Secondary battery and electric device

Abstract

The invention relates to the technical field of batteries, in particular to a secondary battery and an electric device. The secondary battery comprises a positive pole piece and a negative pole piece, the positive pole piece comprises a positive active material, and the negative pole piece comprises a negative active material; wherein the positive electrode active material comprises a manganese element, and the negative electrode active material comprises graphite particles and a hard carbon material layer coating the surfaces of the graphite particles. According to the secondary battery provided by the invention, the hard carbon material is of a short-range ordered and long-range disordered graphite-like microcrystalline structure, has a large number of defects and micropores, and can selectively adsorb manganese ions, so that the manganese ions enter the hard carbon material layer in the negative electrode active material of the negative electrode plate after being dissolved out from the positive electrode plate; the deposition of manganese ions on the surface of the negative electrode is avoided, and the decomposition and regeneration speed of the SEI membrane catalyzed by the manganese ions is slowed down, so that the consumption of electrolyte is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and particularly to a secondary battery and an electrical device using the same. Background Art

[0002] In recent years, secondary batteries have been widely used in energy storage power systems such as hydroelectric, thermal, wind, and solar power stations, as well as in many fields such as power tools, electric bicycles, electric motorcycles, and electric vehicles.

[0003] Due to the rich reserves and low price of manganese, manganese-containing cathodes such as lithium manganate, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, and lithium iron manganese phosphate have relatively low maintenance costs, and thus have become a research hotspot.

[0004] However, due to the structural deformation caused by the Jahn-Teller effect in manganese-containing cathodes, manganese ions are likely to dissolve during the charge and discharge cycles of the battery. The dissolved manganese ions continuously catalyze the decomposition and regeneration of the SEI film on the surface of the negative electrode, resulting in a large consumption of the electrolyte, and further affecting the cycle performance of the battery. Summary of the Invention

[0005] Based on this, it is necessary to provide a secondary battery and an electrical device using the same, which can inhibit the deposition of manganese ions on the surface of the negative electrode from damaging the SEI film, reduce the side reaction between the negative electrode active material and the electrolyte, and improve the cycle performance of the battery.

[0006] In a first aspect of the present application, a secondary battery is provided. The secondary battery includes a positive electrode plate and a negative electrode plate. The positive electrode plate includes a positive electrode active material, and the negative electrode plate includes a negative electrode active material. Among them, the positive electrode active material includes manganese, and the negative electrode active material includes graphite particles and a hard carbon material layer coated on the surface of the graphite particles.

[0007] In some embodiments, the thickness of the hard carbon material layer is 0.1 μm to 10 μm.

[0008] In some embodiments, the porosity of the hard carbon material layer is 50% to 80%.

[0009] In some embodiments, a solid electrolyte layer is provided between the graphite particles and the hard carbon material layer.

[0010] In some embodiments, the thickness of the solid electrolyte layer is 0.1 μm to 1 μm.

[0011] In some embodiments, the particle size D v 50 of the negative electrode active material is 5 μm to 20 μm.

[0012] In some embodiments, the positive electrode active material includes one or more of lithium manganate, lithium manganese iron phosphate, lithium nickel manganate, and lithium-rich manganese-based materials.

[0013] In some embodiments, the negative electrode sheet includes: a negative electrode current collector; and a negative electrode active material layer, the negative electrode active material layer including a negative electrode active material, a negative electrode conductive agent, and a negative electrode binder.

[0014] In some embodiments, in the negative electrode active material layer, the mass percentage of the negative electrode active material is 94% - 96%, the mass percentage of the negative electrode conductive agent is 2% - 3.2%, and the mass percentage of the negative electrode binder is 2% - 2.8%.

[0015] The second aspect of the present application provides an electrical device, which includes the secondary battery provided in the first aspect above.

