Negative electrode material for lithium ion battery, and lithium ion battery

Abstract

Provided in the present invention is a negative electrode material for a lithium ion battery. The negative electrode material comprises: a current collector; and a polymer layer, the polymer layer being formed on a surface of the current collector, the polymer layer comprising a polymer, a lithium salt, and an inorganic filler, and the mass ratio of the polymer, the lithium salt, and the inorganic filler being 1-25:1:0.1-2. In the negative electrode material for a lithium ion battery of the present invention, by means of forming the polymer layer on the surface of the current collector, the negative electrode current collector and lithium deposited on the current collector during charging can be isolated from direct contact with an electrolyte, side reactions are reduced, and cycle coulombic efficiency is improved.

Description

A negative electrode material for lithium ion battery and lithium ion battery Technical Field

[0001] The present invention relates to a negative electrode material for a lithium ion battery and a lithium ion battery using the negative electrode material. Background Art

[0002] Lithium-ion batteries have been widely used due to their high energy density, low self-discharge, environmental friendliness, and lack of memory effect. The current collector is a component in lithium-ion batteries that carries the active material and collects and outputs the current generated by the electrode active material. This helps reduce the internal resistance of lithium-ion batteries and improves the battery's Coulombic efficiency (CE) and cycling stability. Copper foil is the most commonly used negative electrode current collector in existing commercial lithium-ion batteries due to its high conductivity and excellent mechanical properties.

[0003] However, lithium ion deposition on the copper foil surface easily forms lithium dendrites, which not only easily induces safety issues but also reduces the reuse of lithium sources, resulting in a shorter service life. To solve this problem, it is necessary to induce lithium to deposit uniformly on the copper foil surface.

[0004] On the other hand, in lithium-ion batteries, the loss of lithium source caused by interfacial side reactions between the negative electrode and the electrolyte (liquid or solid electrolyte) also leads to a decrease in the cycle coulombic efficiency.

[0005] Therefore, there is a need for a negative electrode material that can induce uniform lithium deposition on the surface of the copper current collector and reduce the side reactions between the negative electrode and the electrolyte.

[0006] Summary of the Invention

[0007] The present invention provides a negative electrode material for a lithium-ion battery. This negative electrode material not only induces uniform lithium deposition on the surface of the negative electrode current collector but also reduces side reactions between the negative electrode and the electrolyte, thereby improving the cycle coulombic efficiency. The present invention also provides a lithium-ion battery using the negative electrode of the present invention.

[0008] A first aspect of the present invention provides a negative electrode material for a lithium ion battery, the negative electrode material comprising:

[0009] a current collector; and

[0010] A polymer layer is formed on the surface of the current collector, and the polymer layer comprises a polymer, a lithium salt and an inorganic filler, and the mass ratio of the polymer, the lithium salt and the inorganic filler is 1 to 25:1:0.1 to 2, preferably 5 to 15:1:0.5 to 1.5, and more preferably 6 to 10:1:1.

[0011] In some specific embodiments, the polymer is one or more selected from polyethylene oxide (PEO), poly(vinylidene fluoride) (PVDF), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), polyacrylonitrile (PAN), polyacrylic acid (PAA) and polyethylene glycol (PEG), preferably polyethylene oxide (PEO) or poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), more preferably poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP).

[0012] In some specific embodiments, the lithium salt is one or more selected from lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium perchlorate (LiClO4) and lithium hexafluorophosphate (LiPF6), preferably lithium bis(fluorosulfonyl)imide (LiFSI).

[0013] In some specific embodiments, the inorganic filler is a metal or non-metal halide, for example, one or more selected from CuF2, MgF2, AlF3, SbF3, ZnF2, AgF, SnF4, SeF6, CuCl2, MgCl2 and ZnCl2, preferably CuF2.

[0014] In some specific embodiments, the current collector is a copper foil, and a surface of the copper foil has a copper oxide modification layer.

[0015] In some specific embodiments, the copper oxide modification layer is a Cu / CuO nanostructure array, preferably a Cu / CuO nanotube array.

