Composite lithium supplementing material, preparation method thereof and secondary battery

Abstract

The invention relates to a composite lithium supplement material, a preparation method thereof and a secondary battery, the composite lithium supplement material comprises a packaging shell and a liquid lithium supplement agent, the packaging shell encloses a cavity, the liquid lithium supplement agent is accommodated in the cavity, and the packaging shell is used for controlling lithium ions in the liquid lithium supplement agent to release and supplement lithium. The composite lithium supplement material can solve the problems that a lithium supplement agent is unstable in air and the lithium supplement performance becomes poor when the lithium supplement agent is dissolved in an electrolyte.

Description

Technical Field

[0001] The present invention relates to the technical field of secondary batteries, and in particular to a composite lithium supplement material and a preparation method thereof, and a secondary battery. Background Art

[0002] During the first charge and discharge of a liquid lithium-ion battery, the lithium ions released from the positive electrode material react with the electrolyte to form a solid electrolyte interface (SEI) on the surface of the negative electrode material. This process will irreversibly consume more than 10% of the lithium source in the positive electrode material, making the first-week coulomb efficiency of the lithium-ion battery less than 90%, and will also continue to consume the active lithium in the positive electrode during the charge and discharge cycle of the lithium-ion battery, resulting in a shortened life of the lithium-ion battery. In response to this phenomenon, the current solution is to add an appropriate lithium supplement to the positive electrode active material, and reduce the lithium loss during the cycle by decomposing the lithium supplement during the battery charging process to release active lithium.

[0003] However, most lithium supplements in the prior art have poor stability. On the one hand, they are very likely to absorb water or react with air in the air; on the other hand, in the electrolyte, some lithium supplements are very easily soluble in the electrolyte, especially organic liquid lithium supplements, which dissolve in the electrolyte in advance due to similar compatibility. The lithium supplement will flow to the negative electrode driven by the electrolyte, and thus cannot play the role of positive electrode lithium supplement. Therefore, how to improve the stability of the lithium supplement in the air and prevent the lithium supplement from dissolving in the electrolyte in advance, which leads to poor lithium supplement performance, has become the key. Summary of the invention

[0004] The purpose of the present invention is to provide a composite lithium supplement material and a preparation method thereof, and a secondary battery, so as to solve the problem that the existing lithium supplement agent is unstable in the air and the lithium supplement agent is easily soluble in the electrolyte, resulting in poor lithium supplement performance.

[0005] To achieve the purpose of the present invention, the present invention provides the following technical solutions:

[0006] In a first aspect, the present invention provides a composite lithium supplement material, comprising a packaging shell and a liquid lithium supplement agent, wherein the packaging shell encloses a cavity, the liquid lithium supplement agent is contained in the cavity, and the packaging shell is used to control the release of lithium ions in the liquid lithium supplement agent to supplement lithium.

[0007] In one embodiment, the liquid lithium supplement comprises a lithium-rich compound, and the lithium-rich compound is liquid at room temperature.

[0008] In one embodiment, the liquid lithium supplement comprises a lithium-rich compound and a solvent, and the lithium-rich compound is dissolved in the solvent.

[0009] In one embodiment, the lithium-rich compound includes an organic lithium-rich compound and / or an inorganic lithium-rich compound.

[0010] In one embodiment, the packaging shell contains one or more of a solid lithium supplement, an ion conductor material, an ion-electron dual-conducting material, and a dissociation material, and the dissociation material can be decomposed in the internal environment of the secondary battery.

[0011] In one embodiment, the solid lithium supplement includes at least one of an organic lithium salt and an inorganic lithium salt.

[0012] In one embodiment, the ion conductor material includes at least one of an organic solid electrolyte and an inorganic solid electrolyte.

[0013] In one embodiment, the ionic-electronic dual-conducting material includes at least one of an organic ionic-electronic dual-conducting composite material and an inorganic ionic-electronic dual-conducting composite material.

[0014] In one embodiment, the dissociation material includes at least one of an organic dissociation material and an inorganic dissociation material.

[0015] In one embodiment, the composite lithium supplement material further includes a functional additive, which is dispersed in the liquid lithium supplement agent. The functional additive includes one or more of a catalyst, a dispersant and a stabilizer.

[0016] In one embodiment, the mass ratio of the catalyst, the dispersant and the stabilizer is (50-98):(1-25):(1-25).

[0017] In one embodiment, the mass ratio of the liquid lithium supplement to the packaging shell is 100:(20-100).

[0018] In one embodiment, the shell layer thickness of the packaging shell is 200 nm to 2 μm.

[0019] In one embodiment, the particle size of the composite lithium supplement material is 1 μm to 10 μm.

[0020] In a second aspect, the present invention provides a method for preparing a composite lithium supplement material, comprising: preparing a liquid lithium supplement agent into a microemulsion; preparing an encapsulation material into an encapsulation solution, and spraying the microemulsion into the encapsulation solution; filtering and drying a mixture of the microemulsion and the encapsulation solution to obtain a composite lithium supplement material.

[0021] In a third aspect, the present invention provides a secondary battery comprising a positive electrode, a negative electrode and an electrolyte, wherein the positive electrode comprises the composite lithium supplement material as described in the first aspect, or the positive electrode comprises the composite lithium supplement material prepared by the preparation method of the composite lithium supplement material as described in the second aspect.

[0022] The present invention provides a composite lithium supplement material with a solid-liquid dual-phase core-shell structure. The advantages of the composite lithium supplement material are as follows: (1) The composite lithium supplement material with a solid-liquid dual-phase core-shell structure can solve the problem of instability of the lithium supplement agent in the air. The packaging shell protects the liquid lithium supplement agent to prevent the liquid lithium supplement agent from directly contacting the air. The liquid lithium supplement agent can be stably stored in the packaging shell for a long time, thereby improving the stability of the composite lithium supplement material during storage, transportation, and processing; (2) The core-shell structure can prevent the conventional lithium supplement agent from dissolving in the electrolyte in advance. Most lithium supplement agents are very easily soluble in the electrolyte, resulting in them being freed to the negative electrode before the battery formation stage and unable to play a lithium supplement effect. The composite lithium supplement material with a core-shell structure can prevent the liquid lithium supplement agent from being freed to the negative electrode in the electrolyte in advance, but the lithium ions in the liquid lithium supplement agent can still be released through the packaging shell, thereby achieving a lithium supplement effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0024] Figure 1 is a schematic cross-sectional view of a composite lithium supplement material according to an embodiment;

[0025] Figure 2 is a cross-sectional schematic diagram of a composite lithium supplement material according to another embodiment;

[0026] Figure 3 is a cross-sectional schematic diagram of a composite lithium supplement material according to another embodiment;

[0027] Figure 4 is a cross-sectional schematic diagram of a composite lithium supplement material according to another embodiment;

[0028] Figure 5 The present invention is a flow chart of a method for preparing a composite lithium supplement material according to an embodiment of the present invention. DETAILED DESCRIPTION

[0029] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] Unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as those commonly understood by those skilled in the art to which the present invention belongs. The terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used in the present invention includes any and all combinations of one or more of the related listed items.

