Negative electrode material and negative electrode using same, electrochemical device, and electronic device

Abstract

The present application relates to a negative electrode material and a negative electrode using same, an electrochemical device, and an electronic device. Specifically, the present application provides a negative electrode material, comprising graphite. The I-stage lithium intercalation plateau potential P1 of the negative electrode material ranges from 30 mV to 75 mV, and the II-stage lithium intercalation plateau potential P2 ranges from 90 mV to 110 mV. According to the negative electrode material of the present application, the high-voltage and high-temperature cycle performance of an electrochemical device using the negative electrode material can be significantly improved, the gram capacity of the negative electrode material is improved, and the initial efficiency of the negative electrode material is also taken into account.

Description

Negative electrode material, negative electrode, electrochemical device, and electronic device using the same Technical Field

[0001] The present application relates to the field of energy storage, and in particular to a negative electrode material and a negative electrode, an electrochemical device, and an electronic device using the negative electrode material. Background Art

[0002] With the widespread use of electrochemical devices (e.g., lithium-ion batteries) in electronic products such as mobile phones, laptops, tablets, Bluetooth headsets, and wearable watches, people are increasingly demanding higher performance. The cycle life and energy density of lithium batteries are their most important performance indicators, significantly impacting the service life and lifespan of electronic products. Increasing voltage can help improve energy density, but the cycling performance of lithium-ion batteries deteriorates in high-voltage systems, especially at high temperatures.

[0003] In view of this, it is indeed necessary to provide an improved negative electrode material with enhanced specific capacity and the ability to significantly improve the cycle performance of electrochemical devices under high temperature and high pressure, while taking into account the initial efficiency of the negative electrode material.

[0004] Summary of the Invention

[0005] The present application attempts to solve at least one problem existing in the related art to at least some extent by providing a negative electrode material.

[0006] According to one aspect of the present application, the present application provides a negative electrode material comprising graphite, wherein the negative electrode material has a first-order lithium insertion platform potential P1 of 30 mV to 75 mV and a second-order lithium insertion platform potential P2 of 90 mV to 110 mV.

[0007] According to an embodiment of the present application, the negative electrode material has a first-order lithium insertion platform potential P1 of 30 mV to 60 mV and a second-order lithium insertion platform potential P2 of 90 mV to 100 mV.

[0008] According to the embodiment of the present application, the specific surface area of ​​the negative electrode material is S m 2 / g, the value range of S is 2 to 8.

[0009] According to an embodiment of the present application, the value range of S is 4 to 7.

[0010] According to an embodiment of the present application, the negative electrode material comprises pores having a pore diameter of no more than 5 nm, and the specific surface area of ​​the pores is S1 m 2 / g, and the ratio of S1 to S ranges from 0.05 to 0.3.

[0011] According to an embodiment of the present application, the ratio of S1 to S ranges from 0.15 to 0.3.

[0012] According to an embodiment of the present application, the value range of S1 is 0.1 to 1.5.

[0013] According to the embodiment of the present application, the negative electrode material is tested by Raman at 1350 cm -1 The peak intensity at 1580 cm is D, and the peak intensity at 1580 cm is D. -1 The peak intensity at is G, the ratio of D to G is R, 0.025≤R / S≤0.25.

[0014] According to an embodiment of the present application, 0.05≤R / S≤0.15.

[0015] According to an embodiment of the present application, 0.1≤R≤0.7.

[0016] According to an embodiment of the present application, 0.2≤R≤0.55.

[0017] According to an embodiment of the present application, the thermogravimetric decomposition temperature of the negative electrode material ranges from 650° C. to 850° C.;

[0018] According to the embodiment of the present application, the powder compaction density of the negative electrode material is 1.90 g / cm 3 to 2.10g / cm 3 , and the powder rebound rate is 15% to 35%.

[0019] According to another aspect of the present application, the present application provides a negative electrode, which includes the negative electrode material of the present application, a dispersant and a binder.

[0020] According to an embodiment of the present application, the porosity of the negative electrode is 17% to 35%.

[0021] According to another aspect of the present application, the present application provides an electrochemical device, which includes a positive electrode, a separator, an electrolyte, and the negative electrode according to the present application.

[0022] According to another aspect of the present application, an electronic device includes the electrochemical device according to the present application.

[0023] This application lowers the positive electrode potential to protect the stability of the positive electrode structure under high voltage systems, thereby increasing the gram capacity of the negative electrode material and improving the cycle performance of the electrochemical device under high temperature and high pressure, while taking into account the initial efficiency of the negative electrode material.

[0024] Additional aspects and advantages of the present application will be described, shown, or explained in part in the following description through implementation of the embodiments of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The following briefly describes the drawings necessary to describe the embodiments of the present application or the prior art to facilitate the description of the embodiments of the present application. Obviously, the drawings described below only represent some of the embodiments of the present application. Those skilled in the art can, without requiring creative effort, derive drawings for other embodiments based on the structures illustrated in these drawings.

