Secondary battery and electric device

Abstract

The present application provides a secondary battery and an electric device. The secondary battery comprises a positive electrode sheet and a negative electrode sheet. The positive electrode sheet comprises a positive electrode active material; the positive electrode active material comprises a ternary material containing a nickel element and a crystalline coating layer located on at least part of the surface of the ternary material; and the ternary material has a molecular formula of LiaNibCocMn1-b-cOe, wherein 0.9≤a≤1.2, 0.55≤b≤0.96, 0<c<≤0.20, 0≤1-b-c≤0.25, and 1.8≤e≤2.2. The negative electrode sheet comprises a negative electrode active material; and the negative electrode active material contains a silicon element. The crystalline coating layer can reduce the interface side reaction between the positive electrode material and an electrolyte, and mitigates the damage to a negative electrode SEI film, thereby improving the cycle stability of the battery.

Description

Secondary batteries and electrical devices

[0001] Cross-references

[0002] This application refers to Chinese Patent Application No. 202410315246.1, filed on March 19, 2024, entitled “Secondary Battery and Electrical Device,” which is incorporated herein by reference in its entirety. Technical Field

[0003] The present application relates to the technical field of secondary batteries, and in particular to a secondary battery and an electrical device. Background Art

[0004] With the implementation of the national dual carbon strategy, carbon reduction has become a key theme for manufacturing development in the 21st century. A green, low-carbon economic development model is favored by both the government and the industry. New energy sources are being sought after for their green, environmentally friendly, and low-carbon characteristics. In particular, new energy power batteries have seen rapid growth in recent years. However, the high cost of power batteries has prevented consumers from fully reaping the benefits of this industry development, limiting further penetration of new energy power batteries. Therefore, developing low-cost, long-range power batteries has become a major challenge and a key area of ​​focus for the industry.

[0005] Increasing the upper voltage limit of ternary materials can increase the energy density of ternary materials and effectively reduce the watt-hour cost of the materials. However, due to the layered structure characteristics of ternary materials, the increase in voltage will cause an increase in side reactions between the positive electrode material and the electrolyte, thereby causing the electrical performance of the material to deteriorate.

[0006] Therefore, improving the structural strength of ternary materials and solving the interface effect between positive electrode materials and electrolytes can effectively expand the use range of ternary materials and reduce material costs. Summary of the Invention

[0007] The present application is made in view of the above-mentioned problem, and its purpose is to provide a positive electrode active material having a crystalline coating layer that can reduce the interfacial side reactions between the positive electrode material and the electrolyte and improve the damage to the negative electrode SEI film, thereby improving the cycle stability of the battery.

[0008] In order to achieve the above object, the first aspect of the present application provides a secondary battery, comprising a positive electrode sheet and a negative electrode sheet, wherein the positive electrode sheet comprises a positive electrode active material, wherein the positive electrode active material comprises a ternary material containing nickel and a crystalline coating layer located on at least a portion of the surface of the ternary material, wherein the ternary material has a molecular formula of Li a Ni b Co c Mn 1-b-c O e, where 0.9 ≤ a ≤ 1.2, 0.55 ≤ b ≤ 0.96, 0 < c ≤ 0.20, 0 ≤ 1 - b - c ≤ 0.25, 1.8 ≤ e ≤ 2.2; the negative electrode sheet includes a negative electrode active material, and the negative electrode active material contains silicon element.

[0009] The surface of the positive electrode active material has a crystalline coating layer, which can effectively shield the corrosion of the electrolyte, reduce the side reaction between the positive electrode active material and the electrolyte, and improve the damage to the SEI film on the surface of the silicon-containing negative electrode, thereby improving the cycle performance of the high-energy density battery.

[0010] In any embodiment, the crystalline coating layer includes a crystalline compound.

[0011] In any embodiment, the crystalline compound includes a lithium oxide compound, and the lithium oxide compound contains one or more of the elements Co, Zr, Nb, W, B, Sr, Al.

[0012] In any embodiment, the chemical formula of the crystalline compound is Li a M b O c , where M includes one or more of Co, Zr, Nb, W, B, Sr, Al, and 0.5 ≤ a ≤ 3, 0.5 ≤ b ≤ 5, 0 < c ≤ 10.

[0013] Coating with the above type of crystalline compound can further improve the corrosion of the electrolyte to the electrode sheet during battery use, thereby further improving the cycle performance of the high-energy density battery.

[0014] In any embodiment, based on the total molar amount of the transition metal elements in the ternary material, the molar proportion of nickel element is 60% - 90%.