[0031] It should be noted that the "range" disclosed in the present invention is defined in the form of a lower limit and an upper limit, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The range defined in this way can be inclusive or exclusive of the end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. For example, if a range of 60 to 120 and 80 to 110 is listed for a specific parameter, it is understood that a range of 60 to 110 and 80 to 120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following ranges can all be expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4 and 2 to 5. In the present invention, unless otherwise specified, the numerical range "a to b" represents an abbreviation of any real number combination between a and b, wherein a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0032] All steps of the present invention may be performed sequentially or randomly, preferably sequentially. For example, a method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, a method may also include step (c), which means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b, etc.

[0033] Some embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. In the absence of conflict, the following embodiments and features in the embodiments can be combined with each other.

[0034] The following are some explanations of terms that appear in the article:

[0035] Pure substance: refers to a substance composed of one element or one compound.

[0036] Mixture: A substance that is a mixture of two or more substances.

[0037] Emulsification: Emulsification is a phenomenon in which one liquid is evenly dispersed in another immiscible liquid in the form of extremely small droplets.

[0038] Oil-in-water / water-in-oil: One phase dispersed in the form of liquid droplets or other forms in an emulsion is called the dispersed phase (or internal phase, discontinuous phase); the other phase is continuous and is called the dispersion medium (or external phase, continuous phase). An emulsion with "water" as the external phase and "oil" as the internal phase is called an oil-in-water emulsion, represented by O / W. An emulsion with "oil" as the external phase and "water" as the internal phase is called a water-in-oil emulsion, represented by W / O.

[0039] The present invention provides a composite lithium supplement material, please refer to Figure 1-Figure 4 .

[0040] In one implementation, see Figure 1 The composite lithium supplement material includes a packaging shell 20 and a liquid lithium supplement agent 10, the packaging shell 20 encloses a cavity, the liquid lithium supplement agent 10 is contained in the cavity, and the packaging shell 20 is used to control the lithium ions in the liquid lithium supplement agent 10 to release lithium supplement. Specifically, the composite lithium supplement material is a core-shell structure, wherein the core of the composite lithium supplement material is the liquid lithium supplement agent 10, and the packaging shell 20 encapsulates the liquid lithium supplement agent 10 inside, thereby isolating the liquid lithium supplement agent 10 from contact with the external environment. It should be noted that the packaging shell 20 controls the lithium ions in the liquid lithium supplement agent 10 to release lithium supplement, which can also be understood as the packaging shell 20 is used to release the lithium ions in the liquid lithium supplement agent 10 to the outside of the cavity. In some specific embodiments, during the operation of the battery, the packaging shell 20 controls the release of lithium ions in the liquid lithium supplement 10 to supplement lithium, including the following two situations: one is that the packaging shell 20 decomposes and ruptures, and the liquid lithium supplement 10 is released from the packaging shell 20, thereby achieving the purpose of positive electrode lithium supplement; the other is that the packaging shell 20 has ion conductivity, and the lithium ions in the liquid lithium supplement 10 can be released through the packaging shell 20, thereby achieving the purpose of positive electrode lithium supplement. Of course, in other embodiments, the packaging shell 20 can also release lithium ions in other ways, which are not specifically limited here.

[0041] The present invention provides a composite lithium supplement material with a solid-liquid dual-phase core-shell structure. The advantages of the composite lithium supplement material are as follows: (1) The composite lithium supplement material with a solid-liquid dual-phase core-shell structure can solve the problem of instability of the lithium supplement agent in the air. The packaging shell 20 protects the liquid lithium supplement agent 10 to prevent the liquid lithium supplement agent 10 from directly contacting the air. The liquid lithium supplement agent 10 can be stably stored in the packaging shell 20 for a long time, thereby improving the stability of the composite lithium supplement material during storage, transportation, and processing; (2) The core-shell structure can prevent the conventional lithium supplement agent from dissolving in the electrolyte in advance. Most lithium supplement agents are very easily soluble in the electrolyte, resulting in them being freed to the negative electrode before the battery formation stage and unable to play a lithium supplement effect. The composite lithium supplement material with a core-shell structure can prevent the liquid lithium supplement agent 10 from being freed to the negative electrode in the electrolyte in advance, but the lithium ions in the liquid lithium supplement agent 10 can still be released through the packaging shell 20, thereby achieving a lithium supplement effect.

[0042] In one embodiment, the liquid lithium supplement 10 contains a lithium-rich compound, and the lithium-rich compound is liquid at room temperature; or, the liquid lithium supplement 10 contains a lithium-rich compound and a solvent, and the lithium-rich compound is dissolved in the solvent. It should be noted that the liquid lithium supplement 10 mainly refers to a pure substance or a mixture that is liquid at room temperature and has a lithium supplement function. Among them, the liquid lithium supplement 10 can be a pure substance or a mixture. The liquid lithium supplement 10 is a pure substance, which means that the liquid lithium supplement 10 has and only contains one lithium-rich compound, and the lithium-rich compound is liquid at room temperature; the liquid lithium supplement 10 is a mixture, which means that the liquid lithium supplement 10 contains multiple lithium-rich compounds, and the multiple lithium-rich compounds are liquid at room temperature, or the liquid lithium supplement 10 contains at least one lithium-rich compound and a solvent, and the lithium-rich compound can be solid at room temperature, but the lithium-rich compound can be dissolved in the solvent at room temperature.

[0043] In one embodiment, the liquid lithium supplement 10 contains a lithium-rich compound, and the lithium-rich compound includes an organic lithium-rich compound and / or an inorganic lithium-rich compound. Specifically, the organic lithium-rich compound refers to a class of compounds containing carbon-lithium bonds, and its molecular formula is R-Li, where R represents an organic group; the inorganic lithium-rich compound refers to a lithium compound that does not contain a carbon-lithium bond, and they are mainly bonded by ionic bonds or covalent bonds.