[0016] A second aspect of the present invention provides a method for preparing a negative electrode material for a lithium ion battery, the negative electrode material comprising: a current collector; and a polymer layer, wherein the polymer layer is formed on the surface of the current collector, the preparation method comprising the following steps:

[0017] (1) coating a polymer layer mother solution on the surface of the current collector to form a polymer layer,

[0018] The polymer layer mother solution comprises a polymer, a lithium salt, an inorganic filler and a solvent, and the mass ratio of the polymer, the lithium salt and the inorganic filler is 1-25:1:0.1-2, preferably 5-15:1:0.5-1.5, and more preferably 6-10:1:1.

[0019] In some specific embodiments, the polymer is one or more selected from polyethylene oxide (PEO), poly(vinylidene fluoride) (PVDF), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), polyacrylonitrile (PAN), polyacrylic acid (PAA) and polyethylene glycol (PEG), preferably polyethylene oxide (PEO) or poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), more preferably poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP).

[0020] In some specific embodiments, the lithium salt is one or more selected from lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium perchlorate (LiClO4) and lithium hexafluorophosphate (LiPF6), preferably lithium bis(fluorosulfonyl)imide (LiFSI).

[0021] In some specific embodiments, the inorganic filler is a metal or non-metal halide, for example, one or more selected from CuF2, MgF2, AlF3, SbF3, ZnF2, AgF, SnF4, SeF6, CuCl2, MgCl2 and ZnCl2, preferably CuF2.

[0022] In some specific embodiments, in the polymer layer mother solution, the content of the solute is 5 wt % to 20 wt %, preferably 5 wt % to 12 wt %, and the solute includes the polymer, the lithium salt, and the inorganic filler.

[0023] In some specific embodiments, the solvent is one or more selected from N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), tetrahydrofuran (THF) and dimethyl sulfoxide (DMSO), preferably N-methylpyrrolidone (NMP).

[0024] In some specific embodiments, the current collector is copper foil.

[0025] In some specific embodiments, the method for preparing the negative electrode material further comprises:

[0026] Before step (1), the surface of the copper foil is treated to form a copper oxide modification layer.

[0027] In some specific embodiments, the copper oxide modification layer is a Cu / CuO nanostructure array, preferably a Cu / CuO nanotube array.

[0028] The third aspect of the present invention provides the use of the negative electrode material of the first aspect of the present invention or the negative electrode material obtained by the preparation method of the second aspect of the present invention in a lithium ion battery.

[0029] A fourth aspect of the present invention provides a lithium-ion battery, which comprises the negative electrode material according to the first aspect of the present invention or the negative electrode material obtained by the preparation method according to the second aspect of the present invention.

[0030] In the negative electrode material for lithium-ion batteries of the present invention, a polymer layer is formed on the surface of the current collector to form an artificial polymeric solid electrolyte interphase (APSEI). The organic layer including polymers and lithium salts in the polymer layer can isolate the negative electrode current collector and the lithium deposited on the surface of the current collector during charging from direct contact with the electrolyte, reduce side reactions, improve the cycle coulomb efficiency, and increase the service life of the lithium battery; the organic layer can also serve as a carrier of inorganic fillers, providing a certain toughness to cope with the volume deformation of the lithium negative electrode during the cycle. The lithium salt in the polymer forms an ion channel in the interface. The inorganic filler in the polymer layer can reduce the degree of crystallization of the polymer during the film formation process, which is beneficial to the chain migration of lithium ions in the polymer and promotes the formation of a polymer layer with high ion flux; at the same time, during the charging process, the inorganic filler reacts with metallic lithium to generate Li with a higher Young's modulus. x M alloy and LiF promote the uniform distribution of lithium ions during the deposition process while suppressing the formation of lithium dendrites. On the other hand, by forming a copper oxide modification layer on the surface of the current collector, it can further induce the uniform deposition of lithium on the surface of the current collector.

