Secondary battery and electric device

Abstract

A secondary battery and an electric device. The secondary battery comprises a positive electrode sheet; the positive electrode sheet comprises a positive electrode current collector and active material layers located on at least one surface of the positive electrode current collector; the active material layers include a first active material layer and a second active material layer; the first active material layer is located on the surface of the positive electrode current collector; the second active material layer is located on the side of the first active material layer facing away from the positive electrode current collector, and the first active material layer comprises a lithium-supplementing composition; the lithium-supplementing composition comprises a lithium-supplementing agent and a reducing agent. The secondary battery has excellent cycle performance and long service life.

Description

Secondary batteries and electrical devices

[0001] Cross-references

[0002] This application refers to Chinese Patent Application No. 202410245337.2, filed on March 4, 2024, entitled “Secondary Batteries and Electrical Devices,” 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] Lithium-ion batteries (LIBs), a type of secondary battery, boast high energy density, long service life, and are energy-efficient and environmentally friendly. However, during the initial charge and discharge process of a lithium-ion battery, the electrolyte forms a solid electrolyte interface film (SEI) on the surface of the negative electrode. This SEI film formation consumes a large amount of active lithium ions. Furthermore, during the battery's charge and discharge cycles, the cracking and shattering of the positive electrode active material particles, and the thickening and repair of the SEI film, all consume active lithium ions, easily leading to a decrease in the battery's cycle capacity and shortening its service life.

[0005] Summary of the Invention

[0006] The present application is made in view of the above-mentioned problems, and its purpose is to provide a secondary battery, aiming to solve the technical problem of how to improve the cycle performance of the secondary battery and extend the service life of the battery.

[0007] A first aspect of the present application provides a secondary battery, comprising a positive electrode plate, the positive electrode plate comprising a positive electrode current collector and an active material layer located on at least one surface of the positive electrode current collector, the active material layer comprising a first active material layer and a second active material layer, the first active material layer being located on the surface of the positive electrode current collector, the second active material layer being located on a side of the first active material layer facing away from the positive electrode current collector, the first active material layer comprising a lithium replenishing composition, wherein the lithium replenishing composition comprises a lithium replenishing agent and a reducing agent.

[0008] The lithium-replenishing composition in the positive electrode of the secondary battery of the present application is located in the first active material layer immediately adjacent to the current collector. On the one hand, the reducing agent in the lithium-replenishing composition reacts with the lithium-replenishing agent, reducing the decomposition potential of the lithium-replenishing agent. This allows the lithium-replenishing agent to maximize its lithium-replenishing effect, improving its lithium-replenishing efficiency and providing a large amount of active lithium for lithium replenishment during the cycle. This results in an excellent number of cycles and a long battery life. Furthermore, the reaction product of the lithium-replenishing agent and the reducing agent exhibits excellent ionic conductivity, enhancing the ionic conductivity of the region in contact between the active material layer and the current collector, improving the ionic conductivity of the first active material layer, improving the lithium ion transport performance, and improving the battery's rate performance.

[0009] In summary, the secondary battery of the present application allows the lithium replenisher to maximize its lithium replenishment effect, improving its lithium replenishment efficiency and providing a large amount of active lithium for lithium replenishment during the cycle. This results in an excellent battery cycle life and a long battery life. Furthermore, the reaction products of the lithium replenisher composition are fully utilized, improving the lithium ion transport performance and enhancing the battery's rate capability.

[0010] In any embodiment, the lithium supplement includes one or more of lithium nickelate, lithium-rich lithium nickelate, lithium ferrite, lithium-rich lithium ferrite, lithium oxalate, lithium quartz, lithium metasilicate, lithium orthosilicate, lithium carbonate, lithium sulfate, lithium hydroxide, lithium phosphate, lithium oxide, lithium peroxide, lithium borate, and lithium metaborate.

[0011] In any embodiment, the lithium supplement includes one or more of lithium-rich nickelate, lithium metasilicate, lithium orthosilicate, lithium sulfate, lithium hydroxide, lithium borate, lithium metaborate, and lithium phosphate.

[0012] The lithium supplement agent has a high irreversible capacity and a good lithium supplement effect. In addition, the lithium supplement agent has good stability in the air and is compatible with the existing battery production process, which is conducive to industrial production.

[0013] In any embodiment, the reducing agent includes one or more of elemental selenium, metal compounds of selenium, elemental sulfur, metal compounds of sulfur, elemental phosphorus, metal compounds of phosphorus, elemental boron, metal compounds of boron, elemental tellurium, metal compounds of tellurium, elemental antimony, metal compounds of antimony, elemental bismuth, metal compounds of bismuth, and selenium disulfide.

[0014] In any embodiment, the reducing agent includes one or more of elemental selenium, elemental tellurium, elemental antimony, elemental bismuth, lithium selenide, sodium selenide, copper selenide, and selenium disulfide.

[0015] The above-mentioned reducing agent can undergo a reduction reaction with the lithium supplement agent, thereby reducing the decomposition potential of the lithium supplement agent, achieving low-potential lithium supplementation, improving the decomposition efficiency and utilization rate of the lithium supplement agent, improving the capacity retention rate of the battery, and increasing the battery life.

[0016] In any embodiment, the mass ratio of the lithium supplement agent to the reducing agent is 0.5-20.

[0017] In any embodiment, the mass ratio of the lithium supplement agent to the reducing agent is 1-10.

[0018] The mass ratio of the lithium supplement agent to the reducing agent is within an appropriate range, so that the lithium supplement agent and the reducing agent fully react with each other, thereby improving the lithium supplement efficiency of the lithium supplement agent, giving full play to the lithium supplement effect of the lithium supplement agent, and achieving the purpose of improving the cycle performance of the battery.

[0019] In any embodiment, the mass fraction of the reducing agent is 0.1% to 10% based on the mass of the active material layer.

[0020] In any embodiment, the mass fraction of the reducing agent is 0.4% to 2.0% based on the mass of the active material layer.

[0021] The reducing agent has an appropriate mass fraction so that the lithium supplement agent can be fully reduced, providing enough lithium ions, improving the lithium supplement efficiency of the lithium supplement agent, and improving the cycle performance of the battery.

[0022] In any embodiment, the mass fraction of the lithium supplement agent is 0.9%-20% based on the mass of the active material layer.

[0023] The mass fraction of the lithium supplement agent is within an appropriate range. On the one hand, the lithium supplement agent can fully exert its lithium supplement effect and improve the cycle performance of the battery. On the other hand, it also avoids excessive lithium supplement agent from having adverse effects on the battery's rate performance, available capacity and safety performance.

[0024] In any embodiment, the ratio of the thickness of the first active material layer to the thickness of the second active material layer is 1:5 to 5:1.