[0044] In a specific embodiment, the liquid organic lithium-rich compounds include lithium diisopropylamide ([(CH3)2CH]2NLi), dilithium ethylene glycol (LiOCH2CH2OLi), butyl lithium (C4H9Li), phenyl lithium (C6H5Li), etc. It should be noted that the above organic lithium-rich compounds are all liquid at room temperature. For example, the boiling point of lithium diisopropylamide is 65° C., so it can be directly used as a liquid lithium supplement 10.

[0045] In a specific embodiment, the solid organic lithium-rich compound is mainly an organic lithium salt. Optionally, the chemical formula of the solid organic lithium-rich compound includes Li x C y O z , where 0<x≤2,y> 0, z>0, specifically, it can be lithium oxalate (Li2C2O4), lithium carbonate (Li2CO3), lithium trioxide (Li2C3O3), lithium butynedioate (Li2C4O4), etc. It should be noted that the above organic lithium-rich compounds are mostly solid at room temperature, but the above organic lithium-rich compounds can be dissolved in a solvent to form a solution and stored at room temperature, so a mixed solution can be made and used as a liquid lithium supplement 10.

[0046] In one embodiment, the solvent contained in the liquid lithium supplement is an electrolyte, and the electrolyte does not enter the cavity from the battery, but is added during the preparation of the composite lithium supplement material. Specifically, the liquid lithium supplement 10 is a mixture of a lithium-rich compound and an electrolyte, wherein the electrolyte refers to all components of the electrolyte or part of the electrolyte, for example, the electrolyte is mainly composed of an electrolyte solvent, an electrolyte lithium salt and an additive, and the electrolyte may include at least one of the electrolyte solvent, the electrolyte lithium salt and the additive.

[0047] In a specific embodiment, the electrolyte may be all the components of the electrolyte, that is, the liquid lithium supplement 10 includes the electrolyte (solvent, electrolyte lithium salt and additives) and the lithium-rich compound. The lithium-rich compound may be solid at room temperature and dissolved in the electrolyte; or the lithium-rich compound may be liquid at room temperature and mixed into the electrolyte.

[0048] In a specific embodiment, the electrolyte may be a part of the electrolyte, that is, the liquid lithium supplement 10 may include an electrolyte solvent (or additive) and a lithium-rich compound, wherein the electrolyte solvent mainly includes carbonates, ethers, and sub-epoxides, such as ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), etc., and the additive includes vinylene carbonate (VC), fluoroethylene carbonate (FEC), etc. The lithium-rich compound may be solid at room temperature and dissolved in the electrolyte; or, the lithium-rich compound may be liquid at room temperature and the lithium-rich compound may be mixed into the electrolyte.

[0049] In a specific embodiment, the electrolyte may be a partial component of the electrolyte, that is, the liquid lithium supplement 10 may include an electrolyte lithium salt and a lithium-rich compound, wherein the electrolyte lithium salt includes lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bis(fluorosulfonyl)imide (LiFSI), etc. The lithium-rich compound may be liquid at room temperature, and the electrolyte lithium salt is dissolved in the lithium-rich compound.

[0050] The present invention not only plays a role in supplementing the electrolyte of the secondary battery by adding electrolyte components to the liquid lithium supplement 10, but also can maximize the advantages of the solid-liquid dual-phase core-shell structure. In the prior art, the electrolyte of the secondary battery participates in ion transmission during the charge and discharge process. As time goes by and the number of cycles increases, the electrolyte may gradually degrade or be consumed, and the insufficient amount of electrolyte will affect the internal resistance, rate and cycle performance of the battery; therefore, the present invention adds electrolyte components to the liquid lithium supplement 10, and the electrolyte in the composite lithium supplement material is dissolved into the secondary battery after the encapsulation shell 20 is decomposed, which can play the role of supplementing the electrolyte. In addition, some solid organic lithium-rich compounds that can be dissolved in the electrolyte can be dissolved in the electrolyte in advance, and the composite lithium supplement material can be made by using the encapsulation shell 20, and released after the encapsulation shell 20 is decomposed, so as to avoid such lithium supplement agents from being freed to the negative electrode in advance and losing the lithium supplement effect.

[0051] In one embodiment, the packaging shell 20 contains one or more of a solid lithium supplement, an ion conductor material, an ion-electron dual-conducting material, and a dissociated material, and the dissociated material can be decomposed in the internal environment of the secondary battery. Specifically, the solid lithium supplement, the ion conductor material, the ion-electron dual-conducting material, and the dissociated material are all solid substances at room temperature, so the above four can be used as the packaging shell 20. Among them, the ion conductor material has an ion-conducting function, and the lithium ions in the liquid lithium supplement 10 can be released through the lattice gaps in the ion conductor material to supplement lithium; the ion-electron dual-conducting material can have both ion and electron dual-conducting properties; after the dissociated material decomposes in the internal environment of the secondary battery, the liquid lithium supplement 10 encapsulated therein is released, and then the lithium supplement continues.

[0052] In one embodiment, the solid lithium supplement includes at least one of an organic lithium salt and an inorganic lithium salt. Specifically, the organic lithium salt and the inorganic lithium salt included in the solid lithium supplement refer to lithium compounds that are solid at room temperature, and the solid lithium supplement is different from the solid organic (inorganic) lithium-rich compound in the above embodiment. The above solid lithium supplement has an additional lithium supplement function while achieving the encapsulation effect. After the solid lithium supplement releases lithium and decomposes, the liquid lithium supplement 10 encapsulated therein is released, and then lithium supplement continues.

[0053] In a specific embodiment, the solid lithium supplement may include a solid organic lithium supplement, which may include lithium oxalate (Li2C2O4), lithium carbonate (Li2CO3), lithium trioxide (Li2C3O3), lithium butynedioate (Li2C4O4), etc. Optionally, the chemical formula of the solid organic lithium-rich compound includes Li x C y O z, where \(0 \lt x \leq 2\), \(y \gt 0\), \(z \gt 0\). It should be noted that the solid-state organic lithium supplement is different from the solid-state organic lithium-rich compound in the above-mentioned liquid lithium supplement 10.

