Positive electrode slurry, positive electrode plate, preparation method of positive electrode plate, secondary battery and electric device

Abstract

The invention provides positive electrode slurry, a positive electrode plate, a preparation method of the positive electrode plate, a secondary battery and an electric device, the positive electrode slurry comprises a positive electrode active material and a chlorine-containing polymer additive, and the surface of the positive electrode active material has residual lithium. The chlorine-containing polymer is added into the positive electrode slurry, the chlorine-containing polymer is decomposed to generate hydrogen chloride in the process of heating and curing the positive electrode slurry when the positive electrode plate is prepared, and the hydrogen chloride reacts with residual lithium on the surface of a positive electrode active material to generate lithium chloride serving as a lithium supplement agent. By adopting the positive electrode slurry, the lithium supplement agent can be effectively formed on the surface of the positive electrode active material, residual lithium on the surface of the positive electrode active material can be removed, and the gram capacity of the positive electrode can be improved. The positive pole piece prepared from the positive pole slurry can improve the energy density of the battery.

Description

Technical Field

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

[0002] The statements herein merely provide background information related to the present application and do not necessarily constitute prior art.

[0003] In recent years, as the application scope of secondary batteries becomes wider and wider, secondary batteries are widely used in energy storage power supply systems such as hydropower, thermal power, wind power and solar power stations, as well as in many fields such as electric tools, electric bicycles, electric motorcycles and electric vehicles.

[0004] As secondary batteries have made great progress, higher requirements have been put forward for their energy density. Batteries with higher energy density have very high requirements for positive electrode plates. For example, batteries with higher energy density usually require positive electrode plates with larger positive electrode gram capacity.

[0005] Therefore, seeking a positive electrode sheet with a larger gram capacity to improve the energy density of the battery is one of the key areas of focus for those skilled in the art. Summary of the invention

[0006] The present application is made in view of the above-mentioned problems, and one of its purposes is to provide a positive electrode slurry, and the positive electrode sheet prepared by using the positive electrode slurry has a larger positive electrode gram capacity.

[0007] In order to achieve the above-mentioned object, a first aspect of the present application provides a positive electrode slurry, comprising a positive electrode active material and a chlorine-containing polymer additive, wherein the surface of the positive electrode active material has residual lithium.

[0008] The present application adds a chlorine-containing polymer to the positive electrode slurry, and during the process of heating and curing the positive electrode slurry when preparing the positive electrode plate, the chlorine-containing polymer decomposes to produce hydrogen chloride, and the hydrogen chloride reacts with the residual lithium on the surface of the positive electrode active material to produce lithium chloride; since the theoretical decomposition potential of lithium chloride is relatively low, during the normal charging process of the battery, the lithium chloride can be used as a lithium supplement to decompose and produce metallic lithium, thereby realizing the lithium supplement function. The use of the above-mentioned positive electrode slurry can not only effectively form a lithium supplement on the surface of the positive electrode active material, but also remove the residual lithium on the surface of the positive electrode active material, which can increase the positive electrode gram capacity, thereby increasing the energy density.

[0009] In any embodiment, the chlorine-containing polymer additive includes one or more of polyvinyl chloride, vinyl chloride-acrylate copolymer, vinyl chloride-acrylonitrile copolymer, vinyl chloride-butadiene copolymer and vinyl chloride-vinyl ether copolymer. In this way, the chlorine-containing polymer can decompose to produce hydrogen chloride at the normal heating and curing temperature of the positive electrode slurry, thereby effectively reacting with the residual lithium on the surface of the positive electrode active material to produce lithium chloride, achieving a good lithium supplementation effect.

[0010] In any embodiment, the chlorine-containing polymer additive includes one or more of polyvinyl chloride, vinyl chloride-acrylate copolymer and vinyl chloride-acrylonitrile copolymer. Thus, the use of these chlorine-containing polymers can not only achieve a good lithium supplement effect, but also improve the bonding force of the positive electrode sheet.

[0011] In any embodiment, based on the total mass of the solute in the positive electrode slurry, the mass fraction of the chlorine-containing polymer additive is 0.1% to 1.5%. In this way, the positive electrode gram capacity can be effectively increased, and the proportion of positive electrode active materials can be reduced due to excessive addition of chlorine-containing polymer, thereby reducing the battery energy density.

[0012] In any embodiment, based on the total mass of the solute in the positive electrode slurry, the mass fraction of the chlorine-containing polymer additive is 0.5% to 1.0%, which can more effectively increase the positive electrode capacity and help increase the content of positive electrode active materials in the positive electrode film layer.

[0013] In any embodiment, based on the total mass of the positive electrode active material, the mass fraction of the residual lithium is 0.005% to 2.0%. In this way, the residual lithium can react with the hydrogen chloride generated by the decomposition of the chlorine-containing polymer to generate an appropriate amount of lithium chloride on the surface of the positive electrode active material as a lithium supplement, thereby achieving a good lithium supplement effect.

[0014] In any embodiment, based on the total mass of the positive electrode active material, the mass fraction of the residual lithium is 0.5% to 2.0%, so that the charge and discharge capacity of the positive electrode plate can be further increased, and the lithium supplementation effect can be further improved.

[0015] The second aspect of the present application provides a method for preparing a positive electrode sheet, comprising the following steps:

[0016] attaching the positive electrode slurry of the first aspect of the present application to the positive electrode current collector; and

[0017] The positive electrode slurry is solidified by heating to form a positive electrode film layer on the positive electrode current collector, and the residual lithium is converted into lithium chloride.

[0018] By adding a chlorine-containing polymer to the positive electrode slurry, the chlorine-containing polymer decomposes to produce hydrogen chloride during the heating and curing process of the positive electrode slurry, and the hydrogen chloride reacts with the residual lithium on the surface of the positive electrode active material to form lithium chloride; the theoretical decomposition potential of lithium chloride is relatively low, and during the normal charging process of the battery, the lithium chloride can be used as a lithium supplement to decompose and generate metallic lithium, thereby realizing the lithium supplement function. The above preparation method can not only effectively form a lithium supplement on the surface of the positive electrode active material, but also remove the residual lithium on the surface of the positive electrode active material, which can increase the positive electrode gram capacity. The positive electrode sheet prepared by this method can increase the energy density of the battery.

