Positive electrode material, positive electrode slurry, positive electrode sheet, secondary battery and electrical device

Abstract

The present application provides a positive electrode material, comprising a positive electrode active material and a coating layer. The positive electrode active material comprises a phosphate. The coating layer is coated on the surface of the positive electrode active material, and the material of the coating layer comprises a phosphate-based polyether. By arranging a coating layer comprising a phosphate-based polyether on the surface of the positive electrode active material, the positive electrode material has good dispersibility in the slurry system, can increase the solid content of the slurry, and improve the slurry gel problem.

Description

Technical Field

[0001] The present application relates to the technical field of secondary batteries, and in particular to a positive electrode material, a positive electrode slurry, a positive electrode sheet, a secondary battery and an electrical device. Background Art

[0002] Lithium-ion battery is a secondary battery that relies on the movement of lithium ions between the positive electrode and the negative electrode to work. The positive electrode active material is a material in the positive electrode sheet that can insert and remove lithium ions. In conventional processes, the positive electrode active material is usually prepared into a slurry and coated on a current collector to prepare a positive electrode sheet. Existing positive electrode materials have problems such as poor dispersibility and easy gelation, so the dispersibility of positive electrode materials still needs to be improved. Summary of the invention

[0003] Based on the above problems, the present application provides a positive electrode material, a positive electrode slurry, a positive electrode plate, a secondary battery and an electrical device with good dispersibility.

[0004] In one aspect of the present application, a positive electrode material is provided, comprising:

[0005] a positive electrode active material, the positive electrode active material comprising a phosphate; and

[0006] A coating layer is coated on the surface of the positive electrode active material, and the coating layer contains phosphate-based polyether.

[0007] The positive electrode material of the embodiment of the present application has good dispersibility by providing a coating layer containing phosphate-based polyether on the surface of the positive electrode active material, which can increase the solid content of the slurry and improve the slurry gel problem.

[0008] In any embodiment, the phosphate is a lithium-containing phosphate;

[0009] Optionally, the lithium-containing phosphate includes at least one of lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate and lithium phosphate. By coating the positive electrode active material with the above coating layer, the slurry dispersibility of the phosphate positive electrode active material can be significantly improved, and the slurry gel problem can be improved.

[0010] In any embodiment, the mass ratio of the coating layer to the positive electrode active material is (1-20): 1000, and can be (3-10): 1000. When the mass ratio of the coating layer to the positive electrode active material is within the above range, the positive electrode material can have both good dispersibility and good electrochemical performance.

[0011] In any embodiment, the coating layer has a thickness of 1 nm to 200 nm, and can be optionally 5 nm to 80 nm. When the coating layer has a thickness within the above range, the positive electrode material can have both good dispersibility and good electrochemical performance.

[0012] In any embodiment, the coating area of ​​the coating layer on the surface of the positive electrode active material accounts for 40% to 100% of the surface area of ​​the positive electrode active material, and can be 60% to 80%. The coating area of ​​the coating layer on the surface of the positive electrode active material accounts for more than 40% of the surface area of ​​the positive electrode active material, and the positive electrode material can have both good dispersibility and good electrochemical performance.

[0013] In any embodiment, the molecular weight of the phosphate-based polyether is 500 to 5000, and can be optionally 1500 to 3500. When the molecular weight of the phosphate-based polyether is within the above range, the dispersibility of the positive electrode material in the slurry system is better.

[0014] In a second aspect, the present application further provides a positive electrode slurry, comprising the positive electrode material described in the first aspect. The positive electrode material has good dispersibility in the positive electrode slurry system, can shorten the stirring time of the positive electrode slurry preparation, reduce production costs, and increase production capacity.

[0015] In any embodiment, the solid content of the positive electrode slurry is ≥ 60%, and can be 60% to 70%. Since the positive electrode material has good dispersibility in the positive electrode slurry, the solid content of the positive electrode slurry can reach more than 60% without generating gel, thereby reducing the amount of solvent used and reducing costs.

[0016] In a third aspect, the present application further provides a positive electrode sheet, comprising the positive electrode material described in the first aspect or prepared using the positive electrode slurry described in the second aspect. The positive electrode sheet prepared by the above positive electrode material or positive electrode slurry has not only a low preparation cost, but also good flexibility, improves the problem of cracking and powder loss of the positive electrode sheet, and has better electrical performance of the secondary battery.