[0026] FIG1 shows the discharge curves of Example 5 and Comparative Example 1 of the present application.

[0027] FIG2 shows the cycle life curves of Example 10 and Comparative Example 1 at 45° C. according to the present application. DETAILED DESCRIPTION

[0028] The embodiments of the present application will be described in detail below. The embodiments of the present application should not be interpreted as limiting the present application.

[0029] In the detailed description and claims, a list of items linked by the term "at least one of" can mean any combination of the listed items. For example, if items A and B are listed, 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, 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 can contain a single element or multiple elements. Item B can contain a single element or multiple elements. Item C can contain a single element or multiple elements.

[0030] Electrochemical devices (e.g., lithium-ion batteries) have been widely used in various fields due to their superior performance. People have increasingly higher requirements for their performance, such as energy density, high-temperature cycle performance, service life, and charging speed. To increase the energy density of lithium-ion batteries, the voltage system of lithium-ion batteries is constantly improving. However, under high-voltage systems, the positive electrode is at a high potential for a long time, making it difficult to maintain a high structural stability, thereby shortening the high-temperature cycle life of lithium-ion batteries.

[0031] The present application solves the above-mentioned problem by lowering the positive electrode potential. The open circuit voltage of the electrochemical device is equal to the positive electrode potential minus the negative electrode potential. The present application introduces a defective lithium insertion mechanism by surface modification of the negative electrode material to make it have defects, which will cause the I-order lithium insertion platform potential and the II-order lithium insertion platform potential of the negative electrode material to change. During the interlayer lithium insertion process, the negative electrode material will undergo phase change at different potentials as the lithium insertion degree increases, that is, each phase change will correspond to a lithium insertion platform. The phase transition process of forming LiC12 corresponds to the II-order lithium insertion platform, and the phase transition process of forming LiC6 corresponds to the I-order lithium insertion platform. When the negative electrode material has a microporous defect structure, the lithium insertion mechanism changes from interlayer lithium insertion to a common lithium insertion mechanism of interlayer lithium insertion and microporous defect adsorption and lithium storage. Therefore, the lithium insertion platform potential corresponding to the interlayer lithium insertion will also change accordingly, that is, the platform potential is reduced, and the degree of potential change is related to the content and proportion of microporous defects. Defective lithium insertion can reduce the negative electrode's lithium insertion potential, thereby lowering the positive electrode's potential. This can protect the stability of the positive electrode structure in high-voltage systems, thereby improving the cycling performance of electrochemical devices under high temperature and high pressure. At the same time, defective lithium insertion can increase the specific capacity of the negative electrode material while also taking into account the initial efficiency of the negative electrode material.

[0032] Specifically, the present application provides a negative electrode material, which includes graphite, and the negative electrode material has an I-order lithium insertion platform potential P1 of 30mV to 75mV and a II-order lithium insertion platform potential P2 of 90mV to 110mV. When P1 is greater than 75mV and P2 is greater than 115mV, the negative electrode lithium insertion potential is too high, and it is impossible to achieve the effect of lowering the positive electrode potential and improving the high-temperature cycle life of the electrochemical device. When P1 is less than 30mV and P2 is less than 90mV, the potential of the negative electrode is too low when it is close to full insertion, close to the nucleation potential of lithium, and it is easy to induce the formation of lithium dendrites, resulting in safety hazards in the electrochemical device. When P1 is 30mV to 75mV and P2 is 90mV to 110mV, not only can the specific capacity of the negative electrode material be improved, but the cycle performance of the electrochemical device under high temperature and high pressure can also be significantly improved, while taking into account the first efficiency of the negative electrode material.

[0033] In some embodiments, P1 is 30 mV to 60 mV, which can further improve the cycling performance of the electrochemical device under high temperature and high pressure.

[0034] In some embodiments, P2 is 90 mV to 100 mV, which can further improve the cycling performance of the electrochemical device under high temperature and high pressure.

[0035] In some embodiments, the terminal delithiation potential slope S0 of the negative electrode material is 2 mAh / g / V to 8 mAh / g / V. In some embodiments, S0 is 2 mAh / g / V to 5 mAh / g / V. The introduction of the defect lithium insertion mechanism will increase the terminal delithiation potential slope. The terminal delithiation potential slope can be calculated based on the lithium insertion curve obtained by plotting the discharge gram capacity and voltage of the negative electrode material. The terminal delithiation potential slope of the negative electrode material can reflect the first efficiency of the negative electrode material. The negative electrode material of the present application can still maintain a terminal delithiation potential slope that is basically equivalent to that of graphite without surface defect modification under a high voltage system. Therefore, the negative electrode material can maintain a higher first efficiency.