[0054] In a specific embodiment, the solid-state lithium supplement may include a solid-state inorganic lithium supplement, specifically a binary lithium supplement, such as lithium oxide (Li2O), lithium peroxide (Li2O2), lithium nitride (Li3N), lithium sulfide (Li2S), lithium fluoride (LiF), lithium phosphide (Li3P), lithium selenide (Li2Se), etc.; the chemical formula of the optional binary lithium supplement includes Li x3 K y3 , where K is at least one element among O, S, P, N, F, B, Se, Te, \(1 \leq x3 \leq 5\), \(0 \lt y3\). In other embodiments, the solid-state lithium supplement may also include lithium hydroxide (LiOH), lithium phosphate (Li3PO4), etc.

[0055] In other embodiments, the solid-state lithium supplement may also include a phosphate containing lithium ions, and the chemical formula may be LiMPO4, where M is a metal cation, including Fe, Mn, Co, Ni, etc. In other embodiments, the phosphate may also include other orthophosphates containing metal ions. In other embodiments, the solid-state lithium supplement may also include a silicate containing lithium ions.

[0056] In one embodiment, when the encapsulation shell 20 contains a solid-state lithium supplement, the decomposition voltage of the solid-state lithium supplement is higher than that of the liquid lithium supplement 10. Specifically, the advantage of this setting is that when the solid-state lithium supplement in the encapsulation shell 20 reaches the decomposition voltage and decomposes, the liquid lithium supplement 10 inside is released and has also reached its own decomposition voltage, and the liquid lithium supplement 10 then decomposes to release lithium. In a specific embodiment, if the decomposition voltage of the solid-state lithium supplement is lower than that of the liquid lithium supplement 10, it will cause part of the liquid lithium supplement 10 to move to the negative electrode with the electrolyte after the solid-state lithium supplement in the encapsulation shell 20 decomposes, resulting in the liquid lithium supplement 10 being unable to exert the effect of supplementing lithium at the positive electrode.

[0057] In the present invention, the solid-state lithium supplement is made into the encapsulation shell 20, which can not only achieve the purpose of decomposing and releasing the liquid lithium supplement 10 from the encapsulation shell 20, but also the solid-state lithium supplement itself has a lithium supplement effect, without the need to introduce non-lithium-supplement materials for coating, maximizing the mass ratio and lithium supplement effect of the composite lithium supplement material; in addition, by reasonably matching the core-shell ratio, the liquid lithium supplement 10 can be dissolved in the electrolyte and dispersed to the lithium-deficient part for decomposition and lithium supplementation after the encapsulation shell 20 decomposes.

[0058] In one embodiment, the ion conductor material includes at least one of an organic solid electrolyte and an inorganic solid electrolyte. Among them, the organic solid electrolyte is generally composed of a polymer macromolecule and a lithium salt; the polymer macromolecule, as a matrix material, does not contain lithium ions itself, but has the function of transferring lithium ions, such as -O-, =O, -S-, -N-, -P-, C=O, C≡N, etc. These groups can coordinate with lithium ions, and through the movement of the polymer chain segments, lithium ions continuously complex and decomplex with polar groups, thereby realizing the conduction of lithium ions. The inorganic solid electrolyte has a high ionic conductivity and can quickly transmit ions, thereby improving the charging and discharging efficiency of the battery.

[0059] In a specific embodiment, the organic solid electrolyte may include a polyethylene oxide system, a polycarbonate system, a polysiloxane system, etc. For example, polyethylene oxide, polycarbonate, etc., can be compounded with additives such as lithium salts to form an organic polymer electrolyte system with ionic conductivity.

[0060] In a specific embodiment, the inorganic solid electrolyte may include a sulfide solid electrolyte, an oxide solid electrolyte, a halide solid electrolyte, etc. For example, lithium phosphide, lithium germanium phosphosulfide, a perovskite solid electrolyte, a garnet solid electrolyte, a LiPON thin film electrolyte, a NASICON solid electrolyte, sodium chloride, potassium chloride, calcium chloride, etc.

[0061] In one embodiment, the ionic-electronic dual-conducting material includes at least one of an organic ionic-electronic dual-conducting composite material and an inorganic ionic-electronic dual-conducting composite material. The organic ionic-electronic dual-conducting composite material realizes dual conduction of ions and electrons by introducing ion conducting groups and electron conducting groups. The inorganic ionic-electronic dual-conducting composite material realizes joint conduction of ions and electrons by introducing ion channels and electron conducting paths in inorganic solids.

[0062] In a specific embodiment, the organic ion-electron dual-conducting composite material includes poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS), which is a solution-processable polymer conductor with ion-electron dual-conducting properties. It can also include a complex of a polymer and an alkali metal salt, such as a complex formed by polyethylene oxide and LiCF3SO3.

[0063] In a specific embodiment, the inorganic ion-electron dual-conducting composite material includes a cubic perovskite material, a layered perovskite material, and an RP-type material, which contain a specific crystal structure inside, so that ions and electrons can be conducted therein.

[0064] In one embodiment, the dissociation material includes at least one of an organic dissociation material and an inorganic dissociation material. Specifically, the dissociation material is decomposed in the internal environment of the secondary battery by changes in pH, temperature, voltage, etc. inside the secondary battery, thereby releasing the liquid lithium supplement 10 encapsulated therein. It should be noted that the organic dissociation material in this embodiment may be different from the ion-conducting or electron-conducting polymer in the above-mentioned embodiment, and the organic dissociation material may not have ion-conducting or electron-conducting characteristics; the inorganic dissociation material may also be different from the solid lithium supplement in the above-mentioned embodiment.

[0065] In one embodiment, the packaging shell 20 may include the above-mentioned multiple materials, and different materials constitute independent layers. Specifically, the packaging shell 20 may be a multi-layer structure, and the materials constituting each layer are different. Figure 3 The packaging shell 20 may include a solid lithium supplement layer 21 and an ion conductor material layer 22, wherein the solid lithium supplement layer 21 may directly wrap the liquid lithium supplement 10, and the ion conductor material layer 22 is coated on the outer surface of the solid lithium supplement layer 21. The advantage of this structure is that after the solid lithium supplement located in the inner layer and the liquid lithium supplement 10 in the cavity are decomposed and lithium is released, the composite lithium supplement material can still maintain the original structural shape, thereby avoiding the occurrence of pits in the battery.

