preferably 200-220°C; exhaust air temperature of 90-110°C, for example 90°C, 95°C, 100°C, 105°C, or 110°C, preferably 100-110°C; and atomization pressure of 0.1-0.5 MPa, for example 0.2 MPa, 0.25 MPa, 0.3 MPa, 0.35 MPa, or 0.4 MPa, preferably 0.2-0.4 MPa.

[0032] Selectively, in step (1), the rotational speed of the high-speed stirring is 6000 to 15000 rpm, the time is 0.5 to 10 min, for example the rotational speed may be 6000 rpm, 6500 rpm, 7000 rpm, 75000 rpm, 8000 rpm, 8500 rpm, 9000 rpm, 10000 rpm, 11000 rpm, 11500 rpm, 12000 rpm, 12500 rpm, 13000 rpm, 14000 rpm, 14500 rpm or 15000 rpm, and the time may be 0.5 min, 1 min, 1.5 min, 2 min, 2.5 min, 3 min, 3.5 min, 4 min, 4.5 min, 5 min, 6 min, 7 min, 8 min, 9 min, 9.5 min or 10 min, preferably the rotational speed is 8000 to 12000 rpm and the time is 1 to 5 min.

[0033] Selectively, in step (2), the first binder comprises one or at least two of the following: polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, polyisobutylene, polytetrafluoroethylene, or sodium carboxymethylcellulose.

[0034] Selectively, in step (2), the organic solvent comprises one or a combination of at least two of the following: N-methylpyrrolidone, a liquid alkane having 5 to 10 carbon atoms, benzene, p-xylene, or petroleum ether, preferably one or a combination of at least two of the following: p-xylene, n-hexane, or heptane.

[0035] In the present invention, the type of conductive agent is not specifically limited. The conductive agent includes, but is not limited to, one or at least two of the following: acetylene black, Ketjen black, conductive graphite, Cabot carbon black, or Super P. Any type commonly used by those skilled in the art is applicable to the present invention.

[0036] In the present invention, the type of binder is not specifically limited, and the second binder includes, but is not limited to, one or at least two of the following: polyvinylidene fluoride, styrene-butadiene rubber, polystyrene, polyisobutylene, styrene-butadiene-styrene block copolymer, or styrene-ethylene-butene-styrene block copolymer. Any type commonly used by those skilled in the art is applicable to the present invention.

[0037] Selectively, the mass ratio of the conductive agent, the first binder, or the second binder to the negative electrode active material is (1-10):(1-10):(80-98), preferably (2-5):(2-5):(90-96).

[0038] As a preferred technical solution of the present invention, the manufacturing process of the negative electrode slurry in step (2) is as follows.

[0039] (a) The negative electrode active material, conductive agent, second binder, and organic solvent are primary mixed, and then a cocoon-structured lithium-carbon material is added and secondary mixing is performed to produce a negative electrode slurry. The duration of the secondary mixing is 30 to 60 minutes, and the rotational speed of the secondary mixing is 3000 to 5000 rpm. The mixing duration may be 30 minutes, 35 minutes, 40 minutes, 45 minutes, 50 minutes, 55 minutes, or 60 minutes, and the rotational speed may be 3000 rpm, 3200 rpm, 3500 rpm, 4000 rpm, 4500 rpm, 4800 rpm, or 5000 rpm, and the mixing duration and rotational speed include, but are not limited to, the values ​​listed above, and should be adjusted according to the actual process.

[0040] (b) The negative electrode slurry is applied to the surface of the current collector to obtain the pre-lithiumized negative electrode.

[0041] Compared to conventional technology, the pre-lithiumized anode and its manufacturing method according to the present invention include at least one of the following beneficial effects.

[0042] (1) The pre-lithiumized negative electrode provided by the present invention employs a lithium-carbon material with a cocoon structure as a lithium replenisher, which is uniformly mixed with the negative electrode active material, resulting in good contact, no obvious cavities being formed in the negative electrode, and no increase in internal resistance. The pre-lithiumized negative electrode has relatively high initial Coulomb efficiency and structural stability.

[0043] (2) The present invention further improves the initial Coulomb efficiency and cycle performance of a pre-lithified anode by selecting the type of lithium-containing particles and adjusting parameters such as the mass ratio of lithium-carbon material to lithium-containing particles.

[0044] (3) The manufacturing method provided by the present invention is easy to operate, highly efficient in production, and in particular the coating process differs from conventional processes, the solvent and binder used are friendly to metallic lithium, and it provides a new concept for precise lithium replenishment to the negative electrode.

[0045] According to a third aspect, the negative electrode of the lithium-ion battery of the present invention is a composite negative electrode, the composite negative electrode includes a current collector and a negative electrode active material layer provided on at least one side of the current collector, the parts by weight composition of the negative electrode active material layer being 40 to 78 parts negative electrode material, 20 to 50 parts cocoon-structured lithium-carbon material, 1 to 5 parts conductive agent, and 1 to 5 parts binder, the total parts by weight of all components being 100 parts by weight, the cocoon-structured lithium-carbon material including a cocoon body formed of a structural carbon material and one or more lithium-containing particles contained in the cocoon body.

[0046] In the present invention, the structural carbon material has good conductivity and improves the utilization rate of lithium-containing particles in the composite anode by forming a cocoon body on lithium-containing particles and constructing a continuous and stable three-dimensional electron network channel. The cocoon body has a confinement effect on lithium-containing particles and effectively mitigates the problem of volume expansion during the cycling process of lithium-containing particles in the composite anode. The surface of the lithium-carbon material of the cocoon structure in the composite anode has a micro-nano-sized pattern formed of the structural carbon material, is relatively rough, and has a certain degree of flexibility and ductility, and has good contact with the anode material, conductive agent and binder. Even if voids or holes are formed after the lithium-containing particles have functioned, the cocoon body maintains the smooth operation of the electron path, regulates the uniformity of current density, and can effectively solve the problem of lithium dendrite growth due to non-uniform current density, resulting in good cycle performance and rate characteristics.

[0047] The design of the weight portions of the cocoon-structured lithium-carbon material and the anode material not only improves the initial Coulombic efficiency of the anode material as a pre-lithification agent, but also continuously provides lithium ions during the cycle process as a lithium source, thereby improving the capacity and cycle performance of the composite anode. If the weight portion of the cocoon-structured lithium-carbon material is too small, it can only function as a pre-lithification agent and cannot replenish the lithium ion loss during the cycle process. If the weight portion of the cocoon-structured lithium-carbon material is too large, the composite anode exhibits performance similar to that of a metallic lithium anode, and the cycle life is significantly reduced. By using the cocoon-structured lithium-carbon material and the anode material in combination, it is possible to solve the problems that exist in the use of a single anode material or a cocoon-structured lithium-carbon material, as well as reduce the amount of conductive agent and binder used in the composite anode.