[0019] In any embodiment, the heating temperature is 80° C. to 120° C., and the heating time is 4 h to 24 h. In this way, the chlorine-containing polymer in the positive electrode slurry can be fully decomposed to generate hydrogen chloride, which further reacts with the residual lithium on the surface of the positive electrode active material to generate lithium chloride.

[0020] In any embodiment, the heating temperature is 90° C. to 100° C., and the heating time is 8 h to 15 h. In this way, not only can the residual lithium on the surface of the positive electrode active material be fully reacted to generate lithium chloride, but also the curing efficiency can be appropriately improved.

[0021] The third aspect of the present application provides a positive electrode sheet, which is prepared by the preparation method of the positive electrode sheet of the second aspect of the present application. Thus, the positive electrode sheet has a larger positive electrode gram capacity.

[0022] The fourth aspect of the present application provides a secondary battery, wherein the secondary battery comprises the positive electrode sheet of the third aspect of the present application, so that the secondary battery has a higher energy density.

[0023] A fifth aspect of the present application provides an electrical device, which includes the secondary battery of the fourth aspect of the present application.

[0024] The details of one or more embodiments of the present application are set forth in the following drawings and description. Other features, objects, and advantages of the present application will become apparent from the description, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to better describe and illustrate the embodiments or examples provided by the present application, reference may be made to one or more drawings. The additional details or examples used to describe the drawings should not be considered as limiting the scope of the disclosed application, the embodiments or examples currently described, and any of the best modes of these applications currently understood. Moreover, the same reference numerals are used throughout the drawings to represent the same components. In the drawings:

[0026] Figure 1 A schematic diagram of a battery cell according to an embodiment of the present application;

[0027] Figure 2 for Figure 1 An exploded view of a battery cell according to an embodiment of the present application is shown;

[0028] Figure 3 FIG. 1 is a schematic diagram of an electrical device using a secondary battery according to an embodiment of the present application as a power source.

[0029] Description of reference numerals:

[0030] 5. Battery cell; 51. Shell; 52. Electrode assembly; 53. Cover plate; 6. Electrical device. DETAILED DESCRIPTION

[0031] Below, the embodiments of the positive electrode slurry, positive electrode sheet and preparation method thereof, secondary battery and electric device of the present application are described in detail with appropriate reference to the drawings. However, there may be 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.

[0032] The "range" disclosed in the present application can be defined in the form of a lower limit and an upper limit, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The range defined in this way can be inclusive or exclusive of the end values, and any end value can be included or excluded independently, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. For example, if a range of 60 to 120 and 80 to 110 is listed for a specific parameter, it is understood that the range of 60 to 110 and 80 to 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 also listed, the following ranges can all be expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4 and 2 to 5. In the present application, unless otherwise specified, the numerical range "a to b" represents an abbreviation of any real number combination between a and b, where a and b are both 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 listing the parameter as, for example, integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For example, when a parameter is expressed as an integer selected from "2-10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9 and 10.

[0033] In the present application, "plurality", "multiple" and the like, unless otherwise specified, refer to a number greater than or equal to 2. For example, "one or more" means one or greater than or equal to two.

[0034] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0035] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment or implementation of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments. The "implementation methods" mentioned herein have a similar understanding.

[0036] Those skilled in the art will appreciate that, in the methods of each embodiment or example, the order in which each step is written does not mean a strict order of execution and does not constitute any limitation on the implementation process, and the detailed order of execution of each step should be determined by its function and possible internal logic. 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), indicating that the method may include steps (a) and (b) performed sequentially, or steps (b) and (a) performed sequentially. For example, the method may also include step (c), indicating that step (c) can be added to the method in any order, for example, the method may include steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0037] In the present application, in the open technical features or technical solutions described by the words "contain", "include", "comprise", etc., unless otherwise specified, additional members other than the listed members are not excluded, and it can be regarded as providing both closed features or solutions consisting of the listed members and open features or solutions including additional members in addition to the listed members. For example, A includes a1, a2 and a3. Unless otherwise specified, it may also include other members or may not include additional members. It can be regarded as providing both the feature or solution of "A consists of a1, a2 and a3" and the feature or solution of "A not only includes a1, a2 and a3, but also includes other members". In the present application, unless otherwise specified, A (such as B) means that B is a non-limiting example of A, and it can be understood that A is not limited to B.

[0038] In this application, "optionally", "optional", and "optional" mean optional, that is, any one of the two parallel schemes of "yes" or "no". If there are multiple "options" in a technical solution, unless otherwise specified and there is no contradiction or mutual restriction, each "option" is independent.

[0039] The weights described in the embodiments of the present application may be μg, mg, g, kg, or other weight units known in the chemical industry.

[0040] At present, due to the great development of secondary batteries, higher requirements are also put forward for the energy density of secondary batteries. Batteries with higher energy density have very high requirements for positive electrode plates. For example, batteries with higher energy density usually require positive electrode plates with larger gram capacity. Therefore, seeking positive electrode plates with larger gram capacity to improve the energy density of batteries is one of the key areas of focus for those skilled in the art. In this regard, the present application provides a positive electrode slurry, which can effectively increase the gram capacity of the positive electrode by adding a chlorine-containing polymer additive to the positive electrode slurry. The chlorine-containing polymer additive can react with the residual lithium on the surface of the positive electrode active material to generate lithium chloride as a lithium supplement.

[0041] In some embodiments, the first aspect of the present application provides a positive electrode slurry, which includes a positive electrode active material and a chlorine-containing polymer additive, and the surface of the positive electrode active material has residual lithium.

[0042] The present application adds a chlorine-containing polymer additive to the positive electrode slurry. During the process of heating and curing the positive electrode slurry when preparing the positive electrode pole piece, the chlorine-containing polymer will decompose to produce hydrogen chloride. The generated hydrogen chloride can further react with the residual lithium on the surface of the positive electrode active material to generate lithium chloride. The theoretical decomposition potential of lithium chloride is relatively low (about 3.68V). The lithium chloride can undergo an oxidation-reduction reaction to generate metallic lithium as a lithium supplement during the normal charging voltage charging process of the battery, thereby realizing the lithium supplement function. The above-mentioned positive electrode slurry can not only effectively form a lithium supplement on the surface of the positive electrode active material, but also remove the residual lithium on the surface of the positive electrode active material, thereby increasing the positive electrode gram capacity. The positive electrode pole piece prepared by the positive electrode slurry is used in a secondary battery to increase the energy density of the battery.

