Negative electrode sheet and preparation method therefor, and secondary battery

Abstract

A negative electrode sheet and a preparation method therefor, and a secondary battery. The negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer arranged on at least one surface of the negative electrode current collector. The negative electrode active material layer comprises a negative electrode active material and inorganic ceramic particle groups. Inorganic ceramic particles in the inorganic ceramic particle groups are arranged on the surface of the negative electrode active material in the form of cluster aggregates. For the negative electrode sheet, during testing by means of a scanning electron microscope, within an area of 5 μm × 5 μm, the number of inorganic ceramic particle groups on the surface of negative electrode active material particles is N', wherein 3≤N'≤20. The secondary battery has high energy density and good dynamic performance.

Description

Negative electrode sheet, method for preparing negative electrode sheet, and secondary battery Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a negative electrode sheet, a method for preparing a negative electrode sheet, and a secondary battery. Background Art

[0002] Secondary batteries, such as lithium-ion batteries, have advantages such as high energy density, long cycle life, and high charge and discharge efficiency, and have been widely used around the world.

[0003] With the increasing development of secondary batteries, higher requirements are being placed on their energy density and dynamic performance. To achieve high energy density, existing technologies generally adopt the method of increasing the initial compaction density of the electrode and increasing its coating weight. To achieve high dynamics, existing technologies generally adopt the method of reducing the initial compaction density of the electrode and reducing the coating weight. It can be seen that existing technologies cannot achieve both high energy density and high dynamics in lithium-ion batteries.

[0004] Summary of the Invention

[0005] In view of this, the present application provides a negative electrode sheet, a method for preparing a negative electrode sheet, and a secondary battery, which can improve both the energy density and kinetic performance of lithium-ion batteries.

[0006] In the first aspect, the present application provides a negative electrode plate, which includes a negative electrode current collector and a negative electrode active material layer arranged on at least one surface of the negative electrode current collector, the negative electrode active material layer includes a negative electrode active material and an inorganic ceramic particle group, and the inorganic ceramic particles in the inorganic ceramic particle group are arranged on the surface of the negative electrode active material in the form of cluster aggregates (see the bright box mark in Figure 1). For the negative electrode plate, when tested by a scanning electron microscope, within the range of 5μm×5μm, the number of inorganic ceramic particle groups on the surface of the negative electrode active material particles is N′, 3≤N′≤20. The present application provides a plurality of inorganic ceramic particle groups attached to the surface of the negative electrode active material in the form of cluster aggregates in the negative electrode plate, while controlling the number of inorganic ceramic particle groups within an appropriate range. On the one hand, it is beneficial to increase the potential of the negative electrode, thereby increasing the capacity of the negative electrode active material, thereby increasing the energy density (ED) without changing the amount of active material. Moreover, due to the increase in the negative electrode potential, lithium deposition is less likely to occur during charging (broadening the lithium deposition window), thereby improving the kinetic performance of the lithium-ion battery. On the other hand, the inorganic ceramic particles are attached to the surface of the negative electrode active material in the form of inorganic ceramic particle groups, which can avoid the obstruction of ion conduction caused by the distribution of a large number of single-particle ceramics, and is more conducive to improving the kinetic performance of the lithium-ion battery. Preferably, 5≤N′≤15.

[0007] In the preparation process of negative electrode slurry, for inorganic ceramic particles with different particle sizes and specific surface areas and their different addition amounts, different agglomeration states of the inorganic ceramic particle group can be achieved by adjusting the stirring time. For example, for inorganic ceramic particles with Dv50 of 5nm and W of 100m 2 / g inorganic ceramic particles, when the addition amount is 0.1%, stirring for 30min can achieve N' of 1 to 3, stirring for 30min to 1h can achieve N' of 3 to 10, stirring for 1 to 2h can achieve N' of 10 to 20; for Dv50 at 15nm and W at 60m 2 When the amount of inorganic ceramic particles added is 0.1%, stirring for 0 min can achieve an N' value of 1-3, stirring for 10-30 min can achieve an N' value of 3-10, and stirring for 30 min to 1 h can achieve an N' value of 10-20. In short, for ceramics with larger Dv50, smaller W, and smaller addition amount, the time required to reach the same N' value range is shorter. The above is for example only and is not limiting in this application.