[0048] In the present invention, the type of current collector is not specifically limited. It may be ordinary copper foil, carbon-coated copper foil, composite copper foil, copper mesh, nickel foil, nickel mesh, or any other type commonly used by those skilled in the art.

[0049] Selectively, the weight-part composition of the negative electrode active material layer is 44-68 parts negative electrode material, 30-50 parts cocoon-structured lithium-carbon material, 1-3.5 parts conductive agent, and 1-2.5 parts binder. This weight-part composition fully demonstrates the advantages of the cocoon-structured lithium-carbon material, not only improving the initial Coulombic efficiency of the negative electrode material as a pre-lithification agent, but also improving the negative electrode capacity and cycle performance. The lithium-containing particles are tacky, which can reduce the amount of binder used in the negative electrode. The cocoon body has good conductivity, which can reduce the amount of conductive agent used in the negative electrode.

[0050] Selectively, the lithium-containing particles include metallic lithium powder and / or lithium alloy powder, preferably lithium alloy powder. Some of the lithium alloy powder may remain after functioning, and this residue may lead to the deposition of metallic lithium during the cycling process, maintaining the structural stability of the composite anode.

[0051] Selectively, the lithium alloy powder comprises one or at least two of the following: lithium-boron alloy, lithium-silver alloy, lithium-tin alloy, lithium-silicon alloy, lithium-zinc alloy, lithium-indium alloy, lithium-aluminum alloy, or lithium-magnesium alloy, preferably one or at least two of the following: lithium-boron alloy, lithium-indium alloy, lithium-silver alloy, or lithium-magnesium alloy.

[0052] Selectively, the average particle size of the lithium-containing particles is 1 to 100 μm, and may be, for example, 1 μm, 3 μm, 5 μm, 7 μm, 10 μm, 15 μm, 20 μm, 30 μm, 40 μm, 45 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, or 100 μm, and preferably 10 to 50 μm. The average particle size of the metallic lithium powder and / or lithium alloy powder is obtained by measuring it using a laser particle size analyzer under a protective atmosphere.

[0053] Selectively, the structural carbon material includes a micro-nanocarbon material, where one dimension may be μm or nm. The micro-nanocarbon material includes one or at least two of the following: graphene nanosheets, graphene nanoribbons, multi-walled carbon nanotubes, single-walled carbon nanotubes, carbon fibers, or multi-layered carbon nanotubes, and includes, but is not limited to, a combination of one or at least two of the following: graphene nanosheets and multi-layered carbon nanotubes, multi-walled carbon nanotubes and single-walled carbon nanotubes, graphene nanoribbons and carbon fibers, single-walled carbon nanotubes and nickel nanowires. Preferably, it is a combination of one or at least two of the following: graphene nanosheets, single-walled carbon nanotubes, or multi-layered carbon nanotubes.

[0054] Selectively, the mass ratio of the lithium-containing particles to the structural carbon material is (1 to 1000):1, and may be, for example, 1:1, 5:1, 10:1, 30:1, 50:1, 100:1, 120:1, 150:1, 200:1, 300:1, 400:1, 500:1, 600:1, 700:1, 750:1, 800:1, 850:1, 900:1, 950:1, or 1000:1. If the mass ratio is too small, the micro-nano carbon material is prone to self-entanglement, resulting in an uneven distribution on the surface of the lithium-containing particles and a decrease in the energy density of the composite material. If the mass ratio is too large, a stable porous framework cannot be formed. Preferably, the ratio is (10 to 500):1.

[0055] Selectively, the lithium-containing particles include metallic lithium powder and lithium alloy powder, and the mass ratio of the metallic lithium powder to the lithium alloy powder is (0.5 to 50):1, for example, 0.5:1, 0.8:1, 1:1, 1.5:1, 3:1, 5:1, 8:1, 10:1, 15:1, 20:1, 25:1, 30:1, 35:1, 40:1, 45:1, or 50:1. If the mass ratio is too small, the specific capacity of the composite anode is relatively low, which is unfavorable for improving energy density. If the mass ratio is too large, the improvement in the cycle performance of the composite anode is limited. Preferably, the ratio is (1 to 30):1.

[0056] Selectively, the negative electrode material includes one or at least two of the following: graphite, tin-based materials, hard carbon, soft carbon, mesocarbon microbeads, silicon-carbon materials, or silicon-oxygen materials.

[0057] Selectively, the conductive agent includes one or at least two of the following: acetylene black, Ketjen black, Cabot carbon black, conductive graphite, Super P, carbon nanotubes, carbon fibers, or graphene.

[0058] Selectively, the binder includes one or at least two of the following: polyvinylidene fluoride, polytetrafluoroethylene, polyvinylidene fluoride-hexafluoropropylene copolymer, sodium carboxymethylcellulose, styrene-butadiene rubber, polystyrene, polyisobutylene, styrene-butadiene-styrene block copolymer, or styrene-ethylene-butene-styrene block copolymer.

[0059] According to a fourth aspect, the present invention provides a method for manufacturing the composite anode, the method comprising the following steps.

[0060] (1) A step of mixing a negative electrode material, a conductive agent, and a binder, and then forming the binder into fibers to obtain a mixture, and (2) A step of mixing the mixture from step (1) with a lithium-carbon material in a cocoon structure, then hot-pressing to form a negative electrode active material layer, and providing the negative electrode active material layer on at least one side of the current collector to obtain the composite negative electrode.

[0061] In this invention, by employing a dry process and mixing the lithium-carbon material with a cocoon structure with a mixture after the binder has been fibrousized, the morphology of the cocoon structure can be well maintained, the lithium-carbon material with a cocoon structure is not consumed during the manufacturing process, and the resulting composite anode has a high energy density.

[0062] In the present invention, the method for producing a lithium-carbon material with a cocoon structure is not specifically limited. Any lithium-carbon material with a cocoon structure consisting of a cocoon body formed of a structural carbon material and one or more lithium-containing particles contained within the cocoon body falls within the scope of protection of the present invention.

[0063] To illustrate with an example, a lithium-carbon material with a cocoon structure is obtained by dispersing a structural carbon material in an organic solvent such as n-hexane or p-xylene, then adding lithium-containing particles and stirring at high speed at a rotational speed of 5000 rpm or more, and / or by spray granulation. The lithium-containing particles include metallic lithium powder and / or lithium alloy powder, and are extremely active in air. The above method is carried out in a protective atmosphere, for example, under the protection of argon gas and / or helium gas.

[0064] The apparatus for binder fiberization in step (1) is not specifically limited and includes, but is not limited to, one or a combination of at least two of the following: a planetary high-speed dispersion apparatus, an ultrasonic vaporizer, or an ultra-high-strength shearing apparatus, and is preferably an ultra-high-strength shearing apparatus.