[0025] In any embodiment, the ratio of the thickness of the first active material layer to the second active material layer is 1:4 to 4:1.

[0026] When the first active material layer and the second active material layer are within a suitable range, the reaction product of the lithium-supplementing composition with excellent ion conductivity in the first active material layer can be fully utilized to improve the lithium ion transport performance of the inner layer of the active material layer, thereby enhancing the kinetic performance of the active material layer, and improving the rate performance and cycle performance of the battery. In addition, the effect of an excessive amount of the first active material layer on the energy density of the battery can be avoided, and the effect of the lithium-supplementing composition in the first active material layer on the conductive properties of the active material layer can be reduced.

[0027] In any embodiment, the thickness of the active material layer is 20 μm to 250 μm.

[0028] In any embodiment, the thickness of the active material layer is 80 μm to 200 μm.

[0029] The thickness of the active material layer is within a suitable range, which can take into account the capacity, rate performance and cycle performance of the battery.

[0030] In any embodiment, the first active material layer and the second active material layer include the same positive electrode active material.

[0031] The first active material layer and the second active material layer contain the same active material, so that the first active material layer and the second active material layer have good compatibility, and lithium ions can migrate stably during charge and discharge of the secondary battery.

[0032] A second aspect of the present application provides an electrical device comprising the secondary battery of the first aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] FIG1 is a schematic diagram of a positive electrode sheet in one embodiment of the present application;

[0034] FIG2 is a schematic diagram of a secondary battery according to an embodiment of the present application;

[0035] FIG3 is an exploded view of the secondary battery according to one embodiment of the present application shown in FIG2 ;

[0036] FIG4 is a schematic diagram of a battery module according to an embodiment of the present application;

[0037] FIG5 is a schematic diagram of a battery pack according to an embodiment of the present application;

[0038] FIG6 is an exploded view of the battery pack shown in FIG5 according to an embodiment of the present application;

[0039] FIG. 7 is a schematic diagram of an electric device using a secondary battery as a power source according to an embodiment of the present application.

[0040] Reference numerals:

[0041] 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 secondary battery; 51 housing; 52 electrode assembly; 53 cover; 6 positive electrode sheet; 61 positive electrode current collector; 62 first active material layer; 63 second active material layer. DETAILED DESCRIPTION

[0042] Below, the embodiments of the secondary battery and the electrical device of the present application are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures 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 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.

[0043] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all 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.

[0044] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0045] 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.

[0046] Unless otherwise specified, all steps of the present application may 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 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.

[0047] 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.

[0048] 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).

[0049] All active lithium in lithium-ion batteries is provided by the positive electrode active material. However, during the initial charging process of the lithium-ion battery, the formation of the solid electrolyte membrane (SEI membrane) on the negative electrode surface and other chemical side reactions during the subsequent charge and discharge cycles will consume active lithium ions, deteriorating the battery's cycle performance. To improve the cycle performance of lithium-ion batteries, the industry's commonly used solution is to add a positive electrode lithium replenisher to the battery's positive electrode. Commonly used positive electrode lithium replenishers generally include binary lithium-containing compounds, ternary lithium-containing compounds, or organic lithium salts. However, most positive electrode lithium replenishers with high lithium capacity also have a high decomposition voltage, which will affect the battery's cycle performance and safety performance. To address the high decomposition potential of positive electrode lithium supplements, a lithium supplement composition containing a lithium supplement and a reducing agent is often added to the lithium supplement layer on the surface of the positive electrode active material. However, common lithium supplements and reducing agents have poor electronic conductivity. Placing the lithium supplement and reducing agent in a separate lithium supplement layer prevents the lithium supplement layer from forming an effective electron pathway for electron gain and loss, resulting in poor battery kinetics and poor lithium supplement efficiency. This prevents the lithium supplement from fully utilizing its lithium supplement function, and thus fails to improve the battery's cycle performance. Prior art lithium supplement compositions containing a lithium supplement and a reducing agent are also added to the entire positive electrode active material layer. However, lithium supplements and reducing agents with relatively large specific surface areas require more binder, resulting in a low active material loading in the positive electrode active material layer, which affects the battery's energy density. Furthermore, distributing the lithium supplement and reducing agent, which have relatively poor electronic conductivity, throughout the entire film layer can significantly impact the electrode's electrical conductivity, affecting the battery's rate capability and cycle performance.

[0050] [Secondary battery]

[0051] The present application provides a secondary battery, comprising a positive electrode plate, the positive electrode plate comprising a positive electrode current collector and an active material layer located on at least one surface of the positive electrode current collector, the active material layer comprising a first active material layer and a second active material layer, the first active material layer being located on a surface of the positive electrode current collector, the second active material layer being located on a side of the first active material layer facing away from the positive electrode current collector, the first active material layer comprising a lithium replenishing composition, wherein the lithium replenishing composition comprises a lithium replenishing agent and a reducing agent.

[0052] In this article, the term "lithium supplement" refers to a material that can undergo a decomposition reaction and provide active lithium within the operating range of a secondary battery, and the active lithium will not be back-intercalated during the discharge process, thereby compensating for the loss of active lithium.

[0053] In this article, the term "reducing agent" refers to a compound that can reduce the lithium supplement agent, so that the lithium supplement agent produces lithium ions at a lower voltage platform, reducing the decomposition voltage of the lithium supplement agent, thereby enabling lithium supplement agents with higher capacity to have a stronger application space.

[0054] As shown in FIG1 , the positive electrode sheet 6 includes a positive electrode current collector 61 and an active material layer located on at least one surface of the positive electrode current collector 61 . The active material layer includes a first active material layer 62 and a second active material layer 63 .

[0055] As an example, the positive electrode current collector has two surfaces facing each other in its thickness direction, and the active material layer is provided on either or both of the two facing surfaces of the positive electrode current collector.

[0056] Compared with a single lithium supplement agent, the present application uses a lithium supplement composition to supplement the lithium of the positive electrode. The lithium supplement agent reacts with the reducing agent to reduce the decomposition potential of the lithium supplement agent. The lithium supplement agent can play its lithium supplement effect as much as possible, improve the lithium supplement efficiency of the lithium supplement agent, provide sufficient active lithium during the cycle to replenish the lithium ions lost during the cycle, improve the cycle performance of the battery, and extend the service life of the battery.

[0057] Compared to placing the lithium supplement composition in a separate lithium supplement layer, the present application places the lithium supplement composition in the first active material layer. The conductive agent or active material in the first active material layer can be used to improve the conductive network between the lithium supplement compositions, provide more electron transmission pathways, and help increase the degree of reaction between the lithium supplement agent and the reducing agent, so that the lithium supplement agent can fully exert its lithium supplement effect. At the same time, the product of the lithium supplement composition has good ion conductivity, which can improve the ion conductivity of the first active material and construct a continuous ion transmission network, thereby improving the rate performance of the battery.