[0016] Compared with the traditional technology, the present application has at least the following beneficial effects:

[0017] For the secondary battery provided in the present application, by adopting a structure of graphite particles and a hard carbon material layer coated on the surface thereof in the negative electrode active material, on the one hand, since the hard carbon material has a graphite-like microcrystalline structure with short-range order and long-range disorder, and has a large number of defects and micropores, it can selectively adsorb manganese ions. Therefore, after the manganese ions dissolve out from the positive electrode sheet, they enter the hard carbon material layer inside the negative electrode active material of the negative electrode sheet, avoiding the deposition of manganese ions on the negative electrode surface and slowing down the rate of manganese ion-catalyzed SEI film decomposition and regeneration, thereby reducing the consumption of the electrolyte; and the negative electrode active material has strong reducibility, and the manganese ions are reduced in the micropores, so that the manganese ions are confined in the micropores, further avoiding the side effects of manganese ions on the negative electrode surface; on the other hand, the hard carbon material layer is coated on the surface of the graphite particles, which can protect the graphite particles from directly contacting with the electrolyte to generate side reactions, improve the mechanical stability of the negative electrode active material while maintaining good electrical conductivity, and thus improve the cycle performance of the battery.

[0018] In addition, the core-shell structure composed of graphite particles and the hard carbon material layer has a good synergistic effect. The graphite particles can provide a good conductive substrate and have a working potential matching the manganese-based positive electrode, which is beneficial to improving the energy density of the battery. Combined with the adsorption and protection effects of the hard carbon material, the electrochemical performance of the manganese-based positive electrode applied to the secondary battery is jointly improved. Specific Embodiments

[0019] Reference will now be made in detail to embodiments of the present application, one or more examples of which are described below. Each example is provided by way of explanation and not limitation of the present application. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made to the present application without departing from the scope or spirit of the present application. For example, features illustrated or described as part of one embodiment can be used in another embodiment to yield a still further embodiment.

[0020] Accordingly, it is intended that the present application cover such modifications and variations that fall within the scope of the appended claims and their equivalents. Other objects, features, and aspects of the present application are disclosed in the following detailed description or are apparent therefrom. Those of ordinary skill in the art should understand that this discussion is only a description of exemplary embodiments and is not intended to limit the broader aspects of the present application.

[0021] In the present application, among the technical features described in an open-ended manner, there are included closed technical solutions composed of the listed features, as well as open technical solutions containing the listed features.

[0022] In the present application, regarding numerical ranges, unless otherwise specified, the above numerical ranges are considered continuous and include the minimum and maximum values of the range, as well as each value between such minimum and maximum values. Further, when the range refers to integers, it includes each integer between the minimum and maximum values of the range. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all sub-ranges subsumed therein.

[0023] If there is no special instruction, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

[0024] If there is no special instruction, all technical features and optional technical features of the present application can be combined with each other to form new technical solutions.

[0025] If there is no special instruction, all steps of the present application can be carried out sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method can include steps (a) and (b) carried out sequentially, or can also include steps (b) and (a) carried out sequentially. For example, it is mentioned that the method may further include step (c), which means that step (c) can be added to the method in any order. For example, the method can include steps (a), (b), and (c), or can also include steps (a), (c), and (b), or can also include steps (c), (a), and (b), etc.

[0026] Unless otherwise specified, the terms "comprising" and "including" mentioned in this application are open-ended and can also be closed-ended. For example, the terms "comprising" and "including" can mean that other components not listed may also be included or comprised, or it can only include or comprise the listed components.

[0027] Unless otherwise specified, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) while B is true (or exists); or both A and B are true (or exist).

[0028] The first aspect of this application provides a secondary battery, which includes a positive electrode plate and a negative electrode plate. The positive electrode plate includes a positive electrode active material, and the negative electrode plate includes a negative electrode active material. Among them, the positive electrode active material includes manganese element, and the negative electrode active material includes graphite particles and a hard carbon material layer coated on the surface of the graphite particles.

[0029] For the secondary battery provided by this application, by adopting the structure of graphite particles and a hard carbon material layer coated on its surface in the negative electrode active material, on the one hand, since the hard carbon material has a graphite-like microcrystalline structure with short-range order and long-range disorder, and has a large number of defects and micropores, it can selectively adsorb manganese ions. Therefore, after the manganese ions dissolve out from the positive electrode plate, they enter the hard carbon material layer inside the negative electrode active material of the negative electrode plate, avoiding the deposition of manganese ions on the negative electrode surface, slowing down the rate of manganese ion-catalyzed SEI film decomposition and regeneration, and thus reducing the consumption of the electrolyte; and the negative electrode active material has strong reducibility, and the manganese ions are reduced in the micropores, so that the manganese ions are confined in the micropores, further avoiding the side effects of manganese ions on the negative electrode surface. On the other hand, the hard carbon material layer is coated on the surface of the graphite particles, which can protect the graphite particles from directly contacting the electrolyte to generate side reactions, improve the mechanical stability of the negative electrode active material while maintaining good electrical conductivity, and thus improve the cycle performance of the battery.