[0066] In one implementation, see Figure 2 and Figure 3 The composite lithium supplement material also includes a functional additive, which is dispersed in the liquid lithium supplement agent. The functional additive includes one or more of a catalyst 30, a dispersant and a stabilizer. Specifically, the catalyst 30 includes a metal element and / or a metal compound, wherein the metal compound includes a metal oxide, a metal carbide, a metal nitride, etc. The dispersant includes polyvinyl alcohol (PVA), polyethylene glycol (PEG), polyvinyl pyrrolidone (PVP), etc. The stabilizer includes hexadecyltrimethylammonium chloride, octadecyldimethylbenzyl ammonium chloride, etc.

[0067] It should be noted that the catalyst 30 is mainly used to catalyze the liquid lithium supplement agent 10 and the encapsulation shell 20 (solid lithium supplement agent) to reduce the decomposition voltage. The dispersant is mainly used to disperse the catalyst so that the catalyst can be dispersed in the liquid lithium supplement agent. The stabilizer is mainly used to separate the materials of the liquid lithium supplement agent 10 and the encapsulation shell 20 during the preparation process so that the two can form a core-shell dual-phase structure.

[0068] In a specific embodiment, the catalyst 30 is in a granular form, and a plurality of catalyst 30 particles are contained in the cavity, and the plurality of catalyst 30 particles are dispersed in the liquid lithium supplement 10. The advantage of dispersing the catalyst 30 particles in the liquid lithium supplement 10 is that the catalytic performance of the catalyst 30 can be maximized. Both the dispersant and the stabilizer can be dissolved in the liquid lithium supplement.

[0069] The present invention disperses the catalyst 30 in the liquid lithium supplement 10. The catalyst 30 can catalyze the liquid lithium supplement 10 to reduce the decomposition voltage. When the packaging shell 20 is a solid lithium supplement, the catalyst 30 can catalyze both the internal and external lithium supplements. One catalyst 30 can reduce the decomposition voltage of the two lithium supplements at the same time.

[0070] In one implementation, see Figure 4 The composite lithium supplement material includes a catalyst 30, and the catalyst 30 can be combined with the outer surface of the packaging shell 20. Specifically, the catalyst 30 is mainly used to reduce the decomposition voltage of the lithium supplement (including liquid and solid), and the catalyst 30 mainly catalyzes the decomposition of the solid lithium supplement in the packaging shell 20 first, so the catalyst 30 can be combined with the outer surface of the packaging shell 20, and catalyzes the packaging shell 20 first. After the packaging shell 20 is decomposed, the liquid lithium supplement 10 inside is released, and the catalyst 30 will not decompose, and the catalyst 30 can continue to catalyze the liquid lithium supplement 10.

[0071] In one embodiment, the mass ratio of the catalyst 30, the dispersant and the stabilizer is (50-98):(1-25):(1-25). When the mass ratio of the catalyst 30, the dispersant and the stabilizer is within the above range, it can be ensured that the mass of the catalyst 30 accounts for a large proportion to give full play to the role of catalysis in reducing the decomposition voltage, and controlling the ratio of the dispersant and the stabilizer can also avoid the excessive proportion of the two affecting the capacity of the composite lithium supplement material. When the mass of the dispersant and the catalyst 30 is too high, since neither of them contributes lithium ions, it will occupy the volume of the liquid lithium supplement 10 and affect the lithium supplement capacity of the liquid lithium supplement 10, and the catalyst 30 is less, resulting in a decrease in the effect of low decomposition voltage. When the mass of the dispersant and the catalyst 30 is too low, the dispersing and stabilizing effects of the two are weak, and the encapsulation effect of the encapsulation shell 20 on the liquid dispersant is deteriorated. Optionally, the mass ratio of the catalyst 30, the dispersant and the stabilizer can be 50:25:25, 60:20:20, 60:25:15, 70:15:15, 70:20:10, 80:10:10, 90:5:5, 98:1:1.

[0072] In one embodiment, the mass ratio of the liquid lithium supplement agent 10 to the packaging shell 20 is 100: (20-100). When the mass ratio of the liquid lithium supplement agent 10 to the packaging shell 20 is within the above range, the lithium supplement capacity of the composite lithium supplement material can be ensured. In addition, by reasonably matching the core-shell ratio, the liquid lithium supplement agent 10 can be dissolved in the electrolyte and dispersed to the lithium-deficient parts for decomposition and lithium supplementation after the packaging shell 20 is decomposed. When the mass of the packaging shell 20 is too high, it will affect the lithium supplement capacity of the liquid lithium supplement agent 10, and the liquid lithium supplement agent 10 will be difficult to disperse to the lithium-deficient parts for decomposition and lithium supplementation. When the mass of the packaging shell 20 is too low, the structural stability of the composite lithium supplement material is affected. Optionally, the mass ratio of the liquid lithium supplement 10 to the packaging shell 20 may be 100:20, 100:30, 100:40, 100:50, 100:60, 100:70, 100:80, 100:90, or 100:100.

[0073] In one embodiment, the shell thickness of the packaging shell 20 is 200nm to 2μm. When the shell thickness of the packaging shell 20 is within the above range, the structural stability of the composite lithium supplement material and the release effect of lithium ions can be ensured. When the shell thickness is too thin, the packaging shell 20 will be easily broken, and the liquid lithium supplement agent 10 will be released prematurely, thereby losing the lithium supplement effect. When the shell thickness is too thick, it is more difficult for the lithium ions in the liquid lithium supplement agent 10 to escape, and the lithium supplement effect becomes worse. Optionally, the shell thickness of the packaging shell 20 can be 200nm, 400nm, 600nm, 800nm, 1μm, 1.2μm, 1.4μm, 1.6μm, 1.8μm, 2μm.

[0074] In one embodiment, the particle size of the composite lithium supplement material is 1μm to 10μm. Meeting the particle size of the composite lithium supplement material within the above range can ensure the lithium supplement effect and stabilize the battery structure, and can also reduce the difficulty of preparation. When the particle size of the composite lithium supplement material is too small, the lithium supplement effect deteriorates. When the packaging shell 20 is a non-lithium material, too much non-lithium supplement material will be introduced, resulting in a decrease in lithium supplement capacity. When the particle size of the composite lithium supplement material is too large, the composite lithium supplement material decomposes, causing pits or cracks to appear inside the battery, affecting battery performance, and the preparation of composite lithium supplement materials with large particle sizes is more difficult. Optionally, the particle size of the composite lithium supplement material can be 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, or 10μm.

[0075] The present invention also provides a method for preparing a composite lithium supplement material, which is used to prepare the composite lithium supplement material provided in the above embodiment. Figure 5 .