[0017] In a fourth aspect, the present application further provides a secondary battery, comprising the positive electrode material described in the first aspect or the positive electrode plate described in the third aspect.

[0018] In a fifth aspect, the present application also provides a battery module, comprising the secondary battery described in the fourth aspect.

[0019] In a sixth aspect, the present application further provides a battery pack comprising at least one of the secondary battery described in the fourth aspect and the battery module described in the fifth aspect.

[0020] In a seventh aspect, the present application further provides an electrical device comprising at least one selected from the secondary battery described in the fourth aspect, the battery module described in the fifth aspect, and the battery pack described in the sixth aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present application. Moreover, the same reference numerals are used throughout the drawings to represent the same components. In the drawings:

[0022] Figure 1 A schematic diagram of a secondary battery according to an embodiment of the present application;

[0023] Figure 2 for Figure 1 An exploded view of a secondary battery according to an embodiment of the present application is shown;

[0024] Figure 3 is a schematic diagram of a battery module according to an embodiment of the present application;

[0025] Figure 4 A schematic diagram of a battery pack according to an embodiment of the present application;

[0026] Figure 5 for Figure 4 An exploded view of a battery pack according to an embodiment of the present application is shown;

[0027] Figure 6 A schematic diagram of an electrical device using a secondary battery according to an embodiment of the present application as a power source;

[0028] Figure 7 This is the gelation state of the positive electrode slurry of Example 1 of the present application after being left to stand for 12 hours;

[0029] Figure 8 The light transmittance of the positive electrode sheet of Example 1 of the present application after being folded five times;

[0030] Fig. 9 This is the gelation condition of the positive electrode slurry of Comparative Example 1 of the present application after being left to stand for 12 hours;

[0031] Fig.10 This is the light transmittance of the positive electrode sheet of comparative example 1 of the present application after being folded twice;

[0032] Description of reference numerals:

[0033] 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 secondary battery; 51 shell; 52 electrode assembly; 53 cover plate; 6 electrical device. DETAILED DESCRIPTION

[0034] Below, the embodiments of the positive electrode material, positive electrode slurry, positive electrode sheet, secondary battery, battery module, battery pack and power device of the present application are specifically disclosed with appropriate reference to the drawings. However, there are cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following descriptions are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0035] "Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values ​​or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0036] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0037] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0038] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0039] If there is no special explanation, the "include" and "comprising" mentioned in this application are open-ended or closed-ended. For example, the "include" and "comprising" may mean that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0040] If not specifically stated, 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) and B is true (or exists); or both A and B are true (or exist).

[0041] An embodiment of the present application provides a positive electrode material, including:

[0042] A positive electrode active material, the positive electrode active material comprising a phosphate; and

[0043] The coating layer is coated on the surface of the positive electrode active material, and the material of the coating layer includes phosphate-based polyether.

[0044] Although the mechanism is not very clear, it is speculated that the phosphate-based polyether is a dispersant with an anchoring group and a solvated segment, and has good wettability in a commonly used positive electrode slurry system, such as an N-methylpyrrolidone (NMP) system. The above-mentioned positive electrode material is provided with a coating layer containing a phosphate-based polyether on the surface of the positive electrode active material. The solvated segment of the phosphate-based polyether in the coating layer can stretch in the slurry system, produce steric hindrance, keep the positive electrode material particles stable, and improve the dispersion effect. And the phosphate-based polyether has good compatibility with the positive electrode active material containing phosphate. Therefore, the above-mentioned positive electrode material has good dispersibility in the slurry system, and can further increase the solid content of the slurry and improve the slurry gel problem.

[0045] The positive electrode active material may be a positive electrode active material for a battery known in the art. In some of the embodiments, the phosphate is a lithium-containing phosphate. However, the present application is not limited to these materials, and other materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Among them, the lithium-containing phosphate may include, but is not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0046] In some embodiments, the mass ratio of the coating layer to the positive electrode active material is (1-20):1000. When the mass ratio of the coating layer to the positive electrode active material is within the above range, the positive electrode material can have both good dispersibility and good electrochemical performance. Further, the mass ratio of the coating layer to the positive electrode active material is (3-10):1000.