[0058] Compared with distributing the lithium supplement composition throughout the entire active material layer, disposing the lithium supplement composition in the first active material layer can, on the one hand, allow the first active material layer to be distributed with sufficient decomposition products of the lithium supplement composition having good ion conductivity, thereby maximizing the ion transport performance of the active material layer close to the current collector and improving the battery's kinetic performance and cycle performance. On the other hand, since the lithium supplement composition has relatively poor electronic conductivity, disposing it in a separate layer reduces the impact of the lithium supplement composition on the conductivity of the entire positive electrode active material layer. At the same time, disposing the lithium supplement composition in the first active material layer reduces the impact of the lithium supplement composition on the energy density of the battery.

[0059] The first active material layer close to the current collector has relatively poor ion transport performance compared to the second active material layer due to insufficient electrolyte infiltration depth and long ion transmission distance. It has a greater demand for ion conductivity. If the lithium supplement composition is set in the second active material layer, the technical problem of relatively poor ion transport performance in the first active material layer is not solved, and the reaction product of the lithium supplement composition with good ion conductivity does not play its advantages. However, if the lithium supplement composition is set in the first active material layer, the reaction product of the lithium supplement composition with good ion conductivity can improve the ion conductivity of the first active material layer, build a continuous ion transmission network, and improve the rate performance of the battery.

[0060] In summary, using the secondary battery of the present application, the lithium replenisher can maximize its lithium replenishment effect, improve the lithium replenishment efficiency of the lithium replenisher, provide a large amount of active lithium for lithium replenishment during the cycle, and achieve an excellent cycle life and a long battery life. Furthermore, the reaction products of the lithium replenisher composition are fully utilized to enhance the lithium ion transport performance of the first active material layer, thereby improving the rate performance of the battery.

[0061] In some embodiments, the lithium supplement includes one or more of lithium nickelate, lithium-rich lithium nickelate, lithium ferrite, lithium-rich lithium ferrite, lithium oxalate, lithium quartz, lithium metasilicate, lithium orthosilicate, lithium carbonate, lithium sulfate, lithium hydroxide, lithium phosphate, lithium oxide, lithium peroxide, lithium borate, and lithium metaborate.

[0062] The lithium replenisher has a high irreversible capacity and a good lithium replenishing effect. In addition, the lithium replenisher has good stability in the air and is compatible with the existing battery production process, which is conducive to industrial production.

[0063] In some embodiments, the lithium supplement includes one or more of lithium-rich nickelate, lithium metasilicate, lithium orthosilicate, lithium sulfate, lithium hydroxide, lithium borate, lithium metaborate, and lithium phosphate.

[0064] The combination of a suitable lithium supplement and a reducing agent can not only lower the decomposition potential of the lithium supplement, fully utilizing the lithium supplement's replenishing effect, but also eliminate the presence of gases such as oxygen, carbon dioxide, or nitrogen in the reaction product, reducing the likelihood of battery gassing and minimizing their impact on battery safety and cycling performance. Furthermore, the decomposition products of the lithium supplement may include silicon oxide, nickel oxide, lithium oxide, boron oxide, or lithium sulfate, which possess excellent ionic conductivity, thereby improving the electrode's ion conductivity and enhancing the battery's rate performance.

[0065] In some embodiments, the lithium supplement comprises one or both of lithium metasilicate and lithium orthosilicate.

[0066] The decomposition potential of lithium metasilicate or lithium orthosilicate is low, which enables lithium supplements with higher capacity to have a stronger application space. The decomposition products contain silicon dioxide and lithium sulfate, which have good ion conductivity, can enhance the ion conductivity of the positive electrode sheet and improve the battery's rate performance and cycle performance.

[0067] In some embodiments, the reducing agent includes one or more of elemental selenium, metal compounds of selenium, elemental sulfur, metal compounds of sulfur, elemental phosphorus, metal compounds of phosphorus, elemental boron, metal compounds of boron, elemental tellurium, metal compounds of tellurium, elemental antimony, metal compounds of antimony, elemental bismuth, metal compounds of bismuth, and selenium disulfide.

[0068] As used herein, the term "selenium metal compound" refers to a compound formed by selenium and a metal element, wherein the chemical valence of selenium in the selenium metal compound is negative, wherein the selenium metal compound includes but is not limited to lithium selenide, sodium selenide or calcium selenide.

[0069] As used herein, the term "sulfur metal compound" refers to a compound formed by sulfur and a metal element, wherein the chemical valence of sulfur in the sulfur metal compound is negative, wherein the sulfur metal compound includes but is not limited to calcium sulfide, lithium sulfide, sodium sulfide, zinc sulfide or iron sulfide.

[0070] As used herein, the term "phosphorus metal compound" refers to a compound formed by phosphorus and a metal element, wherein the chemical valence state of phosphorus in the phosphorus metal compound is negative, wherein the phosphorus metal compound includes but is not limited to lithium phosphide, sodium phosphide, iron phosphide, calcium phosphide, zinc phosphide, aluminum phosphide or copper phosphide.

[0071] As used herein, the term "boron metal compound" refers to a compound formed by boron and a metal element, wherein the chemical valence of boron in the boron metal compound is negative, wherein the boron metal compound includes but is not limited to titanium diboride, calcium hexaboride, molybdenum boride or cobalt boride.

[0072] Herein, the term "tellurium metal compound" refers to a compound formed by tellurium and a metal element, wherein the chemical valence state of tellurium in the tellurium metal compound is negative, wherein the tellurium metal compound includes but is not limited to copper telluride or molybdenum telluride.

[0073] Herein, the term "antimony metal compound" refers to a compound formed by antimony and a metal element, wherein the chemical valence of antimony in the antimony metal compound is negative, wherein the antimony metal compound includes but is not limited to lithium antimonide, sodium antimonide or indium antimonide.

[0074] Herein, the term "bismuth metal compound" refers to a compound formed by bismuth and a metal element, wherein the chemical valence state of bismuth in the bismuth metal compound is negative, wherein the bismuth metal compound includes but is not limited to sodium bismuthide.

[0075] The above-mentioned reducing agent can chemically react with the lithium supplement agent to reduce the decomposition potential of the lithium supplement agent, achieve low-potential lithium supplementation, improve the decomposition efficiency and utilization rate of the lithium supplement agent, improve the capacity retention rate of the battery, and increase the battery life.

