A negative electrode and an electrochemical and electronic device comprising the negative electrode.

Abstract

This application relates to a negative electrode and an electrochemical and electronic device comprising the negative electrode. The negative electrode includes a current collector and a layer of negative electrode active material located on the current collector. The negative electrode active material layer comprises negative electrode active material particles, which include secondary particles. The negative electrode active material layer contains pores A, and when tested using mercury porosimetry, the pore size of pore A is 59 nm–73 nm, and the C004 / C110 value of the negative electrode active material layer is 6–20. Electrochemical devices using the negative electrode provided in this application exhibit higher capacity and improved resistance to cyclic expansion.

Description

[0001] This application is a divisional application of the invention patent application filed on March 29, 2021, with application number 202110333773.1 and invention title "A negative electrode and an electrochemical device and electronic device comprising the negative electrode". Technical Field

[0002] This application relates to the field of energy storage, specifically to a negative electrode and an electrochemical and electronic device containing the negative electrode, particularly a lithium-ion battery. Background Technology

[0003] Electrochemical devices (e.g., lithium-ion batteries) are widely used due to their advantages such as environmental friendliness, high operating voltage, large specific capacity, and long cycle life, making them one of the most promising new green chemical power sources in the world today. Small-sized lithium-ion batteries are commonly used as power sources for portable electronic communication devices (e.g., portable cameras, mobile phones, or laptops), especially high-performance portable devices. In recent years, medium-sized and large-sized lithium-ion batteries with high output characteristics have been developed for use in electric vehicles (EVs) and large-scale energy storage systems (ESS). With the widespread application of lithium-ion batteries, their cycle performance has become a key technical problem that urgently needs to be solved. Improving the active materials in the electrodes is one of the research directions for solving these problems.

[0004] Existing technologies primarily employ graphite coating and carbonization to suppress interparticle expansion through the surface coating layer. Furthermore, coating reduces polarization and the accumulation of by-reaction products, thereby mitigating the cycle expansion problem. However, this significantly impacts the energy density of lithium-ion batteries, resulting in a trade-off and making it difficult to achieve a balanced overall performance. Therefore, it is indeed necessary to provide an improved negative electrode active material and the negative electrode, electrochemical devices, and electronic devices made from it. Summary of the Invention

[0005] This application provides a negative electrode, an electrochemical device including the negative electrode, and an electronic device, in an attempt to solve at least one problem existing in the relevant field to some extent.

[0006] In one embodiment, this application provides a negative electrode, the negative electrode comprising a current collector and a negative electrode active material layer located on the current collector, the negative electrode active material layer comprising negative electrode active material particles, the negative electrode active material particles comprising secondary particles, the negative electrode active material layer comprising pore A, and when tested by mercury porosimetry, the pore size of pore A is 59nm-73nm, and the C004 / C110 value of the negative electrode active material layer is 6-20.

[0007] In some embodiments, the differential mercury injection rate of orifice A is 0.150-0.190 mL / g·μm.-1 .

[0008] In some embodiments, the negative electrode active material layer includes pores B, the pore size of which is 661.6 nm-793.3 nm, and the differential mercury ingress rate of pores B is 0.160-0.230 mL / g·μm. -1 .

[0009] In some embodiments, the volume ratio of hole B to hole A is 0.7:1 to 1.42:1.

[0010] In some embodiments, the negative electrode active material particles satisfy at least one of conditions (a)-(d): (a) the Dv50 of the negative electrode active material particles is 7.2-21.6 μm; (b) the Dv90 of the negative electrode active material particles is 28.4-40 μm; (c) the Dn10 of the negative electrode active material particles is 1.4-9.4 μm; and (d) the Dv90 and Dn10 of the negative electrode active material particles satisfy: Dv90 / Dn10 ≤ 26.

[0011] In some embodiments, the particle size of the negative electrode active material is D1v50 before being compressed, and D2v50 after applying 1t of pressure, and (D1v50-D2v50) / D1v50×100%≤25%.

[0012] In some embodiments, the specific surface area of ​​the negative electrode active material particles is 0.8-2.0 m². 2 / g.

[0013] In some embodiments, the specific surface area of ​​the negative electrode active material particles before being subjected to pressure is B1, and the specific surface area after applying 1t of pressure is B2, and (B2-B1) / B1×100%≤140%.

[0014] In another embodiment, this application provides an electrochemical device including a negative electrode as described in embodiments of this application.

[0015] In some embodiments, when the electrochemical device discharges to a voltage of 3V, the specific surface area of ​​the negative electrode active material particles is 1.9-2.4m². 2 / g.