[0008] In some embodiments, the particle size Dv50 of the inorganic ceramic particles is 2 nm to 20 nm. Inorganic ceramic particles of the above particle size range are introduced into the negative electrode plate, and the cluster aggregates formed after aggregation are more conducive to improving the potential of the negative electrode. Inorganic ceramic particles with a particle size Dv50 that is too small or too large (for example, less than 2 nm or greater than 20 nm) are not conducive to forming a suitable number of cluster aggregates. Preferably, the particle size Dv50 of the inorganic ceramic particles is 5 nm to 15 nm.

[0009] In some embodiments, the number of inorganic ceramic particles is N, where N>3. This can avoid the obstruction of ion conduction caused by the distribution of a large number of single ceramic particles. Clusters of inorganic ceramic particles with N≤3 can be considered single ceramic particles. Preferably, 4≤N≤40.

[0010] In some embodiments, the specific surface area of ​​the inorganic ceramic particles is W, W>50m 2 / g. The specific surface area of ​​the inorganic ceramic particles is within the above range, and the inorganic ceramic particle group formed after aggregation is more conducive to improving the potential of the negative electrode and is more conducive to improving the energy density and dynamic performance of the lithium-ion battery. Preferably, 60m 2 / g≤W≤150m 2 / g.

[0011] In some embodiments, the inorganic ceramic particles are selected from at least one of lithium fluoride, lithium sulfate, sodium titanate, calcium carbonate, calcium sulfate, calcium phosphate, aluminum hydroxide, aluminum oxide, aluminum sulfate, aluminum carbonate, magnesium hydroxide, magnesium oxide, magnesium sulfate, magnesium carbonate, or silicon oxide. The weight percentage of the inorganic ceramic particles is 0.05 wt % to 0.3 wt % based on the weight of the negative electrode active material layer. Preferably, the inorganic ceramic particles are selected from any one of aluminum hydroxide, silicon dioxide, and magnesium hydroxide. When the type and content of the inorganic ceramic particles are within the above ranges, the energy density and kinetic performance of the lithium-ion battery are further improved.

[0012] In some embodiments, the thickness of the negative electrode sheet is 30 μm to 300 μm, and the thickness of the negative electrode current collector is 4 μm to 25 μm.

[0013] In a second aspect, the present application provides a method for preparing a negative electrode sheet, comprising the following steps: mixing a negative electrode active material, inorganic ceramic particles, a binder and a dispersant, preparing an aqueous slurry with a solid content of 50% with deionized water, and stirring for 0.5h to 3h.

[0014] In some embodiments, the dispersant includes an organic acid having a molecular weight of less than 10w, containing at least one of a hydroxyl group, an amino group, or an imino group, and being soluble in an aqueous solution having a pH of greater than 7 and less than 13.

[0015] In some embodiments, the mass ratio of the negative electrode active material, the inorganic ceramic particles, the dispersant, and the binder is (96-98):(0.1-0.5):(1-2):(1-2).

[0016] In a third aspect, the present application provides a secondary battery, which includes any negative electrode sheet according to the first aspect; or, the secondary battery includes a negative electrode sheet prepared by any preparation method according to the second aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without paying any creative work.

[0018] FIG1 is a SEM test image of the negative electrode sheet in this application;

[0019] FIG2 is a SEM test image of the negative electrode sheet of Example 1 of the present application within a range of 5 μm×5 μm;

[0020] FIG3 is a partially enlarged SEM test image of the negative electrode sheet in FIG2 . DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solutions and advantages of this application more clearly understood, the present application is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0022] Negative electrode

[0023] A first aspect of an embodiment of the present application provides a negative electrode plate, which includes a negative electrode current collector and a negative electrode active material layer arranged on at least one surface of the negative electrode current collector, the negative electrode active material layer including a negative electrode active material and an inorganic ceramic particle group, the inorganic ceramic particles in the inorganic ceramic particle group being arranged on the surface of the negative electrode active material in the form of cluster aggregates. For the negative electrode plate, when tested by a scanning electron microscope, within the range of 5μm×5μm, the number of inorganic ceramic particle groups on the surface of the negative electrode active material particles is N′, 3≤N′≤20. A plurality of inorganic ceramic particle groups are arranged in the negative electrode plate and attached to the surface of the negative electrode active material in the form of cluster aggregates. At the same time, the number of inorganic ceramic particle groups on the surface of the negative electrode active material is controlled within the above-mentioned range. On the one hand, the potential of the negative electrode can be increased, which is beneficial to improving the capacity of the negative electrode active material. Moreover, due to the increase in the potential of the negative electrode, lithium deposition is less likely to occur during charging, which is beneficial to improving the kinetic performance. On the other hand, the inorganic ceramic particles are attached to the surface of the negative electrode active material in the form of inorganic ceramic particle groups, which can avoid the obstruction of ion conduction caused by the distribution of a large number of single-particle ceramics (N≤3), and is more conducive to the improvement of kinetic performance, that is, taking into account the improvement of the energy density and kinetic performance of the lithium-ion battery.