[0076] In one embodiment, the preparation method of the composite lithium supplement material specifically comprises the following steps:

[0077] Step S10, preparing the liquid lithium supplement into a microemulsion.

[0078] Step S20, preparing the encapsulation material into an encapsulation solution, and spraying the microemulsion into the encapsulation solution.

[0079] Step S30, filtering and drying the mixture of the microemulsion and the encapsulation solution to obtain a composite lithium supplement material.

[0080] The packaging material forms a packaging shell and encloses a cavity, and the liquid lithium supplement is contained in the cavity. Specifically, the packaging material includes one or more of the solid lithium supplement, ion conductor material and dissociation material provided in the above embodiment. The liquid lithium supplement includes the organic lithium-rich compound and / or the inorganic lithium-rich compound provided in the above embodiment.

[0081] In one embodiment, the density of the microemulsion is different from the density of the encapsulation solution, and the microemulsion is insoluble in the encapsulation solution. It should be noted that in the preparation method provided by the present invention, the principle of forming a solid-liquid dual-phase composite lithium supplement material is that the microemulsion will not dissolve in the encapsulation solution. It is understandable that due to the different densities of the two, an emulsification phenomenon occurs after the two are mixed, and only the amount of microemulsion added needs to be controlled to allow the encapsulation solution (external phase) to coat the liquid lithium supplement agent (internal phase). After filtering and drying, the solvent in the encapsulation solution evaporates, and the encapsulation material precipitates, so that the encapsulation material forms an encapsulation shell.

[0082] In one embodiment, the boiling point of the solvent in the encapsulation solution is lower than the boiling point of the liquid lithium supplement agent. It is understandable that when the mixture of the microemulsion and the encapsulation solution is filtered and dried, the solvent in the encapsulation solution can be evaporated to dryness by only controlling the drying temperature to be no higher than the boiling point of the liquid lithium supplement agent, and the liquid lithium supplement agent will not vaporize or precipitate, and can always remain in the liquid state in the composite lithium supplement material.

[0083] In a specific embodiment, in step S10, the liquid lithium supplement may be an organic lithium-rich compound, specifically lithium diisopropylamide. It is understood that lithium diisopropylamide is a liquid organic substance with a density of about 0.864 g / cm 3 (25°C), and there is no hydroxyl or carboxyl group in lithium diisopropylamide that is similar to water and is soluble in water, so lithium diisopropylamide will not dissolve in a saturated lithium oxalate solution; after lithium diisopropylamide is sprayed into a saturated lithium oxalate solution, the two form a mixed solution of lithium diisopropylamide coated with a saturated lithium oxalate solution.

[0084] In a specific embodiment, in step S20, the packaging material can be a solid lithium supplement, specifically lithium oxalate, and the solvent in the packaging solution can be deionized water. Since lithium oxalate can be dissolved in water, the packaging solution is a saturated lithium oxalate solution. In other embodiments, the solid lithium supplement can also be lithium carbonate, lithium sulfide, lithium hydroxide, etc.

[0085] In a specific embodiment, in step S30, after filtering and drying the mixed solution of lithium oxalate saturated solution coated with lithium diisopropylamide, deionized water is evaporated and lithium oxalate crystals are precipitated, thereby obtaining a solid-liquid dual-phase composite lithium supplement material of lithium oxalate coated with lithium diisopropylamide.

[0086] In other embodiments, in step S10, the liquid lithium supplement may be a mixture of an organic lithium-rich compound and an electrolyte, such as a mixture of lithium oxalate and an electrolyte, a mixture of butyl lithium and an electrolyte, etc. The above organic lithium-rich compounds are not limited to being solid or liquid at room temperature, but the above organic lithium-rich compounds can be dissolved in an electrolyte to form a liquid lithium supplement.

[0087] In other embodiments, in step S20, the packaging material may be an organic solid electrolyte, specifically a complex of polyethylene oxide and lithium, and the solvent in the packaging solution may be deionized water. Since polyethylene oxide can be dissolved in water, the packaging solution is a saturated solution of the complex of polyethylene oxide and lithium; the complex of polyethylene oxide and lithium can be used as a conductor to conduct lithium ions. In other embodiments, the ion conductor material may also be an inorganic solid electrolyte.

[0088] In one embodiment, step S10 further includes: adding a catalyst, a dispersant and a stabilizer into a liquid lithium supplement to prepare a microemulsion.

[0089] Specifically, the catalyst includes the metal element and / or the metal compound provided in the above-mentioned embodiment. Dispersant can include high molecular polymer, such as polyvinyl pyrrolidone (PVP), and the purpose of adding dispersant is to disperse the catalyst to avoid dispersant agglomeration. Stabilizer can include nonionic surfactant, such as fatty alcohol polyoxyethylene ether, alkylphenol polyoxyethylene ether, fatty acid polyoxyethylene ester, polyoxyethylene alkylamine, polyoxyethylene alkylamide and polyethers etc. Stabilizer has a hydrophobic group, is mainly used for making the mixed material into a water-insoluble microemulsion, and stabilizer can form a hydrophobic layer, so that microemulsion and encapsulation solution are insoluble.

[0090] In other embodiments, the solvent in the encapsulation solution is not limited to water, but may be other organic solvents. The solvent of the liquid lithium supplement is not limited to an organic solvent, but may be water, for example, the liquid lithium supplement is an aqueous solution of lithium oxalate. It is understandable that the solvent in the encapsulation solution and the solvent of the liquid lithium supplement are two immiscible liquids, so that emulsification can be achieved, but in the specific embodiment, whether it is "water-in-oil" or "oil-in-water" is not limited.

[0091] In one embodiment, after filtering and drying to obtain the composite lithium supplement material, post-processing may also be included to make the encapsulation shell into a multilayer structure, or to combine a catalyst on the surface of the encapsulation shell. In a specific embodiment, the encapsulation solution prepared in step S20 can be a saturated lithium oxalate solution, that is, the inner layer of the encapsulation shell is lithium oxalate. Then, a layer of ion conductor material layer (such as an organic solid electrolyte) can be coated on the outside of the lithium oxalate layer by solid phase or liquid phase mixing, thereby forming a two-layer structure of the encapsulation shell. In other embodiments, a catalyst can be combined with the outside of the encapsulation shell by solid phase mixing or ALD technology to enhance catalytic properties.