[0031] In short, the negative electrode material for lithium-ion batteries of the present invention achieves the following technical advantages by forming a polymer layer APSEI on the surface of the current collector: (i) excellent chemical and electrochemical stability, electronic insulation, preventing the continuous decomposition of the electrolyte and the consumption of lithium; (ii) high Young's modulus and toughness, while inhibiting dendrite growth, can cope with the volume change of the negative electrode during the cycle; (iii) high ionic conductivity and high Li + The ability of ions to transport across layers. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] FIG1 is a schematic diagram of a negative electrode material for a lithium-ion battery according to an embodiment of the present invention.

[0033] FIG2 is a graph showing the results of a room temperature cycle performance test of lithium ion batteries according to an embodiment of the present invention and a comparative example. DETAILED DESCRIPTION

[0034] The present invention will be further described below by way of specific embodiments. Unless otherwise specified, the terms used herein have the same meanings as those generally understood by those of ordinary skill in the art. The numerical limits or ranges stated herein include endpoints, specifically including all values ​​and subranges within the numerical limits or ranges. Unless otherwise specified, ratios, proportions, and percentages appearing in this specification are all weight ratios.

[0035] A first aspect of the present invention provides a negative electrode material for a lithium ion battery (hereinafter sometimes referred to as "negative electrode"), the negative electrode material comprising:

[0036] a current collector; and

[0037] A polymer layer is formed on the surface of the current collector and includes a polymer, a lithium salt, and an inorganic filler.

[0038] In the polymer layer, the mass ratio of polymer, lithium salt and inorganic filler can be 1-25:1:0.1-2, preferably 5-25:1:0.5-1.5, and more preferably 6-10:1:1. When the polymer content is too low, the ASEI formed has poor stability and is easy to break during the cycle. When the polymer content is too high, the mother liquor formed has high viscosity and is not easy to be evenly coated. The addition of lithium salt mainly affects the crystallization process of the polymer. When the lithium salt content is too low, it cannot effectively hinder the formation of polymer crystals, and when the lithium salt content is too high, the generated ASEI is more brittle. Inorganic fillers affect the glass transition temperature of the polymer and enhance the migration ability of the polymer chain segments. When the content of inorganic fillers is too low, the ionic conductivity of the ASEI formed is poor, and when the content of inorganic fillers is too high, the stability of the membrane is affected.

[0039] In some specific embodiments of the present invention, the polymer in the polymer layer of the negative electrode material may be one or more selected from polyethylene oxide (PEO), poly(vinylidene fluoride) (PVDF), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), polyacrylonitrile (PAN), polyacrylic acid (PAA) and polyethylene glycol (PEG). The polymer is closely related to the stability of the lithium metal, the surface morphology after film formation and the ASEI performance. From the perspective of helping to form a porous structure and promoting the formation of lithium ion transport channels to regulate the uniform distribution of lithium ions, the polymer in the polymer layer of the negative electrode material is preferably polyethylene oxide (PEO) or poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), more preferably poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP).

[0040] In some specific embodiments, the lithium salt in the polymer layer of the negative electrode material can be one or more selected from lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium perchlorate (LiClO4) and lithium hexafluorophosphate (LiPF6). The fluoride ion in LiFSI has a strong electron-withdrawing property, which weakens the coordination effect between the anion and cation of the lithium salt, making the salt more soluble in the polymer mother solution configuration solvent, which helps to form high ionic conductivity ASEI. At the same time, the salt has high thermal stability and electrochemical stability, and basically no side reactions occur. Therefore, the lithium salt in the polymer layer of the negative electrode material is preferably lithium bis(fluorosulfonyl)imide (LiFSI).

[0041] In some specific embodiments, the inorganic filler in the polymer layer of the negative electrode material can be a metal or non-metal halide, preferably a metal or non-metal fluoride or chloride, for example, one or more selected from CuF2, MgF2, AlF3, SbF3, ZnF2, AgF, SnF4, SeF6, CuCl2, MgCl2, and ZnCl2. As described above, the inorganic filler affects the glass transition temperature of the polymer and enhances the migration ability of the polymer chain segments. Considering the above-mentioned technical effects and cost, the inorganic filler in the polymer layer of the negative electrode material is preferably CuF2.