[0024] Specifically, in some embodiments, 3 ≤ N′ ≤ 20. In some embodiments, 4 ≤ N′ ≤ 18. In some embodiments, 5 ≤ N′ ≤ 15. In some embodiments, 6 ≤ N′ ≤ 13. In some embodiments, 8 ≤ N′ ≤ 10. Exemplarily, when tested under a scanning electron microscope, within a range of 5 μm × 5 μm, the number N′ of the inorganic ceramic particle group on the surface of the negative electrode active material particle is 3, 4, 5, 6, 8, 10, 12, 13, 15, 18, 20, or a range consisting of any two of the foregoing values.

[0025] In some embodiments, the particle size Dv50 of the inorganic ceramic particles in the inorganic ceramic particle group is 2 nm to 20 nm. Inorganic ceramic particles of the above particle size range are introduced into the negative electrode plate. After aggregation, it is more conducive to forming a suitable number of cluster aggregates (N>3) to improve the potential of the negative electrode. Exemplarily, the particle size Dv50 of the inorganic ceramic particles is 2 nm, 4 nm, 5 nm, 8 nm, 10 nm, 12 nm, 15 nm, 18 nm, 20 nm, or a range consisting of any two of the above values.

[0026] In some embodiments, the number of inorganic ceramic particles in the inorganic ceramic particle group is N, where N>3. When the number of inorganic ceramic particles in the inorganic ceramic particle group is within the above range, the inorganic ceramic particle group has a suitable secondary particle size, which is more conducive to improving the kinetic performance of lithium-ion batteries. Specifically, in some embodiments, N≥6, in some embodiments, N≥10, in some embodiments, N≥15, and in some embodiments, N≥20. The above is only an example and is not limited in this application. Preferably, 4≤N≤40.

[0027] In some embodiments, the specific surface area of ​​the inorganic ceramic particles in the inorganic ceramic particle group is W, W>50m 2 / g. The specific surface area of ​​the inorganic ceramic particles is within the above range, and the inorganic ceramic particle group formed after aggregation is more conducive to improving the potential of the negative electrode, while also improving the energy density and dynamic performance of the lithium-ion battery. Specifically, in some embodiments, 55m 2 / g≤W≤160m 2 / g. In some embodiments, 60m 2 / g≤W≤150m 2 / g. In some embodiments, 65m 2 / g≤W≤140m 2 / g. In some embodiments, 85m 2 / g≤W≤110m 2 / g. In some embodiments, 90m 2 / g≤W≤105m 2 / g. For example, the specific surface area W of the inorganic ceramic particles in the inorganic ceramic particle group is 51m 2 / g、53m 2 / g、55m 2 / g、58m 2 / g, 60m 2 / g、65m 2 / g、70m 2 / g、85m 2 / g、90m 2 / g、105m 2 / g、110m 2 / g, 130m 2 / g, 140m 2 / g, 150m 2 / g, 160m 2 / g or a range consisting of any two of the above values.

[0028] In some embodiments, the inorganic ceramic particles are selected from at least one of lithium fluoride, lithium sulfate, sodium titanate, calcium carbonate, calcium sulfate, calcium phosphate, aluminum hydroxide, aluminum oxide, aluminum sulfate, aluminum carbonate, magnesium hydroxide, magnesium oxide, magnesium sulfate, magnesium carbonate, or silicon oxide, and the mass percentage of the inorganic ceramic particles is 0.05 wt % to 0.3 wt % based on the mass of the negative electrode active material layer. When the mass percentage of the inorganic ceramic particles is within the above range, it is more conducive to improving the energy density and kinetic performance of the lithium-ion battery. Exemplarily, the mass percentage of the inorganic ceramic particles is 0.05 wt %, 0.08 wt %, 0.1 wt %, 0.15 wt %, 0.25 wt %, 0.3 wt %, or a range consisting of any two of the above values.