[0015] When the positive electrode active material contains nickel element with the above molar proportion, it has good electrochemical reaction activity, so that the battery has the advantage of high energy density.

[0016] In any embodiment, based on the total mass of the negative electrode active material, the mass fraction of silicon element is 5% - 15%.

[0017] When the negative electrode active material contains silicon element with the above mass fraction, it can further improve the cycle stability of the battery.

[0018] In any embodiment, the bulk part of the ternary material includes a layered phase, and the surface part of the ternary material includes a layered phase, a spinel phase and a rock salt phase.

[0019] Spinel and rock salt phases have the characteristics of structural stability. By distributing spinel and rock salt structures on the surface of the ternary material, the stability of the material can be further improved.

[0020] In any embodiment, the negative electrode active material includes a silicon-based material and a carbon-based material, the silicon-based material includes at least one of elemental silicon, silicon oxides, and silicon-carbon composites, and the carbon-based material includes at least one of artificial graphite and natural graphite.

[0021] When the above-mentioned types of negative electrode active materials are selected, the cycle stability of the battery can be further improved.

[0022] In any embodiment, the specific surface area of ​​the positive electrode active material is 0.3 m 2 / g~0.9m 2 / g.

[0023] When the specific surface area of ​​the positive electrode active material is within the above range, it has a good gram capacity and moderate activity, and can avoid side reactions induced by excessive activity.

[0024] In any embodiment, the positive electrode active material includes secondary particles, and the particle strength of the positive electrode active material is 50 MPa to 300 MPa.

[0025] When the particle strength of the positive electrode active material is within the above range, the material is not prone to cracking, which can improve the cycle performance of the battery.

[0026] In any embodiment, the Dv50 of the positive electrode active material is 8 μm to 15 μm.

[0027] In any embodiment, the powder compaction density of the positive electrode active material under 5 tons of pressure is 3.1 g / cm 3 ~3.5g / cm 3 .

[0028] When the Dv50 and powder compaction density of the positive electrode active material are within the above ranges, the cycle performance of the battery can be further improved.

[0029] A second aspect of the present application provides an electrical device comprising the secondary battery described in the first aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] FIG1 is a schematic diagram of a secondary battery according to an embodiment of the present application;

[0031] FIG2 is an exploded view of the secondary battery according to one embodiment of the present application shown in FIG1 ;

[0032] FIG3 is a schematic diagram of an electric device using a secondary battery as a power source according to an embodiment of the present application.

[0033] Description of reference numerals: 5 secondary battery; 51 housing; 52 electrode assembly; 53 cover plate. DETAILED DESCRIPTION

[0034] Below, embodiments of the secondary battery, electrical device, and method for manufacturing the same of the present application are described in detail. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repeated descriptions of substantially identical structures may be omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the drawings and the following description 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] The "ranges" disclosed herein are defined in terms of lower and upper limits, where a given range is defined by selecting a lower limit and an upper limit, and the selected lower and upper limits define the boundaries of the particular range. Ranges defined in this manner can be inclusive or exclusive of the end values ​​and can be combined arbitrarily, i.e., any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 to 120 and 80 to 110 are listed for a particular parameter, it is understood that ranges of 60 to 110 and 80 to 120 are also contemplated. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, the following ranges are all contemplated: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. In this application, unless otherwise indicated, the numerical range "a to b" is a shorthand representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this 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] Unless otherwise specified, all steps of the present application may be performed sequentially, randomly, or optionally sequentially. For example, the method includes steps (a) and (b), indicating 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), indicating 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] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0040] Unless otherwise specified, the term "or" is used in this application to be inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any of the following conditions are met: 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] Ternary materials, especially high nickel materials, have strong electrochemical reactivity, which can bring higher energy density. However, the strong electrochemical reactivity will also make the high nickel material prone to side reactions with the electrolyte solution, resulting in material loss of the high nickel material, and the lost material will eventually be deposited on the negative electrode surface through the electrolyte and the separator, destroying the SEI film on the negative electrode surface and affecting the capacity of the negative electrode, ultimately causing the battery life to deteriorate. Therefore, protecting the positive electrode material from electrolyte corrosion has become a current research hotspot. The present application is made in view of the above-mentioned topic, and its purpose is to provide a positive electrode active material having a crystalline coating layer that can reduce the interface side reactions between the positive electrode material and the electrolyte, and improve the damage to the negative electrode SEI film, thereby improving the cycle stability of the battery.