[0092] In one embodiment, the method provided by the present invention can also be applied to insoluble packaging materials, and the soluble packaging materials (such as solid lithium supplement agents) and insoluble packaging materials can be simultaneously prepared into a composite packaging shell. Taking an inorganic solid electrolyte as an example, the main method includes that after step S30, the obtained composite lithium supplement material can be mixed and ball-milled with the inorganic solid electrolyte to combine the two; the obtained packaging shell can include a solid lithium supplement agent layer and an ion conductor material layer, wherein the solid lithium supplement agent layer can directly wrap the liquid lithium supplement agent, and the ion conductor material layer is coated on the outer surface of the solid lithium supplement agent layer.

[0093] The present invention provides a method for preparing a composite lithium supplement material with a solid-liquid dual-phase core-shell structure, wherein the packaging material is prepared into a liquid state, and then the liquid lithium supplement agent is mixed into the packaging solution of the packaging material, and the liquid lithium supplement agent is insoluble in the packaging solution, so that the two form an emulsion, and then the composite lithium supplement material with the liquid lithium supplement agent inside can be formed by high-temperature recrystallization or spray drying. The preparation method is simple and efficient, and the obtained composite lithium supplement material can protect the liquid lithium supplement agent inside to the greatest extent, and can effectively improve the lithium supplement effect of the liquid lithium supplement agent.

[0094] In one embodiment, the present invention further provides a positive electrode material, the positive electrode material comprising a positive electrode active material and a lithium supplement. The lithium supplement is a composite lithium supplement material provided in the above embodiment. Optionally, the positive electrode active material can be a phosphate positive electrode active material or a ternary positive electrode active material. In a specific embodiment, the positive electrode active material includes one or more of lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadium oxyphosphate, lithium vanadium phosphate fluoride, lithium titanate, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide.

[0095] In one embodiment, the content of the composite lithium-supplementing material in the positive electrode material can be controlled at 1% to 6% of the mass of the positive electrode active material. This ratio can just make up for the loss of active lithium in the battery during the first charging process. If the amount of composite lithium-supplementing material added to the positive electrode material is too low, the active lithium lost in the positive electrode active material cannot be fully replenished, which is not conducive to improving the energy density and capacity retention rate of the battery. If the amount of composite lithium-supplementing material added to the positive electrode active material is too high, the original reversible capacity will be occupied and the cost will be increased. In some specific embodiments, in the positive electrode material, the mass percentage of the composite lithium-supplementing material can be 1%, 2%, 4%, 6%, etc.

[0096] In one embodiment, the present invention further provides a positive electrode plate, the positive electrode plate includes a current collector and an active material layer disposed on the current collector, the active material layer includes the composite lithium supplement material of any one of the above embodiments. Or the active material layer includes the composite lithium supplement material obtained by the preparation method of the composite lithium supplement material in the above embodiments.

[0097] In one embodiment, the positive electrode sheet includes a positive current collector, and the positive current collector has a positive active layer, and the positive active layer includes components such as positive active materials, composite lithium supplement materials, conductive agents, and binders. The present invention does not specifically limit these materials, and suitable materials can be selected according to actual application requirements. The positive current collector includes but is not limited to any one of copper foil and aluminum foil. The conductive agent includes one or more of graphite, carbon black, acetylene black, graphene, carbon fiber, C60 and carbon nanotubes, and the content of the conductive agent in the positive active layer is 3wt% to 5wt%. The types of binders include polyvinylidene chloride, soluble polytetrafluoroethylene, styrene-butadiene rubber, hydroxypropyl methylcellulose, methylcellulose, carboxymethyl cellulose, polyvinyl alcohol, acrylonitrile copolymer, sodium alginate, chitosan and chitosan derivatives, and the content of the binder in the positive active layer is 2wt% to 4wt%.

[0098] In one embodiment, the present invention further provides a secondary battery, the secondary battery comprising a negative electrode, a positive electrode and an electrolyte, wherein the positive electrode comprises the above-mentioned positive electrode material; the electrolyte may be an electrolyte solution, in which case the secondary battery further comprises a diaphragm disposed between the positive electrode plate and the negative electrode plate; or, the electrolyte may be a solid electrolyte solution, in which case the secondary battery does not have a diaphragm and is replaced by a solid electrolyte.

[0099] The technical solution of the present invention is described in detail below through specific embodiments.

[0100] Example 1

[0101] This embodiment provides a composite lithium supplement material. The composite lithium supplement material includes a packaging shell of a solid lithium supplement agent (lithium oxalate), a liquid lithium supplement agent (lithium diisopropylamine) and a nano catalyst (cobalt oxide). Among them, the packaging shell of the solid lithium supplement agent encloses a cavity, and the liquid lithium supplement agent and the catalyst are both contained in the cavity. In addition, the liquid lithium supplement agent also contains a dispersant (polyvinyl alcohol) and a stabilizer (hexadecyltrimethylammonium bromide).

[0102] The mass ratio of the liquid lithium supplement agent and the packaging shell is 100:30; the shell thickness of the packaging shell is 300nm; the particle size of the composite lithium supplement material is 5μm; the mass proportion of the nanocatalyst in the composite lithium supplement material is 10%; the mass ratio of the nanocatalyst, dispersant and stabilizer is 8:1:1.

[0103] The preparation method of the composite lithium supplement material comprises the following steps:

[0104] (1) The nano catalyst, dispersant and stabilizer are ultrasonically mixed into lithium diisopropylamine to prepare a stable water-insoluble microemulsion.

[0105] (2) Then, lithium oxalate is dissolved in deionized water to prepare a saturated lithium oxalate solution, and the water-insoluble microemulsion is sprayed into the saturated lithium oxalate solution.

[0106] (3) The mixed solution of the liquid lithium supplement agent and lithium oxalate is filtered and dried to obtain a composite lithium supplement material having a solid-liquid dual phase.

[0107] Example 2

[0108] This embodiment provides a composite lithium supplement material. The difference between this embodiment and embodiment 1 is that the liquid lithium supplement agent is replaced by a solution of lithium carbonate and electrolyte, wherein lithium carbonate is dissolved in the electrolyte to prepare the liquid lithium supplement agent.

[0109] Example 3

[0110] This embodiment provides a composite lithium supplement material. The difference between this embodiment and embodiment 1 is that the packaging shell is replaced with an ion conductor material (polyethylene oxide / lithium complex).

