Secondary battery, electric device, and lithium supplement agent

Abstract

The invention relates to a secondary battery, an electric device and a lithium supplement agent. The secondary battery comprises a positive pole piece and a lithium supplement agent, the positive pole piece comprises a lithium-containing positive active material, and the lithium supplement agent comprises an inner core and a coating layer coating the surface of the inner core; the inner core comprises lithium sulfide, and the chemical general formula of the lithium sulfide is LixSyMz; wherein x is equal to 1-5, y is equal to 1-6, z is equal to 0-2, and M comprises a doping element; and the coating layer comprises inorganic carbonate. The lithium supplement agent in the secondary battery is good in stability and has a slow-release effect, the first effect of the secondary battery can be improved by using the lithium supplement agent, the cycle performance of the secondary battery is further improved, and the storage life of the secondary battery is further prolonged.

Description

Technical Field

[0001] This application belongs to the field of battery technology, specifically relating to a secondary battery, an electrical device, and a lithium replenishing agent. Background Technology

[0002] With the booming development of new energy vehicles, battery drive systems have become an important factor affecting the performance and cost of new energy vehicles. Due to their high energy density, low memory effect, and high operating voltage, rechargeable batteries have become the preferred power source for battery drive systems.

[0003] A secondary battery typically includes a positive electrode, a negative electrode, and a separator between the positive and negative electrodes. Taking lithium-ion batteries as an example, lithium-ion batteries are prone to lithium loss during storage or use. For instance, the formation of a solid electrolyte interface (SEI) during the first charge and discharge process consumes some lithium ions, leading to an irreversible reduction in the battery's charge and discharge performance. Summary of the Invention

[0004] The purpose of this application is to provide a secondary battery, an electrical device, and a lithium replenishing agent, aiming to solve the technical problem of how to better replenish lithium in batteries.

[0005] To achieve the above-mentioned objectives, the technical solution adopted in this application is as follows:

[0006] In a first aspect, embodiments of this application provide a secondary battery, including a positive electrode sheet and a lithium replenishing agent, wherein the positive electrode sheet includes a lithium-containing positive electrode active material, and the lithium replenishing agent includes a core and a coating layer covering the surface of the core;

[0007] The core comprises a lithium sulfide, the general chemical formula of which is Li. x S y M z Where x = 1-5, y = 1-6, z = 0-2, and M includes dopant elements;

[0008] The coating layer comprises inorganic carbonates.

[0009] In the secondary battery of this application, the lithium replenishing agent used has a core-shell structure, with a coating layer containing inorganic carbonates formed on its surface. This core-shell structure improves the stability of lithium sulfides in the core, making the lithium sulfide replenishment function less prone to failure and ensuring stable lithium replenishment for the secondary battery. Simultaneously, the inorganic carbonates are slowly decomposed by acidic products in the battery, resulting in the slow release of lithium sulfides from the replenishing agent, achieving sustained-release lithium replenishment and better extending the replenishment effect. Therefore, the lithium replenishing agent in the secondary battery of this application not only has good stability but also a sustained-release effect. The use of this lithium replenishing agent not only improves the initial efficiency of the secondary battery but also further enhances its cycle performance and storage life.

[0010] In some embodiments, the inorganic carbonate includes at least one of calcium carbonate, magnesium carbonate, zinc carbonate, and aluminum carbonate;

[0011] And / or, the doping element includes at least one of silicon, nitrogen, phosphorus, oxygen, fluorine, and bromine.

[0012] The metal ions released after the carbonates dissolve are those corresponding to elements such as calcium, magnesium, zinc, and aluminum. Their reduction potential is lower than that of lithium ions, therefore these released metal ions are not easily reduced and can adhere to the surface of the lithium metal deposit, thus preventing further lithium ion deposition on top and inhibiting dendrite growth. The lithium sulfides formed after doping with these elements can improve sulfide activity and better replenish lithium.

[0013] In some embodiments, the inorganic carbonate includes calcium carbonate;

[0014] And / or, the doping element includes at least one of nitrogen, phosphorus, and fluorine.

[0015] Calcium carbonate can not only stably coat lithium sulfides, but the released calcium ions attached to the surface of lithium metal deposits can also inhibit dendrite growth. Furthermore, calcium carbonate is widely available and inexpensive. Nitrogen, phosphorus, and fluorine-doped lithium sulfides can better improve the SEI film formation on the negative electrode, which is beneficial for enhancing the electrochemical performance of secondary batteries.

[0016] In some embodiments, the particle size D of the lithium supplement is... V 50 refers to 50-150nm.

[0017] The aforementioned nanoscale lithium replenishing agent exhibits good uniformity and a short lithium ion diffusion distance, thereby resulting in good rate performance of the secondary battery.

[0018] In some embodiments, the secondary battery includes an electrolyte containing the lithium replenishing agent.

[0019] Using lithium replenishing agents as electrolyte additives in secondary batteries allows the use of acidic substances such as hydrofluoric acid generated by side reactions in the electrolyte to decompose carbonates in the coating layer, thereby achieving the slow release of lithium sulfides from the lithium replenishing agent and better realizing slow-release lithium replenishment.