[0036] In some embodiments, the specific surface area of ​​the negative electrode material is S m 2 / g, S ranges from 2 to 8. In some embodiments, S ranges from 4 to 7. In some embodiments, S ranges from 5 to 6. In some embodiments, the specific surface area S m 2 / g is 2m 2 / g、3m 2 / g、4m 2 / g、5m 2 / g、6m 2 / g、7m 2 / g、8m 2 / g or a value within the range of any two of the above values. Introducing defects on the surface of the negative electrode material will form a porous structure, thereby increasing the specific surface area of ​​the negative electrode material. When the specific surface area of ​​the negative electrode material S m 2 When the ratio of lithium ions to niobium is within the above range, the negative electrode has a low-potential defect lithium insertion characteristic, thereby improving the gram capacity of the negative electrode material and the cycle performance of the electrochemical device under high temperature and high pressure. In addition, the reaction area between the negative electrode surface and the electrolyte is appropriate, which can avoid the occurrence of excessive side reactions and excessive consumption of the electrolyte, thereby taking into account the initial efficiency of the negative electrode material.

[0037] In some embodiments, the negative electrode material comprises pores having a pore diameter of no greater than 5 nm, and the specific surface area of ​​the pores is S1 m 2 / g, the ratio of S1 to S ranges from 0.05 to 0.3. In some embodiments, the ratio of S1 to S ranges from 0.15 to 0.3. In some embodiments, the ratio of S1 to S ranges from 0.2 to 0.25. In some embodiments, the ratio of S1 to S is 0.05, 0.1, 0.15, 0.2, 0.25, 0.3 or a value within the range formed by any two of the above values. The specific surface area of ​​pores with a pore size of not more than 5 nm refers to the sum of the specific surface areas of each pore with a pore size of not more than 5 nm. Pores with a pore size of not more than 5 nm can provide storage space for lithium ions, thereby improving the gram capacity of the negative electrode material and the cycle performance of the electrochemical device under high temperature and high pressure, while taking into account the first efficiency of the negative electrode material.

[0038] In some embodiments, the value range of S1 is 0.1 to 1.5, which can further increase the gram capacity of the negative electrode material. In some embodiments, the value range of S1 is 0.5 to 1.2. In some embodiments, S1m 2 / g is 0.8m 2 / g to 1m 2 / g. In some embodiments, S1m 2 / g is 0.1m 2 / g, 0.3m 2 / g, 0.5m 2 / g, 0.8m 2 / g, 1.0m 2 / g, 1.2m 2 / g, 1.5m 2 / g or a value within the range consisting of any two of the above values.

[0039] In some embodiments, the negative electrode material has a Raman wavelength of 1350 cm -1 The peak intensity at 1580 cm is D, and the peak intensity at 1580 cm is D. -1The peak intensity at the D peak is G, the ratio of D to G is R, and 0.025≤R / S≤0.25. In some embodiments, 0.05≤R / S≤0.15. In some embodiments, 0.08≤R / S≤0.1. In some embodiments, R / S is 0.025, 0.05, 0.08, 0.1, 0.15, 0.2, 0.25, or a value within the range of any two of the above values. The ratio R of the D peak to the G peak in the Raman spectrum can indicate the degree of defects on the surface of the material. The ratio R / S of the R value to the specific surface area S can indicate the proportion of defects per unit specific surface area. When R / S is within the above range, the negative electrode material contains appropriate defects per unit specific surface area, and the negative electrode has low-potential defect lithium insertion characteristics. At the same time, excessive consumption of the electrolyte can be avoided, thereby improving the specific capacity of the negative electrode material and the cycle performance of the electrochemical device under high temperature and high pressure, while taking into account the initial efficiency of the negative electrode material.

[0040] In some embodiments, 0.1≤R≤0.7. In some embodiments, 0.2≤R≤0.55. In some embodiments, 0.2≤R≤0.4. In some embodiments, R is 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7 or a value within the range formed by any two of the above values. Introducing defects on the surface of the graphite material increases the ratio R of the D peak to the G peak of the Raman spectrum. When R is within the above range, the negative electrode material has a low-potential defect lithium insertion characteristic, thereby improving the cycle performance of the electrochemical device under high temperature and high pressure, and avoiding the occurrence of excessive side reactions and excessive consumption of the electrolyte, thereby taking into account the gram capacity and first efficiency of the negative electrode material and the cycle performance and thermal shock safety performance of the electrochemical device under high temperature and high pressure.