[0030] In addition, the core-shell structure composed of graphite particles and the hard carbon material layer has good synergistic effects. The graphite particles can provide a good conductive substrate and have a working potential matching the manganese-based positive electrode, which is beneficial to improving the energy density of the battery. Combined with the adsorption and protection effects of the hard carbon material, it jointly improves the electrochemical performance of the manganese-based positive electrode applied to the secondary battery.

[0031] It can be understood that the amorphous pores of the hard carbon material can selectively adsorb manganese ions. At the same time, since the ionic radius of manganese ions is much larger than that of lithium ions, the micropore adsorption effect of the hard carbon material layer will not affect the insertion and extraction of lithium ions.

[0032] This application places no restrictions on the hard carbon materials in the hard carbon material layer. For example, the hard carbon material layer includes hard carbon materials prepared using one or more of phenolic resin, furfural resin, epoxy resin, glucose, sucrose, coconut shell, cyclodextrin, starch, and styrene-butadiene rubber as carbonization precursors.

[0033] In some embodiments, the thickness of the hard carbon material layer is 0.1 μm to 10 μm. Exemplarily, the thickness of the hard carbon material layer can be, but is not limited to, 0.1 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm. Within the above thickness range, while ensuring the effective adsorption of manganese ions by the hard carbon layer and the surface protection of graphite particles, the problem of extended lithium ion diffusion path or decreased conductivity caused by an overly thick hard carbon layer is avoided, and at the same time, insufficient adsorption capacity or weakened protection effect caused by an overly thin hard carbon layer is prevented, further improving the cycle stability and energy efficiency of the battery.

[0034] In some embodiments, the porosity of the hard carbon material layer is 50% to 80%. Exemplarily, the porosity of the hard carbon material layer can be, but is not limited to, 50%, 55%, 60%, 65%, 70%, 75%, 80%. Within the above porosity range, sufficient microporous structures are provided to efficiently adsorb and confine manganese ions, and reasonable pore connectivity is maintained to promote electrolyte penetration and rapid lithium ion deintercalation / insertion, avoiding a decrease in mechanical strength caused by too high porosity or insufficient adsorption capacity caused by too low porosity, thereby enhancing the rate performance and cycle life of the battery.

[0035] In some embodiments, a solid electrolyte layer is provided between the graphite particles and the hard carbon material layer. In this way, the solid electrolyte layer forms a transition interface between the graphite and the hard carbon material layer, blocking the further migration of manganese ions from the hard carbon material layer to the graphite particles. In addition, the solid electrolyte layer can provide a fast and stable ion transport channel, reduce the interfacial impedance, and improve the rate performance of the battery.

[0036] In some embodiments, the thickness of the solid electrolyte layer is 0.1 μm to 1 μm. Exemplarily, the thickness of the solid electrolyte layer can be, but is not limited to, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm. Within the above thickness range, the solid electrolyte layer can both form a suitable transition interface to inhibit manganese ion diffusion and maintain a low interfacial impedance and an efficient ion conduction path, thereby synergistically enhancing the interfacial stability, rate performance, and cycle life of the battery.

[0037] This application does not limit the type of solid electrolyte in the solid electrolyte layer, which can be either an organic solid electrolyte or an inorganic solid electrolyte.

[0038] In some preferred embodiments, the solid electrolyte is an inorganic solid electrolyte, and the inorganic solid electrolyte is selected from one or more of oxide solid electrolytes, sulfide solid electrolytes, and halide solid electrolytes.

[0039] In some embodiments, the oxide solid electrolyte includes at least one of garnet-type lithium lanthanum zirconium oxide (LLZO), NASICON-type, and LISICON-type.