[0076] In some embodiments, the reducing agent includes one or more of elemental selenium, non-transition metal compounds of selenium, elemental sulfur, non-transition metal compounds of sulfur, elemental phosphorus, non-transition metal compounds of phosphorus, elemental boron, non-transition metal compounds of boron, elemental tellurium, non-transition metal compounds of tellurium, elemental antimony, non-transition metal compounds of antimony, elemental bismuth, non-transition metal compounds of bismuth, and selenium disulfide.

[0077] In this article, the term "non-transition metal compound of selenium" refers to a compound formed by selenium and a non-transition metal element, wherein the chemical valence state of selenium in the non-transition metal compound of selenium is negative, wherein the metal compound of selenium includes but is not limited to lithium selenide, sodium selenide or calcium selenide.

[0078] As used herein, the term "non-transition metal compound of sulfur" refers to a compound formed by sulfur and a non-transition metal element, wherein the chemical valence of sulfur in the non-transition metal compound of sulfur is negative, wherein the non-transition metal compound of sulfur includes but is not limited to calcium sulfide, lithium sulfide or sodium sulfide.

[0079] As used herein, the term "non-transition metal compound of phosphorus" refers to a compound formed by phosphorus and a non-transition metal element, wherein the chemical valence state of phosphorus in the non-transition metal compound of phosphorus is negative, and the non-transition metal compound of phosphorus includes but is not limited to lithium phosphide, sodium phosphide, iron phosphide, calcium phosphide, and aluminum phosphide.

[0080] As used herein, the term "non-transition metal compound of boron" refers to a compound formed by boron and a non-transition metal element, wherein the chemical valence state of boron in the non-transition metal compound of boron is negative, wherein the non-transition metal compound of boron includes but is not limited to calcium hexaboride.

[0081] As used herein, the term "non-transition metal compound of tellurium" refers to a compound formed by tellurium and a non-transition metal element, wherein the chemical valence state of tellurium in the non-transition metal compound of tellurium is negative, and the non-transition metal compound of tellurium includes but is not limited to lithium telluride and sodium telluride.

[0082] In this article, the term "non-transition compound of antimony" refers to a compound formed by antimony and a non-transition metal element, wherein the chemical valence state of antimony in the non-transition metal compound of antimony is negative, wherein the non-transition metal compound of antimony includes but is not limited to lithium antimonide, sodium antimonide or indium antimonide.

[0083] Herein, the term "non-transition metal compound of bismuth" refers to a compound formed by bismuth and a non-transition metal element, wherein the chemical valence state of bismuth in the non-transition metal compound of bismuth is negative, wherein the non-transition metal compound of bismuth includes but is not limited to sodium bismuth.

[0084] The above-mentioned reducing agent does not contain transition metal elements, which can reduce the impact of the catalytic oxidation of the transition metal elements on the electrolyte on the cycle or safety performance of the battery.

[0085] In some embodiments, the reducing agent includes one or more of elemental selenium, elemental tellurium, elemental antimony, elemental bismuth, lithium selenide, sodium selenide, copper selenide, and selenium disulfide.

[0086] Compared to elemental sulfur or elemental boron, elemental selenium, elemental tellurium, elemental antimony, elemental bismuth, lithium selenide, sodium selenide, copper selenide, or selenium disulfide have higher electronic conductivity. Reducing agents with excellent electronic conductivity can establish an excellent conductive electron network with the lithium replenisher, facilitating the reaction between the two agents and allowing the lithium replenisher to fully exert its lithium replenishment effect. Furthermore, to ensure that the lithium replenisher is fully reduced and provides as much active lithium as possible, an excess of reducing agent is generally added. However, the addition of reducing agents with excellent electronic conductivity, such as elemental selenium, elemental tellurium, elemental antimony, elemental bismuth, lithium selenide, sodium selenide, copper selenide, or selenium disulfide, ensures that the remaining reducing agent still has excellent electronic conductivity. This, compared to elemental sulfur or elemental boron, is beneficial for improving the battery's rate performance.

[0087] The reducing agent includes one or more of elemental selenium, elemental tellurium, elemental antimony, elemental bismuth, lithium selenide, sodium selenide, copper selenide, and selenium disulfide. It can improve the rate performance of the battery without significantly changing the cycle performance of the battery, and is more suitable for improving the cycle performance of power batteries.

[0088] In some embodiments, the reducing agent includes one or more of elemental tellurium, elemental antimony, and elemental bismuth.

[0089] Elemental tellurium, elemental antimony, or elemental bismuth have higher electronic conductivity. While reducing the lithium replenisher and improving battery cycle performance, they also ensure that the excess residual reducing agent still has excellent electronic conductivity, improving the battery's rate performance. Using reducing agents such as tellurium, antimony, or bismuth in combination with a lithium replenisher is suitable for improving the cycle performance of rate-type batteries.

[0090] In some embodiments, the mass ratio of the lithium supplement agent to the reducing agent is 0.5-20. In some embodiments, the mass ratio of the lithium supplement agent to the reducing agent can be selected from 0.5, 1, 5, 10, 15, 20 or any range therebetween.

[0091] In some embodiments, the mass ratio of the lithium supplement agent to the reducing agent is 1 to 10. In some embodiments, the mass ratio of the lithium supplement agent to the reducing agent can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or any range therebetween.

[0092] The mass content of the lithium supplement agent and the reducing agent is within an appropriate range, which allows the lithium supplement agent and the reducing agent to fully react with each other to improve the lithium supplement efficiency while avoiding excessive residual lithium supplement agent and / or reducing agent from deteriorating the rate performance of the battery.

[0093] In some embodiments, the mass fraction of the reducing agent is 0.1%-10% based on the mass of the active material layer. In some embodiments, the mass fraction of the reducing agent is 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.2%, 1.4%, 1.6%, 1.8%, 2.0%, 2.2%, 2.5%, 5%, 6%, 7%, 8%, 9%, 10%, or any range therebetween, based on the mass of the active material layer.

[0094] In some embodiments, the mass fraction of the reducing agent is 0.4%-2.0% based on the mass of the active material layer.

[0095] The mass fraction of the reducing agent is within an appropriate range, providing sufficient reducing agent for the redox reaction with the lithium supplement, thereby maximizing the reduction of the lithium supplement, improving the lithium supplement efficiency, and preventing excessive reducing agent from affecting the energy density of the battery.

[0096] In some embodiments, the mass fraction of the lithium supplement agent is 0.9%-20% based on the mass of the active material layer. In some embodiments, the mass fraction of the lithium supplement agent is 0.9%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 12%, 14%, 16%, 18%, 20%, or any range therebetween, based on the mass of the active material layer.

[0097] The mass fraction of the lithium supplement agent is within an appropriate range. On the one hand, the lithium supplement agent can fully exert its lithium supplement effect and improve the cycle performance of the battery. On the other hand, it also avoids excessive lithium supplement agent from having adverse effects on the diaphragm resistance of the electrode and the rate performance, available capacity and safety performance of the battery.