[0047] In some of the embodiments, the thickness of the coating layer is 1nm to 200nm. When the thickness of the coating layer is within the above range, the positive electrode material can take into account both good dispersibility and good electrochemical performance. Optionally, the thickness of the coating layer can be within the range of any of the following numerical values: 1nm, 5nm, 10nm, 20nm, 50nm, 80nm, 100nm, 120nm, 150nm, 180nm or 200nm. Further, the thickness of the coating layer is 5nm to 80nm. Specifically, the thickness of the coating layer can be obtained by observing the scanning electron microscope (SEM) image of the positive electrode material.

[0048] In some embodiments, the coating area of ​​the coating layer on the surface of the positive electrode active material accounts for 40% to 100% of the surface area of ​​the positive electrode active material. The percentage of the coating area of ​​the coating layer on the surface of the positive electrode active material accounts for more than 40% of the surface area of ​​the positive electrode active material, and the positive electrode material can take into account both good dispersibility and good electrochemical performance. Optionally, the percentage of the coating area of ​​the coating layer on the surface of the positive electrode active material to the surface area of ​​the positive electrode active material can be within the range of any of the following numerical values: 40%, 50%, 60%, 70%, 80%, 90% or 100%. Further, the percentage of the coating area of ​​the coating layer on the surface of the positive electrode active material accounts for 60% to 80% of the surface area of ​​the positive electrode active material. Specifically, the percentage of the coating area of ​​the coating layer on the surface of the positive electrode active material to the surface area of ​​the positive electrode active material can be observed by scanning electron microscope (SEM) images of the positive electrode material.

[0049] In some of the embodiments, the molecular weight of the phosphate-based polyether is 500 to 5000. When the molecular weight of the phosphate-based polyether is within the above range, the dispersibility of the positive electrode material in the slurry system is better. Optionally, the molecular weight of the phosphate-based polyether can be within the range of any of the following numerical values: 500, 600, 800, 1000, 1200, 1500, 1800, 2000, 2500, 3000, 3500, 4000, 4500 or 5000. Further, the molecular weight of the phosphate-based polyether is 1500 to 3500.

[0050] In some embodiments, the positive electrode material can be prepared by steps S110 and S120:

[0051] Step S110: dispersing the raw material of the coating layer in a volatile organic solvent to prepare a dispersion, and controlling the solid content of the dispersion to be 40% to 70%. The raw material of the coating layer includes phosphate-based polyether. As an example, the volatile organic solvent may be selected from but not limited to N-methylpyrrolidone (NMP).

[0052] Step S120: Mix the dispersion with the alcohol solvent and the positive electrode active material, react at 80°C to 120°C for 3h to 6h, and dry to coat the coating layer material on the surface of the positive electrode active material to prepare the positive electrode material. As an example, the alcohol solvent may be selected from but not limited to at least one of methanol and ethanol.

[0053] Another embodiment of the present application further provides a positive electrode slurry, comprising the positive electrode material of the first aspect. The positive electrode material has good dispersibility in the positive electrode slurry system, can shorten the stirring time of the positive electrode slurry preparation, reduce production costs, and increase production capacity.

[0054] In some embodiments, the solid content of the positive electrode slurry is ≥ 60%. Since the positive electrode material has good dispersibility in the positive electrode slurry, the solid content of the positive electrode slurry can reach more than 60% without generating gel; the amount of solvent used can be reduced. Furthermore, the solid content of the positive electrode slurry is 60% to 70%. Optionally, the solid content of the positive electrode slurry can be within the range of any of the following values: 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69% or 70%.

[0055] In some embodiments, the positive electrode slurry further comprises a solvent. As an example, the solvent may be, but is not limited to, N-methylpyrrolidone (NMP).

[0056] In some of the embodiments, the viscosity of the positive electrode slurry is 4000 mPa·s to 30000 mPa·s.

[0057] In some embodiments, the positive electrode slurry may further include a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers. In some embodiments, the mass content of the conductive agent in the positive electrode slurry solids is 0.3% to 3%.

[0058] In some of the embodiments, the positive electrode slurry may further include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin. In some of the embodiments, the mass content of the binder in the positive electrode slurry solid content is 0.3% to 3%.

[0059] In one embodiment of the present application, a secondary battery is also provided.

[0060] Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator. During the battery charging and discharging process, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is set between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing ions to pass through.

[0061] Positive electrode

[0062] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer includes the above-mentioned positive electrode material or is prepared by the above-mentioned positive electrode slurry.

[0063] The inventors have found that the positive electrode sheets prepared with the above positive electrode materials or positive electrode slurries not only have lower preparation costs, but also have better flexibility, improve the problems of cracking and powder loss of the positive electrode sheets, and improve the electrical performance of the secondary battery.