[0040] The NASICON-type oxide solid electrolyte is AM′M″P 3 O 12 The molecular formula is sodium superionic conductor. In the molecular formula, A is usually a monovalent transport cation, such as at least one alkali metal ion including Na, K, Li, etc. The M′ and M″ positions can be either divalent or trivalent cations (such as at least one of Zn 2+ 、Mg 2+ 、Ni 2+ 、Cr 3+ 、Al 3+ 、Sc 3+ 、Fe 3+ 、In 3+ and Y 3+ etc.), or can be tetravalent or pentavalent cations (such as at least one of Ti 4+ 、Zr 4+ 、Ge 4+ 、Sn 4+ 、V 5+ 、Nb 5+ 、As 5+ etc.). In addition, P 5+ can also be doped or replaced by other high-valence ions such as Si 4+ 、V 5+ 、Nb 5+ etc. Exemplarily, the NASICON-type oxide solid electrolyte can be but is not limited to Na 3 Zr 2 Si 2 PO 12 .

[0041] The LISICON-type oxide solid electrolyte is a lithium ion conductor, which contains a solid three-dimensional anion framework, and the framework ions provide a transport channel for migratable lithium ions. The Li +In the interstitial position, it can conduct electricity by migration. Interstitial lithium ions have good proton exchange ability. In the exemplary embodiment, this LISICON-type oxide solid electrolyte may include, but is not limited to, Li 4-x Ge 1-x P x S 4 , where x can be from 0.01 to 0.99. In the exemplary embodiment, the value of x can be typical but non-limiting values such as 0.01, 0.05, 0.1, 0.5, 0.75, 0.9, 0.99, etc.

[0042] In some of these embodiments, the sulfide solid electrolyte includes Li 2 S-P 2 S 5 、Li 2 S-SiS 2 、Li 2 S-B 2 S 3 or at least one of them.

[0043] In some of these embodiments, the halide solid electrolyte includes LiaMY 4 、LiaMY 6 and LiaMY 8 , where M may include at least one of metals such as Mn, Zn, Fe, Al, Yb, etc., and Y may include at least one of halogens F, Cl, Br, I.

[0044] In some of these embodiments, the surface of the hard carbon material layer is coated with a soft carbon material layer. The combination of the hard carbon material layer and the soft carbon material layer forms a multi-layer coating structure. The hard carbon material layer adsorbs manganese ions, while the soft carbon material layer further enhances flexibility and interfacial stability, jointly improving the cycle stability of the secondary battery.

[0045] This application places no restrictions on the soft carbon material in the soft carbon material layer. For example, the soft carbon material layer includes a soft carbon material prepared using one or more of tetracarboxylic anhydride, pitch, petroleum coke, and needle coke as carbonization precursors.

[0046] In some of these embodiments, the particle size D of the negative electrode active material v 50 is 5 μm to 20 μm. Exemplarily, the particle size D of the negative electrode active material v 50 can be, but is not limited to, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm.

[0047] In some of these embodiments, the negative electrode plate includes a negative electrode current collector and a negative electrode active material layer, and the negative electrode active material layer includes a negative electrode active material, a negative electrode conductive agent, and a negative electrode binder.

[0048] In some of these embodiments, in the negative electrode active material layer, the mass percentage of the negative electrode active material is 94% - 96%, the mass percentage of the negative electrode conductive agent is 2% - 3.2%, and the mass percentage of the negative electrode binder is 2% - 2.8%.

[0049] In some of these embodiments, the negative electrode conductive agent includes one or more of conductive carbon black, acetylene black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0050] In some of these embodiments, the negative electrode binder includes one or more of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), polytetrafluoroethylene (PTFE), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0051] Positive electrode plate:

[0052] In some of these embodiments, the positive electrode plate includes a positive electrode current collector and a positive electrode active material layer provided on the surface of the positive electrode current collector. The positive electrode active material layer includes a positive electrode active material, and the positive electrode active material includes manganese element.

[0053] In some of these embodiments, the positive electrode active material includes one or more of lithium manganate, lithium iron manganese phosphate, lithium nickel manganese oxide, and lithium-rich manganese-based materials.