[0042] [Active Materials]

[0043] In order to achieve the above-mentioned objectives, the present application provides a secondary battery, including a positive electrode plate and a negative electrode plate, wherein the positive electrode plate includes a positive electrode active material, wherein the positive electrode active material includes a ternary material containing nickel and a crystalline coating layer located on at least a portion of the surface of the ternary material; the negative electrode plate includes a negative electrode active material, wherein the negative electrode active material contains silicon.

[0044] As used herein, "ternary material" has the meaning commonly understood in the art. In some non-limiting examples, the ternary material may refer to NCM (lithium nickel cobalt manganese oxide) or NCA (lithium nickel cobalt aluminum oxide), etc.

[0045] As used herein, "crystalline state" has the meaning commonly understood in the art, and refers to a substance formed by a regular, periodic, and repetitive arrangement of atoms, molecules, or ions in three-dimensional space.

[0046] As used herein, "amorphous state" has the meaning commonly understood in the art, and refers to a substance with disordered structure or short-range order but long-range disorder.

[0047] As used herein, "coating layer" refers to the portion coated on the ternary material, which may but does not necessarily completely coat the ternary material. The use of "coating layer" is only for the convenience of description and is not intended to limit the present application.

[0048] The crystalline coating on the surface of the positive electrode active material can effectively shield the electrolyte corrosion, reduce the side reaction between the positive electrode active material and the electrolyte, and improve the damage to the SEI film on the surface of the silicon-containing negative electrode, thereby improving the cycle performance of high energy density batteries.

[0049] In some embodiments, the crystalline coating comprises a crystalline compound.

[0050] In some embodiments, the crystalline compound includes a lithium oxygen compound, and the lithium oxygen compound contains one or two or more of the elements Co, Zr, Nb, W, B, Sr, and Al.

[0051] In some embodiments, the chemical formula of the crystalline compound is Li a M b O c , where M includes one or two or more of Co, Zr, Nb, W, B, Sr, and Al, where 0.5≤a≤3, 0.5≤b≤5, 0 <c≤10。

[0052] The use of the above-mentioned crystalline compound for coating can further improve the corrosion of the electrode by the electrolyte during the use of the battery, thereby further improving the cycle performance of the high energy density battery.

[0053] When used in this article, "having a molecular formula" is not limited to the substance represented by the molecular formula, but also includes other substances formed after further appropriate modification on the basis of the molecular formula, which is not limited here. The use of "having a molecular formula" is only for the convenience of description and is not intended to limit this application. It can be understood that new materials or new substances obtained by appropriate modification on the basis of the listed positive active materials are also within the scope of positive active materials. The aforementioned appropriate modification refers to an acceptable modification method for the positive active material, and a non-limiting example is coating modification.

[0054] In the enumeration of positive electrode active materials in this application, unless otherwise specified, the Li content refers to the initial state of the material. When the positive electrode active material is applied to the positive electrode sheet in the battery system, the Li content in the positive electrode active material contained in the positive electrode sheet will usually change after charge and discharge cycles. The Li content can be measured by atomic molar content, but is not limited to this. Regarding "the Li content refers to 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.

[0055] In the list of positive electrode active materials in this application, the oxygen (O) content is only a theoretical value. Lattice oxygen release will cause the atomic molar content of oxygen to change, and the actual O content will fluctuate. The O content can be measured by atomic molar content, but is not limited to this.

[0056] In some embodiments, the bulk portion of the ternary material includes a lamellar phase, and the surface portion of the ternary material includes a lamellar phase, a spinel phase, and a rock salt phase.

[0057] As used herein, the term "surface portion" refers to the portion within 50 nm (including 50 nm) of the depth from the surface of the ternary material. As used herein, the term "bulk portion" refers to the portion other than the "surface portion" that is outside 50 nm of the depth from the surface of the ternary material.

[0058] Spinel and rock salt phases have the characteristics of structural stability. By distributing spinel and rock salt structures on the surface of the ternary material, the stability of the material can be further improved.

[0059] In some embodiments, based on the total molar amount of the transition metal elements in the ternary material, the molar proportion of the nickel element is 55%-96%, for example, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 96%, etc., or other values ​​not listed in the range of 55%-96%. In some preferred embodiments, the molar proportion of the nickel element in the total amount of the transition metal elements is 60%, 80%, or 90%.

[0060] In some preferred embodiments, based on the total molar number of transition metal elements in the ternary material, the molar proportion of nickel element is 60%-90%.

[0061] When the positive electrode active material contains nickel element with the above-mentioned molar proportion, it has good electrochemical reaction activity, thus enabling the battery to have the advantage of high energy density.