[0020] In some embodiments, the mass percentage of the lithium supplement in the electrolyte is 0.5-10%.

[0021] When the lithium replenishing agent is added to the electrolyte at the above-mentioned mass percentage, it can effectively replenish lithium while having little impact on the performance of the electrolyte.

[0022] In some embodiments, the electrolyte further contains a surfactant.

[0023] The surfactant helps the lithium supplement to disperse more evenly in the electrolyte, preventing it from agglomerating.

[0024] In some embodiments, the surfactant includes at least one of sucrose fatty acid ester, sodium fatty acid, potassium fatty acid, and calcium fatty acid;

[0025] And / or, the surfactant is present in the electrolyte at a mass percentage of 0.5-2%.

[0026] The surfactants described above can effectively reduce the surface tension between the electrolyte and the lithium supplement, making it less likely for the lithium supplement to agglomerate in the electrolyte. Adding the surfactant to the electrolyte at the above-mentioned mass percentages allows for better and more uniform dispersion of the lithium supplement.

[0027] In some embodiments, the solvent in the electrolyte includes ethylene carbonate.

[0028] Through the sulfur catalytic effect of lithium-containing sulfides in the lithium supplement, ethylene carbonate can be catalytically decomposed into EC into PEO (polyethylene oxide) and polysulfide polymers, which can better stabilize the SEI film formation and thus improve the battery's storage life.

[0029] Secondly, this application provides an electrical device, which includes the secondary battery provided in the first aspect of this application.

[0030] The electrical device uses a secondary battery unique to this application. Based on the fact that the lithium replenishing agent in the secondary battery not only has good stability but also has a slow-release lithium replenishing effect, the electrical device of this application has excellent cycle performance and storage life, and can work better.

[0031] Thirdly, this application provides a lithium replenishing agent, which includes a core and a coating layer covering the surface of the core;

[0032] The core comprises a lithium sulfide, the general chemical formula of which is Li. x S y M z Where x = 1-5, y = 1-6, z = 0-2, and M includes dopant elements;

[0033] The coating layer comprises inorganic carbonates.

[0034] The lithium replenishing agent provided in this application has a core-shell structure. The lithium sulfide in the core provides lithium replenishment, and the coating layer improves the stability of the lithium sulfide in the core, thus making the lithium sulfide replenishment function less prone to failure. Simultaneously, the inorganic carbonate in the coating layer can be slowly decomposed by acidic products in the electrolyte, thereby achieving a slow-release lithium replenishment and better extending the replenishment effect. Therefore, the lithium replenishing agent of this application, when used in lithium-ion secondary batteries, can stably and slowly replenish lithium, resulting in excellent initial efficiency, cycle performance, and storage life.

[0035] In some embodiments, the inorganic carbonate includes at least one of calcium carbonate, magnesium carbonate, zinc carbonate, and aluminum carbonate;

[0036] And / or, the doping element includes at least one of silicon, nitrogen, phosphorus, oxygen, fluorine, and bromine.

[0037] The metal ions released after the carbonates dissolve are those corresponding to elements such as calcium, magnesium, zinc, and aluminum. Their reduction potential is lower than that of lithium ions, therefore these released metal ions are not easily reduced and can adhere to the surface of the lithium metal deposit, thus preventing further lithium ion deposition on top and inhibiting dendrite growth. The lithium sulfides formed after doping with these elements can improve sulfide activity and better replenish lithium.

[0038] In some embodiments, the inorganic carbonate includes calcium carbonate;

[0039] And / or, the doping element includes at least one of nitrogen, phosphorus, and fluorine.

[0040] Calcium carbonate can not only stably coat lithium sulfides, but the released calcium ions attached to the surface of lithium metal deposits can also inhibit dendrite growth. Furthermore, it is widely available and inexpensive. Nitrogen, phosphorus, and fluorine-doped lithium sulfides can better improve the SEI film formation on the negative electrode, which is beneficial for enhancing the electrochemical performance of secondary batteries.

[0041] In some embodiments, the particle size D of the lithium supplement is... V 50 refers to 50-150nm.

[0042] The aforementioned nanoscale lithium supplement has good uniformity and a short lithium ion diffusion distance, resulting in good rate performance. Attached Figure Description

[0043] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0044] Figure 1 This is a schematic diagram of the battery cell structure of one embodiment of the secondary battery in this application;

[0045] Figure 2 for Figure 1 The diagram shows an exploded view of a single battery cell.

[0046] Figure 3 This is a schematic diagram of one embodiment of the battery module of this application;

[0047] Figure 4 This is a schematic diagram of one embodiment of the battery pack of this application;

[0048] Figure 5 for Figure 4 The diagram shows the exploded structure of the battery pack.

[0049] Figure 6 This is a schematic diagram of one embodiment of an electrical device that uses a secondary battery as a power source, as described in the present application.

[0050] Explanation of reference numerals in the attached figures:

[0051] 10-Battery cell; 11-Housing casing; 12-Top cover assembly; 13-Electrode assembly; 20-Battery module; 30-Battery pack; 31-Upper casing; 32-Lower casing. Detailed Implementation

[0052] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0053] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0054] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0055] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0056] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0057] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces). "At least one" refers to one or more (including one, two, three, etc.).