[0065] Selectively, the temperature of binder fiberization in step (1) is 50 to 150°C, for example, 50°C, 55°C, 60°C, 70°C, 80°C, 90°C, 95°C, 100°C, 105°C, 110°C, 120°C, 130°C, 140°C, or 150°C, and includes, but is not limited to, the values ​​listed above. Any temperature within the above numerical range falls within the protected range of the present invention, preferably 90 to 110°C.

[0066] Selectively, the mixing apparatus in step (2) is not specifically limited and includes, but is not limited to, one or at least two of the following: a V-type mixer, a tumbler mixer, or a planetary high-speed dispersion apparatus, and is preferably a V-type mixer and / or a tumbler mixer.

[0067] Selectively, the mixing time in step (2) is 10 to 60 min, and may be, for example, 10 min, 15 min, 20 min, 25 min, 30 min, 40 min, 45 min, 50 min, or 60 min, and includes, but is not limited to, the values ​​listed above, and any value within the above numerical range falls within the protected range of the present invention, preferably 20 to 45 min.

[0068] Selectively, in step (2), the mixing rotation speed is 2000 to 5000 rpm, and may be, for example, 2000 rpm, 2500 rpm, 3000 rpm, 3500 rpm, 4000 rpm, 4500 rpm, or 5000 rpm, and includes, but is not limited to, the values ​​listed above, and any value within the above numerical range falls within the protected range of the present invention, preferably 3000 to 4500 rpm.

[0069] Selectively, the temperature of the hot press in step (2) may be 80 to 120°C, for example, 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C, or 120°C, and includes, but is not limited to, the values ​​listed above. Any value within the above numerical range falls within the protected range of the present invention, and preferably is 90 to 110°C.

[0070] Selectively, in step (2), the pressure of the hot press may be 10 to 50 t, for example 10 t, 15 t, 20 t, 25 t, 30 t, 35 t, 40 t, 45 t or 50 t, and preferably 20 to 40 t.

[0071] A more preferred technical solution of the present invention includes the following steps in the method.

[0072] (1) The negative electrode material, conductive agent, and binder are mixed by weight, and the binder is fibrousized at 90-110°C to obtain the mixture.

[0073] The negative electrode material comprises one or at least two of the following: graphite, tin-based material, hard carbon, soft carbon, mesocarbon microbead, silicon-carbon material, or silicon-oxygen material, in an amount of 44 to 68 parts by weight.

[0074] The conductive agent comprises one or at least two of the following: acetylene black, Ketjen black, Cabot carbon black, conductive graphite, Super P, carbon nanotubes, carbon fibers, or graphene, in an amount of 1 to 3.5 parts by weight.

[0075] The binder comprises one or at least two of the following: polyvinylidene fluoride, polytetrafluoroethylene, polyvinylidene fluoride-hexafluoropropylene copolymer, sodium carboxymethylcellulose, styrene-butadiene rubber, polystyrene, polyisobutylene, styrene-butadiene-styrene block copolymer, or styrene-ethylene-butene-styrene block copolymer, in an amount of 1 to 2.5 parts by weight.

[0076] (2) The mixture from step (1) and the lithium-carbon material with a cocoon structure are mixed at 3000 to 4500 rpm for 20 to 45 minutes, so that the amount of lithium-carbon material with a cocoon structure is 30 to 50 parts by weight. Then, a negative electrode active material layer is formed by hot pressing under conditions of 90 to 110°C and 20 to 40 t, and the negative electrode active material layer is provided on at least one side of the current collector to obtain the composite negative electrode.

[0077] The composite anode and its manufacturing method of the present invention have at least one of the following beneficial technical effects.

[0078] 1. In the composite anode provided by the present invention, by constructing a structurally carbon material with good conductivity on the surface of a cocoon-structured lithium-carbon material, the utilization rate of lithium-containing particles is improved while mitigating the problem of volume expansion. The cocoon-structured lithium-carbon material has a relatively rough surface and possesses a certain degree of flexibility and ductility, and has good contact with the anode material, conductive agent and binder, and by adjusting the current density, the problem of lithium dendrite growth due to non-uniform current density is effectively solved, thereby enabling the composite anode to have good cycle performance and rate characteristics.

[0079] 2. In the composite anode provided by the present invention, the cocoon-structured lithium-carbon material is uniformly dispersed, not only improving the initial Coulomb efficiency of the anode as a lithium replenisher, but also replenishing lithium ions that are continuously consumed during the cycle process while improving the specific capacity of the anode as a lithium source. Through a rational design of the weight of the cocoon-structured lithium-carbon material and the anode material, the amount of conductive agent and binder used in the composite anode is reduced, and specific capacity, cycle performance, and rate characteristics can be achieved simultaneously.

[0080] 3. The present invention further improves the cycle performance and rate characteristics of a composite anode by optimizing parameters such as the mass ratio of lithium-containing particles to structural carbon material in a cocoon-structured lithium-carbon material, and the weight ratio of each component in the anode active material layer.

[0081] 4. The manufacturing method for the composite anode provided by the present invention employs a dry process, preventing the consumption of the cocoon-structured lithium-carbon material during the manufacturing process. The structural design of the cocoon-structured lithium-carbon material ensures good contact with the anode material, conductive agent, and binder, improving the specific capacity and structural stability of the composite anode. The manufacturing method is simple and easy, making it suitable for industrial production.

[0082] A fifth aspect of the present invention provides an energy storage device comprising a pre-lithified negative electrode as described in the first aspect or a composite negative electrode as described in the third aspect. The energy storage device includes, but is not limited to, a lithium-ion battery and a lithium-ion supercapacitor. [Brief explanation of the drawing]

[0083] [Figure 1] Figure 1 is a schematic diagram of the pre-lithiumized negative electrode of the present invention. [Figure 2] Figure 2 is an SEM image of the lithium-carbon material with a cocoon structure from Example 4. [Figure 3] Figure 3 is a cross-sectional SEM view of the pre-lithiumized negative electrode in Example 4. [Figure 4] Figure 4 is an SEM diagram of the lithium-carbon material with a cocoon structure in Example 9. [Figure 5] Figure 5 is a cross-sectional SEM view of the composite negative electrode in Example 9. [Figure 6] Figure 6 is a cross-sectional SEM view of the composite anode in Comparative Example 4. [Modes for carrying out the invention]

[0084] To facilitate understanding of the present invention, the following embodiments are listed. Those skilled in the art will understand that the above embodiments are merely for the purpose of facilitating understanding of the present invention and do not specifically limit it.