[0042] In some specific embodiments, the current collector of the negative electrode material can be copper foil, porous copper foil or foam copper, etc., preferably copper foil. And as shown in Figure 1, preferably, in some specific embodiments, the surface of the copper foil can have a copper oxide modification layer. In some specific embodiments, the copper oxide modification layer can be a Cu / CuO nanostructure array. The Cu / CuO nanostructure array can be a nanostructure such as a Cu / CuO nanotube array, a Cu / CuO nanoparticle array, a Cu / CuO nanowire array, etc., preferably a Cu / CuO nanotube array. By forming a modification layer on the surface of the current collector, the local current density can be effectively reduced, the formation of lithium dendrites can be suppressed, and the internal contact resistance of the battery cell can be reduced.

[0043] A second aspect of the present invention provides a method for preparing a negative electrode material for a lithium ion battery, the negative electrode material comprising: a current collector; and a polymer layer formed on a surface of the current collector, the preparation method comprising the following steps:

[0044] (1) Coating a polymer layer mother solution on the surface of the current collector to form a polymer layer.

[0045] In some embodiments of the present invention, the polymer layer mother liquor used to coat the current collector surface may include a polymer, a lithium salt, an inorganic filler, and a solvent. The mass ratio of polymer, lithium salt, and inorganic filler is 1-25:1:0.1-2, preferably 5-15:1:0.5-1.5, and more preferably 6-10:1:1. When the polymer content is too low, the resulting ASEI is less stable and prone to breakage during cycling. When the polymer content is too high, the resulting mother liquor has a high viscosity, making uniform coating difficult. The addition of lithium salt primarily affects the crystallization process of the polymer. When the lithium salt content is too low, it cannot effectively hinder the formation of polymer crystals, while when the lithium salt content is too high, the resulting ASEI is more brittle. Inorganic fillers affect the glass transition temperature of the polymer and enhance the mobility of polymer segments. When the inorganic filler content is too low, the resulting ASEI has poor ionic conductivity, while when the inorganic filler content is too high, the membrane stability is affected.

[0046] In some specific embodiments, the polymer in the polymer layer mother solution can be one or more selected from polyethylene oxide (PEO), poly(vinylidene fluoride) (PVDF), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), polyacrylonitrile (PAN), polyacrylic acid (PAA) and polyethylene glycol (PEG). The polymer is closely related to the stability of lithium metal, the surface morphology after film formation and the ASEI performance. From the perspective of helping to form a porous structure and promoting the formation of lithium ion transmission channels to regulate the uniform distribution of lithium ions, the polymer in the polymer layer mother solution is preferably polyethylene oxide (PEO) or poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), more preferably poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP).

[0047] In some specific embodiments, the lithium salt in the polymer layer mother solution can be one or more selected from lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium perchlorate (LiClO4), and lithium hexafluorophosphate (LiPF6). The fluoride ion in LiFSI has a strong electron-withdrawing property, which weakens the coordination effect between the anion and cation of the lithium salt, making the salt more soluble in the polymer mother solution solvent, thereby contributing to the formation of high ionic conductivity ASEI. At the same time, the salt has high thermal and electrochemical stability and basically no side reactions. Therefore, the lithium salt in the polymer layer mother solution is preferably lithium bis(trifluoromethanesulfonyl)imide (LiFSI).

[0048] In some specific embodiments, the inorganic filler in the polymer layer mother solution can be a metal or non-metal halide, preferably a metal or non-metal fluoride or chloride, for example, one or more selected from CuF2, MgF2, AlF3, SbF3, ZnF2, AgF, SnF4, SeF6, CuCl2, MgCl2, and ZnCl2. As described above, the inorganic filler affects the glass transition temperature of the polymer and enhances the migration ability of the polymer segments. Considering the above-mentioned technical effects and cost, the inorganic filler in the polymer layer of the negative electrode material is preferably CuF2.