[0058] In the description of the embodiments of this application, the technical terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0059] In the description of the embodiments of this application, unless otherwise expressly specified and limited, technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0060] With the dwindling availability of traditional energy resources, the development of new energy storage devices is receiving increasing attention. Among these, secondary batteries have garnered significant interest due to their high energy density, high theoretical capacity, excellent cycle stability, and environmental friendliness. Secondary batteries can be applied not only to energy storage systems in hydropower, thermal power, wind power, and solar power plants, but also widely in electric vehicles such as electric bicycles, electric motorcycles, and electric cars. As the application areas of secondary batteries as power batteries continue to expand, the market demand for them is also constantly increasing.

[0061] A rechargeable battery, also known as a rechargeable battery or accumulator, is a battery that can be recharged after discharge to reactivate its active materials and continue to be used. A lithium-ion battery is a rechargeable battery that uses lithium ions as its active ions and employs lithium-containing positive electrode active materials. Lithium-ion batteries experience lithium loss during use or storage, such as irreversible active lithium loss due to the growth of the SEI film. Furthermore, as the SEI film repairs, active lithium is continuously consumed, leading to an irreversible decrease in the battery's charge and discharge performance. To address lithium loss in lithium-ion batteries, the industry has designed various lithium replenishing agents. However, common lithium replenishing agents are unstable and cannot provide continuous, long-term lithium replenishment when used in batteries.

[0062] Based on this, this application uses a lithium replenishing agent with a core-shell structure in lithium-ion batteries. The core-shell structure of the lithium replenishing agent not only improves the initial coulombic efficiency of the battery but also enhances its cycle performance and storage life. The specific technical solution is as follows.

[0063] Lithium supplement

[0064] In order to better replenish lithium in batteries, this application presents an embodiment of a lithium replenishing agent with a core-shell structure. Specifically, the lithium replenishing agent comprises two parts: (1) a core, the material of which includes lithium sulfide, the general chemical formula of which is Li. x S y M z , where x = 1-5, y = 1-6, z = 0-2, M includes doping elements, which can be undoped lithium sulfide or doped lithium sulfide, and can be selected according to actual improvement needs. (2) Coating layer, the material of the coating layer includes carbonate. The coating layer is mainly used to protect the core. The lithium sulfide in the core is prone to react with moisture and become ineffective. Therefore, coating the core surface can improve the stability of the core.

[0065] The lithium replenishing agent of this application has a core-shell structure with an inorganic carbonate coating layer on its surface. This core-shell structure improves the stability of lithium sulfides in the core, making the lithium sulfide replenishment function less prone to failure and allowing for stable lithium replenishment of secondary batteries. The release of lithium ions from the lithium sulfides in the core offsets the irreversible capacity loss caused by the formation of the SEI film during the first charge-discharge cycle, effectively improving the battery's initial coulombic efficiency. Simultaneously, the inorganic carbonate is slowly decomposed by acidic products in the battery, resulting in the slow release of lithium sulfides from the replenishing agent, achieving sustained-release lithium replenishment and extending the replenishment effect. Therefore, the lithium replenishing agent of this application not only has good stability but also a sustained-release effect. When used in batteries, it can improve the battery's initial efficiency and further enhance its cycle performance and storage life.

[0066] In some embodiments, the general chemical formula of the lithium sulfide in the lithium supplement core is Li. x S y M z x = 1-5, y = 1-6, z = 0-2; the choice of x, y, and z ensures that the total valence of the general chemical formula is zero. M is the dopant element, which can be an undoped lithium sulfide (z = 0) or a doped lithium sulfide (z not equal to 0). Specifically, in the undoped case, the core of the lithium replenisher can be at least one of Li₂S, Li₂S₂, Li₂S₄, and Li₂S₆; in the doped case, the dopant element includes at least one of silicon, nitrogen, phosphorus, oxygen, fluorine, and bromine. The core of the lithium replenisher can specifically be lithium sulfides such as Li₂S, Li₂S₂, Li₂S₄, and Li₂S₆ doped with at least one of nitrogen, phosphorus, oxygen, fluorine, and bromine. The lithium sulfides formed after doping with these dopant elements can improve the activity of the sulfides and better replenish lithium. For example, taking phosphorus doping as an example, the lithium sulfide after phosphorus doping is represented by Li2S@P, for example, it can be Li3PS4; taking silicon doping as an example, the lithium sulfide after silicon doping is represented by Li2S@Si, for example, it can be Li2SiS3.

[0067] In some embodiments, the doping element includes at least one of nitrogen, phosphorus, and fluorine. Nitrogen, phosphorus, and fluorine-doped lithium sulfides can better improve the formation of the SEI film on the negative electrode, for example, by stabilizing the SEI film and reducing the film resistance, thereby improving the electrochemical performance of the secondary battery.