[0043] It should be noted that compared to directly adding small molecule lithium compounds (such as lithium chloride) as lithium supplement agents in the positive electrode film layer, the present application adds a chlorine-containing polymer as an additive in the positive electrode slurry. During the heating and curing process of the positive electrode slurry, the chlorine-containing polymer can react with the residual lithium on the surface of the positive electrode active material, and react in situ on the surface of the positive electrode active material to generate lithium chloride, which can form extremely nano-sized and evenly dispersed lithium chloride particles on the surface of the positive electrode active material, achieve better lithium supplement effect, and remove residual lithium on the surface of the positive electrode active material. If the chlorine-containing polymer is replaced by a fluorine-containing polymer or a bromine-containing polymer, since the fluorine-containing polymer and the bromine-containing polymer have good thermal stability, their general decomposition temperature is about 300°C, and they will not decompose to produce hydrogen fluoride and hydrogen bromide at the normal heating and curing temperature of the positive electrode slurry, so they cannot react with the residual lithium on the surface of the positive electrode active material to generate lithium fluoride, lithium bromide, etc. as lithium supplement agents, and the lithium supplement effect cannot be achieved.

[0044] It can be understood that the residual lithium on the surface of the positive electrode active material refers to the residual lithium compounds such as Li2CO3, LiHCO3, LiOH, etc. on the surface of the positive electrode active material. The presence of these residual lithium will not only increase the instability of the positive electrode active material and cause the decline of the electrochemical performance of the positive electrode active material, but also cause safety problems of the battery.

[0045] In some embodiments, the chlorine-containing polymer additive includes one or more of polyvinyl chloride, vinyl chloride-acrylate copolymer, vinyl chloride-acrylonitrile copolymer, vinyl chloride-butadiene copolymer, and vinyl chloride-vinyl ether copolymer. The above-mentioned types of chlorine-containing polymers are used as additives, which can be decomposed to produce hydrogen chloride at the normal heating and curing temperature of the positive electrode slurry, so that hydrogen chloride can be effectively reacted with the residual lithium on the surface of the positive electrode active material to generate lithium chloride, achieving a good lithium supplementation effect.

[0046] In some embodiments, the chlorine-containing polymer additive includes one or more of polyvinyl chloride, vinyl chloride-acrylate copolymer and vinyl chloride-acrylonitrile copolymer. Thus, using one or more of polyvinyl chloride, vinyl chloride-acrylate copolymer and vinyl chloride-acrylonitrile copolymer as the chlorine-containing polymer additive can not only achieve a good lithium supplement effect, but also these polymers can enhance the bonding force between particles and between particles and substrates through their strong intermolecular forces or hydrogen bonding, thereby improving the bonding force between the positive electrode film layer and the positive electrode current collector in the positive electrode sheet.

[0047] In some of the embodiments, the mass fraction of the chlorine-containing polymer additive is 0.1% to 1.5% based on the total mass of the solute in the positive electrode slurry. Controlling the mass fraction of the chlorine-containing polymer additive in the solute of the positive electrode slurry within the range of 0.1% to 1.5% can not only effectively increase the positive electrode gram capacity, but also avoid reducing the proportion of positive electrode active materials and reducing battery energy density due to excessive addition of chlorine-containing polymers. It can be understood that the solute of the positive electrode slurry refers to other components in the positive electrode slurry except the solvent. In the present application, the solute of the positive electrode slurry includes positive electrode active materials, conductive agents, binders and chlorine-containing polymer additives.

[0048] It can be understood that the mass fraction of the chlorine-containing polymer additive in the solute of the positive electrode slurry can be but not limited to 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%.

[0049] In some embodiments, the mass fraction of the chlorine-containing polymer additive is 0.5% to 1.0% based on the total mass of the solute in the positive electrode slurry. Controlling the mass fraction of the chlorine-containing polymer additive in the solute of the positive electrode slurry within the range of 0.5% to 1.0% can more effectively increase the positive electrode gram capacity, and can better avoid the situation where too much chlorine-containing polymer reduces the proportion of positive electrode active materials and reduces the battery energy density.

[0050] In some embodiments, based on the total mass of the positive electrode active material, the mass fraction of residual lithium on the surface of the positive electrode active material is 0.005% to 2.0%. The residual lithium on the surface of the positive electrode active material can react with the hydrogen chloride produced after the decomposition of the chlorine-containing polymer additive to generate lithium chloride on the surface of the positive electrode active material as a lithium supplement. It can be understood that the amount of chlorine-containing polymer additive added to the positive electrode slurry can be adjusted accordingly according to the amount of residual lithium on the surface of the positive electrode active material. If the amount of residual lithium on the surface of the positive electrode active material is small, the amount of chlorine-containing polymer additive added to the positive electrode slurry can be reduced accordingly; if the amount of residual lithium on the surface of the positive electrode active material is large, the amount of chlorine-containing polymer additive added to the positive electrode slurry can be increased accordingly.

[0051] Understandably, the mass fraction of residual lithium on the surface of the positive electrode active material can be but is not limited to 0.005%, 0.008%, 0.01%, 0.015%, 0.02%, 0.03%, 0.05%, 0.08%, 0.1%, 0.15%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%.

[0052] In some embodiments, the mass fraction of residual lithium on the surface of the positive electrode active material is 0.5% to 2.0% based on the total mass of the positive electrode active material. Controlling the mass fraction of residual lithium on the surface of the positive electrode active material within the above range can further increase the charge and discharge capacity of the positive electrode sheet and further improve the lithium replenishment effect.