[0054] In some of these embodiments, the positive electrode current collector is selected from metal foils and composite current collectors; the composite current collector has a sandwich-like laminated structure, and the middle polymer layer is mainly made of materials such as high molecular insulating resins. Metal layers are deposited on both sides of the middle polymer layer by electroplating, electroless plating or other methods. Schematically, the high molecular resin includes polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polyether ether ketone, polyimide, polyamide, polyethylene glycol, polyamide-imide, polycarbonate, cyclic polyolefin, polyphenylene sulfide, polyvinyl acetate, polytetrafluoroethylene, polymethylene naphthalene, polyvinylidene fluoride, polyethylene naphthalate, polypropylene carbonate, poly(vinylidene fluoride-hexafluoropropylene), poly(vinylidene fluoride-co-trifluorochloroethylene), silicone, vinylon, polypropylene, polyethylene, polyvinyl chloride, polystyrene, polyether nitrile, polyurethane, polyphenylene ether, polyester, polysulfone and its derivatives, sodium carboxymethyl cellulose, styrene-butadiene rubber, fluororubber, polyvinyl alcohol or polyvinylidene fluoride, etc., one or more of them. The material of the metal layer is selected from at least one of aluminum, copper, nickel, cobalt, tungsten, tin, lead, iron, silver or gold. Further, the positive electrode current collector is aluminum foil.

[0055] In some of these embodiments, the positive electrode active material layer further includes a positive electrode conductive agent. The positive electrode conductive agent includes one or more of conductive carbon black, acetylene black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0056] In some of these embodiments, the positive electrode active material layer further contains a positive electrode binder. The positive electrode binder includes one or more of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), polytetrafluoroethylene (PTFE), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).

[0057] Electrolyte:

[0058] The electrolyte functions to conduct ions between the positive electrode plate and the negative electrode plate.

[0059] In some of these embodiments, the electrolyte includes a solvent and an electrolyte salt. The electrolyte salt can be lithium hexafluorophosphate (LiPF 6 ), lithium hexafluoroarsenate (LiAsF 6 ), lithium perchlorate (LiClO 4 ), lithium bis(fluorosulfonyl)imide (LiFSI), lithium tetrafluoroborate (LiBF 4 ), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium difluorophosphate (LiPO 2 F 2) at least one of lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiODFB), lithium difluoro(oxalato)phosphate (LiODFP), or lithium tetrafluoro(oxalato)phosphate (LiTFOP).

[0060] In some embodiments, the solvent includes one or more of carbonate solvents, carboxylate solvents, and aromatic hydrocarbon solvents.

[0061] In some embodiments, the carbonate solvents include halogenated carbonates and / or non-halogenated carbonates.

[0062] In some embodiments, the halogenated carbonates include one or more of fluoroethylene carbonate, difluoropropylene carbonate, trifluoroethyl methyl carbonate, trifluoromethyl ethylene carbonate, 4-trifluoromethyl ethylene carbonate, chloroethylene carbonate, bis(2,2,2-trifluoroethyl) carbonate, or 1,1,1,3,3,3-hexafluoroisopropyl acrylate.

[0063] In some embodiments, the non-halogenated carbonates include one or more of ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, or ethyl methyl carbonate.

[0064] In some embodiments, the carboxylate solvents include halogenated carboxylates and / or non-halogenated carboxylates.

[0065] In some embodiments, the halogenated carboxylates include one or more of propyl fluorobutyrate, propyl fluoroacetate, ethyl fluoroacetate, isopropyl fluoroacetate, butyl fluoropropionate, isopropyl fluoropropionate, ethyl fluorobutyrate, methyl fluoropropionate, ethyl fluoropropionate, or propyl fluoropropionate.

[0066] In some embodiments, the non-halogenated carboxylates include one or more of ethyl acetate, methyl acetate, propyl butyrate, propyl acetate, isopropyl acetate, butyl propionate, isopropyl propionate, ethyl butyrate, methyl propionate, ethyl propionate, or propyl propionate.

[0067] In some embodiments, the aromatic hydrocarbon solvents include halogenated aromatic hydrocarbons and / or non-halogenated aromatic hydrocarbons.

[0068] In some embodiments, the halogenated aromatic hydrocarbons include one or more of monofluorobenzene, difluorobenzene, 1,3,5-trifluorobenzene, trifluorotoluene, 2-fluorotoluene, or 2,4-dichlorotrifluorotoluene.

[0069] In some of these embodiments, the electrolyte further contains additives. The additives include at least one of 1,3 - propane sultone, 1,4 - butane sultone, allyl - 1,3 - sulfonic acid lactone, ethylene sulfate, 4 - methyl ethylene sulfate, propylene sulfate, saturated phosphate compounds and unsaturated phosphate compounds, tris(trimethylsilyl) phosphate, tris(trimethylsilyl) borate, tris(triethylsilyl) borate, succinonitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexane trinitrile, adiponitrile, pimelonitrile, suberonitrile, azelaonitrile, sebaconitrile.