[0068] In some embodiments, the inorganic carbonates in the coating layer of the lithium supplement include at least one of calcium carbonate, magnesium carbonate, zinc carbonate, and aluminum carbonate. These carbonates, upon dissolution, release metal ions with reduction potentials lower than lithium ions. For example, calcium carbonate releases calcium ions, magnesium carbonate releases magnesium ions, zinc carbonate releases zinc ions, and aluminum carbonate releases aluminum ions. Since the reduction potentials of calcium, magnesium, zinc, and aluminum ions are lower than those of lithium ions, they are not easily reduced. Therefore, the metal ions released by these carbonates can adhere to the surface of the lithium metal deposit, preventing further deposition of lithium ions on top of the deposit and thus inhibiting dendrite growth.

[0069] In some embodiments, the inorganic carbonate in the lithium supplement coating layer includes calcium carbonate; calcium carbonate can not only stably coat lithium sulfides, but the released calcium ions attached to the surface of the lithium metal deposit can also inhibit dendrite growth. At the same time, calcium carbonate is widely available and inexpensive.

[0070] In some embodiments, the particle size D of the lithium supplement is... V The 50 refers to a diameter of 50-150 nm, with an exemplary low value. The Dv50 of the lithium replenisher can be 50 nm, 70 nm, 80 nm, 100 nm, 120 nm, 140 nm, 150 nm, etc. Furthermore, the thickness of the lithium replenisher coating layer is 20-70 nm, with an exemplary thickness of 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, etc.

[0071] Particle size refers to the size of particulate material, also known as particle size. The percentage of particles within different size ranges in the total quantity is called particle size distribution, while volumetric particle size distribution is calculated cumulatively based on particle volume. For example, Dv50 represents the equivalent diameter corresponding to a cumulative volumetric particle size distribution percentage of 50% in a sample. In specific embodiments, a particle size analyzer (e.g., a laser particle size analyzer) can be used to test the average particle size. For the identification of the size of the lithium replenisher after it is added to a secondary battery, a particle size analyzer can be used to test the Dv50 of the entire lithium replenisher, and then the thickness of the coating layer can be observed using a scanning electron microscope. Subtracting the two measurements yields the core particle size Dv50.

[0072] The lithium replenisher core and coating layer can ultimately form a nanoscale lithium replenisher with a total size of approximately 50-150 nm, exhibiting good uniformity and short lithium-ion diffusion distance, thus resulting in good rate performance of the secondary battery. It should be noted that the carbonate in the coating layer can be a nanoscale particulate inorganic carbonate, and the coating layer can either completely cover the core surface or leave some pores on the core surface. To further improve the stability of the core, the coating layer can completely cover the core.

[0073] In this embodiment, the lithium replenishing agent can be used in the positive electrode of the battery, for example, by mixing it with the lithium-containing positive electrode active material in the positive electrode to form a film; or the lithium replenishing agent can be used in the negative electrode of the battery, for example, by mixing it with the negative electrode active material in the negative electrode to form a film; or, the lithium replenishing agent can be used as an electrolyte additive in the electrolyte of the battery. In some embodiments, the lithium replenishing agent is used in the electrolyte of the battery.

[0074] Specifically, the aforementioned lithium supplement can be prepared using a commonly used coating process.

[0075] For example, a solid-phase grinding and coating method can be used to distribute carbonates on the outer surface of lithium-containing sulfide particles by using mechanical forces such as extrusion, impact, shearing, and friction, so that various components can penetrate and diffuse into each other to form a coating. During the coating process, the grinding and stirring speed can be 5000-6500 r / min, and the stirring time is 30-100 min. The mass ratio of lithium sulfide to carbonate can be 1:0.5-5.

[0076] Rechargeable batteries

[0077] Firstly, embodiments of this application provide a secondary battery. The secondary battery of this application is a lithium-ion battery, wherein the active material in the positive electrode is a lithium-containing positive electrode active material. To address the issue of lithium loss easily occurring with this lithium-containing positive electrode active material, embodiments of this application also use a lithium replenishing agent in the secondary battery.

[0078] The lithium replenishing agent used in the secondary battery of this application embodiment has a core-shell structure. Specifically, the lithium replenishing agent includes two parts: (1) a core, the core material of which includes lithium sulfide, the general chemical formula of which is Li. x S y M z , where x = 1-5, y = 1-6, z = 0-2, M includes doping elements, which can be undoped lithium sulfide or doped lithium sulfide, and can be selected according to actual improvement needs. (2) Coating layer, the material of the coating layer includes carbonate. The coating layer is mainly used to protect the core. The lithium sulfide in the core is prone to react with moisture and become ineffective. Therefore, coating the core surface can improve the stability of the core.

[0079] In the secondary battery of this application embodiment, the lithium replenishing agent used has a core-shell structure, with a coating layer containing inorganic carbonates formed on its surface. This core-shell structure improves the stability of lithium sulfides in the core, making the lithium sulfide replenishment function less prone to failure and allowing for stable lithium replenishment of the secondary battery. Based on the release of lithium ions from the lithium sulfides in the core, the irreversible capacity loss caused by the formation of the SEI film during the first charge-discharge cycle of the lithium battery can be offset, effectively improving the battery's initial coulombic efficiency. Simultaneously, the inorganic carbonates can be slowly decomposed by acidic products in the battery, achieving a slow release of lithium sulfides from the lithium replenishing agent, thus achieving sustained-release lithium replenishment and better extending the replenishment effect. Therefore, the lithium replenishing agent in the secondary battery of this application not only has good stability but also a sustained-release effect. The use of the lithium replenishing agent not only improves the initial efficiency of the secondary battery but also further enhances its cycle performance and storage life.