[0029] In some embodiments, the thickness of the negative electrode active material layer is 30 μm to 300 μm. For example, the thickness of the negative electrode active material layer is 30 μm, 50 μm, 80 μm, 100 μm, 120 μm, 150 μm, 180 μm, 200 μm, 220 μm, 250 μm, 280 μm, 300 μm, or a range consisting of any two of the foregoing values.

[0030] In some embodiments, the thickness of the negative electrode current collector is 4 μm to 25 μm. For example, the thickness of the negative electrode current collector is 4 μm, 6 μm, 8 μm, 10 μm, 15 μm, 20 μm, 25 μm, or a range consisting of any two of the above values.

[0031] Preparation method of negative electrode sheet

[0032] The negative electrode active material, inorganic ceramic particles, binder and dispersant are mixed and prepared into an aqueous slurry with deionized water with a solid content of 50%. After stirring for 0.5h to 3h, the obtained slurry is coated on the negative electrode current collector by coating. The coating method is preferably extrusion coating to coat the electrode material. Gravure, micro-gravure, electrospraying, transfer coating and other methods can also be used. After the electrode is dried, a coating of electrode material with excellent adhesion and a smooth surface is obtained, and the other side of the current collector is coated in the same way. There is no special limitation on the drying of the electrode as long as the method can evaporate and remove the solvent in the slurry. For example, a method of heat treatment in an atmosphere of 50 to 300°C in the atmosphere can be cited. Drying methods include natural drying, warm air drying, heating drying, far-infrared radiation drying, etc., and any method can be used.

[0033] The negative electrode active material is graphite, silicon, or a mixture of silicon and graphite, wherein the silicon is a mixture of pure silicon, silicon alloy, silicon-carbon composite, or silicon-oxygen material. The binder includes one or more of SBR (styrene-butadiene rubber), PAA (polyacrylic acid), PVA (polyvinyl alcohol), polyacrylate, etc. The dispersant includes an organic acid having a molecular weight of less than 10w, containing at least one of a hydroxyl group, an amino group, or an imino group, and being soluble in an aqueous solution having a pH of greater than 7 and less than 13. CMC (carboxymethyl cellulose) is preferably used as the dispersant.

[0034] For the negative electrode current collector, there is no particular limitation as long as the material has electronic conductivity and can be energized in the negative electrode active material maintained. For example, conductive materials such as C, Cu, Ni, Fe, V, Nb, Ti, Cr, Mo, Ru, Rh, Ta, W, Os, Ir, Pt, Au, Al, and alloys containing two or more of these conductive materials (such as stainless steel) can be used. Or it can be a material obtained by plating different conductive materials on a conductive material (for example, a material obtained by plating Cu on Fe). From the viewpoint of high conductivity, stability in the electrolyte and good oxidation resistance, Cu, Ni, stainless steel, etc. are preferred as current collectors. From the viewpoint of material cost, Cu and Ni are preferred. There is no particular limitation on the shape of the negative electrode current collector layer, but it is preferably in the form of a plate or foil. The thickness of the negative electrode current collector is preferably 4-25 μm.

[0035] In some embodiments, the mass ratio of the negative electrode active material, the inorganic ceramic particles, the dispersant, and the binder is (96-98):(0.1-0.5):(1-2):(1-2).

[0036] secondary batteries

[0037] A second aspect of an embodiment of the present application provides a secondary battery, which includes a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte. The separator is arranged between the positive electrode sheet and the negative electrode sheet, and the negative electrode sheet is any negative electrode sheet of the first aspect mentioned above.