[0070] Separator:

[0071] In some of these embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of the separator, and any well - known porous structure separator with good chemical stability and mechanical stability can be selected.

[0072] In some of these embodiments, the material of the separator may include one or more of glass fiber, non - woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single - layer film or a multi - layer composite film, without particular limitation. When the separator is a multi - layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0073] In some of these embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be made into an electrode assembly by a winding process or a stacking process.

[0074] In some of these embodiments, the secondary battery may include an outer package. The outer package can be used to encapsulate the above - mentioned electrode assembly and electrolyte.

[0075] In some of these embodiments, the outer package of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of a lithium - ion battery can also be a soft package, such as a pouch - type soft package. The material of the soft package can be plastic. Further, non - limiting examples of the plastic can include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate, etc.

[0076] The second aspect of the present application provides an electrical device, which includes the secondary battery provided in the first aspect above.

[0077] The electrical device of the present application is not particularly limited and can be any electrical device known in the prior art. For example, the electrical device may include, but is not limited to, a laptop computer, a pen-input computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, a liquid crystal TV, a portable cleaner, a portable CD player, a minidisc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, an automobile, a motorcycle, a moped, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flash, a camera, a large household battery, and a lithium-ion capacitor.

[0078] The present application will be further described below in conjunction with specific examples and comparative examples.

[0079] Example 1

[0080] Negative electrode plate:

[0081] (1) Add the ball-milled phenolic resin powder to the tetrahydrofuran solvent, perform ultrasonic stirring for 2 hours until completely dissolved; then add graphite and stir for 4 hours to mix evenly, and then heat to 80 °C to evaporate the solvent. Place the dried sample in a tube furnace, heat it to 200 °C at a rate of 2 °C / min under a nitrogen atmosphere, hold for 2 hours to preliminarily crosslink and cure the phenolic resin, and then put it into the tube furnace and heat it to 800 °C - 1000 °C and hold for 2 h for carbonization to obtain a negative electrode material with hard carbon-coated graphite. The mass ratio of graphite to hard carbon is 88:12.

[0082] Among them, the negative electrode active material includes graphite particles and a hard carbon material layer coated on the surface of the graphite particles. The thickness of the hard carbon material layer is 5 μm, and the porosity of the hard carbon material layer is 70%; the particle size D v 50 of the negative electrode active material is 15 μm.

[0083] (2) Mix 95% of the negative electrode active material, 2.6% of the negative electrode conductive agent carbon black, and 2.4% of the negative electrode binder polyacrylonitrile evenly according to the ratio, and add the solvent deionized water to obtain a negative electrode slurry.

[0084] (3) Coat the negative electrode slurry on the negative electrode current collector copper foil, then perform rolling, and then dry at 100 °C. After the negative electrode slurry is cured and formed, a negative electrode plate is obtained.

[0085] Positive electrode plate:

[0086] The positive electrode plate includes a positive electrode current collector aluminum foil and a positive electrode active material layer provided on the positive electrode current collector aluminum foil. The positive electrode active material layer includes lithium manganate as the positive electrode active material, carbon black as the positive electrode conductive agent, and polyvinylidene fluoride as the positive electrode binder with a mass ratio of 96:2:2.

[0087] Secondary battery:

[0088] The positive electrode plate, negative electrode plate, and separator are laminated and placed in an aluminum-plastic film. Electrolyte is injected and formed to obtain a secondary battery. Among them, the separator is a polyethylene separator; the electrolyte is a 1 mol / L LiPF 6 solution, and the solvent is EC:DEC = 1:1 (volume ratio).

[0089] Example 2

[0090] The preparation methods of the negative electrode plate, positive electrode plate, and secondary battery in this example are basically the same as those in Example 1, except that:

[0091] Negative electrode plate:

[0092] In step (1), the thickness of the hard carbon material layer is 0.1 μm, and the particle size D v 50 of the negative electrode active material is 10.1 μm.

[0093] Example 3

[0094] The preparation methods of the negative electrode plate, positive electrode plate, and secondary battery in this example are basically the same as those in Example 1, except that:

[0095] Negative electrode plate:

[0096] In step (1), the thickness of the hard carbon material layer is 10 μm, and the particle size D v 50 of the negative electrode active material is 20 μm.