[0064] As an example, the positive electrode current collector has two surfaces facing each other in its thickness direction, and the positive electrode active material layer is disposed on any one or both of the two facing surfaces of the positive electrode current collector.

[0065] In some of the embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy on a polymer material substrate. The polymer material substrate includes substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0066] In some embodiments, the positive electrode active material layer may further include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0067] In some embodiments, the positive electrode active material layer may further include a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0068] In some of the embodiments, the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0069] Negative electrode

[0070] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material.

[0071] As an example, the negative electrode current collector has two surfaces facing each other in its thickness direction, and the negative electrode active material layer is disposed on any one or both of the two facing surfaces of the negative electrode current collector.

[0072] In some of the embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, a copper foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy on a polymer material substrate. The polymer material substrate includes substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0073] In some of the embodiments, the negative electrode active material may adopt the negative electrode active material for batteries known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0074] In some embodiments, the negative electrode active material layer may further include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).

[0075] In some embodiments, the negative electrode active material layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0076] In some of the embodiments, the negative electrode active material layer may further include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0077] In some of the embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0078] Electrolytes

[0079] The electrolyte plays the role of conducting ions between the positive electrode and the negative electrode. The present application has no specific restrictions on the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be liquid, gel or all-solid.

[0080] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0081] In some of the embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate and lithium tetrafluorooxalatophosphate.

[0082] In some of the embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane sulfone, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0083] In some embodiments, the electrolyte may further include additives, such as negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.

[0084] Isolation film

[0085] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical stability and mechanical stability can be selected.

[0086] In some embodiments, the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane can be a single-layer film or a multi-layer composite film without particular limitation. When the isolation membrane is a multi-layer composite film, the materials of each layer can be the same or different without particular limitation.

[0087] In some of the embodiments, the positive electrode sheet, the negative electrode sheet and the separator can be formed into an electrode assembly by a winding process or a lamination process.

[0088] In some embodiments, the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.

[0089] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery can also be a soft package, such as a bag-type soft package. The material of the soft package can be plastic, and as the plastic, polypropylene, polybutylene terephthalate, and polybutylene succinate can be listed.

[0090] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square or any other shape. Figure 1 The secondary battery 5 is a square structure as an example.

[0091] In some of these embodiments, reference Figure 2 , the outer package may include a shell 51 and a cover plate 53. Among them, the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0092] In some of the embodiments, the secondary batteries may be assembled into a battery module. The number of the secondary batteries contained in the battery module may be one or more, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery module.

[0093] Figure 3 4 is an example of a battery module. Figure 3 In the battery module 4, the plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. Further, the plurality of secondary batteries 5 may be fixed by fasteners.

[0094] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of secondary batteries 5 are received in the receiving space.

[0095] In some of the embodiments, the battery modules may be assembled into a battery pack. The battery pack may contain one or more battery modules. The specific number may be selected by those skilled in the art according to the application and capacity of the battery pack.

[0096] Figure 4 and Figure 5 1 is a battery pack 1 as an example. Figure 4 and Figure 5The battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0097] In addition, the present application also provides an electrical device, which includes at least one of the secondary batteries, battery modules, or battery packs provided in the present application. The secondary batteries, battery modules, or battery packs can be used as power sources for electrical devices, and can also be used as energy storage units for electrical devices. Electrical devices may include mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc., but are not limited to these. Among them, mobile devices may be, for example, mobile phones, laptop computers, etc.; electric vehicles may be, for example, pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc., but are not limited to these.

[0098] As an electrical device, a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.

[0099] Figure 6 The power consumption device 6 is taken as an example. The power consumption device 6 is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the power consumption device's requirements for high power and high energy density of secondary batteries, a battery pack or a battery module can be used.

[0100] Another example of a device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be thin and light, and a secondary battery may be used as a power source.