[0041] In some embodiments, the thermogravimetric decomposition temperature of the negative electrode material is in the range of 650°C to 850°C. After defects are introduced on the surface of the negative electrode material, the surface reaction activity increases, thereby causing the negative electrode material to begin to decompose at a lower temperature. The thermogravimetric decomposition temperature of the negative electrode material can reflect the number of surface defects. When the thermogravimetric decomposition temperature of the negative electrode material is within the above range, the surface defects of the negative electrode material are appropriate, the surface has appropriate reactivity, and the increase in side reactions and excessive consumption of the electrolyte can be avoided, thereby improving the gram capacity of the negative electrode material and the cycle performance of the electrochemical device under high temperature and high pressure, while taking into account the initial efficiency of the negative electrode material.

[0042] In some embodiments, the powder compaction density of the negative electrode material is 1.90 g / cm 3 to 2.10g / cm 3 , and the powder rebound rate is 15% to 35%. In some embodiments, the powder compaction density of the negative electrode material is 1.90g / cm 3 Up to 2.00g / cm3 , and the powder rebound rate is 20% to 25%. When the negative electrode material is compacted under a certain pressure, powder rebound will occur after the pressure is released. When the negative electrode material has the above-mentioned higher powder compaction density, its powder rebound rate is lower, which is conducive to maintaining a higher compaction density of the negative electrode after the electrode is made, thereby improving the volume energy density of the electrochemical device, while not causing a sharp decrease in the pores inside the electrode and reducing the amount of electrolyte retained, thereby taking into account the cycle performance of the electrochemical device under high temperature and high pressure.

[0043] In some embodiments, the negative electrode has a gram capacity greater than or equal to 360 mAh / g as measured by a charge-discharge test.

[0044] In some embodiments, the first efficiency of the negative electrode material using the negative electrode material of the present application is 94% to 95%.

[0045] The present application also provides a negative electrode, which includes the negative electrode material described in the present application, a dispersant and a binder.

[0046] In some embodiments, the negative electrode has a porosity of 17% to 35%. In some embodiments, the negative electrode has a porosity of 20% to 30%. In some embodiments, the negative electrode has a porosity of 25% to 30%. In some embodiments, the negative electrode has a porosity of 17%, 20%, 22%, 25%, 28%, 30%, 32%, 35%, or a value within a range consisting of any two of the foregoing values. When the negative electrode porosity is within the above range, the cycling performance of the electrochemical device under high temperature and high pressure can be improved.

[0047] In some embodiments, the negative electrode binder includes at least one of styrene-butadiene rubber, polyacrylic acid, polyacrylate, polyimide, polyamide-imide, polyvinylidene fluoride, polyvinylidene fluoride, polytetrafluoroethylene, water-based acrylic resin, polyvinyl formal, or styrene-acrylic copolymer resin.

[0048] In some embodiments, any conductive material can be used as the negative electrode conductive material as long as it does not cause chemical changes. In some embodiments, the negative electrode conductive material includes at least one of conductive carbon black, acetylene black, carbon nanotubes, Ketjen black, conductive graphite, or graphene.

[0049] In some embodiments, the negative electrode includes a negative electrode current collector, which can be copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, or a combination thereof.

[0050] The present application also provides an electrochemical device, which includes a positive electrode, a separator, an electrolyte and the negative electrode according to the present application.

[0051] In some embodiments, the positive electrode includes a positive electrode active material layer and a positive electrode current collector.

[0052] In some embodiments, the positive electrode active material layer includes a positive electrode active material, a positive electrode binder, and a positive electrode conductor.

[0053] In some embodiments, the positive electrode active material may include at least one of lithium cobaltate, lithium nickel manganese cobaltate, lithium nickel manganese aluminum oxide, lithium iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium iron silicate, lithium vanadium silicate, lithium cobalt silicate, lithium manganese silicate, spinel lithium manganese oxide, spinel lithium nickel manganese oxide, or lithium titanate.

[0054] In some embodiments, the positive electrode binder may include a binder polymer such as, but not limited to, at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyolefins, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, modified polyvinylidene fluoride, modified SBR rubber, or polyurethane.

[0055] In some embodiments, any conductive material can be used as the positive electrode conductive agent, as long as it does not cause chemical changes. Examples of positive electrode conductive agents include, but are not limited to, carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.; metal-based materials such as metal powders or metal fibers including copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0056] In some embodiments, the positive electrode current collector can be a metal foil or a composite current collector. For example, aluminum foil can be used. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer substrate.

[0057] There is no particular limitation on the material and shape of the isolation membrane used in the electrochemical device of the present application, and it may be any technology disclosed in the prior art. In some embodiments, the isolation membrane includes a polymer or inorganic substance formed from a material that is stable to the electrolyte of the present application. In some embodiments, the isolation membrane may include a substrate layer and a surface treatment layer. In some embodiments, the substrate layer is a non-woven fabric, a film or a composite film having a porous structure. In some embodiments, the material of the substrate layer includes at least one of polyethylene, polypropylene, polyethylene terephthalate and polyimide. In some embodiments, the material of the substrate layer includes at least one of a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene non-woven fabric, a polyethylene non-woven fabric or a polypropylene-polyethylene-polypropylene porous composite membrane.