[0049] In some specific embodiments, the solvent in the polymer layer mother liquor can be one or more selected from N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), tetrahydrofuran (THF) and dimethyl sulfoxide (DMSO). Among these solvents, NMP, as a polar aprotic solvent, has properties such as low toxicity, high boiling point, and non-flammability. In addition, NMP is a commonly used solvent for PVDF-HFP polymers and has outstanding solubility. Therefore, the solvent in the polymer layer mother liquor is preferably N-methylpyrrolidone (NMP). In some specific embodiments, the content of solutes including polymers, lithium salts and inorganic fillers in the polymer layer mother liquor is 5wt% to 20wt%, preferably 5wt% to 12wt%. When the solute content is too high, it will lead to a higher viscosity of the polymer layer mother liquor, and the ASEI formed during the coating process of the polymer layer mother liquor will have poor uniformity, resulting in poor performance after film formation.

[0050] In some embodiments, for example, a polymer layer mother solution can be formed by adding a solute including a polymer, a lithium salt, and an inorganic filler into a solvent in a predetermined ratio, stirring vigorously, and then cooling to room temperature.

[0051] In some embodiments, a polymer layer mother solution can be applied to the surface of the current collector by common film-forming methods such as dip coating, drop coating, spin coating, spray coating, and doctor blade coating to form a polymer layer. The amount of the polymer layer mother solution applied can be 5 to 20 μL / cm 2 Considering the convenience of the operation process, the preferred coating method is spin coating.

[0052] In some specific embodiments, the current collector used to prepare the negative electrode material can be copper foil, porous copper foil or foam copper, etc., preferably copper foil.

[0053] In some specific embodiments, the method for preparing the negative electrode material further comprises:

[0054] Before step (1), the surface of the current collector may be treated to form a copper oxide modification layer.

[0055] In some specific embodiments, the copper oxide modified layer can be a Cu / CuO nanostructure array. The Cu / CuO nanostructure array can be a nanostructure such as a Cu / CuO nanotube array, a Cu / CuO nanoparticle array, a Cu / CuO nanowire array, and is preferably a Cu / CuO nanotube array. By forming a modified layer on the surface of the current collector, the local current density can be effectively reduced, the formation of lithium dendrites can be suppressed, and the contact internal resistance of the battery cell can be reduced. Preferably, a three-dimensional copper oxide modified layer is formed on the surface of the current collector by chemical etching.

[0056] The third aspect of the present invention provides the use of the negative electrode material of the first aspect of the present invention or the negative electrode material obtained by the preparation method of the second aspect of the present invention in a lithium ion battery.

[0057] A fourth aspect of the present invention provides a lithium-ion battery comprising the negative electrode material of the first aspect of the present invention or the negative electrode material prepared by the preparation method of the second aspect of the present invention. Materials other than the negative electrode material in the lithium-ion battery, such as the anode material and the electrolyte, may be conventional commercially available materials, as long as they are capable of preparing the lithium-ion battery of the present invention.

[0058] Example

[0059] The present invention is described in detail below by way of examples, which are not intended to limit the present invention. The experimental methods in the following examples are conventional methods unless otherwise specified. The various reagents and equipment used in the following examples are all commercially available products and there are no special requirements.

[0060] Example 1

[0061] (1) Preparation of copper oxide modified current collector

[0062] Prepare 5 mol / L sodium hydroxide solution and 1 mol / L ammonium persulfate solution; then prepare 8 mL of sodium hydroxide solution and 2 mL of ammonium persulfate solution into a mixed solution; immerse commercial copper foil in the prepared mixed solution for 20 minutes, then remove it, wash it and dry it to obtain copper hydroxide nanotube arrays (Cu / Cu(OH)2) on the surface of the copper foil; then, vacuum dry the copper foil at 200°C to obtain a current collector with a Cu / CuO nanotube array on the surface.