[0098] In some embodiments, the ratio of the thickness of the first active material layer to the second active material layer is 1:5-5:1.

[0099] In some embodiments, the thickness ratio of the first active material layer to the second active material layer may be 1:5, 1:4, 1:3, 1:2, 1:1, 5:1, 4:1, 3:1, 2:1, or any range therebetween.

[0100] In some embodiments, the ratio of the thickness of the first active material layer to the thickness of the second active material layer is 1:4-4:1.

[0101] In some embodiments, the thickness ratio of the first active material layer to the second active material layer may be 1:4, 1:3, 1:2, 1:1, 4:1, 3:1, 2:1, or any range therebetween.

[0102] The test method for the thickness ratio of the first active material layer to the second active material layer can use any method known in the art. For example, the electrode can be cut perpendicularly to the electrode plane (for example, a plane with a relatively large area) using an argon ion beam to expose the cross section. The cross section is photographed using an X-Max energy dispersive spectrometer (EDS) from the Oxford Instruments Group of the United Kingdom in combination with a Sigma-02-33 scanning electron microscope (SEM) from the ZEISS of Germany. A linear scan of the characteristic element content of the first active material layer (the characteristic element of the lithium supplement composition) is performed along the cross section. The thickness of the electrode is measured as L. The distance from the site where the characteristic element of the first active material layer begins to increase compared to the end face of the electrode is L1 from the end face of the electrode. Then, the thickness of the first active material layer is L1, the thickness of the second active material layer is L2=L-L1, and the ratio of the thickness of the first active material layer to the second active material layer is L1 / L2.

[0103] When the first active material layer and the second active material layer are within a suitable range, on the one hand, the reaction product of the lithium-supplementing composition with excellent ion conductivity in the first active layer can be fully utilized to achieve the purpose of improving the lithium ion transport performance of the inner layer of the active material layer, thereby improving the kinetic performance of the active material layer, and improving the rate performance and cycle performance of the battery. In addition, the excessive amount of the first active material layer is avoided to affect the energy density of the battery, and the influence of the lithium-supplementing composition in the first active material layer on the conductive performance of the active material layer is also reduced.

[0104] In some embodiments, the first active material layer comprises a first active material, and the second active material layer comprises a second active material.

[0105] In some embodiments, based on the mass of the first active material layer, the mass content of the first active material is A%;

[0106] The mass content of the second active material is B% based on the mass of the second active material layer;

[0107] The secondary battery satisfies: B%>A%.

[0108] The first active material layer contains a lithium supplement composition, which can be used to improve the cycle performance and rate performance. However, due to the addition of the lithium supplement composition, part of the battery's energy density will be lost. Therefore, the second active material layer is required to contain a relatively large amount of active material to compensate for the part of the energy density sacrificed by the first active material layer, thereby comprehensively achieving a balance between the battery's energy density, cycle performance, and rate performance.

[0109] In some embodiments, the first active material and the second active material each independently include a lithium-containing phosphate having an olivine structure, a lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials. The first active material or the second active material may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM211), LiNi0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2) and its modified compounds. Examples of olivine-structured lithium-containing phosphates may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0110] In some embodiments, the first active material includes lithium iron phosphate or a modified form of lithium iron phosphate, wherein the modified form includes one or more of doping modification and coating modification.

[0111] In some embodiments, the second active material includes lithium iron phosphate or a modified form of lithium iron phosphate, wherein the modified form includes one or more of doping modification and coating modification.

[0112] In some embodiments, the first active material layer comprises a first binder, and the mass content of the first binder is C% based on the mass of the first active material layer;

[0113] The second active material layer comprises a second binder, and the mass content of the second binder is D% based on the mass of the second active material layer;

[0114] The secondary battery satisfies: C%>D%.

[0115] The specific surface area of ​​the lithium replenisher and reducing agent in the first active material layer is relatively large, and the demand for a binder is greater. In order to ensure good adhesion between the components such as the lithium replenisher, reducing agent and active material in the first active material layer, the mass content of the binder in the first active material layer is relatively high. The second active material layer requires more active materials to increase the energy density of the battery, and its binder content is relatively low.

[0116] In some embodiments, the first binder and the second binder each independently include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin.

[0117] In some embodiments, the thickness of the active material layer is 20 micrometers (μm) to 250 μm. In some embodiments, the thickness of the active material layer can be 20 μm, 30 μm, 40 μm, 50 μm, 100 μm, 150 μm, 200 μm, 250 μm, or any range therebetween.

[0118] In some embodiments, the thickness of the active material layer is 80 μm-200 μm. In some embodiments, the thickness of the active material layer can be 80 μm, 100 μm, 120 μm, 140 μm, 160 μm, 180 μm, 200 μm, or any range therebetween.

[0119] To increase battery capacity, the thickness of the positive electrode is often increased. However, due to insufficient electrolyte penetration depth and excessive ion transmission distance, the ion transmission performance of the active material layer near the current collector in thick electrodes is relatively poor, thereby affecting the battery's rate performance. The lithium-supplementing composition of the present application is located in the first active material layer near the current collector. The decomposition products of the lithium-supplementing composition have excellent ionic conductivity, which can significantly enhance the ionic conductivity of thick electrodes and improve the battery's rate performance.

[0120] The secondary battery of the present application can improve the battery capacity while taking into account the cycle performance and rate performance of the battery, thereby comprehensively improving the performance of the battery.

[0121] In some embodiments, the first active material and the second active material are positive electrode active materials having the same material.

[0122] In some embodiments, the first active material and the second active material comprise lithium iron phosphate.

[0123] The first active material layer and the second active material layer contain the same active material, so that the first active material layer and the second active material layer have good compatibility, and lithium ions can migrate stably during charge and discharge of the secondary battery.

[0124] 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 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 polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0125] In some embodiments, the secondary battery comprises a lithium-ion battery. Specifically, it comprises a positive electrode sheet, a negative electrode sheet, and a separator disposed between the positive and negative electrodes. During the battery's charge and discharge processes, active ions are intercalated and released between the positive and negative electrodes. The electrolyte acts as an ion conductor between the positive and negative electrodes. The separator, disposed between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0126] In some embodiments, the first active material layer further includes a first conductive agent, and the second active material layer further includes a second conductive agent.