[0053] In some embodiments, the positive electrode slurry may further include a binder, which may be, but is not limited to, one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0054] In some embodiments, the positive electrode slurry may further include a conductive agent, which may be, but is not limited to, one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0055] In some embodiments, the second aspect of the present application further provides a method for preparing a positive electrode sheet, comprising the following steps:

[0056] The positive electrode slurry of the first aspect of the present application is provided, wherein the positive electrode slurry comprises a positive electrode active material and a chlorine-containing polymer additive, and the surface of the positive electrode active material has residual lithium;

[0057] attaching the positive electrode slurry to the positive electrode current collector; and

[0058] The positive electrode slurry on the positive electrode current collector is solidified by heating to form a positive electrode film layer on the positive electrode current collector, and the residual lithium on the surface of the positive electrode active material is converted into lithium chloride.

[0059] By adding a chlorine-containing polymer to the positive electrode slurry, the chlorine-containing polymer decomposes to produce hydrogen chloride during the heating and curing process of the positive electrode slurry, and the hydrogen chloride reacts with the residual lithium on the surface of the positive electrode active material to form lithium chloride; the theoretical decomposition potential of lithium chloride is relatively low, and during the normal charging process of the battery, the lithium chloride can be used as a lithium supplement to decompose and generate metallic lithium, thereby realizing the lithium supplement function. The above preparation method can not only effectively form a lithium supplement on the surface of the positive electrode active material, but also remove the residual lithium on the surface of the positive electrode active material, which can increase the positive electrode gram capacity. The positive electrode sheet prepared by this method can increase the energy density of the battery.

[0060] In some embodiments, the heating temperature for heating the positive electrode slurry on the positive electrode current collector to solidify and converting the residual lithium on the surface of the positive electrode active material into lithium chloride is 80°C to 120°C, and the heating time is 4h to 24h. Under this heating temperature and heating time condition, the positive electrode slurry can be solidified on the positive electrode current collector to form a positive electrode film layer, and the chlorine-containing polymer in the positive electrode slurry can be decomposed to generate hydrogen chloride, and the hydrogen chloride reacts with the residual lithium on the surface of the positive electrode active material to generate lithium chloride.

[0061] It will be appreciated that the heating temperature may be, but is not limited to, 80°C, 82°C, 85°C, 88°C, 90°C, 92°C, 95°C, 98°C, 100°C, 102°C, 105°C, 108°C, 110°C, 112°C, 115°C, 118°C, 120°C; the heating time may be, but is not limited to, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, 20h, 21h, 22h, 23h, 24h.

[0062] In some embodiments, the heating temperature of the positive electrode slurry for heating and curing is 90°C to 100°C, and the heating time is 8h to 15h. Controlling the heating and curing temperature and heating time of the positive electrode slurry on the positive electrode current collector within the above range can not only make the positive electrode slurry well cured to form a positive electrode film layer, but also make the residual lithium on the surface of the positive electrode active material fully react to generate lithium chloride, and have a high curing efficiency.

[0063] In some embodiments, the third aspect of the present application further provides a positive electrode sheet, which is prepared by the preparation method of the positive electrode sheet of the second aspect of the present application. Thus, the positive electrode sheet has a higher gram capacity.

[0064] In some embodiments, the fourth aspect of the present application further provides a secondary battery, the secondary battery comprising the positive electrode sheet of the third aspect of the present application, so that the secondary battery has a higher energy density.

[0065] In some embodiments, the fifth aspect of the present application further provides an electrical device, which includes the secondary battery of the fourth aspect of the present application.

[0066] The secondary battery and the electric device of the present application will be described below with reference to the drawings as appropriate.

[0067] Unless otherwise specified, the components, material types or contents of the batteries mentioned are applicable to both lithium-ion secondary batteries and sodium-ion secondary batteries.

[0068] In one embodiment of the present application, a secondary battery is provided.

[0069] 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.

[0070] Positive electrode

[0071] The positive electrode plate includes a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector.

[0072] As a non-limiting example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0073] In some 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 layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be obtained by forming a metal material on a polymer material substrate. In the positive electrode current collector, non-limiting examples of the metal material may include one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. In the positive electrode current collector, non-limiting examples of the polymer material substrate may include one or more of substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0074] In some embodiments, the positive electrode active material may include a positive electrode active material for a battery known in the art.

[0075] As a non-limiting example, the positive electrode active material of the lithium-ion secondary battery may include one or more of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries can also be used. These positive electrode active materials can be used alone or in combination of two or more. Among them, examples of lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide and their modified compounds. Non-limiting examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon. Non-limiting examples of lithium cobalt oxides may include LiCoO2; non-limiting examples of lithium nickel oxides may include LiNiO2; non-limiting examples of lithium manganese oxides may include LiMnO2, LiMn2O4, etc.; non-limiting examples of lithium nickel cobalt manganese oxides may include LiNi 1 / 3Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 )、LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 )、LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 )、LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 )、LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ) etc.; Non-limiting examples of lithium nickel cobalt aluminum oxide may include LiNi 0.8 Co 0.15 Al 0.05 O2.

[0076] It is understandable that the battery will be accompanied by lithium (Li) deintercalation and consumption during the charging and discharging process, and the content of Li in the positive electrode plate is different when the battery is discharged to different states. In the list of positive electrode materials in this application, unless otherwise specified, the content of Li is the initial state of the material. The positive electrode material is applied to the positive electrode plate in the battery system, and after the charge and discharge cycle, the content of Li in the positive electrode material contained in the plate usually changes. Among them, the content of Li can be measured by molar content, but is not limited to this. Regarding "the content of Li is the initial state of the material", the initial state of the material refers to the state before the material is added to the positive electrode slurry. It is understandable that the new material obtained by appropriate modification on the basis of the listed positive electrode materials is also within the scope of the positive electrode material. The aforementioned appropriate modification refers to the acceptable modification method for the positive electrode material, and non-limiting examples include coating modification.

[0077] In the list of positive electrode materials in this application, the content of oxygen (O) is only a theoretical state value. The release of oxygen from the lattice will cause the molar content of oxygen to change, and the actual content of O will fluctuate. Among them, the content of O can be measured by molar content, but is not limited to this.