[0101] Example

[0102] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. If the manufacturer is not indicated in the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0103] In an embodiment of the present application, the preparation method of the phosphate polyether is as follows: first, 1.5:1:1 propylene oxide and ethylenediamine, distilled water are put into an alkaline environment of 50wt% KOH solution, reacted at 80°C to 90°C, stirred for 1h to 2h, and then dehydrated by -50kPa negative pressure to obtain 270g of a white viscous substance, and the white viscous substance is transferred to a polymerization kettle under N2 atmosphere protection, and then 930g of ethylene oxide is added, and the reaction is stirred at 70°C for 1h to 2h to synthesize the polyether, presenting a light yellow waxy solid, and the obtained polyether is added to the reactor, and under sufficient stirring and at a temperature of 40°C to 60°C, phosphorus pentoxide is gradually added to the reactor in a molar ratio of 2.5:1 to the polyether, and the temperature is raised to 80°C, and the reaction time is 6h to finally obtain a phosphate polyether.

[0104] Embodiment 1:

[0105] (1) Preparation of positive electrode material: 50 g of phosphate-based polyether was dispersed in N-methylpyrrolidone solvent to prepare a dispersant with a solid content of 50%. The dispersant was added into a stirring tank and mixed with 1000 g of ethanol and lithium iron phosphate according to the mass ratio in Table 1. The mixture was stirred at 1200 rpm for 4 h at 80° C. and dried to obtain a positive electrode material.

[0106] (2) Preparation of positive electrode sheet: The positive electrode material, conductive agent acetylene black, and binder PVDF were fully stirred and mixed in an NMP solvent system at a mass ratio of 97:2:1, and then coated on both surfaces of an Al foil with a thickness of 13 μm. The single-side coating weight was 400 mg / 1540.25 mm 2 , drying and cold pressing to obtain the positive electrode sheet.

[0107] (3) Preparation of negative electrode sheet: The negative electrode active material artificial graphite, conductive agent acetylene black, binder SBR, and dispersant CMC-Na were fully stirred and mixed in a deionized water solvent system at a mass ratio of 96:2:1:1, and then coated on both surfaces of a 6 μm thick Cu foil. The single-side coating weight was 180 mg / 1540.25 mm 2 , drying and cold pressing to obtain the negative electrode sheet.

[0108] (4) Preparation of electrolyte: In an argon atmosphere glove box with a water content of <10 ppm, equal volumes of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed to obtain an organic solvent, and then LiPF6 was uniformly dissolved in the above organic solvent at a concentration of 1 mol / L to obtain an electrolyte.

[0109] (5) Preparation of secondary battery: PE porous polymer film is used as the separator. The positive electrode sheet, separator, and negative electrode sheet are wound in order and size to make a battery cell, which is then packaged, injected with electrolyte, formed, and vented to obtain a secondary battery.

[0110] Embodiment 2~5:

[0111] The difference between Examples 2 to 5 and Example 1 is that the mass ratio of the coating layer to the positive electrode active material is different.

[0112] Embodiment 6~12:

[0113] The difference between Examples 6 to 12 and Example 1 is that the thickness of the coating layer is different.

[0114] Embodiments 13 to 15:

[0115] The difference between Examples 13 to 15 and Example 1 is that the coverage rates of the coating layers are different.

[0116] Embodiments 16 to 20:

[0117] The difference between Examples 16 to 20 and Example 1 is that the molecular weight of the coating layer material is different.

[0118] Embodiment 21:

[0119] The difference between Example 21 and Example 1 is that the positive electrode active material is different, namely lithium manganese iron phosphate (LMFP), in which the molar ratio of Mn to Fe is 6:4.

[0120] Comparative Example 1:

[0121] The difference between Comparative Example 1 and Example 1 is that lithium iron phosphate without a coating layer is used as the positive electrode material.

[0122] Comparative Example 2:

[0123] The difference between Example 2 and Example 21 is that LMFP (the molar ratio of Mn to Fe is 6:4) without a coating layer is used as the positive electrode material.

[0124] Comparative Example 3:

[0125] The difference between Comparative Example 3 and Comparative Example 1 is that the positive electrode material is lithium iron phosphate that has not been coated. Preparation of the positive electrode sheet: lithium iron phosphate, conductive agent acetylene black, binder PVDF and phosphate ester polyether are fully stirred and mixed in an NMP solvent system according to a mass ratio of 96.7:2:1:0.3, and then coated on both surfaces of an Al foil with a thickness of 13 μm, with a single-side coating weight of 400 mg / 1540.25 mm 2 , drying and cold pressing to obtain a positive electrode sheet. The number average molecular weight of the phosphate polyether is 2000.

[0126] Test part:

[0127] Cathode material morphology test:

[0128] The thickness of the coating layer of the positive electrode material and the percentage of the coating area of ​​the coating layer on the surface of the positive electrode active material to the surface area of ​​the positive electrode active material (referred to as the coating rate) were tested by scanning electron microscopy (SEM) observation.