[0016] In some embodiments, when the electrochemical device is charged to a voltage of 4.45V, the maximum exothermic peak of the negative electrode active material layer is 280-330℃ when DSC testing is performed.

[0017] In some embodiments, the electrochemical device discharges to a voltage of 3V, and the particle size of the negative electrode active material is D. av50, and the particle size of the negative electrode active material particles after applying a pressure of 1t is D. b v50, (D a v50-D b v50) / D a y50×100%≤2%.

[0018] In some embodiments, the electrochemical device discharges to a voltage of 3V, and the specific surface area of ​​the negative electrode active material particles before being subjected to pressure is B. 11 And the specific surface area after applying a pressure of 1t is B. 22 (B) 22 -B 11 ) / B 11 ×100%≤40%.

[0019] In another embodiment, this application provides an electronic device that includes the electrochemical device described in the embodiments of this application.

[0020] This application improves the capacity and anti-cycle swelling performance of lithium-ion batteries by optimizing the particle bulk structure and the degree of particle-to-particle composite.

[0021] Additional aspects and advantages of the embodiments of this application will be described and shown in part in the following description, or illustrated by practice of the embodiments of this application. Attached Figure Description

[0022] The accompanying drawings, necessary for describing embodiments of this application or the prior art, will be briefly described below to facilitate the depiction of embodiments of this application. It is obvious that the drawings described below represent only a portion of the embodiments in this application. Those skilled in the art will be able to derive other embodiments from the structures illustrated in these drawings without requiring inventive effort.

[0023] Figure 1 The differential mercury ingress curves of the negative electrode active materials of Example 11 and Comparative Example 1 of this application are shown. Detailed Implementation

[0024] The embodiments of this application will be described in detail below. These embodiments should not be construed as limiting the scope of this application.

[0025] In this application, Dv50 is the particle size corresponding to a cumulative volume percentage of 50% of the negative electrode active material, in μm; Dv90 is the particle size corresponding to a cumulative volume percentage of 90% of the negative electrode active material, in μm; and Dn10 is the particle size corresponding to a cumulative quantity percentage of 10% of the negative electrode active material, in μm.

[0026] Additionally, quantities, ratios, and other numerical values ​​are sometimes presented in range format in this document. It should be understood that such range format is for convenience and brevity and should be interpreted flexibly to include not only the numerical values ​​explicitly specified as range limits, but also all individual numerical values ​​or subranges covered within the range, as if each numerical value and subrange were explicitly specified.

[0027] In the detailed description and claims, a list of items connected by the terms "one of," "among," "a kind of," or other similar terms may mean any of the listed items. For example, if items A and B are listed, then the phrase "one of A and B" means only A or only B. In another example, if items A, B, and C are listed, then the phrase "one of A, B, and C" means only A; only B; or only C. Item A may contain a single element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements.

[0028] In the detailed description and claims, a list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements.

[0029] Electrochemical device

[0030] In one embodiment, this application provides an electrochemical device, which includes a positive electrode, a negative electrode, a separating membrane, and an electrolyte.

[0031] In some embodiments, the electrochemical device of this application includes, but is not limited to, a primary battery or a secondary battery.

[0032] In some embodiments, the electrochemical device is a lithium secondary battery.

[0033] In some embodiments, the lithium secondary battery includes, but is not limited to, a lithium metal secondary battery, a lithium-ion secondary battery, a lithium polymer secondary battery, or a lithium-ion polymer secondary battery.

[0034] I. Negative electrode

[0035] This application provides a negative electrode comprising a current collector and a negative electrode active material layer located on the current collector. The negative electrode active material layer contains negative electrode active material particles, which include secondary particles. The negative electrode active material layer contains pores A. When tested using mercury porosimetry, the pore size of pore A is 59nm-73nm, and the C004 / C110 value of the negative electrode active material layer is 6-20.

[0036] In some embodiments, the aperture of the aperture A is 59nm, 60nm, 61nm, 62nm, 63nm, 64nm, 65nm, 66nm, 67nm, 68nm, 69nm, 70nm, 71nm, 73nm, or a range of any two of these values.

[0037] In some embodiments, the C004 / C110 value of the negative electrode active material layer is 6, 8, 10, 12, 14, 16, 18, 20, or a range of any two of these values.

[0038] In some embodiments, the differential mercury injection rate of orifice A is 0.150-0.190 mL / g·μm. -1 .