[0078] As a non-limiting example, the positive electrode active material of the sodium ion secondary battery may include one or more of the following materials: one or more of sodium transition metal oxides, polyanionic compounds, and Prussian blue compounds. However, the present application is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials for sodium ion batteries may also be used.

[0079] As an optional technical solution of the present application, in the sodium transition metal oxide, the transition metal can be one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce. Sodium transition metal oxide is, for example, Na x MO2, wherein M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, and 0<x≤1.

[0080] As an optional technical solution of the present application, the polyanionic compound can be a compound having sodium ions, transition metal ions and tetrahedral (YO4) n- A class of compounds with anionic units. The transition metal can be one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce; Y can be one or more of P, S and Si; n represents (YO4) n- valence state.

[0081] Polyanionic compounds can also be those with sodium ions, transition metal ions, tetrahedral (YO4) n-A class of compounds with anion units and halogen anions. The transition metal can be one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce; Y can be one or more of P, S and Si, and n represents (YO4) n- valence state; the halogen can be one or more of F, Cl and Br.

[0082] Polyanionic compounds can also be sodium ions, tetrahedral (YO4) n- Anion unit, polyhedral unit (ZO y ) m+ and an optional halogen anion. Y can be one or more of P, S and Si, and n represents (YO4) n- valence state; Z represents a transition metal, which may be one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce; m represents (ZO y ) m+ valence state; the halogen can be one or more of F, Cl and Br.

[0083] Polyanionic compounds include NaFePO4, Na3V2(PO4)3 (sodium vanadium phosphate, abbreviated as NVP), Na4Fe3(PO4)2 (P2O7), NaM'PO4F (M' is one or more of V, Fe, Mn and Ni) and Na3(VO y )2(PO4)2F 3-2y One or more of (0≤y≤1).

[0084] Prussian blue compounds can be sodium ions, transition metal ions and cyanide ions (CN - ) compounds. The transition metal may be one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce. Prussian blue compounds are, for example, Na a Me b Me' c (CN)6, wherein Me and Me' are each independently one or more of Ni, Cu, Fe, Mn, Co and Zn, 0<a≤2, 0<b<1, 0<c<1.

[0085] In some embodiments, the positive electrode film layer may also optionally include a binder. As a non-limiting example, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin. The weight ratio of the binder in the positive electrode film layer is 0% to 20% by weight, based on the total weight of the positive electrode film layer.

[0086] In some embodiments, the positive electrode film layer may further include a conductive agent. As a non-limiting example, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The weight ratio of the conductive agent in the positive electrode film layer is 0 wt % to 20 wt %, based on the total weight of the positive electrode film layer.

[0087] In some embodiments, the positive electrode sheet can be prepared by the following method: 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, wherein the positive electrode slurry has a solid content of 40wt% to 80wt%, and the viscosity at room temperature is adjusted to 5000mPa·s to 25000mPa·s, the positive electrode slurry is coated on the surface of the positive electrode collector, and after drying, the positive electrode sheet is formed by cold rolling; the positive electrode powder coating unit surface density is 150mg / m 2 ~350 mg / m 2 The compaction density of the positive electrode is 3.0g / cm 3 ~3.6g / cm 3 , optional 3.3g / cm 3 ~3.5g / cm 3 .

[0088] The calculation formula of the compacted density is:

[0089] Compacted density = coating surface density / (thickness of the electrode after extrusion - thickness of the current collector).

[0090] The mass M of the positive electrode active material per unit area of ​​the positive electrode film can be obtained by weighing using a standard balance.

[0091] The thickness T of the positive electrode film can be measured by using a micrometer, for example, a Mitutoyo 293-100 micrometer with an accuracy of 0.1 μm. It should be noted that the thickness of the positive electrode film described in this application refers to the thickness of the positive electrode film in the positive electrode sheet used for assembling the battery after cold pressing.

[0092] Negative electrode

[0093] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0094] As a non-limiting example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0095] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. 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 obtained by forming a metal material on a polymer material substrate. Among them, in the negative electrode current collector, non-limiting examples of the metal material may include one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. In the negative electrode current collector, non-limiting examples of the polymer material substrate may include one or more of substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0096] In some embodiments, the negative electrode active material may be a negative electrode active material for a battery known in the art.

[0097] As a non-limiting example, the negative electrode active material of the lithium ion secondary battery may include one or more of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. Silicon-based materials may include one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may include one or more 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.

[0098] As a non-limiting example, the negative electrode active material of the sodium ion secondary battery is generally a hard carbon material, a two-dimensional metal carbide or a nitride. Preferably, the negative electrode active material of the sodium ion secondary battery is generally a hard carbon material.

[0099] In some embodiments, the negative electrode film layer may further include a binder. The binder may include one or more 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).

[0100] In some embodiments, the negative electrode film layer may further include a conductive agent, which may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0101] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0102] In some 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 (a non-limiting example of the solvent is deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on at least one side of the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained. The surface of the negative electrode collector coated with the negative electrode slurry can be on a single surface of the negative electrode collector or on both surfaces of the negative electrode collector. The solid content of the negative electrode slurry can be 40wt% to 60wt%. The viscosity of the negative electrode slurry at room temperature can be adjusted to 2000mPa·s to 10000mPa·s. When coating the negative electrode slurry, the coating unit surface density on a dry weight basis (excluding the solvent) can be 75g / m 2 ~220g / m 2 The compaction density of the negative electrode sheet can be 1.0g / cm 3 ~1.8g / cm 3 .

[0103] Electrolytes

[0104] The electrolyte has the function of conducting ions between the positive electrode and the negative electrode. The present application has no particular restrictions on the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be liquid, gel or all-solid.

[0105] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0106] In some embodiments, the electrolyte salt of the lithium ion secondary battery may include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobis(oxalatophosphate) (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).

[0107] In some embodiments, the solvent may include one or more of fluoroethylene carbonate (FEC), ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS) and diethyl sulfone (ESE).

[0108] 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.

[0109] In some embodiments, the additives in the electrolyte may include, but are not limited to, one or more of fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), trifluoromethylethylene carbonate (TFPC), and the like.

[0110] Isolation film

[0111] 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.

[0112] In some embodiments, the material of the isolation membrane may include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane may 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 may be the same or different, without particular limitation.