[0085] To illustrate with an example, the present invention provides a pre-lithiumized negative electrode, a schematic diagram of which is shown in Figure 1. The pre-lithiumized negative electrode includes a current collector 1, on the surface of the current collector 1 a negative electrode active material 2 and a cocoon-structured lithium-carbon material 3, the cocoon-structured lithium-carbon material 3 is distributed between the negative electrode active material 2 and is uniformly mixed, the cocoon-structured lithium-carbon material includes a cocoon body formed of a structural carbon material and one or more lithium-containing particles contained in the cocoon body (see the SEM diagram shown in Figure 2), the cocoon body and the negative electrode active material 2 are in good contact, a good electron path is established, no obvious void is formed in the negative electrode after lithium replenishment, and internal resistance is not increased, the pre-lithiumized negative electrode has relatively high initial Coulomb efficiency and structural stability.

[0086] Example 1 This embodiment provides a pre-lithiumized negative electrode, which comprises graphite and a cocoon-structured lithium-carbon material, the cocoon-structured lithium-carbon material being distributed between the graphite particles.

[0087] The method for manufacturing the pre-lithium-treated negative electrode described above includes the following steps.

[0088] (1) Graphene (XF001W 7440-44-0, Jiangsu Xianfeng Nanomaterials Technology Co., Ltd.), multi-walled carbon nanotubes (XFM01 1333-86-4, Jiangsu Xianfeng Nanomaterials Technology Co., Ltd.), Cabot BP2000, metallic lithium powder with an average particle size of 5 μm, and n-hexane are mixed, with a mass ratio of 1:1000 between the total mass of graphene, multi-walled carbon nanotubes, and Cabot BP2000 and the metallic lithium powder. The mixture is then rapidly dispersed at a rotation speed of 5000 rpm for 10 minutes to obtain a cocoon-structured lithium-carbon material.

[0089] (2) Graphite, acetylene black, and styrene-butadiene rubber (SBR, 1502, China Petroleum Ginki Co., Ltd.) are mixed in masses of 800 g, 100 g, and 100 g, with n-hexane as the solvent, to prepare a first slurry. Then, 8 g of a cocoon-structured lithium-carbon material is added and the mixture is stirred at a rotation speed of 3000 rpm for 60 mins to obtain a second slurry. Subsequently, the second slurry is applied to the surface of a 6 μm carbon-coated copper foil and dried to obtain the pre-lithified negative electrode described above.

[0090] Example 2 This embodiment provides a pre-lithiumized anode, the pre-lithiumized anode comprising a silicon-carbon and a lithium-carbon material with a cocoon structure, wherein the lithium-carbon material with a cocoon structure is distributed between the silicon and carbon atoms.

[0091] The method for manufacturing the pre-lithium-treated negative electrode described above includes the following steps.

[0092] (1) Acetylene black, polyethylene oxide (Alading, P432440), and metallic lithium powder are mixed in p-xylene in a mass ratio of 5:5:90, dried to remove p-xylene, and metallic lithium powder containing an organic transmission layer is formed.

[0093] (2) A single-walled carbon nanotube and a metallic lithium powder containing an organic transmission layer with an average particle size of 45 μm are mixed with n-hexane, with a mass ratio of single-walled carbon nanotube to metallic lithium powder of 1:500. The mixture is then rapidly dispersed at a rotation speed of 8000 rpm for 8 minutes to obtain a lithium-carbon material with a cocoon structure.

[0094] (3) Silicon-carbon (Bai Te Rui, DXB8), carbon fiber, and polyvinylidene fluoride (Su Wei, 5130) are mixed in masses of 800g, 100g, and 100g, with N-methylpyrrolidone as the solvent to prepare a first slurry. Then, 160g of cocoon-structured lithium-carbon material is added and stirred at a rotation speed of 4500 rpm for 45 minutes to obtain a second slurry. Subsequently, the second slurry is applied to the surface of 6 μm carbon nanotube paper and dried to obtain the pre-lithiumized anode described above.

[0095] Example 3 This embodiment provides a pre-lithiumized negative electrode, which comprises a silicon-oxygen and a cocoon-structured lithium-carbon material, the cocoon-structured lithium-carbon material being distributed between the silicon and oxygen atoms.

[0096] The method for manufacturing the pre-lithium-treated negative electrode described above includes the following steps.

[0097] (1) Carbon nanofibers (Alading, C478418), conductive graphite KS-6, lithium-magnesium alloy particles with an average particle size of 100 μm (magnesium mass fraction of 10%), and p-xylene are mixed so that the total mass of single-walled carbon nanotubes and conductive carbon black is in a mass ratio of 1:100 to the above metallic lithium powder. Then, the mixture is rapidly dispersed at a rotation speed of 12000 rpm for 5 minutes to obtain a lithium-carbon material with a cocoon structure.

[0098] (2) Silicon-oxygen (Biteru, DXA5), Super P, and polyisobutylene (Arading, P418837) are mixed in masses of 800g, 100g, and 100g, with heptane as the solvent, to prepare a first slurry. Then, 240g of a cocoon-structured lithium-carbon material is added and stirred at a rotation speed of 4500 rpm for 45 minutes to obtain a second slurry. Subsequently, the second slurry is applied to the surface of a 6 μm perforated copper foil and dried to obtain the pre-lithified negative electrode described above.

[0099] Example 4 This embodiment provides a pre-lithiumized negative electrode, which comprises graphite and a cocoon-structured lithium-carbon material, the cocoon-structured lithium-carbon material being distributed between the graphite particles.

[0100] The method for manufacturing the pre-lithium-treated negative electrode described above includes the following steps.

[0101] (1) Single-walled carbon nanotubes (XFS02 1333-86-4, Jiangsu Xianfeng Nanomaterials Technology Co., Ltd.), metallic lithium powder with an average particle size of 50 μm, and n-hexane were mixed, with a mass ratio of single-walled carbon nanotubes to metallic lithium powder of 1:500. The mixture was then spray-dried at an intake temperature of 220°C, an exhaust temperature of 100°C, and an atomization pressure of 0.5 MPa to obtain a cocoon-structured lithium-carbon material. The SEM characterization of the above cocoon-structured lithium-carbon material is shown in Figure 2. As is clear from the figure, the single-walled carbon nanotubes entangle the surface of the metallic lithium powder to form a cocoon body, and the metallic lithium powder is contained within the cocoon body, forming a cocoon-structured lithium-carbon material.

[0102] (2) Graphite, acetylene black, and polytetrafluoroethylene are mixed in masses of 900g, 50g, and 50g, and then processed with an ultra-high-strength shearing device to fibrousize the polytetrafluoroethylene binder. 180g of cocoon-structured lithium-carbon material is added, and a negative electrode film sheet with a thickness of 120μm is obtained by pressing and rolling at 80°C. The negative electrode film sheet and carbon-coated copper foil are combined by hot pressing to obtain the pre-lithified negative electrode. The cross-sectional SEM characterization of the pre-lithified negative electrode is shown in Figure 3. As is clear from the figure, the cocoon-structured lithium-carbon material (the part within the black circular frame in the figure) is uniformly distributed among materials such as graphite (the part outside the black circular frame in the figure), and a good cocoon structure can be maintained.