[0097] Example 4

[0098] Negative electrode plate:

[0099] (1) Use atomic deposition method to prepare solid electrolyte-coated graphite. First, pretreat the graphite. Milling natural graphite (particle size 10 μm - 20 μm) until the surface is smooth (reduce defects), pickling (HNO 3 :H 2 SO 4 = 1:3) to remove impurities, and dry for later use; secondly, use atomic layer deposition (ALD) to deposit the solid electrolyte zirconia on the graphite surface, and the deposition parameters are:

[0100] a. Temperature: 250°C - 300°C (to avoid damage to the graphite structure);

[0101] b. Number of cycles: 500 - 1000 cycles (about 0.1 nm grows per cycle);

[0102] c. Vacuum degree: <1×10 -2 Pa;

[0103] d. Thickness control: adjusted by the number of cycles (1000 cycles ≈ 100 nm);

[0104] Finally, annealing was performed at 600°C for 2 hours in an inert atmosphere (Ar) to improve the crystallinity of the oxide solid electrolyte (rapid heating / cooling is required to prevent graphite oxidation), thus preparing solid electrolyte-coated graphite particles.

[0105] Among them, the thickness of the solid electrolyte layer is 0.5 μm.

[0106] (2) Add the ball-milled phenolic resin powder to tetrahydrofuran solvent and stir ultrasonically for 2 hours until it is completely dissolved; then add the zirconium oxide-coated graphite prepared in step 1 and stir for 4 hours to mix evenly; then heat to 80°C to evaporate the solvent; place the dried sample in a tubular furnace and heat to 200°C at 2°C / min under a nitrogen atmosphere for 2 hours to allow the phenolic resin to initially cross-link and solidify; then place the sample in a tubular furnace and heat to 800°C~1000°C and hold for 2 hours for carbonization to obtain a negative electrode material of hard carbon and solid electrolyte double-layer coated graphite, with a mass ratio of graphite to hard carbon of 88:12.

[0107] The thickness of the hard carbon material layer is 5 μm, the porosity of the hard carbon material layer is 75%; the particle size D of the negative electrode active material is v 50 is 15.5 μm.

[0108] (3) 95% of the negative electrode active material, 2.6% of the negative electrode conductive agent conductive carbon black, and 2.4% of the negative electrode binder polyacrylonitrile were mixed evenly according to a proportion, and deionized water solvent was added to obtain a negative electrode slurry.

[0109] (4) The negative electrode slurry is coated on the negative electrode current collector copper foil, and then rolled and dried at 100° C. After the negative electrode slurry is solidified and formed, a negative electrode sheet is obtained.

[0110] Positive electrode:

[0111] The positive electrode sheet includes a positive electrode collector aluminum foil and a positive electrode active material layer arranged on the positive electrode collector aluminum foil, and the positive electrode active material layer includes a positive electrode active material lithium manganese oxide, a positive electrode conductive agent conductive carbon black and a positive electrode binder polyvinylidene fluoride in a mass ratio of 96:2:2.

[0112] Secondary battery:

[0113] The positive electrode sheet, negative electrode sheet and separator are stacked, placed in an aluminum plastic film, and the electrolyte is injected and formed to obtain a secondary battery. The separator is a polyethylene separator; the electrolyte is 1 mol / L LiPF 6The solution has a solvent of EC:DEC = 1:1 (volume ratio).

[0114] Example 5

[0115] The preparation methods of the negative electrode sheet, positive electrode sheet and secondary battery in this example are basically the same as those in Example 4, except that:

[0116] Negative electrode sheet:

[0117] In step (1), the thickness of the solid electrolyte layer is 0.1 μm, and the particle size D v 50 of the negative active material is 15.1 μm.

[0118] Example 6

[0119] The preparation methods of the negative electrode sheet, positive electrode sheet and secondary battery in this example are basically the same as those in Example 4, except that:

[0120] Negative electrode sheet:

[0121] In step (1), the thickness of the solid electrolyte layer is 1 μm, and the particle size D v 50 of the negative active material is 16 μm.

[0122] Example 7

[0123] The preparation methods of the negative electrode sheet, positive electrode sheet and secondary battery in this example are basically the same as those in Example 1, except that:

[0124] Positive electrode sheet:

[0125] The positive active material in the positive electrode sheet is replaced with lithium iron manganese phosphate.