[0038] other

[0039] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer arranged on the surface of the positive electrode current collector. The present application has no special restrictions on the positive electrode current collector, as long as the purpose of the present application can be achieved. For example, it can include aluminum foil, aluminum alloy foil or a composite current collector (for example, a composite current collector with a metal layer arranged on the surface of a polymer layer). The present application has no special restrictions on the thickness of the positive electrode current collector, as long as the purpose of the present application can be achieved. For example, the thickness of the positive electrode current collector is 5μm to 13μm. The positive electrode active material layer includes a positive electrode active material. The present application has no special restrictions on the positive electrode active material, as long as the purpose of the present application can be achieved. For example, the positive electrode active material can include a composite metal oxide containing one or more selected from the group consisting of cobalt, manganese, and nickel, or an olivine-type phosphate containing lithium containing one or more selected from iron, cobalt, nickel and manganese. These positive electrode active materials can be used alone or in combination of two or more. As such lithium composite metal oxides, suitable examples include LiCoO2, LiMn2O4, LiNiO2, LiCo 1-x Ni x O2(0.01 <x<1)、LiNi x MnyCo z O2 (x + y + z = 1), solid solution of Li2MnO3 and LiMO2 (M is a transition metal such as Co, Ni, Mn, Fe), LiNi 1 / 2 Mn 3 / 2 O4, LiFePO4, LiMnPO4, and LiMn 1-x Fe xOne or more of PO4(0.01 < x < 1), more preferably two or more. A part of these composite metal oxides with lithium or lithium-containing olivine-type phosphates can be replaced by other elements, or a part of cobalt, nickel, manganese, and iron can be replaced by one or two or more elements selected from Co, Mn, Ni, Mg, Al, B, Ti, V, Nb, Cu, Zn, Mo, Ca, Sr, W, and Zr, or coated with a compound containing these other elements or a carbon material. There is no particular limitation on the thickness of the positive electrode active material layer in the present application as long as the object of the present application can be achieved. For example, the thickness of the positive electrode active material layer is 30 μm to 120 μm. The positive electrode active material layer may further include a conductive agent and a binder. There is no particular limitation on the types of the conductive agent and the binder in the present application as long as the object of the present application can be achieved. For example, the conductive agent may include, but is not limited to, at least one of conductive carbon black, carbon nanotubes (CNT), carbon fibers, Ketjen black, graphene, metal materials, or conductive polymers. The binder may include, but is not limited to, at least one of polyacrylic acid, polyacrylates, acrylate polymers, polyvinyl alcohol, polyvinylidene fluoride, polytetrafluoroethylene, or vinylidene fluoride-hexafluoropropylene copolymers. There is no particular limitation on the mass ratio of the positive electrode active material, the conductive agent, and the binder in the positive electrode active material layer in the present application, and those skilled in the art can select according to actual needs as long as the object of the present application can be achieved.

[0040] The separator can be any known porous structure separator having electrochemical stability and chemical stability, such as a single-layer or multi-layer film of one or more of glass fiber, non-woven fabric, polyethylene (PE), polypropylene (PP), and polyvinylidene fluoride (PVDF).

[0041] The electrolyte includes an organic solvent, an electrolyte lithium salt and an additive. The present invention does not specifically limit its type and can be selected according to actual needs. Exemplarily, the organic solvent includes ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), cyclopentane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS) or diethyl sulfone (ESE) One or more, preferably two or more. Exemplarily, the electrolyte lithium salt includes one or more of LiPF6 (lithium hexafluorophosphate), LiBF4 (lithium tetrafluoroborate), LiClO4 (lithium perchlorate), LiAsF6 (lithium hexafluoroarsenate), LiFSI (lithium bis(fluorosulfonyl imide), LiTFSI (lithium bis(trifluoromethanesulfonyl imide), LiTFS (lithium trifluoromethanesulfonate), LiDFOB (lithium difluorooxalatoborate), LiBOB (lithium dioxalatoborate), LiPO2F2 (lithium difluorophosphate), LiDFOP (lithium difluorooxalatophosphate) or LiTFOP (lithium tetrafluorooxalatophosphate). The electrolyte may optionally include other additives, which may be any additive that can be used as a lithium-ion secondary battery. The present invention is not specifically limited thereto and may be selected according to actual needs. As an example, the additive may be one or more of vinylene carbonate (VC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), 1,3-propane sultone (PS), succinonitrile (SN), adiponitrile (ADN), 1,3-propylene sultone (PST), tris(trimethylsilyl) phosphate (TMSP) or tris(trimethylsilyl) borate (TMSB).

[0042] Secondary batteries can be prepared according to conventional methods in the art. For example, the aforementioned positive electrode sheet, separator, and negative electrode sheet are stacked in sequence, with the separator positioned between the positive and negative electrode sheets to provide isolation, to form an electrode assembly. Alternatively, the electrode assembly can be wound together. The electrode assembly is then placed in a packaging case, injected with electrolyte, and sealed to form a secondary battery.

[0043] The structure of the lithium battery is not particularly limited, and a coin-type battery, a cylindrical battery, a square-type battery, a pouch battery, or the like having a single-layer or multi-layer separator can be applied.

[0044] The application of the lithium-ion battery of the present application is not particularly limited, and it can be used in any electronic device known in the prior art.