[0080] In some embodiments, in a secondary battery, the general chemical formula of the lithium sulfide in the lithium replenishment core is Li. x S y M z x = 1-5, y = 1-6, z = 0-2; the choice of x, y, and z ensures that the total valence of the general chemical formula is zero. M is the dopant element, which can be an undoped lithium sulfide or a doped lithium sulfide. Specifically, when undoped, the core of the lithium replenisher can be at least one of Li₂S, Li₂S₂, Li₂S₄, and Li₂S₆; when doped, the dopant element includes at least one of nitrogen, phosphorus, oxygen, fluorine, and bromine. The core of the lithium replenisher can specifically be lithium sulfides such as Li₂S, Li₂S₂, Li₂S₄, and Li₂S₆ doped with at least one of silicon, nitrogen, phosphorus, oxygen, fluorine, and bromine. For example, taking phosphorus doping as an example, the lithium sulfide after phosphorus doping is represented by Li₂S@P, for example, it can correspond to Li₃PS₄; taking silicon doping as an example, the lithium sulfide after silicon doping is represented by Li₂S@Si, for example, it can correspond to Li₂SiS₃. The lithium sulfides formed after these doping elements are applied can improve the activity of the sulfides and better replenish lithium.

[0081] In some embodiments, the doping element includes at least one of nitrogen, phosphorus, and fluorine. Nitrogen, phosphorus, and fluorine doped lithium sulfides can better improve the SEI film formation on the negative electrode, which is beneficial to improving the electrochemical performance of the secondary battery.

[0082] In some embodiments, in the secondary battery, the inorganic carbonate in the coating layer of the lithium replenisher includes at least one of calcium carbonate, magnesium carbonate, zinc carbonate, and aluminum carbonate. These carbonates, upon dissolution, release metal ions with reduction potentials lower than lithium ions. For example, calcium carbonate releases calcium ions, magnesium carbonate releases magnesium ions, zinc carbonate releases zinc ions, and aluminum carbonate releases aluminum ions. Since the reduction potentials of calcium, magnesium, zinc, and aluminum ions are lower than those of lithium ions, they are not easily reduced. Therefore, the metal ions released by these carbonates can adhere to the surface of the lithium metal deposit, repelling further deposition of lithium ions on top of the deposit and thus inhibiting dendrite growth.

[0083] In some embodiments, in the secondary battery, the inorganic carbonate in the lithium replenishment coating layer includes calcium carbonate; calcium carbonate can not only stably coat lithium sulfides, but the released calcium ions attached to the surface of the lithium metal deposit can inhibit dendrite growth, and calcium carbonate is widely available and inexpensive.

[0084] In some embodiments, the particle size Dv50 of the lithium replenishing agent is 50-150 nm. For example, the overall Dv50 of the lithium replenishing agent can be 50 nm, 70 nm, 80 nm, 100 nm, 120 nm, 140 nm, 150 nm, etc. The thickness of the lithium replenishing agent coating layer is 20-70 nm. For example, the coating layer thickness can be 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, etc.

[0085] In the embodiments of this application, the lithium replenishing agent can be used in the positive electrode of the secondary battery, for example, mixed with the lithium-containing positive electrode active material in the positive electrode to form a film; or the lithium replenishing agent can be used in the negative electrode of the secondary battery, for example, mixed with the negative electrode active material in the negative electrode to form a film; or, the lithium replenishing agent can be used as an electrolyte additive in the electrolyte of the secondary battery.

[0086] In some embodiments, the secondary battery includes an electrolyte containing the lithium replenishing agent with a core-shell structure described above. By using this unique lithium replenishing agent as an electrolyte additive in the secondary battery electrolyte, acidic substances such as hydrofluoric acid generated by electrolyte side reactions can decompose the carbonates in the coating layer, thereby achieving a slow release of lithium sulfides from the lithium replenishing agent and better achieving sustained-release lithium replenishment.

[0087] In some embodiments, the mass percentage of the lithium replenishing agent in the electrolyte is 0.5-10%. Exemplarily, the mass percentage of the lithium replenishing agent can be 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, etc. Adding the lithium replenishing agent to the electrolyte at the above-mentioned mass percentages can effectively achieve lithium replenishment while having minimal impact on the electrolyte's performance.

[0088] In some embodiments, the electrolyte also contains a surfactant. That is, the lithium supplement and the surfactant are added together to the electrolyte, and rapid stirring forms a dispersed liquid. Through the action of the surfactant, the lithium supplement is less likely to agglomerate in the electrolyte, resulting in better and more uniform dispersion.

[0089] In some embodiments, the surfactant includes at least one selected from sucrose fatty acid esters, sodium fatty acids, potassium fatty acids, and calcium fatty acids; wherein the fatty acid can be a fatty acid with 10-20 carbon atoms, for example, sodium stearate, potassium stearate, calcium stearate, etc. The surfactants of the above types can effectively reduce the surface tension between the electrolyte and the lithium supplement, making it less likely for the lithium supplement to agglomerate in the electrolyte.