[0113] In some embodiments, the isolation film has a thickness of 6 μm to 40 μm, and may be 12 μm to 20 μm.

[0114] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly by a winding process or a lamination process.

[0115] In some embodiments, the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.

[0116] In some embodiments, the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, and further, non-limiting examples of plastic may include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0117] The secondary battery includes at least one battery cell. The secondary battery may include one or more battery cells.

[0118] In this application, unless otherwise specified, "battery cell" refers to a basic unit that can realize the mutual conversion of chemical energy and electrical energy, and further, generally speaking, at least includes a positive electrode sheet, a negative electrode sheet and an electrolyte. 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 active ions between the positive electrode sheet and the negative electrode sheet.

[0119] The present application has no particular restrictions on the shape of the battery cell, which can be cylindrical, square or any other shape. For example, Figure 1 The battery cell 5 is a square structure as an example.

[0120] In some embodiments, reference Figure 2 , the outer packaging 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 battery cell 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0121] In some embodiments, the battery cells 5 can be assembled into a battery module. The number of battery cells 5 contained in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0122] In the battery module, the plurality of battery cells 5 may be arranged in sequence along the length direction of the battery module. Of course, they may also be arranged in any other manner. Further, the plurality of battery cells 5 may be fixed by fasteners.

[0123] Optionally, the battery module may further include a housing having a receiving space, and the plurality of battery cells 5 are received in the receiving space.

[0124] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery pack.

[0125] The battery pack may include a battery box and a plurality of battery modules disposed in the battery box. The battery box includes an upper box body and a lower box body, and the upper box body can be covered on the lower box body to form a closed space for accommodating the battery modules. The plurality of battery modules can be arranged in the battery box in any manner.

[0126] In addition, the present application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in the present application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, and can also be used as an energy storage unit for the electrical device. The electrical device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.

[0127] As the electrical device, a secondary battery, a battery module or a battery pack may be selected according to its usage requirements.

[0128] Figure 3 The power consumption device 6 is taken as an example. The power consumption device 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.

[0129] 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 light and thin, and a secondary battery may be used as a power source.

[0130] The following are some examples.

[0131] In order to make the technical problems, technical solutions and beneficial effects solved by the present application clearer, the present application will be further described in detail below in conjunction with the embodiments and drawings. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present application and its applications. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0132] If no specific techniques or conditions are specified in the examples, the techniques or conditions described in the literature in the field or the product instructions are used. If no manufacturer is specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0133] 1. Implementation

[0134] Embodiment 1:

[0135] 1) Preparation of positive electrode

[0136] The positive electrode active material NCM 811 (whose residual lithium content is 1.2%), conductive carbon black, carbon nanotubes, 5130 binder, and chlorine-containing polymer additive polyvinyl chloride (PVC) are mixed evenly in a mass ratio of 97:1.0:0.5:1.0:0.5, and then N-methylpyrrolidone (NMP) is added as a solvent. The mixture is stirred under the action of a vacuum stirrer until the system is uniform to obtain a positive electrode slurry with a solid content of 75wt%.

[0137] The positive electrode slurry was evenly coated on the surface of the positive electrode current collector aluminum foil with a thickness of 13 μm to obtain a single-sided film with a weight of 300 mg / 1540.25 mm 2 The double-sided electrode sheet (excluding substrate) is dried at 105°C for 24 hours, cold pressed, and then subjected to processes such as tab forming and slitting to obtain the positive electrode sheet.

[0138] 2) Preparation of negative electrode sheet

[0139] The negative electrode active material artificial graphite, the conductive agent conductive carbon black, the binder styrene butadiene rubber (SBR), and the thickener carboxymethyl cellulose (CMC) are mixed in a mass ratio of 96:0.9:1.6:1.5, deionized water is added as a solvent, and stirred under the action of a vacuum mixer until the system is uniform to obtain a negative electrode slurry with a solid content of 54wt%.

[0140] The negative electrode slurry is evenly coated on the surface of the negative electrode current collector copper foil with a thickness of 8 μm, dried at 110°C, cold pressed, and subjected to processes such as tab forming and slitting to obtain a negative electrode sheet. The thickness of the negative electrode film layer in the negative electrode sheet is 110 μm.

[0141] 3) Preparation of electrolyte

[0142] In an argon atmosphere glove box (H2O<0.1ppm, O2<0.1ppm), non-aqueous organic solvents ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate were mixed in a volume ratio of 1:1:1 to obtain an electrolyte solvent, and then lithium salt LiPF6 was dissolved in the above mixed solvent to prepare an electrolyte with a lithium salt concentration of 1 mol / L.

[0143] 4) Isolation film

[0144] Polypropylene film is used as the isolation film.

[0145] 5) Preparation of lithium-ion batteries

[0146] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, so that the separator is between the positive electrode sheet and the negative electrode sheet to play an isolating role, and then they are wound to obtain an electrode assembly; the electrode assembly is placed in an outer packaging shell, and after drying, the electrolyte is injected, and after vacuum packaging, standing, forming, shaping and other processes, a lithium-ion secondary battery is obtained.

[0147] Embodiment 2:

[0148] This embodiment is basically the same as Embodiment 1, except that the mass ratio of the positive electrode active material, the conductive agent carbon black, the carbon nanotubes, the 5130 binder, and the chlorine-containing polymer additive PVC in the positive electrode slurry is 97.4:1.0:0.5:1.0:0.1.

[0149] Embodiment 3:

[0150] This embodiment is basically the same as Embodiment 1, except that the mass ratio of the positive electrode active material, the conductive agent carbon black, the carbon nanotubes, the 5130 binder, and the chlorine-containing polymer additive PVC in the positive electrode slurry is 96.5:1.0:0.5:1.0:1.0.

[0151] Embodiment 4:

[0152] This embodiment is basically the same as Embodiment 1, except that the mass ratio of the positive electrode active material, the conductive agent carbon black, the carbon nanotubes, the 5130 binder, and the chlorine-containing polymer additive PVC in the positive electrode slurry is 96:1.0:0.5:1.0:1.5.