[0045] In some embodiments, the lithium-ion battery of the present application can be used for, but is not limited to, laptop computers, pen-type computers, mobile computers, e-book players, portable phones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, LCD televisions, portable cleaners, portable CD players, mini-discs, transceivers, electronic notepads, calculators, memory cards, portable recorders, radios, backup power supplies, motors, cars, motorcycles, power-assisted bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries and lithium-ion capacitors, etc.

[0046] The following examples and comparative examples are given to illustrate the embodiments of the present application in more detail. Unless otherwise stated, the parts, percentages and ratios listed are all based on weight.

[0047] Example 1

[0048] (1) Preparation of lithium-ion batteries

[0049] <Preparation of negative electrode sheet>

[0050] 97.4% active material (artificial graphite), 0.1% Al(OH)3, 1.3% binder (SBR), and 1.2% dispersant (CMC) were mixed and prepared with deionized water to form an aqueous slurry with a solid content of 50%. The mixture was stirred for 1.5 hours. The prepared negative electrode slurry was evenly applied to a 6μm copper foil by extrusion coating. After coating, the electrode was dried at 100°C to obtain a electrode with a coating thickness of 100μm. The above steps were repeated on the other surface of the electrode to obtain an electrode coated with a negative electrode active material layer on both sides. The negative electrode sheet was roller-pressed to obtain a negative electrode sheet with a thickness of 81μm. The resulting negative electrode sheet was cut into a size of 78.5mm x 732mm for future use.

[0051] The difference between Examples 2 to 18 and Example 1 is that, during the preparation of the negative electrode sheet, the type of inorganic ceramic particles, particle size Dv50 and its specific surface area parameters are regulated, as shown in Table 1. At the same time, the number N′ of the inorganic ceramic particle group and the number N of inorganic ceramic particles in the inorganic ceramic particle group are controlled by adjusting the stirring time of the aqueous slurry, as shown in Table 1. Other aspects are the same as in Example 1. For example, in Example 5, the ceramic Dv50 is 15 nm and W is 100 nm. 2 / g, stirring time is 1h, in Example 11, the ceramic Dv50 is 2nm, W is 160m 2 / g, stirring time is 3h.

[0052] <Preparation of positive electrode sheet>

[0053] The positive electrode active material, lithium cobalt oxide (LiCoO2), conductive carbon black (Super P), and binder (PVDF) were mixed to a weight ratio of 97.5:1.0:1.5. NMP was then added as a solvent to form a slurry with a solids content of 75%, which was then stirred thoroughly. The slurry was evenly applied to one surface of a 9μm thick aluminum foil by extrusion coating and dried at 90°C to obtain a positive electrode sheet with a coating thickness of 100μm. The above steps were then repeated on the other surface of the positive electrode sheet to obtain a positive electrode sheet coated with a layer of positive electrode active material on both sides. The negative electrode sheet was roll-pressed to obtain a rolled positive electrode sheet with a thickness of 79μm. The positive electrode sheet was cut into sheets measuring 77mm x 735mm for later use.

[0054] <Preparation of Electrolyte>

[0055] In a dry argon atmosphere, organic solvents ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) are mixed in a mass ratio of 30:50:20, and then lithium hexafluorophosphate (LiPF6) is added to the organic solvent to dissolve and mix evenly to obtain an electrolyte, wherein the molar concentration of LiPF6 in the electrolyte is 1.1 mol / L.

[0056] <Preparation of lithium-ion batteries>

[0057] Using a 7μm-thick PE porous polymer film as a separator, the prepared positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator positioned between the positive and negative electrodes to provide separation. The electrode assembly is then wound to form an electrode assembly. The electrode assembly is then placed in an outer packaging, injected with the prepared electrolyte, and packaged. The lithium-ion battery is then produced through a series of processes including formation, degassing, and trimming.

[0058] Comparative Examples 1 to 6

[0059] The difference between Comparative Examples 1 to 6 and Example 1 is that the type of inorganic ceramic particles, particle size Dv50, specific surface area, number of inorganic ceramic particle groups N′, and number N of inorganic ceramic particles in the inorganic ceramic particle group are controlled during the preparation of the negative electrode plate. The control method can be found in Examples 2 to 18. The rest is the same as Example 1.