[0126] Comparative Example 1

[0127] Negative electrode sheet:

[0128] (1) 95% of the negative active material graphite, 2.6% of the negative conductive agent conductive carbon black, and 2.4% of the negative binder polyacrylonitrile are mixed evenly according to the ratio, and deionized water is added as the solvent to obtain a negative electrode slurry.

[0129] (2) The negative electrode slurry is coated on a negative current collector copper foil, then roll-pressed, and then dried at 100 °C. After the negative electrode slurry is solidified and formed, a negative electrode sheet is obtained.

[0130] Positive electrode sheet:

[0131] The positive electrode sheet includes a positive current collector aluminum foil and a positive active material layer provided on the positive current collector aluminum foil. The positive active material layer includes a positive active material lithium manganese oxide, a positive conductive agent conductive carbon black, and a positive binder polyvinylidene fluoride with a mass ratio of 96:2:2.

[0132] Secondary battery:

[0133] The positive electrode plate, negative electrode plate, and separator are laminated, placed in an aluminum-plastic film, electrolyte is injected, and formation is carried out to obtain a secondary battery. Among them, the separator is a polyethylene separator; the electrolyte is a 1mol / L LiPF 6 solution, and the solvent is EC:DEC = 1:1 (volume ratio).

[0134] Performance test

[0135] The secondary batteries of the above embodiments and comparative examples are tested, and the test steps are as follows:

[0136] ① First, activate for 2 cycles at 0.1C;

[0137] ② Charge at a current of 0.2C to the cut-off voltage at a temperature of 45°C ± 2°C, with a cut-off current of 0.05C, and let it stand for 30 min;

[0138] ③ Discharge at 0.2C to the discharge cut-off voltage (2.75V), record the discharge capacity, and let it stand for 30 min;

[0139] ④ Repeat steps ② to ③, and test the capacity retention rate of the lithium-ion battery after 100 cycles. The test results are shown in Table 1.

[0140] Table 1

[0141]

[0142] In Table 1: " / " indicates non-existence.

[0143] As shown in Table 1, by comparing Examples 1 to 7 and Comparative Example 1, it can be seen that the secondary battery provided by the present application has improved cycle performance.

[0144] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0145] The above embodiments only represent several implementation manners of the present application. The description is relatively specific and detailed, but it should not be construed as a limitation on the patent scope of the present application. It should be noted that for those of ordinary skill in the art, without departing from the technical concept of the present application, several deformations and improvements can still be made, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the appended claims.

Claims

1. A secondary battery, characterized in that: It includes a positive electrode sheet and a negative electrode sheet, wherein the positive electrode sheet includes a positive electrode active material, and the negative electrode sheet includes a negative electrode active material; The positive electrode active material includes manganese element, and the negative electrode active material includes graphite particles and a hard carbon material layer coated on the surface of the graphite particles.

2. The secondary battery according to claim 1, characterized in that: The thickness of the hard carbon material layer is 0.1 μm to 10 μm.

3. The secondary battery according to claim 1, characterized in that: The porosity of the hard carbon material layer is 50% to 80%.

4. The secondary battery according to claim 1, characterized in that: A solid electrolyte layer is disposed between the graphite particles and the hard carbon material layer.

5. The secondary battery according to claim 4, characterized in that: The thickness of the solid electrolyte layer is 0.1 μm to 1 μm.

6. The secondary battery according to any one of claims 1 to 5, characterized in that: The particle size D of the negative electrode active material v 50 is 5 μm~20 μm.

7. The secondary battery according to any one of claims 1 to 5, characterized in that: The positive electrode active material includes one or more of lithium manganese oxide, lithium iron manganese phosphate, lithium nickel manganese oxide and lithium-rich manganese-based materials.

8. The secondary battery according to any one of claims 1 to 5, characterized in that: The negative electrode plate comprises: A negative electrode current collector; and The negative electrode active material layer comprises the negative electrode active material, a negative electrode conductor and a negative electrode binder.

9. The secondary battery according to claim 8, characterized in that: In the negative electrode active material layer, the mass percentage of the negative electrode active material is 94% to 96%, the mass percentage of the negative electrode conductor is 2% to 3.2%, and the mass percentage of the negative electrode binder is 2% to 2.8%.

10. An electrical device, characterized in that: A secondary battery comprising the secondary battery according to any one of claims 1 to 9.

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