[0153] Embodiment 5:

[0154] This embodiment is basically the same as Embodiment 1, except that vinyl chloride-acrylate copolymer is used as the chlorine-containing polymer additive in the positive electrode slurry.

[0155] Embodiment 6:

[0156] This embodiment is basically the same as Embodiment 1, except that vinyl chloride-acrylonitrile copolymer is used as the chlorine-containing polymer additive in the positive electrode slurry.

[0157] Embodiment 7:

[0158] This embodiment is basically the same as Embodiment 1, except that vinyl chloride-butadiene copolymer is used as the chlorine-containing polymer additive in the positive electrode slurry.

[0159] Embodiment 8:

[0160] This embodiment is basically the same as Embodiment 1, except that vinyl chloride-vinyl ether copolymer is used as the chlorine-containing polymer additive in the positive electrode slurry.

[0161] Embodiment 9:

[0162] This embodiment is basically the same as Embodiment 1, except that the electrode sheet coated with the positive electrode slurry is dried at 80° C. for 24 hours.

[0163] Embodiment 10:

[0164] This embodiment is basically the same as Embodiment 1, except that the electrode sheet coated with the positive electrode slurry is dried at 120° C. for 4 hours.

[0165] Embodiment 11:

[0166] This embodiment is basically the same as Embodiment 1, except that the electrode sheet coated with the positive electrode slurry is dried at 90° C. for 15 hours.

[0167] Embodiment 12:

[0168] This embodiment is basically the same as the embodiment 1, except that the electrode sheet coated with the positive electrode slurry is dried at 100° C. for 8 hours.

[0169] Embodiment 13:

[0170] This embodiment is basically the same as embodiment 1, except that the positive electrode active material in the positive electrode slurry is NCM 811 The mass fraction of residual lithium on the surface of the positive electrode active material is 0.005%.

[0171] Embodiment 14:

[0172] This embodiment is basically the same as embodiment 1, except that the positive electrode active material in the positive electrode slurry is NCM 811 The mass fraction of residual lithium on the surface of the positive electrode active material is 0.5%.

[0173] Embodiment 15:

[0174] This embodiment is basically the same as embodiment 1, except that the positive electrode active material in the positive electrode slurry is NCM 811 , the mass fraction of residual lithium on the surface of the positive electrode active material is 2.0%.

[0175] 2. Comparison

[0176] Comparative Example 1:

[0177] This comparative example is basically the same as Example 1, except that: PVC is not added to the positive electrode slurry; the mass ratio of the positive electrode active material, the conductive agent carbon black, the carbon nanotubes, and the 5130 binder in the positive electrode slurry is 97.0:1.0:0.5:1.5.

[0178] Comparative Example 2:

[0179] This comparative example is basically the same as Example 1, except that: PVC is not added to the positive electrode slurry, and polyvinyl fluoride (PVF) is added to the positive electrode slurry as an additive; the mass ratio of the positive electrode active material, conductive agent carbon black, carbon nanotubes, 5130 binder, and PVF in the positive electrode slurry is 97:1.0:0.5:1.0:0.5.

[0180] Comparative Example 3:

[0181] This comparative example is basically the same as Example 1, except that: PVC is not added to the positive electrode slurry, and lithium chloride is added to the positive electrode slurry as a lithium supplement; the mass ratio of the positive electrode active material, the conductive agent carbon black, the carbon nanotubes, the 5130 binder, and the lithium chloride in the positive electrode slurry is 97:1.0:0.5:1.0:0.5.

[0182] 3. Performance Test

[0183] 1) Positive electrode bonding test

[0184] A tensile testing machine is used to perform a 90° peeling test on the positive electrode sheet;

[0185] Sample preparation: stick the cold pressed positive electrode sheet on the substrate with double-sided tape;

[0186] Test: Place the pasted positive electrode sheet sample on the tensile testing machine, use the 90° peel test method to test the adhesion between the positive electrode film layer and the positive electrode current collector, and record the tensile force (N / m) of the tensile testing machine when the positive electrode film layer is peeled off from the positive electrode current collector.

[0187] 2) Positive electrode capacity test

[0188] At 25°C, the lithium-ion battery was charged at a constant current of 1 / 3C to a voltage of 4.35V, and then charged at a constant voltage of 4.35V to a current of 0.05C, and the charged gram capacity C0 was recorded; after standing for 5 minutes, the lithium-ion battery was discharged at a constant current of 1 / 3C to 2.8V, and the discharged gram capacity D0 was recorded;

[0189] Charge gram capacity = C0 / m1;

[0190] Discharge gram capacity = D0 / m1;

[0191] Wherein, m1=m0*a; m1 represents the mass of positive electrode active material per unit area in the positive electrode film layer, m0 represents the total solid weight per unit area in the positive electrode film layer, and a represents the mass percentage of the positive electrode active material in the positive electrode film layer.

[0192] 3) First calculation of battery coulombic efficiency

[0193] The first coulombic efficiency of the battery = discharge gram capacity / charge gram capacity = D0 / C0.

[0194] 4) Residual lithium test on the surface of positive electrode active materials

[0195] Reference standard: "Chemical reagents: General rules for potentiometric titration (GB / T 9725-2007)";

[0196] The specific test method is as follows:

[0197] 4.1) Power on: Turn on the power and software of the device and wait for 20 to 30 minutes for it to stabilize;

[0198] 4.2) Sample weighing: Use a balance to weigh 30.0000±0.5000g of sample into a 250mL iodine volumetric flask;

[0199] 4.3) Stirring: Add 100 mL of pure water into the iodine volumetric flask and place it on a magnetic stirrer and stir for 30 min;

[0200] 4.4) Standing: Seal and let stand for 10 minutes;

[0201] 4.5) Filtration: vacuum filtration with a 0.45 μm microporous membrane;

[0202] 4.6) Pipetting: Pipette the quantitative filtrate V3 into a 100 mL clean beaker according to the sample type;

[0203] 4.7) Draining: In the "Manual Control" interface of the test software, select "Liquid Adder 2" to drain;

[0204] 4.8) Electrode: completely immerse the composite pH electrode and the liquid adding tube in the solution;

[0205] 4.9) Titration: Use potentiometric titration method. Click the "Working Platform" of the software to switch to the working interface. Enter the name and number of the sample in the "ID1" column, enter the mass of the sample in the "Sample size" column, and click "Start" to test.