[0060] (2) Performance test

[0061] (1) SEM characterization of inorganic ceramic particle group

[0062] The battery was fully discharged and disassembled to obtain the negative electrode sheet. The disassembled electrode sheet was soaked in DMC solvent for 6 hours and then dried in a 60°C oven for 3 hours to remove the solvent to obtain a dry electrode sheet. A cross-section of the negative electrode sheet with an area of ​​5μm×5μm was cut, ensured to be dry and fixed on the sample stage. The sample stage and the bracket were placed in a CP instrument (IB-09010CP / ion polisher) and adjusted to the appropriate position for cross-section polishing. After cutting, the sample was removed and placed in a SEM-EDS instrument (ZEISS SEM-OXFORD EDS) for scanning electron microscopy analysis and testing. The accelerating voltage was adjusted to 10kV, and the focus, contrast, and brightness were adjusted under the condition of 3KX magnification. The photograph was taken and the number of inorganic ceramic particle groups was determined. For example, the test image of Example 1 at 3KX magnification can be seen in Figure 2. For the inorganic ceramic particle group, the focus, contrast, and brightness were adjusted under the condition of 30KX magnification. The photograph was taken and the specific number of individual inorganic ceramic particles, specific surface area, and particle size were determined. For example, the test chart of Example 1 at 30KX magnification can be seen in FIG3 .

[0063] (2) Battery lithium deposition window test

[0064] Place the battery in a 12°C incubator and let it rest for 1 hour. Then perform the following test procedure: 1) 0.7C DC to 3V; 2) Let it rest for 10 minutes; 3) XC CC to 4.5V, 4.5V CV to 0.05C; 4) Let it rest for 10 minutes; 5) Cycle 10 times from 1 to 4. Adjust X to different values ​​(e.g., 1.2, 1.4, 1.6, etc.) and disassemble the battery. When no grayish-white lithium deposits are observed on the negative electrode surface, the maximum X value is considered the lithium deposition window.

[0065] (3) Energy density test

[0066] In an environment of 25°C, the lithium-ion battery is charged and discharged according to the following operating procedures to obtain the discharge capacity of the lithium-ion battery: the lithium-ion battery is charged to 4.45V at a constant current of 0.5C, then charged to 0.025C at a constant voltage of 4.45V, left to stand for 5 minutes, and discharged to 3.0V at a constant current of 0.5C, left to stand for 5 minutes, and the discharge capacity C and discharge platform V are obtained. p After the above lithium-ion battery charging steps are completed, the length L, width W, and height H of the lithium-ion battery are measured with a laser thickness gauge to obtain the volume V = L × W × H of the lithium-ion battery. Its energy density (ED) = C * V p / V, unit is Wh / L.

[0067] (4) 600-cycle capacity retention test

[0068] The battery was allowed to stand for 30 minutes at a test temperature of 25°C, then charged at a constant current of 1.5C to 4.3V and constant voltage to 1.3C. The battery was then charged at a constant current of 1.3C to 4.35V and constant voltage to 1.2C. The battery was then charged at a constant current of 1.2C to 4.4V and constant voltage to 1.0C. The battery was then charged at a constant current of 1.0C to 4.5V and constant voltage to 0.05C. The battery was allowed to stand for 5 minutes, and discharged at a current density of 0.7C to 3.0V. The battery was allowed to stand for 5 minutes. This cycle was repeated 600 times. The capacity retention rate at the 600th cycle = (discharge capacity at the 600th cycle / discharge capacity at the first cycle) × 100%.

[0069] Table 1 Note: “ / ” in Table 1 indicates no relevant parameters. The negative electrode sheet of Comparative Example 1 does not contain the inorganic ceramic particle group, and the mass content of the negative electrode active material artificial graphite is 97.5%.

[0070] Combined with Table 1, compared with Example 1, the negative electrode plate of Comparative Example 1 does not contain an inorganic ceramic particle group, and its lithium precipitation window at 12°C is only 2.3C, its energy density is 765Wh / L, and its capacity retention rate after 600 cycles is only 73%, which is significantly lower than the energy density of Example 1 of 780Wh / L and the capacity retention rate of Example 1 after 600 cycles of 90%.

[0071] Among Comparative Examples 2 to 6, the inorganic ceramic particles in Comparative Example 2 had an excessively high particle size Dv50, resulting in a small number of inorganic ceramic particle groups N', which was not conducive to improving the potential of the negative electrode sheet. The inorganic ceramic particles in Comparative Example 3 had an excessively small specific surface area, which was also not conducive to the formation of inorganic ceramic particle groups. The excessive number of inorganic ceramic particle groups in Comparative Example 4 hindered ion conduction and was not conducive to improving the potential of the negative electrode sheet. The number of inorganic ceramic particle groups in Comparative Examples 5 and 6 was also inappropriate. Combined with the data in Table 1, the energy density and cycle performance of the lithium-ion batteries corresponding to Comparative Examples 2 to 5 did not show significant improvement.