[0058] In some embodiments, a surface treatment layer is provided 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 a polymer and an inorganic layer.

[0059] In some embodiments, the inorganic layer includes inorganic particles and a binder, wherein the inorganic particles are selected from at least one of aluminum oxide, 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 at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyethylene alkoxide, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene.

[0060] In some embodiments, the polymer layer comprises a polymer, and the material of the polymer is selected from at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyethylene alkoxide, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0061] The electrochemical device of the present application further comprises an electrolyte. The electrolyte that can be used in the present application can be an electrolyte known in the prior art.

[0062] In some embodiments, the electrolyte includes an organic solvent, an electrolyte salt and an optional additive. The organic solvent of the electrolyte according to the present application may be any organic solvent known in the prior art that can be used as a solvent for the electrolyte. There is no restriction on the electrolyte used in the electrolyte according to the present application, and it may be any electrolyte known in the prior art. The additive of the electrolyte according to the present application may be any additive known in the prior art that can be used as an electrolyte additive. 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. In some embodiments, the organic solvent includes an ether solvent, for example, including at least one of 1,3-dioxolane (DOL) and ethylene glycol dimethyl ether (DME). In some embodiments, the electrolyte salt may be a lithium salt, a sodium salt, etc. In some embodiments, the lithium salt includes at least one of an organic lithium salt or an inorganic lithium salt. 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(oxalatoborate) LiB(C2O4)2 (LiBOB), or lithium difluorooxalatoborate LiBF2(C2O4) (LiDFOB). In some embodiments, the sodium salt includes, but is not limited to, at least one of NaClO4, NaPF6, NaBF4, Na(FSO2)2N, Na(CF3SO2)2N, Na(C2F5SO2)2N, NaCF3SO3, NaSbF6, NaBC4O8, NaFSI, NaTFSI, sodium salts of lower aliphatic carboxylates, NaAlCl4, NaPO2F2, or Na2PO3F.

[0063] In some embodiments, the electrochemical device of the present application includes, but is not limited to, all types of primary batteries, secondary batteries, or capacitors. In some embodiments, the electrochemical device is a lithium secondary battery. 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. In some embodiments, the electrochemical device is a sodium ion battery.

[0064] The present application further provides an electronic device, which includes the electrochemical device according to the present application.

[0065] The electronic devices or devices of the present application are not particularly limited. In some embodiments, the electronic devices of the present application include, but are 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.

[0066] The preparation process of electrochemical devices and electronic devices is well known to those skilled in the art and is not particularly limited in this application. For example, the battery can be prepared by the following method: the positive electrode and the negative electrode are overlapped via an isolation membrane, and are wound, folded, and the like as needed to form a bare cell. Stainless steel is selected as the packaging shell, and the bare cell is placed inside the packaging shell. The aluminum tabs of the bare cell and the poles in the sealing assembly are laser welded together to achieve electronic conduction between the poles and the bare cell. The steel shell cover and the shell are connected by laser welding to achieve sealing of the battery. There are through holes on the surface of the steel shell, and the electrolyte is injected into the interior of the cell through the through holes. After sufficient infiltration, the cell is activated under certain current and voltage conditions, and the preparation of the battery is completed.

[0067] The preparation of lithium-ion batteries is described below using lithium-ion batteries as an example and in combination with specific embodiments. 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.

[0068] Example

[0069] The following describes the performance evaluation of the lithium-ion battery according to the embodiments and comparative examples of the present application.

[0070] 1. Preparation of lithium-ion batteries

[0071] 1. Preparation of negative electrode materials

[0072] Artificial graphite was used as a raw material and placed in an atmosphere furnace. A water vapor / air mixture was introduced at a flow rate of F. Three constant temperature reactions were performed in this atmosphere: the first reaction was at a temperature of T1 for 1 hour, the second reaction was at a temperature of T2 for 2 hours, and the third reaction was at a temperature of T3 for 3 hours. After the reaction was completed, the reaction was naturally cooled to room temperature to obtain a negative electrode material. The reaction conditions of the various examples and comparative examples are shown in the following table, where comparative example 1 is unreacted graphite:

[0073] 2. Preparation of negative electrode

[0074] The negative electrode material, sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) were evenly dispersed in an appropriate amount of deionized water at a mass ratio of 97.5:1.2:1.3 to produce a negative electrode slurry. Using copper foil as the current collector, the negative electrode slurry was evenly coated on the current collector. After coating, the negative electrode was dried and cold-pressed to produce the negative electrode.