[0063] (2) Preparation of negative electrode materials

[0064] According to the components and ratios in Table 1, the polymer, lithium salt and inorganic filler were added to the solvent, stirred vigorously at 85°C for 60 minutes and then cooled to room temperature to obtain a polymer layer mother solution. Subsequently, the polymer layer mother solution was spin-coated at a rate of 10 μL / cm 2Finally, the copper current collector coated with the polymer layer mother solution was allowed to stand at room temperature for 4 hours in a glove box, and then heat-treated at 50° C. for 4 hours to obtain a negative electrode material.

[0065] (3) Preparation of positive electrode

[0066] The ternary cathode material (LiNi 0.8 Co 0.1 Mn 0.1 O2), conductive agent Super P, and binder PVDF are mixed in a mass ratio of 8:1:1, dispersed in an organic solvent NMP (N-methylpyrrolidone), and stirred until stable and uniform to form a positive electrode slurry. The positive electrode slurry is scraped onto an aluminum foil with a thickness of 10 μm, dried at 80°C, and then heated to 120°C for further vacuum drying. The positive electrode sheet is then made by rolling and slicing.

[0067] (4) Preparation of electrolyte

[0068] Fluoroethylene carbonate (FEC) and dimethyl carbonate (DMC) were mixed in a ratio of 1:4, lithium hexafluorophosphate (LiPF6) was added, and the concentration was controlled to be 1M. A magnetic stirrer was used to stir the mixture until the lithium salt was completely dissolved to obtain an electrolyte.

[0069] (5) Lithium battery assembly

[0070] In an inert atmosphere of a glove box, a button-type full battery was assembled. The positive and negative electrode shells, springs and gaskets of the assembled button-type battery were commercially available CR2032, and the negative electrode was the negative electrode material prepared in step (1). The positive electrode sheet was as described above. The battery was assembled in the order of negative electrode shell | springs | gasket | copper current collector | electrolyte | diaphragm | positive electrode sheet | positive electrode shell. The button-type battery was assembled and pressed at 800 kPa for 5 s to complete the assembly.

[0071] (6) Normal temperature cycle performance test

[0072] A lithium battery using the sample electrolyte was charged at 0.2C constant current and constant voltage at 25°C to 4.2V, and then discharged at 0.2C constant current to 3.0V. This cycle was considered one cycle (1@cls). Coulombic efficiency was calculated as the ratio of discharge capacity to charge capacity during the same cycle.

[0073] Comparative Example 1

[0074] The lithium-ion battery of Comparative Example 1 was prepared in the same manner as steps (3) to (6) of Example 1, except that steps (1) to (2) were not performed and copper foil was directly used as the current collector, and its room temperature cycling performance was tested.

[0075] Comparative Example 2

[0076] The lithium-ion battery of Comparative Example 2 was prepared in the same manner as steps (1) and (3) to (6) of Example 1, except that step (2) was not performed and the copper foil modified with copper oxide was directly used as the current collector, and its room temperature cycling performance was tested.

[0077] Examples 2-8 and Comparative Examples 3-5

[0078] Except that the polymer layer mother solution was prepared according to the components and ratios in Table 1, the lithium ion batteries of Examples 2-8 and Comparative Examples 3-5 were prepared in the same manner as Example 1, and their room temperature cycle performance was tested.

[0079] Example 9

[0080] The lithium-ion battery of Example 9 was prepared in the same manner as steps (2) to (6) of Example 1, except that step (1) was not performed and the polymer layer mother solution was directly coated on the copper foil surface to prepare the negative electrode material. Its room temperature cycle performance was tested.

[0081] Example 10

[0082] The lithium-ion battery of Example 10 was prepared in the same manner as steps (2) to (6) of Example 1, except that step (1) was not performed and the polymer layer mother solution was directly coated on the surface of the copper foil to prepare the negative electrode material, and the polymer layer mother solution was prepared according to the components and ratios in Table 1. The room temperature cycle performance of the battery was tested.