[0039] In some embodiments, the differential mercury injection rate of orifice A is 0.150 mL / g·μm. -1 0.160 mL / g·μm -1 0.170 mL / g·μm -1 0.180 mL / g·μm -1 0.190 mL / g·μm -1 Or a range consisting of any two of these values.

[0040] In some embodiments, the negative electrode active material layer includes pores B, the pore size of which is 660 nm-800 nm, and the differential mercury ingress rate of pores B is 0.160-0.230 mL / g·μm. -1 .

[0041] In some embodiments, the aperture of the aperture B is 660nm, 670nm, 680nm, 690nm, 700nm, 710nm, 720nm, 730nm, 740nm, 750nm, 760nm, 770nm, 780nm, 790nm, 790nm, 800nm, or a range of any two of these values.

[0042] In some embodiments, the volume ratio of pore B to pore A is 0.7:1 to 1.42:1. In some embodiments, the volume ratio of pore B to pore A is 0.7:1, 0.8:1, 0.9:1, 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.42:1, or any combination of these values. When the volume ratio of pore B to pore A is within the above range, the area of ​​the negative electrode active material exposed in the electrolyte can be controlled, reducing side reactions and avoiding a decrease in initial efficiency; at the same time, it ensures the flow and wetting of the electrolyte, avoiding an increase in impedance.

[0043] In some embodiments, the negative electrode active material particles satisfy at least one of conditions (a)-(d): (a) the Dv50 of the negative electrode active material particles is 7.2-21.6 μm; (b) the Dv90 of the negative electrode active material particles is 28.4-40.0 μm; (c) the Dn10 of the negative electrode active material particles is 1.4-9.4 μm; or (d) the Dv90 and Dn10 of the negative electrode active material particles satisfy: Dv90 / Dn10≤26.

[0044] In some embodiments, the Dv50 of the negative electrode active material particles is 7.2 μm, 8 μm, 10 μm, 12 μm, 14 μm, 16 μm, 18 μm, 20 μm, 21.6 μm, or a range of any two of these values.

[0045] In some embodiments, the Dv90 of the negative electrode active material particles is 28.4 μm, 30 μm, 32 μm, 34 μm, 35.7 μm, 38 μm, 40 μm, or a range of any two of these values.

[0046] In some embodiments, the Dn10 of the negative electrode active material particles is 1.4 μm, 2.0 μm, 3.0 μm, 4.0 μm, 5.0 μm, 6.0 μm, 7.0 μm, 8.0 μm, 9.4 μm, or any combination of these values.

[0047] In some embodiments, Dv90 / Dn10 is a range of 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26 or any combination of these values.

[0048] In some embodiments, the particle size of the negative electrode active material is D1v50 before being compressed, and D2v50 after applying 1t of pressure, and (D1v50-D2v50) / D1v50×100%≤25%.

[0049] In some embodiments, the value of (D1v50-D2v50) / D1v50×100% is 1%, 3%, 6%, 9%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 25%, or a range of any two of these values. When the value of (D1v50-D2v50) / D1v50×100% is within the above range, the bonding strength of the negative electrode active material particles is higher, the particles are more stable during the cycling of the electrochemical device, and the expansion rate of the electrochemical device is reduced.

[0050] In some embodiments, the specific surface area of ​​the negative electrode active material particles is 0.8-2.0 m². 2 / g. In some embodiments, the specific surface area of ​​the negative electrode active material particles is 0.8m². 2 / g, 0.9m 2 / g, 1.0m 2 / g, 1.1m 2 / g, 1.2m 2 / g, 1.3m 2 / g, 1.4m 2 / g, 1.6m 2 / g, 1.7m 2 / g, 1.8m 2 / g, 2.0m 2 / g or a range of any two of these values.

[0051] In some embodiments, the specific surface area of ​​the negative electrode active material particles before pressure is B1, and the specific surface area after applying 1t of pressure is B2, and (B2-B1) / B1×100% ≤ 140%. In some embodiments, (B2-B1) / B1×100% is a range of 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, 110%, 120%, 130%, 140%, or any combination of these values. When (B2-B1) / B1×100% is within the above range, side reactions in the electrochemical device are reduced, and the expansion rate is decreased.

[0052] In some embodiments, the negative electrode active material is graphite particles. In some embodiments, the negative electrode active material includes primary graphite particles and secondary graphite particles. In some embodiments, pore A is the packing void between primary graphite particles in the secondary graphite particles. In some embodiments, pore B is mainly due to the voids caused by the packing between secondary graphite particles.