[0062] In some embodiments, the ternary material has the molecular formula Li a Ni b Co c Mn 1-b-c O e , where 0.9 ≤ a ≤ 1.2, 0.55 ≤ b ≤ 0.96, 0 < c ≤ 0.20, 0 ≤ 1 - b - c ≤ 0.25, 1.8 ≤ e ≤ 2.2. [[ID=十七]]

[0063] The molecular formula Li a Ni b Co c Mn 1-b-c O e In the value range of b in is 0.55 ≤ b ≤ 0.96, such as 0.55, 0.60, 0.65, 0.70, 0.75, 0.80, 0.85, 0.90, 0.95, 0.96, etc., or other unlisted values within the range of 0.55 ≤ b ≤ 0.96. In some non-limiting embodiments, in the molecular formula Li a Ni b Co c Mn 1-b-c O e the value of b is 0.60, 0.80, 0.90.

[0064] The molecular formula Li<000阗031>Ni b Co c Mn 1-b-c O e In the value range of c in is 0 < c ≤ 0.20, such as 0.01, 0.05, 0.10, 0.15, 0.20, etc., or other unlisted values within the range of 0 < c ≤ 0.20. In some non-limiting embodiments, in the molecular formula Li a Ni b Co c Mn 1-b-c O e the value of c is 0.05, 0.10, 0.20.

[0065] When the ternary material has the above molecular formula, it has good electrochemical reaction activity, thus enabling the battery to have the advantage of high energy density.

[0066] In some embodiments, based on the total mass of the negative electrode active material, the mass fraction of silicon is 5% to 15%, for example, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%. 、 15%, etc., or other values ​​not listed in the range of 5% to 15%. In some preferred embodiments, the molar proportion of the nickel element in the total amount of the transition metal elements is 5%, 10%, or 15%.

[0067] In some embodiments, the negative electrode active material includes a silicon-based material and a carbon-based material, the silicon-based material includes at least one of elemental silicon, silicon oxides, and silicon-carbon composites, and the carbon-based material includes at least one of artificial graphite and natural graphite.

[0068] When the above-mentioned type of negative electrode active material is selected, or when the negative electrode active material contains silicon element with the above-mentioned mass fraction, the cycle stability of the battery can be further improved.

[0069] In some embodiments, the specific surface area of ​​the positive electrode active material is 0.3 m 2 / g~0.9m 2 / g, for example 0.3m 2 / g, 0.4m 2 / g, 0.5m 2 / g, 0.6m 2 / g, 0.7m 2 / g, 0.8m 2 / g, 0.9m 2 / g, or 0.3m 2 / g~0.9m 2 In some preferred embodiments, the specific surface area of ​​the positive electrode active material is 0.6 m 2 / g.

[0070] As used herein, "specific surface area" refers to the total surface area per unit mass of a material. This specific surface area can be determined according to GB / T 19587-2017 using nitrogen adsorption specific surface area analysis and calculation using the Brunauer-Emmett-Teller (BET) method. Nitrogen adsorption specific surface area analysis can be performed using a Micromeritics Tri-Star 3020 specific surface area pore size analyzer.

[0071] When the specific surface area of ​​the positive electrode active material is within the above range, it has a good gram capacity and moderate activity, and can avoid side reactions induced by excessive activity.

[0072] In some embodiments, the positive electrode active material includes secondary particles, and the particle strength of the positive electrode active material is 50 MPa to 300 MPa, such as 50 MPa, 60 MPa, 70 MPa, 80 MPa, 90 MPa, 100 MPa, 150 MPa, 200 MPa, 250 MPa, 300 MPa, or other values ​​within the range of 50 MPa to 300 MPa not listed. In some preferred embodiments, the specific surface area of ​​the positive electrode active material is 100 MPa.

[0073] When the particle strength of the positive electrode active material is within the above range, the material is not prone to cracking, which can improve the cycle performance of the battery.

[0074] In some embodiments, the Dv50 of the positive electrode active material is 8 μm to 15 μm, such as 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, or other values ​​not listed in the range of 8 μm to 15 μm. In some preferred embodiments, the Dv50 of the positive electrode active material is 10 μm.

[0075] As used herein, "Dv50" refers to the particle size at which the cumulative volume percentage reaches 50% of the particle size distribution, starting from the smallest particle size. This value is determined using a Malvern MasterSizer 2000 laser particle size analyzer, as per GB / T19077-2016 / ISO 13320:2009.