[0083] As shown in Table 1 and Figure 2, in the lithium-ion battery of Comparative Example 1, since unmodified copper foil without a polymer layer is used as the negative electrode material, the capacity retention rate decays rapidly, and at the 4th charging cycle (4@cls), charging is no longer possible. In Comparative Example 2, since a copper hydroxide nanotube array (Cu / Cu(OH)2) is formed on the surface of the current collector modified with copper oxide, the cycle reversibility is improved to a certain extent, and the capacity retention rate of about 70% is still maintained at the 10th charging cycle. However, since there are more side reactions without a polymer layer, the capacity retention rate still decreases rapidly, and at the 13th charging cycle (13@cls), charging is no longer possible.

[0084] The capacity retention rates of Examples 1-10 are all better than those of Comparative Example 2, thanks to the fact that the polymer layer on the surface of the current collector isolates the deposited lithium from direct contact with the electrolyte, thereby reducing the consumption of active lithium during the cycle and improving the cycle performance.

[0085] Specifically, the results of Examples 1 and 2 show that using PVDF-HFP as the polymer can achieve a higher capacity retention rate, maintaining approximately 90% of the capacity retention rate after 50 charge cycles. This is because its porous structure and polar functional groups can regulate uniform lithium ion flux and promote rapid lithium ion transport compared to PEO.

[0086] According to the results of Example 1, Example 3, and Example 4, as well as the results of Example 3 and Comparative Example 3, it can be seen that when CuF2 is used as an inorganic filler, a better capacity retention rate can be obtained. This is because CuF2 reacts with the deposited lithium in situ to generate Li x Cu and LiF have a Young's modulus and a lithium ion affinity that is superior to that of LiCl formed when CuCl2 is used as an inorganic filler in Example 3 and that of LiF formed when AlF3 is used as an inorganic filler in Example 4. x Al.

[0087] According to the results of Example 1 and Examples 6 to 10, when the mass ratio of the polymer, the lithium salt and the inorganic filler is about 10:1:1, a better capacity retention rate can be obtained.

[0088] In addition, according to the results of Example 9, it can be seen that even if a polymer layer is directly formed on the surface of a copper foil current collector that has not been surface-modified (for example, the surface of the current collector does not have a copper hydroxide nanotube array (Cu / Cu(OH)2)), the lithium-ion battery can maintain a good capacity retention rate (about 70% at 50@cls).

[0089] In addition, according to the results of Comparative Examples 3 to 5, when the polymer content is too high (Comparative Example 4), the ASEI formed is too dense, which hinders the transmission of lithium ions, resulting in poor ionic conductivity and a rapid decay in the capacity retention rate of the assembled battery; when the content of the inorganic filler is too high (Comparative Example 3), the stability of the ASEI formed is also poor, resulting in a rapid decay in the capacity retention rate of the assembled battery; and when the content of the polymer layer mother liquor is too high (Comparative Example 5), the coating process product yield is low, the ASEI thickness consistency after spin coating is poor, and the assembled battery cell impedance is large.

[0090] The above examples are used to describe exemplary embodiments of the present invention, but the present invention is not limited thereto. It should be understood by those skilled in the art that the above examples are for illustrative purposes only, and the specific embodiments and examples of the present invention should not be construed as limiting the scope of the present invention. The embodiments can be changed and modified within the scope of the present invention, and such changes and modifications should fall within the scope of protection of the present invention.

Claims

1. A negative electrode material for a lithium ion battery, characterized in that The negative electrode material includes: a current collector; and A polymer layer is formed on the surface of the current collector, and the polymer layer comprises a polymer, a lithium salt and an inorganic filler, and the mass ratio of the polymer, the lithium salt and the inorganic filler is 1 to 25:1:0.1 to 2, preferably 5 to 15:1:0.5 to 1.5, and more preferably 6 to 10:1:

1.

2. The negative electrode material for lithium-ion batteries according to claim 1, characterized in that The polymer is one or more selected from polyethylene oxide (PEO), poly(vinylidene fluoride) (PVDF), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), polyacrylonitrile (PAN), polyacrylic acid (PAA) and polyethylene glycol (PEG), preferably polyethylene oxide (PEO).