[0090] In some embodiments, the surfactant comprises 0.5-2% by mass in the electrolyte. Exemplarily, the surfactant mass percentage can be 0.5%, 1%, 1.5%, 2%, etc. Since the lithium supplement in the electrolyte comprises 0.5-10% by mass, it can be understood that the mass ratio of the lithium supplement to the surfactant in the electrolyte is (0.5-10):(0.5-2). Adding the surfactant to the electrolyte at the above-mentioned mass percentage allows for better and more uniform dispersion of the lithium supplement.

[0091] The electrolyte includes an electrolyte salt and a solvent. For secondary batteries that are lithium-ion batteries, 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 difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0092] In some embodiments, the solvent in the electrolyte may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone. The solvent in the electrolyte includes ethylene carbonate.

[0093] In some embodiments, the solvent in the electrolyte includes ethylene carbonate. Through the sulfur catalytic effect of the lithium-containing sulfides in the lithium supplement, ethylene carbonate can catalytically decompose EC into PEO (ethylene oxide) and polysulfide polymers, thereby better stabilizing SEI film formation and thus improving battery storage life.

[0094] Specifically, the structure of ethylene carbonate decomposed into PEO (polyethylene oxide) and polysulfide polymers is as follows:

[0095] PEO: Polysulfide polymers:

[0096] Polysulfides undergo ring-opening polymerization with organic matter in the electrolyte to form a dense SEI film on the negative electrode. This can significantly improve the battery's storage life.

[0097] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0098] Typically, a secondary battery consists of individual cells, which in turn include a negative electrode, a positive electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0099] In some embodiments, positive and negative electrode sheets are disposed opposite to each other and injected with electrolyte. The positive electrode sheet includes a positive current collector and a positive active layer stacked on at least one surface of the positive current collector, the positive active layer including a lithium-containing positive active material. The lithium supplement agent can be used in the positive electrode sheet, the negative electrode sheet, or the electrolyte. Exemplarily, embodiments of this application can use a core-shell structured lithium supplement agent as an electrolyte additive in the electrolyte.

[0100] In some embodiments, the positive electrode active layer contains a positive electrode active material, namely a lithium-containing positive electrode active material. As an example, the positive electrode active material of a lithium-ion secondary battery may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials 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 oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNiO2). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites. The positive electrode active material accounts for 80-100% by weight of the positive electrode active layer, based on the total weight of the positive electrode active layer.

[0101] In some embodiments, the positive electrode active layer may optionally include a binder. As an example, the binder in the positive electrode active layer may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins. The binder accounts for 0-20% by weight of the positive electrode active layer, based on the total weight of the positive electrode active layer.

[0102] In some embodiments, the positive electrode active layer may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, carbon black (e.g., acetylene black or Ketjen black), carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The conductive agent accounts for 0-20% by weight of the positive electrode active layer, based on the total weight of the positive electrode active layer.

[0103] In some embodiments, the current collector of the positive electrode sheet, also known as 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 substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate such as polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.

[0104] In one embodiment, the separator may be a separator membrane, which may be made of materials known in the art for battery separator membranes. As an example, the separator membrane base film may include one or more of polyethylene film, polypropylene film, and polyvinylidene fluoride film.

[0105] The electrolyte acts as a conductor of ions between the positive and negative electrodes. In this application, a liquid electrolyte is used. In some embodiments, an electrolyte solution is employed.

[0106] In some embodiments, the negative electrode includes a negative current collector and a negative active layer disposed on at least one surface of the negative current collector. The negative 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 substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer substrate such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0107] In some embodiments, the negative electrode active layer contains a negative electrode active material, including at least one selected from artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, etc. Optionally, it may also include a binder. The binder may be selected from at least one selected from styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol (PVA), sodium alginate, polymethacrylic acid, and carboxymethyl chitosan.

[0108] In some embodiments, the negative electrode active layer further includes a conductive agent. For example, the conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In the negative electrode active layer, the weight ratio of the negative electrode active material, the conductive agent, and the binder may be 94–97:1–2:1–3, while the metal particles account for 1%–2% of the total weight of the negative electrode active layer.

[0109] In some embodiments, the negative electrode active layer may optionally include other additives, such as dispersants, thickeners (e.g., sodium carboxymethyl cellulose), etc.

[0110] Furthermore, embodiments of this application provide a method for preparing the above-mentioned secondary battery, comprising:

[0111] Prepare positive and negative electrode sheets separately;

[0112] The prepared negative electrode, positive electrode, separator, and electrolyte are assembled to obtain a secondary battery. The core-shell lithium supplement can be added to the positive electrode, the negative electrode, or the electrolyte.

[0113] In some embodiments, the core-shell lithium supplement can be added to the electrolyte. For example, the prepared positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrode, and then wound to obtain an electrode assembly; the electrode assembly is placed in a battery casing, dried, and then injected with an electrolyte containing the above-mentioned lithium supplement, and then subjected to formation and settling processes to obtain a secondary battery.