[0076] In some embodiments, the powder compaction density of the positive electrode active material under 5 tons of pressure is 3.1 g / cm 3 ~3.5g / cm 3 , for example 3.1 g / cm 3 、3.2g / cm 3 , 3.3g / cm 3 、3.4g / cm 3 , 3.5g / cm 3 , or 3.1g / cm 3 ~3.5g / cm 3 In some preferred embodiments, the powder compaction density of the positive electrode active material is 3.3 g / cm 3 .

[0077] As used herein, "compacted density" is defined as: compacted density = surface density / (thickness of the electrode after rolling - thickness of the current collector). The determination method can refer to GB / T24533-2009.

[0078] When the Dv50 and powder compaction density of the positive electrode active material are within the above ranges, the cycle performance of the battery can be further improved.

[0079] [Positive electrode]

[0080] The present application also provides a positive electrode plate, characterized in that it includes a positive electrode current collector and a positive electrode active material arranged on at least one surface of the positive electrode current collector, wherein the positive electrode active material is the positive electrode active material described in the present application.

[0081] 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 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 (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0082] In some embodiments, the positive electrode plate may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0083] In some embodiments, the positive electrode plate may further include a conductive agent. For 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.

[0084] 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; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0085] [Negative electrode]

[0086] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer arranged on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material, wherein the negative electrode active material is the negative electrode active material described in this application.

[0087] As an 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 either or both of the two opposite surfaces of the negative electrode current collector.

[0088] 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 base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0089] In some embodiments, the negative electrode film 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).

[0090] In some embodiments, the negative electrode film 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.

[0091] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0092] In some embodiments, the negative electrode sheet can be prepared by the following method: 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 current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0093] [Electrolytes]

[0094] The electrolyte plays the role of conducting ions between the positive electrode and the negative electrode. This application has no specific restrictions on the type of electrolyte, and it can be selected according to needs.

[0095] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0096] In some embodiments, the electrolyte salt may 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.

[0097] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl 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, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0098] In some embodiments, the electrolyte may further include additives. For example, the additives may include 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, and additives that improve battery high or low temperature performance.

[0099] [Isolation film]

[0100] 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 and mechanical stability can be selected.

[0101] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0102] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0103] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0104] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the secondary battery can be a soft shell, such as a pouch-type soft shell. The soft shell can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0105] [Secondary battery]

[0106] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square, or any other shape. For example, FIG1 shows a secondary battery 5 with a square structure as an example.

[0107] In some embodiments, referring to Figure 2, the outer packaging may include a shell 51 and a cover plate 53. 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 be formed into 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.

[0108] [Electrical devices]

[0109] In addition, the present application also provides an electrical device, which includes the secondary battery provided by the present application. The lithium secondary battery can be used as a power source for the electrical device, or 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 is not limited thereto.

[0110] As the electrical device, a secondary battery can be selected according to its usage requirements.

[0111] Figure 3 shows an example of an electric device. This device can be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery, a battery pack or battery module can be used.

[0112] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is generally required to be lightweight and thin, and may use a secondary battery as a power source.

[0113] Example

[0114] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0115] I. Preparation Method

[0116] Example 1

[0117] 1.1. Preparation of Cathode Active Material

[0118] Mix LiOH:Ni 0.80 Co 0.1 Mn 0.1 OH2 in a molar ratio of 1:1, and then sinter and react for 30 h under the conditions of 800 °C and an oxygen atmosphere to prepare Li 1-x Ni 0.80 Co 0.1 Mn 0.1 O2 (0 < x < 0.05). Then mix LiOH:Li 1-x [[ID=~]]Ni 0.80 Co 0.1 Mn 0.1 O2:ZrO2 in a molar ratio of 2:100:0.5 (where the ZrO2 used is crystalline), and then react with the material for 10 h under the conditions of 600 °C and an oxygen atmosphere to prepare LiNi 0.80 Co 0.1 Mn 0.1 O2 modified with a lithium oxygen compound containing Zr element.

[0119] 1.2. Preparation of Cathode Plate

[0120] Mix the cathode active material, polyvinylidene fluoride, and conductive carbon black in a mass ratio of 90:5:5, then add N-methylpyrrolidone (NMP), stir for 2 h, then stir it in a homogenizer at 1200 r / min until it is evenly mixed, and then evenly coat it on both sides of a 13-μm-thick aluminum foil current collector. After coating, dry it in an oven at 120 °C, cold press it, and slit it to obtain the cathode plate.

[0121] 1.3. Preparation of Electrolyte

[0122] Mix a mixed solution of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 1:2 to obtain a mixed solvent. Then, in a glove box under an argon atmosphere, dissolve thoroughly dried lithium hexafluorophosphate in the mixed solvent and mix it evenly to obtain the electrolyte. The lithium salt concentration in the electrolyte is 1 mol / L.