[0103] Example 5 This method differs from Example 4 in that the mass of the cocoon-structured lithium-carbon material is replaced with 0.9 g in step (2), but all other conditions are the same.

[0104] Example 6 This method differs from Example 4 in that the mass of the cocoon-structured lithium-carbon material is replaced with 300g in step (2), but all other conditions are the same.

[0105] Example 7 This method differs from Example 4 in that step (1) replaces metallic lithium powder with lithium-indium alloy powder and sets the mass fraction of indium to 20%, but all other conditions are the same.

[0106] Comparative Example 1 This method differs from Example 4 in that the lithium-carbon material with a cocoon structure in step (2) is replaced with the metallic lithium powder in step (1), but all other conditions are the same.

[0107] Comparative Example 2 This method differs from Example 4 in that a lithium-carbon material with a cocoon structure is not added in step (2), but all other conditions are the same.

[0108] Comparative Example 3 This method differs from Example 4 in that the rotation speed in step (1) is replaced with 2000 rpm, but all other conditions are the same. At the above rotation speed, the single-walled carbon nanotubes can be sufficiently mixed with the metallic lithium powder, but they do not form a cocoon structure.

[0109] Anode performance measurement: The negative electrodes of Examples 1-7 and Comparative Examples 1-3 were assembled with the lithium nickel-cobalt manganese oxide positive electrode into a pouch battery, and measurements were taken. The initial Coulomb efficiency and cycle measurement data at 0.2C are shown in Table 1 below.

[0110] [Table 1]

[0111] From Table 1, the following points were found.

[0112] (1) As can be seen from Examples 4 to 6 together, the degree of pre-lithiumization is closely related to the amount of lithium-carbon material used in the cocoon structure. When the amount used was small (Example 5), there was no clear improvement in initial Coulomb efficiency and cycle performance, while when the amount used was too large (Example 6), initial Coulomb efficiency and cycle performance were clearly improved, but this was unfavorable for manufacturing high-energy-density batteries.

[0113] (2) As can be seen from combining Examples 4 and 7, the initial Coulomb efficiency of the battery corresponding to Example 4 is close to that of Example 7, and the cycle performance is inferior to that of Example 7. This is because in Example 7, a lithium-indium alloy is used to replenish lithium, and indium can transport electrons while regulating the deposition of metallic lithium, and when combined with single-walled carbon nanotubes, which are structural carbon materials, the negative electrode has excellent cycle performance.

[0114] (3) As can be seen from Example 4 and Comparative Examples 1 to 3 together, when the same mass of lithium replenisher is used, pre-lithiumizing agents with different structures show different degrees of improvement in the initial Coulomb efficiency and cycle performance of the negative electrode. When the lithium-carbon material with a core-shell structure of the present invention is used as a lithium replenisher, the above-mentioned cocoon-structured lithium-carbon material contains a structural carbon material that has good conductivity and a certain degree of rigidity, thereby improving the conductivity and structural stability of the pre-lithiumized negative electrode, and enabling the pre-lithiumized negative electrode to have high initial Coulomb efficiency and excellent cycle performance.

[0115] Example 8 This embodiment provides a composite anode, the composite anode comprising a copper foil and an anode active material layer provided on one side of the copper foil, the parts by weight composition of the anode active material layer being 40 parts graphite, 50 parts cocoon-structured lithium-carbon material, 5 parts multilayer carbon nanotubes, and 5 parts polytetrafluoroethylene, the cocoon-structured lithium-carbon material comprising a cocoon body formed from a graphene sheet and metallic lithium powder contained in the cocoon body.

[0116] The method for manufacturing the above composite anode includes the following steps.

[0117] (1) 60 g of metallic lithium powder with an average particle size of 10 μm, 60 g of structural carbon material graphene sheet, and 300 g of n-hexane are rapidly dispersed at a rotation speed of 8000 rpm for 30 minutes, filtered by suction, and then dried to obtain a lithium-carbon material with a cocoon structure.

[0118] (2) Parts by weight of graphite (Bei Tesui, AGP-7), multi-walled carbon nanotubes, and polytetrafluoroethylene are dry-mixed, and then the mixture is subjected to binder fiberization in an ultra-high-strength shearing apparatus at a temperature of 50°C to obtain the mixture.

[0119] (3) The mixture from step (2) is mixed with a cocoon-structured lithium-carbon material by weight in a V-type mixing apparatus for 10 minutes at a mixing speed of 5000 rpm. Thereafter, it is hot-pressed at 80°C and under a pressure of 50t to obtain a negative electrode active material layer. Subsequently, the negative electrode active material layer is bonded to a copper foil by pressure bonding to obtain the composite negative electrode described above.

[0120] Example 9 This embodiment provides a composite anode comprising a carbon-coated copper foil and a negative electrode active material layer provided on both sides of the carbon-coated copper foil, wherein the weight composition of the negative electrode active material layer is 78 parts silicon-carbon, 20 parts cocoon-structured lithium-carbon material, 1 part Ketjenblack, and 1 part styrene-butadiene-styrene block copolymer, wherein the cocoon-structured lithium-carbon material comprises a cocoon body formed of single-walled carbon nanotubes and lithium-boron alloy powder contained in the cocoon body, and the boron content in the lithium-boron alloy was 20 wt%.

[0121] The method for manufacturing the above composite anode includes the following steps.

[0122] (1) 60 g of lithium-boron alloy powder with an average particle size of 50 μm, 0.15 g of single-walled carbon nanotubes (purchased from OCSiAl), and 300 g of p-xylene (purchased from Aladdin) were dispersed at high speed at a rotation speed of 12,000 rpm for 15 minutes, filtered by suction, and dried at 80°C to obtain a lithium-carbon material with a cocoon structure. The lithium-carbon material with a cocoon structure was characterized using SEM, and the results of the characterization are shown in Figure 1. As is clear from the figure, the single-walled carbon nanotubes entangle the surface of the lithium-boron alloy powder, forming a cocoon structure and acting to restrain the lithium-boron alloy powder.

[0123] (2) A dry mix of silicon-carbon (Bitez, DXB8), Ketjenblack, and styrene-butadiene-styrene block copolymer is performed by weight, and then the mixture is subjected to binder fiberization in an ultra-high-strength shearing apparatus at a temperature of 100°C to obtain the mixture.