[0206] 4.10) Cleaning: Clean the glassware after the test is completed.

[0207] Data processing:

[0208] Li2CO3%=(V2-V1)×C×73.886×n×100 / 1000m

[0209] LiOH%=[V2-2×(V2-V1)]×C×23.946×n×100 / 1000m

[0210] Li + % = V2×C×6.94×n×100 / (m×1000)

[0211] In the above formula:

[0212] C is the concentration of the hydrochloric acid standard solution, in mol / L;

[0213] n is the ratio of the pipetted volume to the total volume, i.e. n = V3 / 100;

[0214] m is the mass of the sample, here 30 g, in g;

[0215] 73.886 is the molecular weight of lithium carbonate;

[0216] 23.946 is the molecular weight of lithium hydroxide;

[0217] 6.94 is the molecular weight of lithium;

[0218] V1 is the volume corresponding to the first titration endpoint, in mL;

[0219] V2 is the volume corresponding to the second titration endpoint, in mL;

[0220] V2-V1 is the volume of hydrochloric acid consumed by LiHCO3 (i.e., the second step reaction of Li2CO3);

[0221] 2×(V2-V1) is the volume of hydrochloric acid consumed by Li2CO3;

[0222] V2-2×(V2-V1) is the volume of hydrochloric acid consumed by LiOH.

[0223] The parameters and performance test data of the lithium-ion secondary batteries of the above embodiments and comparative examples are shown in Table 1.

[0224] Table 1

[0225]

[0226]

[0227]

[0228] From Table 1, we can see that:

[0229] In each embodiment of the present application, by adding chlorine-containing polymer polyvinyl chloride, vinyl chloride-acrylate copolymer, vinyl chloride-acrylonitrile copolymer, vinyl chloride-butadiene copolymer or vinyl chloride-vinyl ether copolymer to the positive electrode slurry, a good lithium replenishment effect can be achieved, and the charge and discharge gram capacity of the positive electrode plate can be improved.

[0230] By comparing Examples 1 to 4, it can be seen that controlling the content of the chlorine-containing polymer additive in the solute of the positive electrode slurry to 0.5% to 1.0% can make the positive electrode plate have a higher charge and discharge gram capacity and a higher first coulomb efficiency, and can achieve a better lithium replenishment effect.

[0231] By comparing Example 1 and Examples 13 to 15, it can be seen that controlling the mass fraction of residual lithium on the surface of the positive electrode active material within the range of 0.5% to 2.0% can further increase the charge and discharge capacity of the positive electrode sheet and further improve the lithium replenishment effect.

[0232] In Comparative Example 1, no chlorine-containing polymer additive is added to the positive electrode slurry, and the charge and discharge gram capacity of the positive electrode plate is significantly lower than that of Example 1; in Comparative Example 2, an equal amount of PVF is added to the positive electrode slurry instead of the chlorine-containing polymer additive. Since polyvinyl fluoride has good thermal stability, it is difficult to decompose to produce hydrogen fluoride at the normal heating and curing temperature of the positive electrode slurry, and the lithium replenishment effect is poor. The charge and discharge gram capacity of the positive electrode plate is significantly lower than that of Example 1; In Comparative Example 3, an equal amount of lithium chloride is used instead of the chlorine-containing polymer additive, and a good lithium replenishment effect cannot be achieved.

[0233] The above description of various embodiments tends to emphasize the differences between the various embodiments. The same or similar aspects can be referenced to each other, and for the sake of brevity, they will not be repeated herein.

[0234] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A positive electrode slurry, characterized in that: The invention comprises a positive electrode active material and a chlorine-containing polymer additive, wherein the surface of the positive electrode active material has residual lithium.

2. The positive electrode slurry according to claim 1, characterized in that The chlorine-containing polymer additive includes one or more of polyvinyl chloride, vinyl chloride-acrylate copolymer, vinyl chloride-acrylonitrile copolymer, vinyl chloride-butadiene copolymer and vinyl chloride-vinyl ether copolymer.

3. The positive electrode slurry according to claim 2, characterized in that The chlorine-containing polymer additive includes one or more of polyvinyl chloride, vinyl chloride-acrylate copolymer and vinyl chloride-acrylonitrile copolymer.

4. The positive electrode slurry according to any one of claims 1 to 3, characterized in that Based on the total mass of the solute in the positive electrode slurry, the mass fraction of the chlorine-containing polymer additive is 0.1% to 1.5%.

5. The positive electrode slurry according to any one of claims 1 to 3, characterized in that Based on the total mass of the solute in the positive electrode slurry, the mass fraction of the chlorine-containing polymer additive is 0.5% to 1.0%.

6. The positive electrode slurry according to any one of claims 1 to 3, characterized in that: Based on the total mass of the positive electrode active material, the mass fraction of the residual lithium is 0.005% to 2.0%.

7. The positive electrode slurry according to any one of claims 1 to 3, characterized in that Based on the total mass of the positive electrode active material, the mass fraction of the residual lithium is 0.5% to 2.0%.

8. A method for preparing a positive electrode sheet, characterized in that: include: Adhere the positive electrode slurry according to any one of claims 1 to 7 to the positive electrode current collector; as well as The positive electrode slurry is solidified by heating to form a positive electrode film layer on the positive electrode current collector, and the residual lithium is converted into lithium chloride.

9. The method for preparing a positive electrode sheet according to claim 8, characterized in that: The heating temperature is 80° C. to 120° C., and the heating time is 4 h to 24 h.

10. The method for preparing a positive electrode sheet according to claim 8 or 9, characterized in that: The heating temperature is 90° C. to 100° C., and the heating time is 8 h to 15 h.

11. A positive electrode sheet, characterized in that: The positive electrode sheet is prepared by the method for preparing a positive electrode sheet according to any one of claims 8 to 10.

12. A secondary battery, characterized in that: Including the positive electrode sheet as claimed in claim 11.

13. An electrical device, characterized in that: Includes the secondary battery as claimed in claim 12.

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