[0075] 3. Preparation of positive electrode

[0076] Lithium cobalt oxide (chemical formula: LiCoO2) is used as the positive electrode active material, and is thoroughly stirred and mixed with a conductive agent, acetylene black, and a binder, polyvinylidene fluoride (abbreviated as PVDF), in a proper amount of N-methylpyrrolidone (abbreviated as NMP) solvent at a weight ratio of 96.3:2.2:1.5 to form a uniform positive electrode slurry. The positive electrode slurry is coated on the current collector aluminum foil, and after coating, it is dried and cold pressed to obtain the positive electrode.

[0077] 4. Preparation of electrolyte

[0078] In a dry argon atmosphere glove box, ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a mass ratio of EC:PC:EMC:DEC = 1:3:3:3. Fluorinated ethylene carbonate and 1,3-propane sultone were then added, dissolved, and thoroughly stirred. Lithium salt LiPF6 was then added and mixed thoroughly to obtain an electrolyte. The mass percentage of LiPF6 was 12.5%, the mass percentage of fluoroethylene carbonate was 2%, and the mass percentage of 1,3-propane sultone was 2%. The mass percentages of each substance were calculated based on the mass of the electrolyte.

[0079] 5. Preparation of isolation membrane

[0080] A polyethylene porous polymer film is used as the separator.

[0081] 6. Preparation of lithium-ion batteries

[0082] The positive electrode, separator, and negative electrode are stacked in order, with the separator placed between the positive and negative electrodes to serve as an isolation, and then wound to obtain an electrode assembly; after welding the tabs, the electrode assembly is placed in an outer packaging foil aluminum-plastic film, and the prepared electrolyte is injected into the dried electrode assembly. After vacuum packaging, standing, formation, shaping, capacity testing and other processes, a soft-pack lithium-ion battery is obtained.

[0083] 2. Test Method

[0084] 1. Testing of negative electrode materials

[0085] Take a fully discharged lithium-ion battery, disassemble it, remove the negative electrode, soak it in ethylene carbonate (DMC) for 20 minutes, then rinse it with DMC and acetone in turn to remove the electrolyte and the surface SEI film. Then, place it in an oven and bake it at 80°C for 12 hours to obtain the treated negative electrode. Then, scrape the powder on the negative electrode with a scraper and bake it at 500°C in an air atmosphere for 3 hours to remove the CMC and SBR contained in the powder to obtain the negative electrode material. The obtained negative electrode material was tested as follows:

[0086] (1) Lithium embedded platform potential test

[0087] The negative electrode material, SBR, CMC, and conductive carbon were mixed in a weight ratio of 93:2.5:2.5:2 in an appropriate amount of deionized water and thoroughly stirred to form a uniform negative electrode slurry. This negative electrode slurry was coated on a current collector copper foil, dried, and cold pressed to produce the negative electrode.

[0088] The prepared negative electrode was used as the positive electrode of a button cell and assembled with a lithium sheet, the separator prepared above, the electrolyte prepared above, a steel sheet, nickel foam, and a button cell case to form a button cell. The cell was then left to stand for 6 hours. The assembled button cell was placed on a blue battery tester and subjected to two cycles of charge and discharge testing according to the following process:

[0089] 1) Set aside for 5 minutes;

[0090] 2) 0.05C discharge to 5mV;

[0091] 3) Set aside for 5 minutes;

[0092] 4) 0.05mA discharge to 5mV;

[0093] 5) Set aside for 5 minutes;

[0094] 6) 0.01mA discharge to 5mV;

[0095] 7) Set aside for 5 minutes;

[0096] 8) 0.1C charge to 2V;

[0097] 9) Set aside for 5 minutes.

[0098] After the test, the lithium insertion curve of the material is obtained by plotting the second cycle discharge capacity and voltage. The I-order lithium insertion platform potential and the II-order lithium insertion platform potential of the negative electrode material can be read out through the lithium insertion curve.

[0099] (2) Terminal delithiation potential slope test

[0100] According to the same method as "(1) Lithium insertion platform potential test", the delithiation curve of the material is obtained by plotting the gram capacity and voltage of the second cycle of charging. The gram capacity corresponding to the potential of 2V is recorded as Cap2, and the gram capacity corresponding to the potential of 1V is recorded as Cap1. The delithiation terminal potential slope S0 (unit is mAh / g / V) is calculated by the following formula: S0 = (Cap2-Cap1) / (2V-1V)mAh / g / V.

[0101] (3) Gram capacity test

[0102] According to the same method as “(1) Lithium Insertion Platform Potential Test”, the gram capacity of the negative electrode material is obtained by dividing the first cycle charging capacity corresponding to 1.0 V by the weight of the negative electrode material.

[0103] (4) First efficiency test

[0104] According to the same method as “(1) Lithium Insertion Platform Potential Test”, the first efficiency of the negative electrode material is calculated by dividing the first cycle charge capacity by the first cycle discharge capacity.