[0124] (3) The mixture from step (2) was mixed with a cocoon-structured lithium-carbon material in a V-type mixing apparatus at a mixing rate of 4000 rpm for 30 minutes by weight. Thereafter, it was hot-press molded at 100°C under a pressure of 30t to obtain a negative electrode active material layer. The negative electrode active material layer was bonded to a carbon-coated copper foil by pressure bonding to obtain the composite negative electrode. A cross-sectional SEM measurement was taken of the composite negative electrode, and the measurement results are shown in Figure 2. As is clear from the figure, the distribution of each component in the composite negative electrode is uniform, the cocoon-structured lithium-carbon material maintains its cocoon structure, and is tightly bonded with the other components.

[0125] Example 10 This embodiment provides a metallic lithium composite anode, the composite anode comprising a copper mesh and a negative electrode active material layer provided on both sides of the copper mesh, the weight composition of the negative electrode active material layer being 55 parts hard carbon, 40 parts cocoon-structured lithium-carbon material, 2.5 parts Ketjenblack, and 2.5 parts styrene-ethylene-butene-styrene block copolymer, the cocoon-structured lithium-carbon material comprising a cocoon body formed of carbon nanofibers and lithium-indium alloy powder contained in the cocoon body, the indium content in the lithium-indium alloy being 20 wt%.

[0126] The method for manufacturing the above composite anode includes the following steps.

[0127] (1) 60 g of lithium-indium alloy powder with an average particle size of 100 μm, 0.06 g of carbon nanofibers (purchased from Aladdin), and 450 g of tetrahydrofuran (purchased from Aladdin) were dispersed at high speed at a rotation speed of 8000 rpm and held for 20 mins. After that, spray granulation was performed at an intake temperature of 220°C, an exhaust temperature of 100°C, and a pressure of 0.5 MPa to obtain a lithium-carbon material with a cocoon structure.

[0128] (2) Hard carbon (BHC-400), Ketjenblack, and styrene-butadiene-styrene block copolymer were dry-mixed by weight, and then bound into fibers in an ultra-high-strength shearing apparatus at a temperature of 120°C to obtain the mixture.

[0129] (3) The mixture from step (2) was mixed with a lithium-carbon material of cocoon structure in a tumbler mixer in parts by weight for 30 minutes at a mixing speed of 4000 rpm. Thereafter, it was hot-pressed at 100°C under a pressure of 30 tons to obtain a negative electrode active material layer. The negative electrode active material layer was bonded to a copper mesh by pressure bonding to obtain the composite negative electrode described above.

[0130] Example 11 The only difference from Example 9 was that in step (1), the mass of the single-walled carbon nanotube was replaced with 65g; all other conditions were the same.

[0131] Example 12 The only difference from Example 9 was that in step (1), the mass of the single-walled carbon nanotube was replaced with 0.05 g; all other conditions were the same.

[0132] Example 13 This example differs from Example 9 in that the weight composition of the negative electrode active material layer is replaced with 68 parts silicon-carbon, 30 parts lithium-carbon material in a cocoon structure, 1 part conductive agent, and 1 part binder.

[0133] Example 14 This example differs from Example 9 in that the weight-part composition of the negative electrode active material layer is replaced with 44 parts silicon-carbon, 50 parts cocoon-structured lithium-carbon material, 3.5 parts conductive agent, and 2.5 parts binder.

[0134] Example 15 This example differed from Example 9 in that the lithium-boron alloy powder was replaced with a mixture of metallic lithium powder and lithium-boron alloy powder, and the mass ratio of metallic lithium powder to lithium-boron alloy powder was set to 1:1; all other conditions were the same.

[0135] Example 16 This example differed from Example 9 in that the lithium-boron alloy powder was replaced with a mixture of metallic lithium powder and lithium-boron alloy powder, and the mass ratio of metallic lithium powder to lithium-boron alloy powder was set to 30:1; all other conditions were the same.

[0136] Example 17 This example differed from Example 9 in that the lithium-boron alloy powder was replaced with a mixture of metallic lithium powder and lithium-boron alloy powder, and the mass ratio of metallic lithium powder to lithium-boron alloy powder was set to 60:1; all other conditions were the same.

[0137] Comparative Example 4 This example differs from Example 9 in that the cocoon-structured lithium-carbon material in the negative electrode active material layer was replaced with metallic lithium powder; all other conditions were the same. Figure 3 shows a cross-sectional SEM view of the above composite negative electrode. As is clear from the figure, there is a large gap between the metallic lithium powder, the negative electrode material, and the conductive agent, resulting in poor contact.

[0138] Comparative Example 5 This example differs from Example 9 in that the lithium-carbon material with a cocoon structure in the negative electrode active material layer is replaced with a lithium-boron alloy, and the boron content in the lithium-boron alloy is 20 wt%, while all other conditions are the same.

[0139] Comparative Example 6 This example differs from Example 9 in that the lithium-carbon material with a cocoon structure in the negative electrode active material layer was replaced with a mixture of lithium-boron alloy and single-walled carbon nanotubes, and the single-walled carbon nanotubes and lithium-boron alloy in the mixture were randomly dispersed and did not form a cocoon structure; all other conditions were the same.

[0140] Comparative Example 7 This example differs from Example 8 in that the lithium-carbon material with a cocoon structure in the negative electrode active material layer was replaced with a metallic lithium-lithium affinity skeletal composite material; all other conditions were the same.

[0141] The above-mentioned method for producing a lithium-lithium affinity composite material includes the following steps.

[0142] (1) Polyvinyl alcohol in a mass ratio of 5:7:10:10:500 (Alading Reagents (Shanghai) Co., Ltd.), polystyrene microspheres (Suzhou Weimai New Materials Co., Ltd.), carbon nanotubes (Shandong Dazhan, carbon tube model number: GTC-304), isothiazolinone (Alading Reagents (Shanghai) Co., Ltd.), and deionized water were uniformly mixed to obtain a slurry with a solid content of 6%.

[0143] (2) The slurry was atomized and granulated using a two-fluid atomizer, with a carrier gas pressure of 0.3 MPa and an atomization chamber temperature of 220°C.

[0144] (3) The carbon particles produced by the spray granulation described above were placed in a crucible and subjected to high-temperature treatment under the protection of an inert gas atmosphere. The high-temperature treatment temperature was 800°C and the treatment time was 3 hours.

[0145] (4) The carbon particles after high-temperature treatment were mixed with molten metallic lithium and uniformly stirred to obtain a metallic lithium-lithium affinity skeletal composite material.

[0146] The method for producing the above mixture includes the following steps.

[0147] 60 g of lithium-boron alloy powder with an average particle size of 50 μm, 0.15 g of single-walled carbon nanotubes (purchased from OCSiAl), and 300 g of p-xylene (purchased from Aladdin) were mechanically stirred at a stirring speed of 1000 rpm for 15 minutes, filtered by suction, and dried at 80°C to obtain a mixture of lithium-boron alloy and single-walled carbon nanotubes.