[0129] Pole brittleness test:

[0130] Take a defect-free positive electrode sheet and cut it into samples with a length*width of 20cm*2.5cm in the longitudinal direction. The number of samples should be ≥8. After pre-folding it in half, place the film on the test platform and roll it once with a 2kg cylindrical roller. If it is light-transmitting, the number of times of brittle light transmission is 1. If it is not light-transmitting, repeat the reverse folding and rolling. Observe the crease against the light to see if it is light-transmitting or broken, record the actual number of folds, and take the average as the test result.

[0131] The first coulombic efficiency test of the battery:

[0132] The capacity of the secondary battery prepared as above is charged at 0.02C rate for 10 h at 45°C, and the capacity is marked as C0. It is then charged at 0.33C rate at 25°C to the rated voltage, and the capacity is measured by constant voltage charging at the rated voltage to 0.05C, and finally the capacity is measured by discharging at 0.33C to the cut-off voltage, and the first coulombic efficiency of the secondary battery = D0 / (C0+C1)×100%.

[0133] Battery cycle performance test:

[0134] The secondary battery prepared as above was discharged at a constant current of 0.33C at a temperature of 25°C and then charged at a constant voltage to the rated voltage. After standing for 5 minutes, it was discharged at a constant current of 0.33C to the cut-off voltage. The discharge capacity at this time was recorded and then stood for another 5 minutes. Thus, the capacity retention rate of the 300th cycle = (300th cycle capacity / first cycle capacity) * 100%.

[0135] Table 1

[0136]

[0137]

[0138] Table 2

[0139]

[0140] It can be seen from the relevant data in Table 1 and Table 2 that the surface of the main positive electrode material lithium iron phosphate in the positive electrode materials of Examples 1 to 20 is coated with acid ester polyether, and the positive electrode material is stirred for 2 hours to prepare a positive electrode slurry with a solid content of 68% to 69%, and the positive electrode slurry has no gel problem. The positive electrode plates prepared in Examples 1 to 20 are light-transmissive only after being folded 4 to 6 times, and the positive electrode plates have good flexibility. The first coulomb efficiency of the secondary batteries of Examples 1 to 20 is 92.0% to 94.9%, and the capacity retention rate after 2000 cycles is 91.4% to 94.4%. The secondary batteries have a high first coulomb efficiency and a high cycle capacity retention rate. See Figure 7 The positive electrode slurry prepared in Example 1 showed no gelation after standing for 12 hours, and the slurry had good dispersibility. Figure 8 , is the light transmittance of the positive electrode sheet prepared in Example 1 after being folded five times, and the light transmittance area of ​​the fold is about 1 mm.

[0141] The positive electrode material of Comparative Example 1 is uncoated lithium iron phosphate. After stirring the positive electrode material for 6 hours, a positive electrode slurry with a solid content of 60% was prepared. The positive electrode slurry had serious gelation. The positive electrode sheet of Comparative Example 1 was light-transmissive after being folded twice, and the flexibility of the positive electrode sheet was poor. The initial coulomb efficiency of the secondary battery of Comparative Example 1 was 88%, and the capacity retention rate after 2000 cycles was 83%. Fig. 9 The positive electrode slurry prepared in Comparative Example 1 was severely gelled after standing for 12 hours, and had poor fluidity. Fig.10 , is the light transmittance of the positive electrode sheet prepared in Comparative Example 1 after being folded twice. It can be seen that the positive electrode sheet of Comparative Example 1 is broken after being folded twice, and the flexibility of the positive electrode sheet is poor.

[0142] In Comparative Example 3, uncoated lithium iron phosphate and phosphate-based polyether were directly mixed to prepare positive electrode slurry, and after stirring for 5 hours, a positive electrode slurry with a solid content of 64% was obtained, and the positive electrode slurry was moderately gelled. The positive electrode sheet prepared in Comparative Example 3 was light-transmissive after being folded in half three times, and the flexibility of the positive electrode sheet was poor. The first coulomb efficiency of the secondary battery of Comparative Example 3 was 91%, and the capacity retention rate after 2000 cycles was 88.8%.