[0105] (5) Specific surface area test

[0106] Weigh 20g to 30g of negative electrode material and press it into tablets. After pressing, weigh 1.5g to 3.5g and put it into the test sample tube. Degas the sample at 200℃ for 2 hours, then pass high-purity nitrogen gas into the sample to make it stand at liquid nitrogen temperature and relative pressure of 10 -6 Nitrogen was adsorbed under conditions of 10 torr until saturation. A N2 adsorption-desorption curve was obtained using testing software. The resulting N2 adsorption-desorption curve was processed according to the BET model to obtain the specific surface area of ​​the negative electrode material. The pore size distribution curve was then extracted according to the BJH model. The integrated area of ​​the curve within a range of no more than 5 nm represents the specific surface area of ​​pores with a pore size of no more than 5 nm.

[0107] (6) Powder compaction density and powder rebound rate test

[0108] Weigh m grams of negative electrode material and place it into a test mold. The mold bottom area is recorded as S. The material is compacted with 5 tons of pressure. The filling height after the material is compressed is recorded as H1. The pressure is then released and the filling height after the material rebounds is recorded as H2. This is calculated using the following formulas: Powder compaction density = m / (S × H1), Powder rebound rate = (1-H1 / H2) × 100%.

[0109] 2. Testing of the cycling performance of lithium-ion batteries under high temperature and high pressure

[0110] The lithium-ion battery is subjected to a charge and discharge cycle test at 45°C according to the following process:

[0111] 1) Set aside for 30 minutes;

[0112] 2) 1C charge to 4.48V, constant voltage to 0.05C;

[0113] 3) Set aside for 10 hours;

[0114] 4) 1C discharge to 3.0V;

[0115] 5) Set aside for 30 minutes;

[0116] 6) Repeat steps 2)-5) 200 times;

[0117] 7) 1C charge to 4.45V, constant voltage to 0.05C;

[0118] 8) Set aside for 10 hours;

[0119] 9) 1C discharge to 3.0V;

[0120] 10) Set aside for 30 minutes;

[0121] 11) Repeat steps 7) to 10) until the battery capacity retention rate decays to 80%. The number of cycles recorded is the cycle life of the lithium-ion battery under high temperature and high pressure.

[0122] 3. Test Results

[0123] Table 1 shows the I-order lithium insertion platform potential and II-order lithium insertion platform potential, gram capacity and first efficiency of the negative electrode material, as well as the cycling performance of lithium-ion batteries under high temperature and high pressure.

[0124] Table 1

[0125] The negative electrode material in Comparative Example 1 had an untreated surface, resulting in high I-order and II-order lithium insertion plateau potentials. While the negative electrode material had a high initial efficiency, its specific capacity was low, and the cycle life of the lithium-ion battery under high temperature and high pressure was short. The surface of the negative electrode material in Comparative Example 2 was modified, resulting in excessively low I-order and II-order lithium insertion plateau potentials. Although the cycle life of the lithium-ion battery under high temperature and high pressure was increased, the specific capacity and initial efficiency of the negative electrode material were low.

[0126] After surface modification, the negative electrode materials of Examples 1-10 have a first-order lithium insertion plateau potential of 30mV to 75mV and a second-order lithium insertion plateau potential of 90mV to 110mV. These negative electrode materials exhibit significantly improved specific capacity and significantly extend the cycle life of lithium-ion batteries under high temperature and high pressure conditions, while also maintaining a high initial efficiency. Figure 1 shows the discharge curves of Example 5 and Comparative Example 1, demonstrating that Example 5 has lower first-order and second-order lithium insertion plateau potentials than Comparative Example 1.

[0127] FIG2 shows the cycle life curves of Example 10 and Comparative Example 1. The results show that the cycle life of Example 10 is significantly longer than that of Comparative Example 1.

[0128] Table 2 shows the effect of the specific surface area of ​​the negative electrode material on its specific capacity and initial efficiency, as well as the cycling performance of the lithium-ion battery under high temperature and high pressure. Except for the parameters listed in Table 2, the other parameters of Examples 11-17 are consistent with those of Example 9.

[0129] Table 2

[0130] The results show that when the specific surface area of ​​the negative electrode material S m 2 / g is 2m 2 / g to 8m 2 / g and / or when the ratio of the specific surface area S1 of pores with a pore diameter of no more than 5 nm to S is in the range of 0.05 to 0.3, the gram capacity of the negative electrode material can be further improved, the cycle life of the lithium-ion battery under high temperature and high pressure can be increased, and the high initial efficiency of the negative electrode material can be taken into account. 2 / g is 4m 2 / g to 7m 2 When the ratio of S1 to S is in the range of 0.15 to 0.3, more excellent effects can be obtained.