[0053] In some embodiments, the secondary graphite particles are prepared from primary graphite particles and a binder. In some embodiments, the binder includes, but is not limited to, low-temperature asphalt, medium-temperature asphalt, high-temperature asphalt, or resin.

[0054] In some embodiments, when the electrochemical device discharges to a voltage of 3V, the specific surface area of ​​the negative electrode active material is 1.9-2.4m². 2 / g. In some embodiments, when the electrochemical device discharges to a voltage of 3V, the specific surface area of ​​the negative electrode active material is 1.9m². 2 / g, 2.0m 2 / g、2.1m 2 / g, 2.2m 2 / g, 2.3m 2 / g, 2.4m 2 / g or a range of any two of these values.

[0055] In some embodiments, when charged to a voltage of 4.45V and subjected to DSC testing, the maximum exothermic peak of the negative electrode active material layer is 280-330℃. In some embodiments, when charged to a voltage of 4.45V and subjected to DSC testing, the maximum exothermic peak of the negative electrode active material layer is 280℃, 286℃, 290℃, 296℃, 300℃, 306℃, 312℃, 318℃, 322℃, 326℃, 328℃, 330℃, or a range of any two of these values.

[0056] In some embodiments, when the electrochemical device discharges to a voltage of 3V, the particle size of the negative electrode active material is D. a v50, and the particle size of the negative electrode active material powder after applying a pressure of 1t is D. b v50, (D a v50-D b v50) / D a v50×100%≤2%.

[0057] In some embodiments, (D a v50-D b v50) / D a v50×100% is a range of 0.2%, 0.4%, 0.6%, 0.8%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, or any combination of these values.

[0058] In some embodiments, when the electrochemical device discharges to a voltage of 3V, the specific surface area of ​​the negative electrode active material particles before being subjected to pressure is B. 11 And the specific surface area after applying a pressure of 1t is B. 22 (B) 22 -B 11 ) / B 11 ×100% ≤ 40%. In some embodiments, (B) 22 -B 11) / B 11 The value of ×100% is 4%, 8%, 10%, 12%, 16%, 18%, 20%, 24%, 28%, 32%, 34%, 36%, 38%, 40%, or a range of any two of these values.

[0059] In some embodiments, the electrochemical device includes a lithium-ion battery, which exhibits an expansion rate of less than 9% after 500 cycles at 25°C. In some embodiments, the expansion rate of the lithium-ion battery is less than 8% or less than 7%.

[0060] In some embodiments, the negative electrode active material layer further includes an adhesive. In some embodiments, the adhesive includes, but is not limited to: polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon.

[0061] In some embodiments, the negative electrode active material layer includes a conductive material. In some embodiments, the conductive material includes, but is not limited to: natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, metal powder, metal fiber, copper, nickel, aluminum, silver, or polyphenylene derivatives.

[0062] In some embodiments, the current collector includes, but is not limited to: copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or a polymer substrate coated with a conductive metal.

[0063] In some embodiments, the negative electrode can be obtained by mixing an active material, a conductive material, and a binder in a solvent to prepare an active material composition, and then coating the active material composition onto a current collector.

[0064] In some embodiments, the solvent may include, but is not limited to, N-methylpyrrolidone.

[0065] II. Positive Electrode

[0066] The materials, composition, and manufacturing methods of the positive electrode that can be used in the embodiments of this application include any techniques disclosed in the prior art.

[0067] In some embodiments, the positive electrode includes a current collector and a layer of positive electrode active material located on the current collector.

[0068] In some embodiments, the positive electrode active material includes, but is not limited to: lithium cobalt oxide (LiCoO2), lithium nickel cobalt manganese (NCM) ternary material, lithium iron phosphate (LiFePO4), or lithium manganese oxide (LiMn2O4).

[0069] In some embodiments, the positive electrode active material layer further includes a binder and optionally a conductive material. The binder improves the bonding between the positive electrode active material particles and also improves the bonding between the positive electrode active material and the current collector.

[0070] In some embodiments, the adhesive includes, but is not limited to: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin or nylon, etc.

[0071] In some embodiments, the conductive material includes, but is not limited to, carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof. In some embodiments, the carbon-based material is selected from natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based material is selected from metal powder, metal fiber, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

[0072] In some embodiments, the current collector may include, but is not limited to, aluminum.

[0073] The positive electrode can be prepared by methods known in the art. For example, the positive electrode can be obtained by mixing an active material, a conductive material, and a binder in a solvent to prepare an active material composition, and then coating the active material composition onto a current collector. In some embodiments, the solvent may include, but is not limited to, N-methylpyrrolidone.