[0114] The secondary battery provided in this application embodiment can specifically include any one of the following: a battery cell, a battery module, or a battery pack. The battery cell refers to a secondary battery comprising a battery casing and a battery cell encapsulated within the battery casing. The shape of the battery cell is not particularly limited; it can be cylindrical, square, or any other arbitrary shape. Figure 1 The shown is a square-structured battery cell 10.

[0115] In some embodiments, such as Figure 2 As shown, the outer packaging of the battery cell 10 may include a housing 11 and a top cover assembly 12. The housing 11 may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates enclosing a receiving cavity. The housing 11 has an opening communicating with the receiving cavity, and the top cover assembly 12 is used to cover the opening to close the receiving cavity. The positive electrode sheet, separator, and negative electrode sheet contained in the secondary battery of this application embodiment may be formed into an electrode assembly 13 by a winding process and / or a stacking process. The electrode assembly 13 is encapsulated in the receiving cavity. Electrolyte is immersed in the electrode assembly 13. The number of electrode assemblies 13 contained in the battery cell 10 may be one or more, which can be adjusted according to actual needs.

[0116] The method for preparing the battery cell 10 is well known. In some embodiments, a positive electrode, a separator, a negative electrode, and an electrolyte can be assembled to form the battery cell 10. As an example, the positive electrode, the separator, and the negative electrode can be formed into an electrode assembly 13 by a winding process or a stacking process. The electrode assembly 13 is placed in an outer packaging, dried, and then injected with an electrolyte. After vacuum sealing, settling, formation, and shaping processes, the battery cell 10 is obtained.

[0117] A battery module is assembled from the battery cell 10, which means it can contain multiple battery cells 10. The specific number can be adjusted according to the application and capacity of the battery module.

[0118] In some embodiments, Figure 3 This is a schematic diagram of battery module 20 as an example. (See diagram for example.) Figure 3 As shown, in the battery module 20, multiple battery cells 10 can be arranged sequentially along the length of the battery module 20. Of course, they can also be arranged in any other manner. Furthermore, the multiple battery cells 10 can be fixed in place using fasteners.

[0119] Optionally, the battery module 20 may also include a housing with a receiving space in which multiple battery cells 10 are received.

[0120] A battery pack refers to an assembly of the aforementioned battery cells 10, meaning it can contain multiple battery cells 10. These multiple battery cells 10 can be assembled into the aforementioned battery module 20. The specific number of battery cells 10 or battery modules 20 contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0121] As in the example, Figure 4 and Figure 5 This is a schematic diagram of a battery pack 30 as an example. The battery pack 30 may include a battery compartment and multiple battery modules 20 disposed within the battery compartment. The battery compartment includes an upper compartment 31 and a lower compartment 32. The upper compartment 31 covers the lower compartment 32, forming a closed space for accommodating the battery modules 20. The multiple battery modules 20 can be arranged in any manner within the battery compartment.

[0122] Electrical appliances

[0123] Secondly, embodiments of this application also provide an electrical device, which includes the secondary battery provided in the first aspect of the embodiments of this application. The secondary battery in this application embodiment serves as the power source for the electrical device, and can also be used as the energy storage unit of the electrical device. The electrical device in this application embodiment has good cycle performance, long storage life, and can work well.

[0124] Electrical devices can be, but are not limited to, 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. The type of electrical device can be selected from individual battery cells, battery modules, or battery packs according to its usage requirements.

[0125] Figure 6This is a schematic diagram of an example electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the device's requirements for high power and high energy density, a battery pack or battery module can be used.

[0126] Another example of an electrical device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use rechargeable batteries as their power source.

[0127] Example

[0128] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0129] Example 1

[0130] Preparation of lithium-ion secondary battery cells

[0131] (1) Preparation of the positive electrode sheet:

[0132] 1 kg of positive electrode active material (lithium iron phosphate), 20 g of conductive agent (acetylene black), and 20 g of binder (vinylidene fluoride) were weighed and added to 1 kg of N-methylpyrrolidone. The mixture was stirred in a mixer for 30 minutes to form a stable and homogeneous positive electrode slurry. This positive electrode slurry was uniformly coated onto the surface of the current collector aluminum foil and dried in an oven at 80°C to obtain the active material layer. The active material layer was then rolled at a pressure of 12 MPa to obtain the battery positive electrode sheet. After spot welding the tabs, the battery positive electrode was obtained. The compaction density of the positive electrode sheet was 2.6 g / cm³. 3 Its surface density is 0.02 mg / cm³. 2 .

[0133] (2) Preparation of negative electrode sheet:

[0134] Weigh 1 kg of negative electrode active material (artificial graphite), 10 g of conductive agent (acetylene black), and 30 g of binder (styrene-butadiene rubber, sodium carboxymethyl cellulose) and add them to 1 kg of deionized water. Stir to obtain a uniformly distributed negative electrode slurry. Coat the negative electrode slurry onto a copper foil current collector, and after drying, rolling, and spot welding of electrode tabs, obtain the negative electrode sheet. The compacted density of the negative electrode sheet is 1.65 g / cm³. 3 Its surface density is 0.01 mg / cm³. 2 .