[0131] Table 3 shows the effects of the ratio R of the D peak to the G peak and its ratio R / S to the S peak, obtained from Raman spectroscopy, on the specific capacity and initial efficiency of the negative electrode material, as well as the cycling performance of the lithium-ion battery under high temperature and high pressure. Except for the parameters listed in Table 3, the other parameters of Examples 18-22 were consistent with those of Example 12.

[0132] Table 3

[0133] Results show that when the R / S ratio ranges from 0.025 to 0.25, the specific capacity of the negative electrode material can be further increased, extending the cycle life of lithium-ion batteries under high temperature and high pressure, while also maintaining a high initial efficiency of the negative electrode material. Even better results are achieved when the R / S ratio ranges from 0.05 to 0.15.

[0134] When R is in the range of 0.1 to 0.7, the specific capacity of the negative electrode material can be further increased, extending the cycle life of the lithium-ion battery under high temperature and high pressure, while also ensuring high initial efficiency of the negative electrode material. When R is in the range of 0.2 to 0.55, even better results can be achieved.

[0135] Table 4 shows the effects of the powder compaction density and powder rebound rate of the negative electrode material and the porosity of the negative electrode on the cycling performance of lithium-ion batteries under high temperature and high pressure. Except for the parameters listed in Table 4, the other parameters of Examples 23-29 are consistent with those of Example 21.

[0136] Table 4

[0137] The results show that when the compacted density of the negative electrode material powder is 1.90 g / cm 3 to 2.10g / cm 3 When the powder rebound rate is 15% to 35%, the cycle life of lithium-ion batteries under high temperature and high pressure can be further improved.

[0138] When the porosity of the negative electrode is 17% to 35%, the cycle life of the lithium-ion battery under high temperature and high pressure can be further improved.

[0139] References throughout this specification to "an embodiment," "part of an embodiment," "one embodiment," "another example," "an example," "a specific example," or "a portion of an example" mean that at least one embodiment or example in this application includes the specific features, structures, materials, or characteristics 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 "an example," are not necessarily references to the same embodiment or example in this application. In addition, the specific features, structures, materials, or characteristics described herein may be combined in any suitable manner in one or more embodiments or examples.

[0140] Although illustrative embodiments have been shown and described, those skilled in the art should understand that the above embodiments should not be construed as limitations on the present application, and that changes, substitutions, and modifications may be made to the embodiments without departing from the spirit, principles, and scope of the present application.

Claims

1. A negative electrode material comprising graphite, wherein the negative electrode material has a first-order lithium insertion platform potential P1 of 30 mV to 75 mV and a second-order lithium insertion platform potential P2 of 90 mV to 110 mV.

2. The negative electrode material according to claim 1, wherein the specific surface area of ​​the negative electrode material is S m 2 / g, the value range of S is 2 to 8.

3. The negative electrode material according to claim 2, wherein the negative electrode material has pores with a pore diameter of no greater than 5 nm, and the specific surface area of ​​the pores is S1 m 2 / g, the ratio of S1 to S ranges from 0.05 to 0.

3.

4. The negative electrode material according to claim 3, wherein the negative electrode material satisfies at least one of the following: (1) The value range of S is 4 to 7; (2) The value range of S1 is 0.1 to 1.5; (3) The ratio of S1 to S ranges from 0.15 to 0.

3. 5 . The negative electrode material according to claim 1 , wherein the I-stage lithium insertion platform potential P1 is 30 mV to 60 mV and the II-stage lithium insertion platform potential P2 is 90 mV to 100 mV.

6. The negative electrode material according to claim 2, wherein the negative electrode material has a Raman wavelength of 1350 cm -1 The peak intensity at 1580 cm -1 The peak intensity at is G, the ratio of D to G is R, 0.025≤R / S≤0.

25.

7. The negative electrode material according to claim 6, wherein the negative electrode material satisfies at least one of the following conditions: (1)0.1≤R≤0.7； (2)0.05≤R / S≤0.

15. The negative electrode material according to claim 6 , wherein 0.2≤R≤0.

55.

9. The negative electrode material according to claim 1, wherein the negative electrode material satisfies at least one of the following conditions: (1) The thermal gravimetric decomposition temperature of the negative electrode material is in the range of 650°C to 850°C; (2) The powder compaction density of the negative electrode material is 1.90 g / cm 3 Up to 2.10g / cm 3 , and the powder rebound rate is 15% to 35%. 10 . A negative electrode comprising the negative electrode material according to claim 1 , a dispersant and a binder. 11 . The negative electrode according to claim 10 , wherein the porosity of the negative electrode is 17% to 35%. 12 . An electrochemical device comprising a positive electrode, a separator, an electrolyte and the negative electrode according to claim 10 or 11 .

13. An electronic device comprising the electrochemical device according to claim 12.

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