[0074] III. Electrolyte

[0075] The electrolyte that can be used in the embodiments of this application can be an electrolyte known in the prior art.

[0076] In some embodiments, the electrolyte comprises an organic solvent, a lithium salt, and additives. The organic solvent of the electrolyte according to this application may be any organic solvent known in the art that can be used as an electrolyte solvent. There are no limitations on the electrolyte used in the electrolyte according to this application; it may be any electrolyte known in the art. The additives of the electrolyte according to this application may be any additives known in the art that can be used as electrolyte additives.

[0077] In some embodiments, the organic solvent includes, but is not limited to: ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate, or ethyl propionate.

[0078] In some embodiments, the lithium salt includes at least one of an organic lithium salt or an inorganic lithium salt.

[0079] In some embodiments, the lithium salt includes, but is not limited to: lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium bis(trifluoromethanesulfonyl)imide LiN(CF3SO2)2 (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO2F)2) (LiFSI), lithium bis(oxalateborate)borate LiB(C2O4)2 (LiBOB), or lithium difluorooxalateborate LiBF2(C2O4) (LiDFOB).

[0080] In some embodiments, the concentration of lithium salt in the electrolyte is 0.5-3 mol / L, 0.5-2 mol / L, or 0.8-1.5 mol / L.

[0081] IV. Separating membrane

[0082] In some embodiments, a separator is provided between the positive and negative electrodes to prevent short circuits. The material and shape of the separator used in the embodiments of this application are not particularly limited, and can be any technology disclosed in the prior art. In some embodiments, the separator comprises a polymer or inorganic material formed from a material stable to the electrolyte of this application.

[0083] For example, the separator may include a substrate layer and a surface treatment layer. The substrate layer is a nonwoven fabric, membrane, or composite membrane with a porous structure, and the material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Specifically, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be selected.

[0084] A surface treatment layer is disposed on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing polymers and inorganic substances.

[0085] The inorganic layer comprises inorganic particles and a binder. The inorganic particles are selected from one or more of the following: alumina, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. The binder is selected from one or more of the following: polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene.

[0086] The polymer layer contains a polymer, the polymer material of which is selected from at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, or poly(vinylidene fluoride-hexafluoropropylene).

[0087] Electronic devices

[0088] The electronic device of this application can be any device that uses the electrochemical device according to the embodiments of this application.

[0089] In some embodiments, the electronic device includes, but is not limited to: laptop computers, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries or lithium-ion capacitors, etc.

[0090] The following uses a lithium-ion battery as an example and combines specific embodiments to illustrate the preparation of a lithium-ion battery. Those skilled in the art will understand that the preparation method described in this application is only an example, and any other suitable preparation method is within the scope of this application.

[0091] Example

[0092] The following describes the performance evaluation based on the embodiments and comparative examples of the lithium-ion battery of this application.

[0093] I. Preparation of Lithium-ion Batteries

[0094] 1. Preparation of the negative electrode

[0095] 1) Preparation of negative electrode active materials

[0096] a) Petroleum coke is used as raw material (i.e., graphite precursor), and the petroleum coke and binder are mixed evenly in a certain proportion. Then, the mixture is fed into a horizontal reactor, heated to 460℃-550℃ and held for 3 hours to obtain a granulated semi-finished product; and b) it undergoes high-temperature graphitization treatment at a temperature of 2500℃-3200℃ for 10hr-200hr to obtain a graphite anode active material. Specific process parameters are shown in Table 1.

[0097] 2) Preparation of the negative electrode

[0098] The graphite anode active material, styrene-butadiene rubber (SBR), and sodium carboxymethyl cellulose (CMC) prepared above were dispersed in deionized water at a weight ratio of 97.7:1.2:1.1 and thoroughly stirred to obtain a negative electrode slurry. Acetylene black was coated onto copper foil to obtain a negative electrode current collector. The negative electrode slurry was coated onto the negative electrode current collector, dried, and cold-pressed to obtain the negative electrode.

[0099] Graphite particles of different sizes can be obtained by crushing and classifying raw materials using any known technology.

[0100] 2. Preparation of the positive electrode

[0101] Lithium cobalt oxide (LiCoO2), acetylene black, and polyvinylidene fluoride (PVDF) were mixed thoroughly in an appropriate amount of N-methylpyrrolidone (NMP) at a weight ratio of 96:2:2. The mixture was then coated onto the aluminum foil of the positive electrode current collector, dried, and cold-pressed to obtain the positive electrode.