[0148] Measurement of material performance: The negative electrodes provided in Examples 8-17 and Comparative Examples 4-7 were assembled into lithium sheets and batteries, respectively, and their specific capacities were measured. The cycle performance and rate characteristics were then measured for the NCM811 assembled batteries, and the measurement results are shown in Table 1.

[0149] [Table 1]

[0150] The following points were found from Table 1.

[0151] (1) As can be seen by comparing Example 9 with Examples 11-12, Example 11 used more structural carbon material than Example 9, resulting in a lower specific capacity of the negative electrode. Example 12 used less structural carbon material than Example 9, resulting in a higher specific capacity of the negative electrode, but its cycle performance and rate characteristics were worse than those of Example 9.

[0152] (2) As can be seen by comparing Example 9 with Examples 13-14, in Examples 13 and 14, by adjusting the proportion of the cocoon-structured lithium-carbon material in the anode, the specific capacity, cycle performance, and rate characteristics of the composite anode were all better than in Example 9. In other words, in Examples 13 and 14, the weight composition of the anode material layer in the composite anode was superior to that of Example 9, and the specific capacity, cycle performance, and rate characteristics of the composite anode were all achieved simultaneously.

[0153] (3) As can be seen by comparing Example 9 with Examples 15-17, the lithium-containing particles used in Examples 15-17 were a mixture of lithium-boron alloy powder and metallic lithium powder. The specific capacity, cycle performance, and rate characteristics of the composite anodes in Examples 15 and 16 were all superior to those of Example 9. This was achieved by adjusting the ratio of metallic lithium powder to lithium-boron alloy powder within an appropriate range. The composite anode in Example 17 had a higher specific capacity than that of Example 9, but its cycle performance and rate characteristics were inferior. This was because the proportion of metallic lithium powder in the lithium-containing particles in Example 10 was high.

[0154] (4) As can be seen by comparing Example 9 with Comparative Examples 4-6, although the specific capacity of the composite anode in Example 9 was lower than that of Comparative Example 4, the cycle performance and rate characteristics were superior to those of Comparative Example 4. This is because the lithium-carbon material of the cocoon structure in Example 9 contains a lithium-containing boron alloy, which not only stabilizes the composite anode structure as a framework but also promotes the deposition of metallic lithium and makes it difficult to form lithium dendrites. The structural carbon material further reduces the volume expansion of the lithium-boron alloy, regulating the conductivity of the composite anode, which in Comparative Example 4 tends to form holes after the metallic lithium powder has functioned, causing the electron pathway to be broken. The performance of the composite anodes in Comparative Examples 5 and 6 was inferior to that of Example 9. This is because the cocoon structure was not constructed on the surface of the lithium-boron alloy in the composite anodes of Comparative Examples 5 and 6.

[0155] (5) As can be seen by comparing Example 8 with Comparative Example 7, the specific capacity, cycle performance, and rate characteristics of the composite anode in Example 8 are all superior to those of Comparative Example 7. This is because the metallic lithium content in the metallic lithium-lithium affinity framework material in Comparative Example 7 is low (limited by the manufacturing method, where molten metallic lithium easily coats the surface of porous particles), and the specific capacity of the composite anode is lower than that of Example 8. The lithium affinity framework is located inside the metallic lithium, and most of its functions on the metallic lithium are not to restrain it, but to support the metallic lithium to regulate the current density and to improve contact with the anode material and conductive agent. In the present invention, the structural carbon material of the cocoon-structured lithium-carbon material restrains the lithium-containing particles, effectively mitigating the problem of volume expansion of the lithium-containing particles, resulting in good contact between the above-mentioned cocoon-structured lithium-carbon material and the anode material and conductive agent, and good stability of the composite anode structure.

[0156] Although the detailed structural features of the present invention have been described by the above embodiments, the present invention is not limited to the above detailed structural features; that is, it does not mean that the present invention must necessarily be implemented only by the above detailed structural features. As those skilled in the art will understand, any improvements to the present invention, equivalent substitutions of parts used in the present invention, addition of auxiliary parts, selection of specific forms, etc., are all included within the scope of protection and disclosure of the present invention.

Claims

1. The negative electrode of a lithium-ion battery, The negative electrode active material layer of the negative electrode contains a negative electrode active material and a cocoon-structured lithium-carbon material, and the cocoon-structured lithium-carbon material is distributed between the negative electrode active materials. The lithium-carbon material having a cocoon structure is characterized in that it comprises a cocoon body formed of a structural carbon material and one or more lithium-containing particles contained within the cocoon body, thereby providing a negative electrode for a lithium-ion battery.

2. The anode is a pre-lithiumized anode, and the mass ratio of the anode active material to the cocoon-structured lithium-carbon material is 1 g: (1 to 300) mg. The negative electrode according to claim 1, characterized in that the mass ratio of the structural carbon material to the lithium-containing particles is 1:(1 to 1000).

3. The negative electrode active material includes one or at least two of the following: graphite, tin-based materials, hard carbon, soft carbon, activated carbon, mesocarbon microbeads, silicon-carbon materials, or silicon-oxygen materials. The structural carbon material is one or a combination of at least two of particulate, linear, or sheet-like nanocarbon materials, and the structural carbon material includes one or a combination of at least two of acetylene black, Ketjen black, Cabot BP2000, Super P, single-walled carbon nanotubes, multi-walled carbon nanotubes, multi-walled carbon nanotubes, doped carbon nanotubes, graphene, doped graphene, carbon nanofibers, or doped carbon nanofibers. The negative electrode according to claim 2, characterized in that the doping elements in the doped carbon nanotube, doped graphene, or doped carbon nanofiber independently include one or at least two of the elements fluorine, nitrogen, oxygen, phosphorus, silver, silicon, tin, or zinc.

4. The lithium-containing particles include metallic lithium particles and / or metallic lithium alloy particles, wherein the mass content of metallic lithium in the metallic lithium alloy particles is 70% or more. The average particle size of the lithium-containing particles is 1 to 100 μm. The negative electrode according to claim 2, wherein the metallic lithium alloy particles include a binary lithium alloy and / or a ternary lithium alloy, the binary lithium alloy powder includes one or at least two of the following: lithium-magnesium alloy, lithium-boron alloy, lithium-silver alloy, lithium-indium alloy, lithium-silicon alloy, lithium-aluminum alloy, or lithium-tin alloy, and the ternary lithium alloy powder includes one or at least two of the following: lithium-tin-silver alloy, lithium-silver-silicon alloy, or lithium-boron-zinc alloy.