3. The negative electrode material for lithium ion batteries according to claim 1 or 2, characterized in that: The lithium salt is one or more selected from lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium perchlorate (LiClO4) and lithium hexafluorophosphate (LiPF6), preferably lithium bis(fluorosulfonyl)imide (LiFSI).

4. The negative electrode material for lithium-ion batteries according to any one of claims 1 to 3, characterized in that The inorganic filler is a metal or non-metal halide, selected from one or more of CuF2, MgF2, AlF3, SbF3, ZnF2, AgF, SnF4, SeF6, CuCl2, MgCl2 and ZnCl2, preferably CuF2.

5. The negative electrode material for lithium-ion batteries according to any one of claims 1 to 4, characterized in that The current collector is a copper foil, and the surface of the copper foil has a copper oxide modification layer; Preferably, the copper oxide modification layer is a Cu / CuO nanostructure array, preferably a Cu / CuO nanotube array.

6. A method for preparing a negative electrode material for a lithium ion battery, the negative electrode material comprising: current collector; and a polymer layer, wherein the polymer layer is formed on the surface of the current collector, and the preparation method comprises the following steps: (1) coating a polymer layer mother solution on the surface of the current collector to form a polymer layer, The polymer layer mother solution comprises a polymer, a lithium salt, an inorganic filler and a solvent, and the mass ratio of the polymer, the lithium salt and the inorganic filler is 1-25:1:0.1-2, preferably 5-15:1:0.5-1.5, and more preferably 6-10:1:

1.

7. The method for preparing a negative electrode material for a lithium ion battery according to claim 6, characterized in that: The polymer is one or more selected from polyethylene oxide (PEO), poly(vinylidene fluoride) (PVDF), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), polyacrylonitrile (PAN), polyacrylic acid (PAA) and polyethylene glycol (PEG), preferably polyethylene oxide (PEO).

8. The method for preparing a negative electrode material for a lithium ion battery according to claim 6 or 7, characterized in that: The lithium salt is one or more selected from lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium perchlorate (LiClO4) and lithium hexafluorophosphate (LiPF6), preferably lithium bis(fluorosulfonyl)imide (LiFSI).

9. The method for preparing a negative electrode material for a lithium ion battery according to any one of claims 6 to 8, characterized in that: The inorganic filler is a metal or non-metal halide, selected from one or more of CuF2, MgF2, AlF3, SbF3, ZnF2, AgF, SnF4, SeF6, CuCl2, MgCl2 and ZnCl2, preferably CuF2.

10. The method for preparing a negative electrode material for a lithium ion battery according to any one of claims 6 to 9, characterized in that: In the polymer layer mother solution, the content of solute is 5 wt% to 20 wt%, preferably 5 wt% to 12 wt%, and the solute includes the polymer, the lithium salt and the inorganic filler.

11. The method for preparing a negative electrode material for a lithium ion battery according to any one of claims 6 to 10, characterized in that: The solvent is one or more selected from N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), tetrahydrofuran (THF) and dimethyl sulfoxide (DMSO), preferably N-methylpyrrolidone (NMP).

12. The method for preparing a negative electrode material for a lithium ion battery according to any one of claims 6 to 11, characterized in that: The current collector is copper foil.

13. The method for preparing a negative electrode material for a lithium ion battery according to any one of claims 6 to 12, characterized in that: The preparation method further comprises: Before step (1), the surface of the copper foil is treated to form a copper oxide modification layer; Preferably, the copper oxide modification layer is a Cu / CuO nanostructure array, preferably a Cu / CuO nanotube array.

14. Use of the negative electrode material for a lithium ion battery according to any one of claims 1 to 5, or the negative electrode material obtained by the method for preparing the negative electrode material for a lithium ion battery according to any one of claims 6 to 13 in a lithium ion battery.

15. A lithium-ion battery, comprising the negative electrode material for a lithium-ion battery according to any one of claims 1 to 5 or the negative electrode material obtained by the method for preparing the negative electrode material for a lithium-ion battery according to any one of claims 6 to 13.

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