[0072] In Examples 1 to 5, Examples 8 to 11, and Examples 13 to 17, when the inorganic ceramic particles are made of the same material, the Dv50 of the inorganic ceramic particles is 5 nm to 15 nm, and the specific surface area of ​​the inorganic ceramic particles is 60 m 2 / g to 150m 2 In the range of / 5≤N′≤15, the lithium plating window is larger, indicating that the battery has better kinetic performance, and the energy density and cycle retention rate are higher.

[0073] In particular, by further regulating the particle size Dv50 of the inorganic ceramic particles and the range of their specific surface area W, it is possible to further improve the energy density and cycle performance of the lithium-ion battery while broadening the lithium precipitation window.

[0074] In particular, further adjusting the type and content of the inorganic ceramic particle group can improve the energy density and cycle performance of the lithium-ion battery.

[0075] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present application should be included in the scope of protection of the present application.

Claims

1. A negative electrode plate, characterized in that: The negative electrode plate includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector; The negative electrode active material layer comprises a negative electrode active material and an inorganic ceramic particle group, wherein the inorganic ceramic particles in the inorganic ceramic particle group are arranged on the surface of the negative electrode active material in the form of cluster aggregates; For the negative electrode sheet, when tested under a scanning electron microscope, within a range of 5 μm×5 μm, the number of inorganic ceramic particle groups on the surface of the negative electrode active material particles is N′, and 3≤N′≤20.

2. The negative electrode sheet according to claim 1, characterized in that: The negative electrode plate satisfies at least one of the following conditions: (1) The particle size Dv50 of the inorganic ceramic particles is 2 nm to 20 nm; (2) The number of the inorganic ceramic particles is N, N>3; (3) The specific surface area of ​​the inorganic ceramic particles is W, W>50m 2 / g; (4)5≤N′≤15。 3. The negative electrode sheet according to claim 2, characterized in that: The negative electrode plate satisfies at least one of the following conditions: (1) The particle size Dv50 of the inorganic ceramic particles is 5 nm to 15 nm; (2)60m 2 / g≤W≤150m 2 / g; (3)4≤N≤40。 4. The negative electrode sheet according to any one of claims 1 to 3, characterized in that: The inorganic ceramic particles are selected from at least one of lithium fluoride, lithium sulfate, sodium titanate, calcium carbonate, calcium sulfate, calcium phosphate, aluminum hydroxide, aluminum oxide, aluminum sulfate, aluminum carbonate, magnesium hydroxide, magnesium oxide, magnesium sulfate, magnesium carbonate or silicon oxide; The inorganic ceramic particles may have a mass percentage of 0.05 wt % to 0.3 wt % based on the mass of the negative electrode active material layer.

5. The negative electrode sheet according to claim 4, characterized in that: The inorganic ceramic particles are selected from any one of aluminum hydroxide, silicon dioxide and magnesium hydroxide.

6. The negative electrode sheet according to any one of claims 1 to 3, characterized in that: The thickness of the negative electrode plate is 30 μm to 300 μm, and the thickness of the negative electrode current collector is 4 μm to 25 μm.

7. A method for preparing a negative electrode sheet, characterized in that: The preparation method comprises the following steps: The negative electrode active material, inorganic ceramic particles, binder and dispersant are mixed, and prepared into an aqueous slurry with a solid content of 50% with deionized water, and stirred for 0.5h to 3h.

8. The preparation method according to claim 7, characterized in that The dispersant includes an organic acid and satisfies: (1) The molecular weight of the organic acid is less than 10w; (2) the organic acid contains at least one of a hydroxyl group, an amino group, or an imino group; (2) The organic acid is soluble in an aqueous solution having a pH of 7 or higher and 13 or lower.

9. The preparation method according to claim 8, characterized in that The mass ratio of the negative electrode active material, the inorganic ceramic particles, the dispersant and the binder is (96-98):(0.1-0.5):(1-2):(1-2).

10. A secondary battery, characterized in that: The secondary battery comprises the negative electrode sheet according to any one of claims 1 to 6; or The secondary battery comprises a negative electrode sheet prepared by the preparation method according to any one of claims 7 to 9.

Images