5. The cocoon structure further includes an organic transmission layer provided between the lithium-containing particles and the structural carbon material, the organic transmission layer comprising an organic ion transmission agent and a conductive agent, The conductive agent comprises at least one of carbon nanotubes, carbon black, graphene, and acetylene black. The negative electrode according to claim 2, characterized in that the organolithium ion transport agent comprises polyethylene oxide, polyethylene glycol, polysiloxane, polytrimethylene carbonate, polycarbonate, polyethylene carbonate, polypropylene carbonate, polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, poly(vinylidene fluoride-hexafluoropropylene), polyphenylene sulfide, p-benzoquinone, and at least two copolymers or mixtures of the above polymers.

6. A method for manufacturing a negative electrode according to any one of claims 1 to 5, characterized by including the following steps. (1) A step of mixing a structural carbon material, lithium-containing particles, and an organic solvent, and then spray-drying or stirring at a rotational speed of 5000 rpm or more to obtain a lithium-carbon material with a cocoon structure, and (2) A process of mixing a negative electrode active material, a conductive agent, and a first binder, then forming the binder into fibers to obtain a first mixture, then mixing the first mixture with a lithium-carbon material in a cocoon structure to obtain a second mixture, hot pressing the second mixture to form a negative electrode active material layer, and then combining it with a current collector to obtain the pre-lithified negative electrode. Alternatively, the process involves mixing a negative electrode active material, a conductive agent, a second binder, a cocoon-structured lithium-carbon material, and an organic solvent to produce a negative electrode slurry, and then applying the negative electrode slurry to the surface of a current collector to obtain the pre-lithified negative electrode.

7. The method according to 6, characterized in that in step (1), the organic solvent is one or at least two of the following: N-methylpyrrolidone, a liquid alkane having 5 to 10 carbon atoms, benzene, p-xylene, or petroleum ether.

8. In step (2), the first binder comprises one or at least two of the following: polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, polytetrafluoroethylene, or sodium carboxymethylcellulose. In step (2), the organic solvent includes one or at least two of the following: N-methylpyrrolidone, liquid alkanes having 5 to 10 carbon atoms, benzene, p-xylene, or petroleum ether. In step (2), the conductive agent includes one or at least two of the following: acetylene black, Ketjen black, conductive graphite, Cabot carbon black, or Super P. In step (2), the second binder comprises one or at least two of the following: polyvinylidene fluoride, styrene-butadiene rubber, polystyrene, polyisobutylene, styrene-butadiene-styrene block copolymer, or styrene-ethylene-butene-styrene block copolymer. The method according to 6, characterized in that the mass ratio of the conductive agent, the first binder or the second binder to the negative electrode active material is (1-10):(1-10):(80-98).

9. The method according to 6, characterized in that the manufacturing process of the negative electrode slurry in step (2) is as follows. (a) The negative electrode active material, conductive agent, second binder, and organic solvent are primary mixed, and then a cocoon-structured lithium-carbon material is added and secondary mixing is performed to produce a negative electrode slurry. The duration of the secondary mixing is 30 to 60 minutes, and the rotational speed of the secondary mixing is 3000 to 5000 rpm. (b) The negative electrode slurry is applied to the surface of the current collector to obtain the pre-lithiumized negative electrode.

10. The negative electrode is a composite negative electrode, which includes a current collector and a negative electrode active material layer provided on at least one side of the current collector, and the weight composition of the negative electrode active material layer is: Negative electrode material: 40-78 parts Lithium-carbon material with cocoon structure: 20-50 parts Conductive material: 1 to 5 parts The binder consists of 1 to 5 parts. The negative electrode according to claim 1, characterized in that the total weight of all components in the negative electrode active material layer is 100 parts by weight.

11. The weight portion composition of the negative electrode active material layer is: Negative electrode material: 44-68 parts Lithium-carbon material with cocoon structure: 30-50 parts Conductive agent: 1 to 3.5 parts The negative electrode according to claim 10, characterized in that the binder is 1 to 2.5 parts.

12. The lithium-containing particles include metallic lithium powder and / or lithium alloy powder. The lithium alloy powder comprises one or at least two of the following: lithium-boron alloy, lithium-silver alloy, lithium-tin alloy, lithium-silicon alloy, lithium-zinc alloy, lithium-indium alloy, lithium-aluminum alloy, or lithium-magnesium alloy. The negative electrode according to claim 10, characterized in that the average particle diameter of the lithium-containing particles is 1 to 100 μm.

13. The negative electrode according to claim 10, wherein the structural carbon material includes a micro-nano carbon material, and the micro-nano carbon material includes one or at least two of the following: graphene nanosheets, graphene nanoribbons, multi-walled carbon nanotubes, single-walled carbon nanotubes, carbon fibers, or multi-walled carbon nanotubes.

14. The mass ratio of the lithium-containing particles to the structural carbon material is (1 to 1000):

1. The negative electrode according to claim 10, characterized in that, when the lithium-containing particles contain metallic lithium powder and lithium alloy powder, the mass ratio of the metallic lithium powder to the lithium alloy powder is (0.5 to 50):

1.

15. The anode material includes one or at least two of the following: graphite, tin-based materials, hard carbon, soft carbon, mesocarbon microbeads, silicon-carbon materials, or silicon-oxygen materials. The conductive agent comprises one or at least two of the following: acetylene black, Ketjen black, Cabot carbon black, conductive graphite, Super P, carbon nanotubes, carbon fibers, or graphene. The negative electrode according to claim 10, characterized in that the binder comprises one or at least two of the following: polyvinylidene fluoride, polytetrafluoroethylene, polyvinylidene fluoride-hexafluoropropylene copolymer, sodium carboxymethylcellulose, styrene-butadiene rubber, polystyrene, polyisobutylene, styrene-butadiene-styrene block copolymer, or styrene-ethylene-butene-styrene block copolymer.

16. A method for manufacturing a negative electrode according to any one of claims 10 to 15, characterized by including the following steps. (1) A step of mixing a negative electrode material, a conductive agent, and a binder, and then performing binder fiberization to obtain a mixture, and (2) A step of mixing the mixture from step (1) with a lithium-carbon material in a cocoon structure, then hot-pressing to form a negative electrode active material layer, and providing the negative electrode active material layer on at least one side of the current collector to obtain the composite negative electrode.

17. The method according to 16, characterized in that the temperature of binder fiberization in step (1) is 50 to 150°C.

18. In step (2), the mixing time is 10 to 60 minutes, and the mixing speed is 2000 to 5000 rpm. In step (2), the temperature of the hot press is 80 to 120°C. The method according to 16, characterized in that the pressure of the hot press in step (2) is 10 to 50 tons.

19. An energy storage device characterized by including a negative electrode according to any one of claims 1 to 5 or a negative electrode according to any one of claims 10 to 15.

Images