[0123] 1.4. Preparation of Anode Plate

[0124] Mix the graphite, silicon dioxide, sodium carboxymethyl cellulose, styrene-butadiene rubber and acetylene black of the negative electrode active material in a mass ratio of 75.5:20.5:1:1:2, add deionized water, stir evenly in a blender, and then coat the slurry on both sides of an 8-micron-thick copper foil, dry in an oven at 120 °C, cold press, and slit to obtain the negative electrode sheet.

[0125] 1.5. Preparation of the battery cell

[0126] Stack the positive electrode sheet, separator, and negative electrode sheet in sequence from top to bottom, ensure that the positive and negative electrode sheets do not contact each other, then wind them into a bare battery cell through a winding needle, place them in a square aluminum shell, inject electrolyte, and perform steps such as standing, forming, and capacity to prepare the battery cell.

[0127] Examples 2 to 9

[0128] The secondary batteries of Examples 2 to 9 are similar to the preparation method of Example 1, but the types of elements in the coating layer are adjusted, or the Ni content, Co content, and Mn content in the ternary material are adjusted, or the mass fraction of silicon element in the negative electrode active material is adjusted. The specific preparation parameters are shown in Tables 1 and 2.

[0129] Example 10

[0130] The secondary battery of Example 10 is similar to the preparation method of Example 1, but the preparation method of the positive electrode active material is adjusted to make the surface part of the ternary material only have the structural characteristics of a layered phase. The specific preparation method is as follows: Mix LiOH:Ni 0.80 Co 0.1 Mn 0.1 OH2 in a molar ratio of 1.08:1, and then sinter and react for 20 h under the conditions of 800 °C and an oxygen atmosphere to prepare Li 1+x Ni 0.80 Co 0.1 Mn 0.1 O2 (0 < x < 0.08), and then mix LiOH:Li 1+x Ni <000008 / 6>Co 0.1 Mn 0.1 O2:ZrO2 in a molar ratio of 2:100:0.5 (where the ZrO2 used is crystalline), and then react with the material for 10 h under the conditions of 600 °C and an oxygen atmosphere to prepare LiNi 0.80 Co 0.1 Mn 0.1 O2 modified with a lithium oxygen compound containing Zr element. The other preparation parameters are shown in Tables 1 and 2.

[0131] Comparative Example 1

[0132] The secondary battery of Comparative Example 1 was prepared in a similar manner to that of Example 1, but the preparation method of the positive electrode active material was adjusted so that the coating layer was amorphous. The preparation method was as follows: LiOH:Ni 0.80 Co 0.1 Mn 0.1 OH2 were mixed at a molar ratio of 1:1, and then sintered and reacted at 800 °C in an oxygen atmosphere for 30 h to prepare Li 1-x Ni 0.80 Co 0.1 [[ID=I2]]Mn 0.1 O2 (0 < x < 0.05). Then, Li 1-x Ni 0.80 Co 0.1 Mn 0.1 O2 and ZrO2 were mixed at a molar ratio of 100:0.5 (where the ZrO2 used was amorphous), and then reacted with the material at 300 °C in an oxygen atmosphere for 10 h to prepare LiNi 0.80 Co 0.1 Mn 0.1 O2 modified with a lithium oxide compound containing Zr element. Other preparation parameters are shown in Tables 1 and 2.

[0133] II. Performance Test

[0134] 1. Test Method for Related Parameters of Positive Electrode Active Material

[0135] (1) Test for Chemical Formula and Elements Contained in Coating Layer and Ternary Material:

[0136] Weigh 0.2 g of positive electrode active powder into a 100 mL beaker, add 10 mL of 10% w / w nitric acid solution, heat and digest at 120 °C for 0.5 h, and then make up the volume to 100 mL with a 100 mL volumetric flask; then pipette 1 mL and make up the volume to 100 mL with a 100 mL volumetric flask to obtain the test solution.

[0137] The mass fractions of each element in the test solution were measured using an inductively coupled plasma optical emission spectrometer (ICP - OES, instrument brand: Agilent 5800), and EDS was used to further determine the position of the modified element.

[0138] (2) Test Method for Volume - Distributed Particle Size Dv50:

[0139] Equipment model: Malvern 2000 (MasterSizer 2000) laser particle size analyzer, reference standard process: GB / T19077 - 2016 / ISO 13320:2009.