[0135] (4) Preparation of electrolyte:

[0136] Lithium supplement: The core is Li₂S, and the coating layer is calcium carbonate. It is prepared by solid-phase grinding coating method, that is, by thoroughly mixing and grinding calcium carbonate and Li₂S, the calcium carbonate is coated on the surface of Li₂S to form a coating layer. The relevant dimensions are shown in Table 1.

[0137] Lithium bisfluorosulfonylimide (LiFSI) was dissolved in a solvent (EC) with a concentration of 1 mol / L. Simultaneously, 1% by mass of the aforementioned lithium supplementer and 0.5% by mass of calcium stearate were added to obtain the electrolyte.

[0138] (3) Battery assembly:

[0139] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. The stacked electrodes are then stacked to obtain small stacks. The bare cell is placed in the outer packaging of the secondary battery. After drying, electrolyte is injected into the outer packaging of the battery. After vacuum sealing, settling, formation, shaping, and capacity testing, a lithium-ion secondary battery cell is obtained.

[0140] Examples 2-7

[0141] The difference from Example 1 is as follows: see Table 1.

[0142] Comparative Example 1

[0143] The difference between this comparative example and Example 1 is that the lithium supplement is Li2S, and there is no coating layer.

[0144] Performance testing

[0145] The following performance tests were performed on the aforementioned secondary battery cells:

[0146] (1) Cyclic performance: Refer to GB / T 31484-2015 for testing the standard cycle life of secondary battery cells.

[0147] Under 45°C conditions, constant current charge-discharge tests were performed on the test objects. Stepped charging (equivalent to 1C) was used. The battery cells of the above embodiments and comparative examples were charged to 100% SOC with constant current. Then, the batteries were discharged to 3% SOC with constant current at 0.5C. This is one charge-discharge process. After 50 cycles, the final capacity retention rate was detected.

[0148] (2) Storage life: Refer to T / CSAE 118-2019 to test the calendar life of secondary battery cells.

[0149] Capacity testing frequency: For the first 3 months of storage, capacity is tested every 15 days, with the first day of storage at 60℃ as the baseline. After 15 days of storage at 60℃, capacity retention is tested.

[0150] The results are shown in Table 1.

[0151] Table 1

[0152]

[0153] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A secondary battery, characterized in that, It includes a positive electrode sheet and a lithium replenishing agent, wherein the positive electrode sheet includes a lithium-containing positive electrode active material, and the lithium replenishing agent includes a core and a coating layer covering the surface of the core; The core comprises a lithium sulfide, the general chemical formula of which is Li. x S y M z Where x = 1-5, y = 1-6, z = 0-2, and M includes dopant elements; The coating layer comprises inorganic carbonates.

2. The secondary battery as described in claim 1, characterized in that, The inorganic carbonates include at least one of calcium carbonate, magnesium carbonate, zinc carbonate, and aluminum carbonate. And / or, the doping element includes at least one of silicon, nitrogen, phosphorus, oxygen, fluorine, and bromine.

3. The secondary battery as described in claim 1, characterized in that, The inorganic carbonates include calcium carbonate; And / or, the doping element includes at least one of nitrogen, phosphorus, and fluorine.

4. The secondary battery according to any one of claims 1-3, characterized in that, The particle size D of the lithium supplement V 50 refers to 50-150nm.

5. The secondary battery according to any one of claims 1-4, characterized in that, The secondary battery includes an electrolyte containing the lithium replenishing agent.

6. The secondary battery as described in claim 5, characterized in that, The lithium supplement in the electrolyte has a mass percentage of 0.5-10%.

7. The secondary battery as described in claim 5 or 6, characterized in that, The electrolyte also contains surfactants.

8. The secondary battery as described in claim 7, characterized in that, The surfactant includes at least one of sucrose fatty acid ester, sodium fatty acid, potassium fatty acid, and calcium fatty acid. And / or, the surfactant is present in the electrolyte at a mass percentage of 0.5-2%.

9. The secondary battery according to any one of claims 5-8, characterized in that, The solvent in the electrolyte includes ethylene carbonate.

10. An electrical device, characterized in that, The electrical device includes the secondary battery as described in any one of claims 1-9.

11. A lithium supplement, characterized in that, The lithium replenishing agent includes a core and a coating layer covering the surface of the core; The core comprises a lithium sulfide, the general chemical formula of which is Li. x S y M z Where x = 1-5, y = 1-6, z = 0-2, and M includes dopant elements; The coating layer comprises inorganic carbonates.

12. The lithium supplement as described in claim 11, characterized in that, The inorganic carbonates include at least one of calcium carbonate, magnesium carbonate, zinc carbonate, and aluminum carbonate. And / or, the doping element includes at least one of silicon, nitrogen, phosphorus, oxygen, fluorine, and bromine.

13. The lithium supplement as described in claim 11, characterized in that, The inorganic carbonates include calcium carbonate; And / or, the doping element includes at least one of nitrogen, phosphorus, and fluorine.

14. The lithium supplement agent according to any one of claims 11-13, characterized in that, The particle size D of the lithium supplement V 50 refers to 50-150nm.

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