[0102] 3. Preparation of electrolyte

[0103] In a dry argon atmosphere, ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) were mixed in a weight ratio of 1:1:1, and LiPF6 was added and mixed thoroughly. Then, 3 wt% fluoroethylene carbonate and 2 wt% adiponitrile were added and mixed thoroughly to obtain the electrolyte, wherein the concentration of LiPF6 was 1.15 mol / L.

[0104] 4. Preparation of the separating membrane

[0105] A 12μm thick porous polyethylene (PE) polymer film was used as the separator.

[0106] 5. Preparation of lithium-ion batteries

[0107] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a barrier between the positive and negative electrodes. The cells are then wound to obtain a bare cell. After welding the tabs, the bare cell is placed in an outer packaging foil aluminum-plastic film. The prepared electrolyte is injected into the dried bare cell. After vacuum sealing, settling, formation, shaping, and capacity testing, a lithium-ion battery is obtained.

[0108] II. Testing Methods

[0109] 1. Test method for pore size distribution of negative electrode active material layer

[0110] The pore size distribution of the negative electrode active material layer was measured using a MicroActive AutoPore V 9600 fully automated mercury porosimetry pore size analyzer: The battery was discharged to 3V, the battery was disassembled, the negative electrode was removed and soaked in dimethyl carbonate solution for 5 hours, and then the negative electrode (including the negative electrode active material layer and current collector) was dried and placed in a dilatometer, sealed and then placed in the mercury porosimetry instrument to test the pore size distribution and pore volume of the negative electrode active layer.

[0111] Figure 1 The differential mercury ingress curves for Embodiment 11 and Comparative Example 1 of this application are shown. Figure 1 The horizontal axis corresponding to the peaks in the graph represents the pore size distribution range, and the area of ​​the peaks represents the pore volume per unit mass of material. Here, the pore sizes corresponding to the two highest peaks are selected to represent the pore sizes of pore A and pore B, with the pore size of pore A being smaller than that of pore B.

[0112] 2. OI value testing method

[0113] The OI value of the negative electrode active material layer was tested using an XRD diffractometer: The negative electrode sample was placed in the XRD diffractometer, and the crystal plane areas of the 004 and 110 peaks were measured to be C004 and C110, respectively. The OI value was then calculated using the following formula:

[0114] OI value = C004 / C110

[0115] 3. Test method for particle size of negative electrode active material

[0116] The particle size of the negative electrode active material was measured using a Malvern particle size analyzer: The negative electrode active material sample was dispersed in ethanol dispersant and sonicated for 30 minutes. The sample was then added into the Malvern particle size analyzer to test the Dv50, Dn10 and Dv90 of the negative electrode active material.

[0117] 4. Test method for specific surface area of ​​negative electrode active material

[0118] The specific surface area of ​​the negative electrode active material was measured using a specific surface area analyzer (Tristar II 3020M) via nitrogen adsorption / desorption: the negative electrode active material sample was dried in a vacuum drying oven and then placed in a sample tube for measurement in the analyzer.

[0119] 5. DSC Test Method

[0120] After charging the lithium-ion battery to 4.45V, it was disassembled, the negative electrode was dried, the active material layer of the negative electrode was scraped off, and its DSC exothermic curve was tested using a synchronous thermal analyzer (STA 449F3) at a heating rate of 10℃ / min under N2 atmosphere.

[0121] 6. Test method for specific capacity of lithium-ion batteries

[0122] The lithium-ion battery was discharged to 5.0mV at 0.05C, discharged to 5.0mV at 50μA, discharged to 5.0mV at 10μA, and then charged to 2.0V at 0.1C. The capacity of the lithium-ion battery at these times was recorded as its specific capacity. 0.05C refers to the current value at 0.05 times the designed specific capacity, and 0.1C refers to the current value at 0.1 times the designed specific capacity.

[0123] 7. Test method for cycle thickness expansion rate of lithium-ion batteries

[0124] At 25°C, the thickness of the lithium-ion battery at 3.95V was measured using a micrometer and recorded as H0. The lithium-ion battery was then cycled 500 times at a 1.5C rate. After every 50 cycles, the thickness of the lithium-ion battery at 4.45V was measured and recorded as H. n The cycle thickness expansion rate of a lithium-ion battery can be calculated using the following formula:

[0125] Cycle thickness expansion rate corresponding to the number of cycles = (H) n -H0) / H0×100%.

[0126] III. Test Results

[0127] Table 1 shows the process parameters for preparing the negative electrode active material. The binder dosage is the ratio of the binder weight to the graphite weight.