[0127] In some embodiments, the first conductive agent and the second conductive agent each independently include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0128] In some embodiments, the positive electrode sheet can be prepared by the following method: dispersing the first active material, the lithium supplement composition, the first binder, the first conductive agent and any other components in a solvent (such as N-methylpyrrolidone) to form a first positive electrode slurry, coating the first positive electrode slurry on the positive electrode current collector, and after drying, cold pressing and other processes, a first active material layer can be obtained; dispersing the second active material, the second binder, the second conductive agent and any other components in a solvent (such as N-methylpyrrolidone) to form a second positive electrode slurry, coating the second positive electrode slurry on the first active material layer, and after drying, cold pressing and other processes, a positive electrode sheet can be obtained.

[0129] In some embodiments, 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.

[0130] 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.

[0131] 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.).

[0132] In some embodiments, the negative electrode active material may be a negative electrode active material for a battery that is well known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxides, 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.

[0133] 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).

[0134] 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.

[0135] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0136] 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.

[0137] In some embodiments, the electrolyte acts as a conductive medium between the positive and negative electrodes. This application does not specifically limit the type of electrolyte, and the electrolyte may be selected based on specific needs. For example, the electrolyte may be liquid, gel, or solid.

[0138] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0139] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonyl imide, lithium bistrifluoromethanesulfonyl imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium bisoxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0140] 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.

[0141] 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.

[0142] 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.

[0143] 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.

[0144] 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.

[0145] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0146] 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.

[0147] 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.

[0148] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0149] 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.

[0150] 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, FIG2 shows a secondary battery 5 having a square structure as an example.

[0151] In some embodiments, referring to Figure 3, 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.

[0152] In some embodiments, secondary batteries can be assembled into a battery module. The number of secondary batteries contained in the battery module can be one or more. The specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0153] Figure 4 shows an example battery module 4. Referring to Figure 4 , within the battery module 4, multiple secondary batteries 5 may be arranged sequentially along the length of the battery module 4. Of course, any other arrangement is also possible. Furthermore, the multiple secondary batteries 5 may be secured together using fasteners.

[0154] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of secondary batteries 5 are received in the receiving space.

[0155] 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 based on the application and capacity of the battery pack.

[0156] Figures 5 and 6 illustrate an example battery pack 1. Referring to Figures 5 and 6 , the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be positioned over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0157] 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, 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.

[0158] As an electrical device, a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.

[0159] Figure 7 shows an example of an electric device. This device is 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.

[0160] 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.

[0161] Example

[0162] 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.

[0163] 1. Preparation method

[0164] Example 1

[0165] 1) Preparation of positive electrode sheet

[0166] First positive electrode slurry: The first active material lithium iron phosphate (LFP), lithium supplement agent lithium metasilicate, reducing agent sulfur powder, conductive carbon (SP), and polyvinylidene fluoride binder are dissolved in solvent N-methylpyrrolidone (NMP) at a mass ratio of 88%:5.6%:2.4%:2%:2%, and the mixture is thoroughly stirred and mixed to prepare the first positive electrode slurry;

[0167] Second positive electrode slurry: The first active material LFP, conductive carbon (SP), and polyvinylidene fluoride binder are dissolved in a solvent N-methylpyrrolidone (NMP) at a mass ratio of 97%:2%:1%, and the mixture is stirred and mixed thoroughly to prepare the second positive electrode slurry;

[0168] The first positive electrode slurry was coated on the positive electrode current collector aluminum foil, and then dried at 100 ° C, cold pressed, and cut to obtain the first active material layer. The coating weight of the first positive electrode slurry was 120 mg / 1540.25 mm 2 ;

[0169] The second positive electrode slurry is coated on the first active material layer, and then dried at 100°C, cold pressed, and cut to obtain a positive electrode sheet. The coating weight of the second positive electrode slurry is 120mg / 1540.25mm 2 ; The thickness of the first active material layer is 48 μm, the thickness of the second active material layer is 48 μm, and based on the total mass of the first active material layer and the second active material layer, the mass fraction of elemental sulfur is 1.2%, and the mass fraction of lithium metasilicate is 2.8%.

[0170] 2) Preparation of negative electrode sheet

[0171] The active material graphite, the conductive agent acetylene black, the binder styrene-butadiene rubber (SBR), and the thickener sodium carboxymethyl cellulose (CMC) are thoroughly stirred and mixed in an appropriate amount of deionized water solvent system in a weight ratio of 96.5%:0.7%:1.8%:1% to obtain a negative electrode slurry. The negative electrode slurry is then coated on a Cu foil, and then dried, cold pressed, and cut to obtain a negative electrode sheet.

[0172] 3) Isolation film

[0173] A polyethylene porous polymer film is used as the separator.

[0174] 4) Preparation of electrolyte

[0175] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1, and then LiPF6 is uniformly dissolved in the above solution to obtain an electrolyte, wherein the concentration of LiPF6 is 1 mol / L.

[0176] 6) Preparation of batteries

[0177] The positive electrode sheet, separator, and negative electrode sheet are stacked in order and wound to obtain a battery cell. The battery cell is placed in an outer package, and the above-mentioned electrolyte is added. After packaging, standing, formation, aging and other processes, a secondary battery is obtained.

[0178] Examples 2-9

[0179] Compared with Example 1, different lithium supplements and / or reducing agents were added in Examples 2-9. Specific parameters are shown in Table 1.

[0180] Examples 10-13

[0181] Compared with Example 5, Examples 10-13 adjusted the mass fractions of the lithium supplement agent and the reducing agent by adjusting the formula of the first positive electrode slurry, as follows:

[0182] Example 10: The mass ratio of the first active material lithium iron phosphate (LFP), the lithium supplement agent lithium metasilicate, the reducing agent elemental tellurium, the conductive carbon (SP), and the polyvinylidene fluoride binder is 88%:3.0%:5.0%:2%:2%;

[0183] Example 11: The mass ratio of the first active material lithium iron phosphate (LFP), the lithium supplement agent lithium metasilicate, the reducing agent elemental tellurium, the conductive carbon (SP), and the polyvinylidene fluoride binder is 88%:4.0%:4.0%:2%:2%;

[0184] Example 12: The mass ratio of the first active material lithium iron phosphate (LFP), the lithium supplement agent lithium metasilicate, the reducing agent elemental tellurium, the conductive carbon (SP), and the polyvinylidene fluoride binder is 88%:7.2%:0.8%:2%:2%;

[0185] Example 13: The mass ratio of the first active material lithium iron phosphate (LFP), the lithium supplement agent lithium metasilicate, the reducing agent elemental tellurium, the conductive carbon (SP), and the polyvinylidene fluoride binder is 88%:7.6%:0.4%:2%:2%.

[0186] Comparative Example 1

[0187] Compared with Example 1, the preparation method of the first positive electrode slurry is adjusted as follows:

[0188] First positive electrode slurry: The first active material lithium iron phosphate (LFP), conductive carbon (SP), and polyvinylidene fluoride binder are dissolved in a solvent N-methylpyrrolidone (NMP) at a mass ratio of 96%:2%:2%, and the mixture is thoroughly stirred and mixed to prepare the first positive electrode slurry.