[0140] Detailed test process: Take an appropriate amount of washed sample (sample concentration ensures 8% to 12% shading), add 20mL of anhydrous ethanol, and ultrasonicate for 5 minutes (53KHz / 120W) to ensure that the sample is completely dispersed. Then, measure the sample according to GB / T19077-2016 / ISO 13320:2009 standard.

[0141] By the above method, it was detected that the Dv50 of the positive electrode active material prepared in Example 1 was 10 μm.

[0142] (3) Specific surface area test method:

[0143] The nitrogen adsorption specific surface area analysis test method is used for testing and is calculated using the BET (Brunauer Emmett Teller) method. The nitrogen adsorption specific surface area analysis test can be performed using a Tri Star II surface area and pore analyzer from Micromeritics, USA. The test steps can refer to GB / T 19587-2004.

[0144] The detailed steps are as follows: dry the sample to be tested in a vacuum drying oven at 200°C for 2 hours; weigh 1g of the sample to be tested and place it in a test tube, fill the liquid nitrogen cup with liquid nitrogen, insert it into the test tube, use nitrogen as the adsorption gas, and use the specific surface and pore analyzer to map the adsorption and desorption curve with a relative pressure P / P0 of 0 to 0.99, where P is the equilibrium adsorption pressure and P0 is the saturated vapor pressure. The BET specific surface area of ​​the positive electrode active material is calculated by the BET method.

[0145] By the above method, it was detected that the specific surface area of ​​the positive electrode active material prepared in Example 1 was 0.6 m 2 / g.

[0146] (4) Test method for particle strength:

[0147] A microhardness tester (Shimadzu DUH-211S) was used to select secondary particles of cathode materials with a Dv50 particle size of ±0.3 μm. The particles were squeezed by moving a probe equipped with a pressure sensor, and the particle strength was recorded.

[0148] By the above method, it was detected that the particle strength of the positive electrode active material prepared in Example 1 was 100 MPa.

[0149] (5) Test method for powder compaction density:

[0150] Weigh 10g of positive electrode material and place it in the compaction density tester mold. The tester automatically applies 5 tons of pressure to the powder until the powder is compacted. The volume of the powder can be calculated based on the cross-sectional area of ​​the mold and the thickness of the powder at this time. According to the compaction density = mass / volume, the compaction density of the powder material can be measured.

[0151] By the above method, it was found that the powder compaction density of the positive electrode active material prepared in Example 1 under a pressure of 5 tons was 3.30 g / cm 3 .

[0152] (6) Test methods for crystalline and amorphous states:

[0153] The boundaries of the positive electrode material are analyzed by TEM-EDS, and the crystallization state of the coating layer is determined based on the electron diffraction patterns and lattice fringes generated by the material.

[0154] The above method was used for detection, and it was confirmed that crystalline coating layers were prepared in Examples 1 to 10, while a non-crystalline coating layer was prepared in Comparative Example 1.

[0155] 2. Test method for battery cycle performance

[0156] At 25°C, the battery is charged at a constant current of 1C to 4.25V, then charged at a constant voltage of 4.25V to 0.05C, and discharged at 1C to 2.80V. This is the first cycle, and the discharge capacity of the first cycle is recorded as C0. The discharge capacity of the nth cycle is recorded as Cn, and the capacity retention rate of each cycle is Cn / C0. The capacity retention rate after 500 cycles is calculated.

[0157] 3. Analysis of test results of various embodiments and comparative examples

[0158] Batteries of various examples and comparative examples were prepared according to the above methods, and various performance parameters were measured. The results are shown in Table 2 below.

[0159] Table 1 Preparation parameters

[0160] Table 2 Preparation and performance parameters

[0161] In the positive electrode active materials in Examples 1 to 10, the surfaces of the ternary materials all have a crystalline coating layer, and the batteries prepared therefrom all have excellent cycle performance.

[0162] In the positive electrode active material of Comparative Example 1, the surface of the ternary material is coated with an amorphous material. A comparison of Comparative Example 1 with Examples 1-10 shows that a crystalline coating on the surface of the ternary material effectively improves the battery's cycling performance, while an amorphous coating does not effectively improve cycling performance.

[0163] It can be seen from Examples 1 to 5 that when the lithium oxygen compound coated on the surface of the ternary material contains one, two or more of Co, Zr, Nb, W, B, Sr, and Al (especially Zr, Sr, Al, and W), the secondary battery can have excellent cycle performance.

[0164] It can be seen from Examples 1, 6, and 7 that, based on the total molar number of transition metal elements in the ternary material, when the molar proportion of nickel element is 55-96% (especially 60%, 80%, and 90%), the secondary battery can have excellent cycle performance.