[0143] The surface of the positive electrode main material lithium manganese iron phosphate in the positive electrode material of Example 21 is coated with acid ester polyether. After stirring the positive electrode material for 2.5 hours, a positive electrode slurry with a solid content of 64% is prepared, and the positive electrode slurry has no gel problem. The positive electrode plate prepared in Example 21 is light-transmissive only after being folded in half 5 times, and the positive electrode plate has good flexibility. The first coulomb efficiency of the secondary battery of Example 21 is 94.2%, and the capacity retention rate after 2000 cycles is 93.8%. The secondary battery has a high first coulomb efficiency and a high cycle capacity retention rate.

[0144] The positive electrode material of Comparative Example 2 is uncoated lithium manganese iron phosphate. After stirring the positive electrode material for 4 hours, a positive electrode slurry with a solid content of 55% was prepared, and the positive electrode slurry had serious gel. The positive electrode sheet of Comparative Example 2 was light-transmissive after being folded twice, and the flexibility of the positive electrode sheet was poor. The first coulomb efficiency of the secondary battery of Comparative Example 2 was 92%, and the capacity retention rate after 2000 cycles was 91%.

[0145] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0146] The above-described embodiments only express several implementation methods of the present application, which is convenient for understanding the technical solutions of the present application in detail, but cannot be understood as limiting the scope of protection of the invention patent. It should be pointed out that for ordinary technicians in this field, without departing from the concept of the present application, several modifications and improvements can be made, which all belong to the protection scope of the present application. It should be understood that the technical solutions obtained by those skilled in the art through logical analysis, reasoning or limited experiments on the basis of the technical solutions provided in the present application are all within the protection scope of the attached claims described in the present application. Therefore, the protection scope of the patent of this application shall be based on the contents of the attached claims, and the description and drawings can be used to explain the contents of the claims.

Claims

1. A positive electrode material, wherein: include: a positive electrode active material, the positive electrode active material comprising a phosphate; and The coating layer is coated on the surface of the positive electrode active material, and the coating layer contains phosphate-based polyether.

2. The positive electrode material according to claim 1, wherein The phosphate is a lithium-containing phosphate.

3. The positive electrode material according to claim 2, wherein The lithium-containing phosphate includes at least one of lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate and lithium phosphate.

4. The positive electrode material according to any one of claims 1 to 3, wherein The mass ratio of the coating layer to the positive electrode active material is (1-20):1000.

5. The positive electrode material according to any one of claims 1 to 3, wherein The mass ratio of the coating layer to the positive electrode active material is (3-10):1000.

6. The positive electrode material according to any one of claims 1 to 3, wherein The coating layer has a thickness of 1 nm to 200 nm.

7. The positive electrode material according to any one of claims 1 to 3, wherein The coating layer has a thickness of 5 nm to 80 nm.

8. The positive electrode material according to any one of claims 1 to 3, wherein The percentage of the coating area of ​​the coating layer on the surface of the positive electrode active material to the surface area of ​​the positive electrode active material is 40% to 100%.

9. The positive electrode material according to any one of claims 1 to 3, wherein The percentage of the coating area of ​​the coating layer on the surface of the positive electrode active material to the surface area of ​​the positive electrode active material is 60% to 80%.

10. The positive electrode material according to any one of claims 1 to 3, wherein The number average molecular weight of the phosphate-based polyether is 500-5000.

11. The positive electrode material according to any one of claims 1 to 3, wherein The number average molecular weight of the phosphate-based polyether is 1500-3500.

12. A positive electrode slurry, wherein: The positive electrode material comprises the positive electrode material according to any one of claims 1 to 11.

13. The positive electrode slurry according to claim 12, wherein: The solid content of the positive electrode slurry is ≥60%.

14. The positive electrode slurry according to claim 12, wherein: The solid content of the positive electrode slurry is 60% to 70%.

15. A positive electrode sheet, wherein: The positive electrode material comprises the positive electrode material according to any one of claims 1 to 11 or is prepared by using the positive electrode slurry according to any one of claims 12 to 14.

16. A secondary battery, wherein: It comprises the positive electrode material according to any one of claims 1 to 11 or the positive electrode sheet according to claim 15.

17. A battery module, wherein: Includes the secondary battery as claimed in claim 16.

18. A battery pack, wherein: The invention comprises at least one of the secondary battery according to claim 16 and the battery module according to claim 17.

19. An electrical device, wherein: The battery comprises at least one selected from the group consisting of the secondary battery of claim 16, the battery module of claim 17, and the battery pack of claim 18.

Images