[0128] Table 1

[0129]

[0130] Table 2 shows the relevant performance test results. The DSC exothermic peak temperature refers to the DSC exothermic peak temperature of the negative electrode active material layer when the lithium-ion battery is charged to a voltage of 4.45V, which is used to characterize the thermal stability of the negative electrode material.

[0131] Table 2

[0132]

[0133] As can be seen from Examples 1, 5, 9, 13, 2, 6, 10, 14, 3, 7, 11, 15, and 4, 8, 12, 16, when preparing the negative electrode active material, keeping the particle size Dv50 of the graphite precursor petroleum coke constant, the particle size Dv50 of the graphite particles in the negative electrode active material increases with the increase of the amount of high-viscosity binder; the pore size of pore A remains basically unchanged, while the differential mercury ingress increases; the pore size and differential mercury ingress of pore B both increase. This may be because the pore size of pore A represents the packing voids between primary particles in the secondary particles, while the pore size of pore B mainly represents the voids caused by the packing between secondary particles. When the particle size of the primary particles remains constant, the size of their packing voids remains constant, therefore the pore size of pore A remains basically unchanged. As the binder content increases, more primary particles are composited within the secondary particles, resulting in a greater number of voids and an increased differential mercury ingress rate in pore A. The composite stability of the secondary particles improves, leading to larger particle sizes and increased voids and void quantities between particles. Consequently, the pore size and differential mercury ingress rate in pore B also increase. With increased binder content, the expansion between particles can be mutually suppressed, resulting in a lower cycle thickness expansion rate for lithium-ion batteries. However, as shown in Comparative Example 2, excessively high binder content reduces the specific capacity of the negative electrode active material, affecting its energy density.

[0134] As shown in Comparative Example 1, no high-viscosity binder was added during the preparation of the negative electrode active material. The negative electrode active material consisted of primary particles without the formation of secondary particles. Therefore, after cold pressing, the particles in the negative electrode active material layer were uniformly oriented and very tightly packed, with a small pore size (B) and low differential mercury ingress. This resulted in a high cycle thickness expansion rate for the lithium-ion battery and poor overall performance. As shown in Comparative Example 2, a higher content of high-viscosity binder was added during the preparation of the negative electrode active material. This resulted in a high degree of inter-particle composite, isotropic particle arrangement in the negative electrode film, and a larger pore size (B) between particles. This led to a high differential mercury ingress rate and a lower cycle thickness expansion rate for the lithium-ion battery. However, the poor lithium storage performance of the binder affected the specific capacity of the negative electrode active material. Furthermore, the larger particle size of the secondary particles affected the processing performance.

[0135] As can be seen from Examples 1-4, 5-8, 9-12 and 13-16, when the content of high-viscosity binder is constant, as the Dv50 of the petroleum coke precursor of the negative electrode active material increases, the pore size A and its differential mercury ingress in the negative electrode active material layer increase, while the pore size B and its corresponding differential mercury ingress decrease, the OI value increases, and the specific capacity increases, but the thickness expansion rate is affected.

[0136] Table 3 shows the effects of Dv90 and Dn10 of the negative electrode active material on the particle size ratio change (D1v50-D2v50) / D1v50, the specific surface area (BET) growth rate, the initial efficiency of the lithium-ion battery, and the cycle thickness expansion rate. The negative electrode active materials in Examples 17-32 were prepared from the negative electrode active material in Example 11. By adding sieving and classification processes to the negative electrode active material in Example 11, large particles and fine powders in the negative electrode active material were removed, thereby achieving particle size adjustment.

[0137] D1v50 is the particle size of the negative electrode active material before being subjected to pressure, and D2v50 is the particle size of the negative electrode active material after applying 1t of pressure. B1 is the specific surface area of ​​the negative electrode active material before being subjected to pressure, and B2 is the specific surface area after applying 1t of pressure.

[0138] The method for applying pressure to the negative electrode active material is as follows: Using an electronic pressure testing machine (Sansi Zongheng UTM7305), place 1.0±0.05g of negative electrode active material powder on a mold with a diameter of 13mm, apply a pressure of 1t to the negative electrode active material powder and hold for 5s, and remove the powder after releasing the pressure.