[0165] It can be seen from Examples 1, 6, and 7 that, based on the total molar number of transition metal elements in the ternary material, when the molar proportion of cobalt is 0-20% (especially 5%, 10%, and 20%), the secondary battery can have excellent cycle performance.

[0166] It can be seen from Examples 1, 6, and 7 that, based on the total molar number of transition metal elements in the ternary material, when the molar proportion of manganese element is 0-20% (especially 5%, 10%, and 20%), the secondary battery can have excellent cycle performance.

[0167] It can be seen from Examples 1, 8 and 9 that when the mass fraction of silicon in the negative electrode active material is 5-15%, the secondary battery can have excellent cycle performance.

[0168] It can be seen from Examples 1 and 10 that when the bulk phase of the ternary material is a layered phase, the surface phase is a layered phase, or the layered phase, spinel phase, and rock salt phase coexist, the secondary battery can have excellent cycle performance.

[0169] In Example 10, both the bulk and surface of the ternary material are layered phases. In Examples 1-9, the bulk of the ternary material is layered, while the surface is a coexistence of layered, spinel, and rock salt phases. Compared to Example 10, the ternary materials in Examples 1-9 are more stable, thus further improving the cycling stability of the battery.

[0170] It should be noted that the present application is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included within the technical scope of the present application. In addition, without departing from the scope of the present application, any other modifications that can be imagined by those skilled in the art to the embodiments, or any other methods constructed by combining some of the constituent elements in the embodiments are also included within the scope of the present application.

Claims

1. A secondary battery, characterized in that: Including positive electrode and negative electrode, The positive electrode plate includes a positive electrode active material, the positive electrode active material includes a ternary material containing nickel and a crystalline coating layer located on at least a portion of the surface of the ternary material, and the ternary material has a molecular formula of Li a Ni b Co c Mn 1-b-c O e , where 0.9≤a≤1.2, 0.55≤b≤0.96, 0 <c≤0.20,0≤1-b-c≤0.25,1.8≤e≤2.2; The negative electrode plate includes a negative electrode active material, and the negative electrode active material contains silicon.

2. The secondary battery according to claim 1, wherein The crystalline coating layer includes a crystalline compound.

3. The secondary battery according to claim 2, wherein The crystalline compound includes a lithium oxygen compound, and the lithium oxygen compound contains one or two or more of the elements Co, Zr, Nb, W, B, Sr, and Al.

4. The secondary battery according to claim 2, wherein: The chemical formula of the crystalline compound is Li a M b O c , where M includes one or two or more of Co, Zr, Nb, W, B, Sr, and Al, where 0.5≤a≤3, 0.5≤b≤5, 0 <c≤10。 5. The secondary battery according to claim 1, wherein Based on the total molar number of transition metal elements in the ternary material, the molar proportion of nickel element is 60% to 90%.

6. The secondary battery according to claim 1, wherein Based on the total mass of the negative electrode active material, the mass fraction of silicon element is 5% to 15%.

7. The secondary battery according to claim 1, wherein The bulk portion of the ternary material includes a lamellar phase, and the surface portion of the ternary material includes a lamellar phase, a spinel phase, and a rock salt phase.

8. The secondary battery according to claim 1, wherein In the ternary material, 0.6≤b≤0.9, 0.05≤c≤0.20, and 0.05≤1-bc≤0.

20.

9. The secondary battery according to claim 1, wherein The negative electrode active material includes silicon-based materials and carbon-based materials, The silicon-based material includes at least one of elemental silicon, silicon oxides, and silicon-carbon composites. The carbon-based material includes at least one of artificial graphite and natural graphite.

10. The secondary battery according to any one of claims 1 to 9, characterized in that: The specific surface area of ​​the positive electrode active material is 0.3 m 2 / g~0.9m 2 / g.

11. The secondary battery according to any one of claims 1 to 9, characterized in that: The positive electrode active material includes secondary particles, and the particle strength of the positive electrode active material is 50 MPa to 300 MPa.

12. The secondary battery according to any one of claims 1 to 9, characterized in that: The Dv50 of the positive electrode active material is 8 μm to 15 μm.

13. The secondary battery according to any one of claims 1 to 9, characterized in that: The powder compaction density of the positive electrode active material under a pressure of 5 tons is 3.1 g / cm 3 ~3.5g / cm 3 .

14. An electrical device, characterized in that: A secondary battery comprising the secondary battery according to any one of claims 1 to 13.

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