[0189] Comparative Example 2

[0190] Compared with Example 1, the preparation method of the positive electrode sheet was adjusted as follows:

[0191] Lithium replenishing layer slurry: dissolve lithium metasilicate (a lithium replenishing agent), sulfur powder (a reducing agent), conductive carbon (SP), and polyvinylidene fluoride (PVDF) binder in N-methylpyrrolidone (NMP) at a mass ratio of 26.9%:11.5%:46.2%:15.4% in the solvent, and stir and mix thoroughly to prepare a lithium replenishing layer slurry;

[0192] Positive electrode slurry: The positive electrode active material LFP, conductive carbon (SP), and polyvinylidene fluoride binder are dissolved in a solvent N-methylpyrrolidone (NMP) at a mass ratio of 97%:2%:1%, and the mixture is stirred thoroughly to prepare a positive electrode slurry;

[0193] The lithium replenishing layer slurry was coated on the positive electrode current collector aluminum foil, and then dried at 100 ° C, cold pressed, and cut to obtain the lithium replenishing layer. The coating weight of the lithium replenishing layer slurry was 25 mg / 1540.25 mm 2 ;

[0194] The positive electrode slurry is coated on the lithium supplement layer, and then dried at 100 ° C, cold pressed, and cut to obtain the positive electrode sheet. The coating weight of the positive electrode slurry is 215mg / 1540.25mm 2 , wherein the thickness of the lithium replenishing layer is 10 μm, the thickness of the active material layer is 85 μm, wherein, based on the total mass of the lithium replenishing layer and the active material, the mass fraction of lithium metasilicate is 2.8%, and the mass fraction of elemental sulfur is 1.2%.

[0195] Comparative Example 3

[0196] Compared with Example 1, the preparation method of the positive electrode sheet was adjusted as follows:

[0197] First positive electrode slurry: The first active material lithium iron phosphate (LFP), lithium supplement agent lithium metasilicate, reducing agent sulfur powder, conductive carbon (SP), and polyvinylidene fluoride binder are dissolved in solvent N-methylpyrrolidone (NMP) at a mass ratio of 88%:5.6%:2.4%:2%:2%, and the mixture is thoroughly stirred and mixed to prepare the first positive electrode slurry;

[0198] Second positive electrode slurry: The first active material LFP, conductive carbon (SP), and polyvinylidene fluoride binder are dissolved in a solvent N-methylpyrrolidone (NMP) at a mass ratio of 97%:2%:1%, and the mixture is stirred and mixed thoroughly to prepare the second positive electrode slurry;

[0199] The second positive electrode slurry was coated on the positive electrode current collector aluminum foil, and then dried at 100 ° C, cold pressed, and cut to obtain the first active material layer. The coating weight of the second positive electrode slurry was 120 mg / 1540.25 mm 2 ;

[0200] The first positive electrode slurry is coated on the first active material layer, and then dried at 100°C, cold pressed, and cut to obtain a positive electrode sheet. The coating weight of the first positive electrode slurry is 120mg / 1540.25mm 2 ; The thickness of the first active material layer is 48 μm, the thickness of the second active material layer is 48 μm, and based on the total mass of the first active material layer and the second active material layer, the mass fraction of elemental sulfur is 1.2%, and the mass fraction of lithium metasilicate is 2.8%.

[0201] Comparative Example 4

[0202] Compared with Example 1, the preparation method of the positive electrode sheet was adjusted as follows:

[0203] Positive electrode slurry: The positive electrode active material lithium iron phosphate (LFP), lithium supplement agent lithium metasilicate, reducing agent sulfur powder, conductive carbon (SP), and polyvinylidene fluoride binder are dissolved in solvent N-methylpyrrolidone (NMP) at a mass ratio of 92%:2.8%:1.2%:2%:2%, and the mixture is thoroughly stirred and mixed to prepare the positive electrode slurry:

[0204] The positive electrode slurry was coated on the positive electrode current collector aluminum foil, and then dried at 100 ° C, cold pressed, and cut to obtain the positive electrode sheet. The coating weight of the positive electrode slurry was 240 mg / 1540.25 mm 2 The thickness of the active material layer is 96 μm. Based on the mass of the positive electrode film layer, the mass fraction of lithium metasilicate is 2.8%, and the mass fraction of elemental sulfur is 1.2%.

[0205] 2. Test Method

[0206] 1. Number of battery cycles

[0207] The secondary batteries prepared in each example and comparative example were charged at a constant current rate of 0.5C to a charge cutoff voltage of 4.0V. They were then charged at a constant voltage rate to a current of ≤0.05C, allowed to rest for 5 minutes, and then discharged at a constant current rate of 0.33C to a discharge cutoff voltage of 2V. The batteries were allowed to rest for 5 minutes. This constituted the first charge-discharge cycle. Starting the second cycle, the charge voltage was reduced to 3.8V, while all other parameters remained unchanged. The batteries were then cyclically charged and discharged in this manner until the battery capacity decayed to 80%. The number of cycles at this point is the battery's cycle life at 25°C.

[0208] 2. Battery 40% SOC discharge time

[0209] The battery cell was discharged at a constant current of 0.33C to 2.0V and allowed to stand for 30 minutes; charged at a constant current of 0.33C to 3.8V and then at a constant voltage of 0.05C until the voltage stabilized and allowed to stand for 30 minutes; discharged at a constant current of 0.33C to 2.0V, at which time the initial capacity C0 was read and allowed to stand for 30 minutes; charged at a constant current of 0.33C to 3.8V and then at a constant voltage of 0.05C until the voltage stabilized and allowed to stand for 30 minutes; discharged at a constant current of 0.33C to 0.4C0Ah (40%) SOC and allowed to stand for 60 minutes; discharged at a constant current of 3C to 2.0V and recorded the discharge time.

[0210] 3. Gas production of the battery

[0211] The battery cell was immersed in silicone oil and the test temperature was controlled at 25°C using a constant temperature water bath. The cell mass (Mx) was measured and the volume change (Vx) was calculated using the Archimedean principle to obtain the gas production. At 25°C, the batteries of the examples and comparative examples were charged at a constant current of 0.05C to 4.5V, then at a constant voltage of 4.5V to 0.05V. The volume change (Vx) was recorded over time and voltage to obtain the formation gas production per unit capacity at the cutoff voltage.

[0212] 3. Analysis of test results of various embodiments and comparative examples

[0213] Secondary batteries of various examples and comparative examples were prepared according to the above methods, and various parameters were measured. The results are shown in the table below.