[0139] Table 3

[0140]

[0141]

[0142] Comparing Examples 17-20, 21-24, 25-28, and 29-32, the results show that when Dn10 remains constant and Dv90 decreases, the particle size ratio change (D1v50-D2v50) / D1v50 decreases, the surface area (BET) growth rate decreases, and the initial efficiency improves, but the cycle thickness expansion rate increases. Comparing Examples 17, 21, 25, 29; Examples 18, 22, 26, 30; Examples 19, 23, 27, 31; and Examples 20, 24, 28, 32, it can be seen that as Dn10 increases, the number of fine particles in the negative electrode decreases, the surface area (BET) growth rate increases significantly, the initial efficiency improves significantly, and the expansion is slightly improved.

[0143] Throughout this specification, references to "some embodiments," "partial embodiments," "one embodiment," "another example," "example," "specific example," or "partial example" mean that at least one embodiment or example in this application includes a specific feature, structure, material, or characteristic described in that embodiment or example. Therefore, descriptions appearing throughout this specification, such as "in some embodiments," "in an embodiment," "in one embodiment," "in another example," "in an example," "in a specific example," or "example," do not necessarily refer to the same embodiments or examples in this application. Furthermore, specific features, structures, materials, or characteristics described herein can be combined in any suitable manner in one or more embodiments or examples.

[0144] Although illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above embodiments should not be construed as limiting the present application, and that changes, substitutions and modifications can be made to the embodiments without departing from the spirit, principles and scope of the present application.

Claims

1. A negative electrode, comprising a current collector and a negative electrode active material layer located on the current collector, the negative electrode active material layer comprising negative electrode active material particles, the negative electrode active material particles comprising secondary particles, the negative electrode active material layer comprising pores A, wherein, when tested by mercury porosimetry, the pore size of pores A is 59 nm-73 nm, and the C004 / C110 value of the negative electrode active material layer is 6-20. The negative electrode active material particles have a particle size of D1v50 before being compressed, and a particle size of D2v50 after applying 1t of pressure, with (D1v50-D2v50) / D1v50×100%≤25%. The negative electrode active material layer includes pores B, the pore diameter of which is 660nm-800nm, and the volume ratio of pores B to pores A is 0.7:1-1.42:

1. Wherein, the pore diameters of pore A and pore B are the pore diameters corresponding to the two highest peaks in the differential mercury ingress curve, and the pore diameter of pore A is smaller than that of pore B; C004 and C110 represent the crystal plane areas of the 004 peak and 110 peak of the negative electrode active material layer as measured by XRD diffractometer, respectively.

2. The negative electrode according to claim 1, wherein the differential mercury inlet rate of pore A is 0.150-0.190 mL / g·μm. -1 .

3. The negative electrode according to claim 1, wherein the differential mercury inlet rate of pore B is 0.160-0.230 mL / g·μm. -1 .

4. The negative electrode according to claim 1, wherein the negative electrode active material particles satisfy at least one of conditions (a)-(d): (a) The Dv50 of the negative electrode active material particles is 7.2-21.6 μm; (b) The Dv90 of the negative electrode active material particles is 28.4-40.0 μm; (c) The Dn10 of the negative electrode active material particles is 1.4-9.4 μm; and (d) The Dv90 and Dn10 of the negative electrode active material particles satisfy: Dv90 / Dn10≤26.

5. The negative electrode according to claim 1, wherein the specific surface area of ​​the negative electrode active material particles is 0.8-2.0 m². 2 / g.

6. The negative electrode according to claim 1, wherein the specific surface area of ​​the negative electrode active material particles before being subjected to pressure is B1, and the specific surface area after applying 1t pressure is B2, and (B2-B1) / B1×100%≤140%.

7. An electrochemical device comprising a negative electrode according to any one of claims 1-6.

8. The electrochemical device according to claim 7, wherein when the electrochemical device discharges to a voltage of 3V, the specific surface area of ​​the negative electrode active material is 1.5-2.4m². 2 / g.

9. The electrochemical device according to claim 7, wherein when the electrochemical device is charged to a voltage of 4.45V, the maximum exothermic peak of the negative electrode active material layer is 280-330℃ when tested by DSC.

10. The electrochemical device according to claim 7, wherein the electrochemical device discharges to a voltage of 3V, and the particle size of the negative electrode active material particles is D. a v50, and the particle size of the negative electrode active material particles after applying a pressure of 1t is D. b v50, (D a v50-D b v50) / D a y50×100%≤2%.

11. The electrochemical device according to claim 7, wherein when the electrochemical device discharges to a voltage of 3V, the specific surface area of ​​the negative electrode active material particles before being subjected to pressure is B. 11 And the specific surface area after applying a pressure of 1t is B. 22 (B) 22 -B 11 ) / B 11 ×100%≤40%.

12. An electronic device comprising an electrochemical device as claimed in any one of claims 7-11.

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