[0214] Table 1

[0215] The secondary battery provided in an embodiment of the present application includes a positive electrode plate, which includes an aluminum foil positive electrode current collector and an active material layer located on at least one surface of the positive electrode current collector, wherein the active material layer includes a first active material layer and a second active material layer, wherein the first active material layer is located on the surface of the aluminum foil positive electrode current collector, and the second active material layer is located on the side of the first active material layer away from the aluminum foil positive electrode current collector, and the first active material layer includes a lithium replenishing composition, and the lithium replenishing agent composition includes a lithium metasilicate, lithium borate, lithium orthosilicate or lithium-rich lithium ferrite lithium replenishing agent and an elemental sulfur, elemental selenium, sodium sulfide, calcium sulfide, elemental tellurium, elemental antimony, elemental bismuth or selenium disulfide reducing agent.

[0216] As can be seen from Table 1, by comparing Examples 1-13 with Comparative Example 1, compared with the positive electrode sheet not containing the lithium-supplementing composition, the lithium-supplementing composition in the positive electrode sheet of the present application can increase the number of battery cycles, improve the cycle performance of the battery, and extend the service life of the battery.

[0217] Table 2

[0218] As can be seen from Table 2, from the comparison between Example 1 and Comparative Example 2, it can be seen that compared with placing the lithium supplement composition in a separate lithium supplement layer close to the positive electrode current collector, the present application places the lithium supplement composition in the first active material layer close to the positive electrode current collector, which can further reduce the decomposition potential of the lithium supplement, increase the number of battery cycles and extend the discharge time of the battery, and improve the cycle performance and rate performance of the battery.

[0219] From the comparison between Example 1 and Comparative Example 3, it can be seen that compared with placing the lithium supplement composition in the second active material layer away from the current collector, the present application places the lithium supplement composition in the first active material layer close to the positive electrode current collector, which can increase the number of battery cycles and extend the battery discharge time, thereby improving the battery's cycle performance and rate performance.

[0220] From the comparison between Example 1 and Comparative Example 4, it can be seen that compared with setting the lithium supplement composition in the entire active material layer, the present application sets the lithium supplement composition in the first active material layer close to the positive electrode current collector, which can increase the number of battery cycles and extend the discharge time of the battery, thereby improving the battery's cycle performance and rate performance.

[0221] Table 3

[0222] As can be seen from Table 3, compared with lithium iron-rich lithium supplement, the use of lithium metasilicate lithium supplement can reduce the gas production of the battery, increase the number of battery cycles and extend the discharge time of the battery, and improve the cycle performance and rate performance of the battery.

[0223] Table 4

[0224] As can be seen from Table 4, compared with the case where the reducing agent is elemental sulfur, the use of reducing agents such as elemental selenium, elemental tellurium, elemental antimony, elemental bismuth or selenium disulfide can not only increase the number of battery cycles, but also further improve the discharge time of the battery and extend the battery life.

[0225] Table 5

[0226] As shown in Table 5, controlling the mass fraction of the reducing agent relative to the active material layer to 0.1%-10% results in a long cycle life and discharge time, as well as excellent cycle and rate performance. Controlling the mass fraction of the reducing agent relative to the active material layer to 0.4%-2.0% further improves the cycle and rate performance of the battery.

[0227] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned 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 in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A secondary battery comprising a positive electrode plate, characterized in that: The positive electrode sheet includes a positive electrode current collector and an active material layer located on at least one surface of the positive electrode current collector, wherein the active material layer includes a first active material layer and a second active material layer, wherein the first active material layer is located on the surface of the positive electrode current collector, and the second active material layer is located on a side of the first active material layer away from the positive electrode current collector, and the first active material layer includes a lithium supplement composition. Wherein, the lithium supplement composition comprises a lithium supplement agent and a reducing agent.

2. The secondary battery according to claim 1, wherein The lithium supplement includes one or more of lithium nickelate, lithium-rich lithium nickelate, lithium ferrite, lithium-rich lithium ferrite, lithium oxalate, lithium squarate, lithium metasilicate, lithium orthosilicate, lithium carbonate, lithium sulfate, lithium hydroxide, lithium phosphate, lithium oxide, lithium peroxide, lithium borate, and lithium metaborate.

3. The secondary battery according to claim 1, wherein The lithium supplement includes one or more of lithium-rich nickelate, lithium metasilicate, lithium orthosilicate, lithium sulfate, lithium hydroxide, lithium borate, lithium metaborate, and lithium phosphate.

4. The secondary battery according to any one of claims 1 to 3, characterized in that The reducing agent includes one or more of elemental selenium, selenium metal compounds, elemental sulfur, sulfur metal compounds, elemental phosphorus, phosphorus metal compounds, elemental boron, boron metal compounds, elemental tellurium, tellurium metal compounds, elemental antimony, antimony metal compounds, elemental bismuth, bismuth metal compounds, and selenium disulfide.

5. The secondary battery according to any one of claims 1 to 3, characterized in that The reducing agent includes one or more of elemental selenium, elemental tellurium, elemental antimony, elemental bismuth, lithium selenide, sodium selenide, copper selenide, and selenium disulfide.

6. The secondary battery according to any one of claims 1 to 5, characterized in that The mass ratio of the lithium supplement agent to the reducing agent is 0.5-20.

7. The secondary battery according to any one of claims 1 to 5, characterized in that The mass ratio of the lithium supplement agent to the reducing agent is 1-10.

8. The secondary battery according to any one of claims 1 to 7, characterized in that The mass fraction of the reducing agent is 0.1%-10% based on the mass of the active material layer.

9. The secondary battery according to any one of claims 1 to 7, characterized in that The mass fraction of the reducing agent is 0.4%-2.0% based on the mass of the active material layer.

10. The secondary battery according to any one of claims 1 to 8, characterized in that Based on the mass of the active material layer, the mass fraction of the lithium supplement agent is 0.9%-20%.

11. The secondary battery according to any one of claims 1 to 10, characterized in that: The thickness ratio of the first active material layer to the second active material layer is 1:5-5:

1.

12. The secondary battery according to any one of claims 1 to 10, characterized in that The thickness ratio of the first active material layer to the second active material layer is 1:4-4:

1.

13. The secondary battery according to any one of claims 1 to 12, characterized in that: The thickness of the active material layer is 20 μm-250 μm.

14. The secondary battery according to any one of claims 1 to 13, characterized in that The thickness of the active material layer is 80 μm-200 μm.

15. The secondary battery according to any one of claims 1 to 14, characterized in that The first active material layer and the second active material layer contain the same positive electrode active material.

16. An electrical device, characterized in that: A secondary battery comprising the secondary battery according to any one of claims 1 to 15.

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