[0111] Example 4

[0112] This embodiment provides a composite lithium supplement material. The difference between this embodiment and embodiment 1 is that the liquid lithium supplement agent is replaced by a solution of lithium carbonate and electrolyte, wherein lithium carbonate is dissolved in the electrolyte to prepare the liquid lithium supplement agent, and the packaging shell is replaced by an ion conductor material (polyethylene oxide / lithium complex).

[0113] Example 5

[0114] This embodiment provides a composite lithium supplement material. The difference between this embodiment and embodiment 1 is that the packaging shell is replaced with a dissociation material (polylactic acid).

[0115] Example 6

[0116] This embodiment provides a composite lithium supplement material. The difference between this embodiment and embodiment 1 is that the liquid lithium supplement agent is replaced by a solution of lithium carbonate and electrolyte, wherein lithium carbonate is dissolved in the electrolyte to prepare the liquid lithium supplement agent, and the packaging shell is replaced by a dissociation material (polylactic acid).

[0117] Example 7

[0118] This embodiment provides a composite lithium supplement material. The difference between this embodiment and embodiment 1 is that the composite lithium supplement material does not include a catalyst.

[0119] Example 8

[0120] This embodiment provides a composite lithium supplement material. The difference between this embodiment and embodiment 1 is that the mass ratio of the liquid lithium supplement agent to the packaging shell is 100:20.

[0121] Example 9

[0122] This embodiment provides a composite lithium supplement material. The difference between this embodiment and embodiment 1 is that the mass ratio of the liquid lithium supplement agent to the packaging shell is 100:100.

[0123] Example 10

[0124] This embodiment provides a composite lithium supplement material. The difference between this embodiment and embodiment 1 is that the shell thickness of the packaging shell is 100 nm.

[0125] Embodiment 11

[0126] This embodiment provides a composite lithium supplement material. The difference between this embodiment and embodiment 1 is that the shell layer thickness of the packaging shell is 1 μm.

[0127] Example 12

[0128] This embodiment provides a composite lithium supplement material. The difference between this embodiment and embodiment 1 is that the particle size of the composite lithium supplement material is 1 μm.

[0129] Embodiment 13

[0130] This embodiment provides a composite lithium supplement material. The difference between this embodiment and embodiment 1 is that the particle size of the composite lithium supplement material is 10 μm.

[0131] Embodiment 14

[0132] This embodiment provides a composite lithium supplement material. The difference between this embodiment and embodiment 1 is that the liquid lithium supplement agent does not contain a dispersant and a stabilizer.

[0133] Comparative Example 1

[0134] This comparative example provides a liquid lithium supplement (lithium diisopropylamide).

[0135] Comparative Example 2

[0136] This comparative example provides a solid lithium supplement (lithium oxalate).

[0137] The parameters of the composite lithium supplement materials provided by Examples 1 to 14 and Comparative Examples 1 to 2 are shown in Table 1:

[0138] Table 1 Parameters of composite lithium supplement materials provided in Examples and Comparative Examples

[0139]

[0140] The composite lithium supplement materials provided in the above-mentioned Examples 1 to 14 and the composite lithium supplement materials provided in Comparative Example 1 are respectively assembled into positive electrode sheets and lithium-ion batteries according to the following methods:

[0141] Positive electrode sheet: The composite lithium supplement material, SP and PVDF are mixed in a mass ratio of 90:4:6 to form a positive electrode slurry, the positive electrode slurry is coated on the surface of aluminum foil, vacuum dried at 110°C overnight, and rolled to obtain a positive electrode sheet;

[0142] Negative electrode: lithium sheet;

[0143] Electrolyte: Ethylene carbonate and ethyl methyl carbonate were mixed in a volume ratio of 3:7, and LiPF6 was added to form an electrolyte, and the concentration of LiPF6 was 1 mol / L;

[0144] Diaphragm: Polypropylene microporous separator;

[0145] Lithium-ion battery assembly: Assemble button-type lithium-ion full batteries in an inert atmosphere glove box in the order of negative electrode sheet - separator - electrolyte - positive electrode sheet.

[0146] The electrochemical performance of each lithium-ion battery assembled in the above lithium-ion battery embodiment was tested under the following test conditions:

[0147] The battery was charged at a rate of 0.1C with a cut-off voltage of 4.7V. The battery was charged at a constant voltage with a cut-off voltage of 4.7V. After the charging process was completed, the battery was allowed to stand for 10 minutes and then discharged at a rate of 0.1C with a cut-off voltage of 2.5V. The charging platform was observed during the charging process to obtain the decomposition voltage of the composite lithium supplement material.

[0148] The test results of the above lithium battery are shown in Table 2 below:

[0149] Table 2. Test results of embodiments and comparative examples

[0150]

[0151] From the test results of Example 1, Comparative Example 1 and Comparative Example 2 in Table 2, it can be seen that the present invention encapsulates the liquid lithium supplement (lithium diisopropylamine) inside the encapsulation shell, which can not only obtain a higher charge and discharge specific capacity, but also reduce the decomposition voltage of the composite lithium supplement material under the action of the nanocatalyst; at the same time, after the composite lithium supplement material in Example 1 is placed in air with a humidity of 40% for 24 hours, its charge specific capacity still has a high retention rate. It can be clearly seen that the core-shell dual-phase structure enhances the stability of the internal liquid lithium supplement, and it also has good stability after being placed in the air.

[0152] It can be seen from the test results of Example 1 and Example 2 in Table 2 that the solution provided by the present invention is also suitable for solid lithium supplement materials that can be dissolved in electrolytes. By dissolving lithium carbonate in an electrolyte to prepare a liquid lithium supplement agent, and then making the liquid lithium supplement agent into a core-shell two-phase structure, the composite lithium supplement material can maintain a high charge and discharge specific capacity and can be stably stored in the air.

[0153] From the test results of Example 1, Example 3-Example 6 in Table 2, it can be seen that the packaging shell material can also be replaced with an ion conductor material and an easily decomposable dissociation material. In Example 3 and Example 5, replacing the packaging shell material with an ion conductor material will further reduce the decomposition voltage and overpotential while maintaining the intrinsic advantage of stability in the air. In addition, in Example 5 and Example 6, replacing the packaging shell material with a dissociation material can also achieve the intrinsic advantage of maintaining stability in the air.

[0154] It can be seen from the test results of Example 1 and Example 7 in Table 2 that the role of adding a catalyst is mainly to catalytically reduce the decomposition voltage of the lithium supplementing agent. Therefore, for the embodiments of using a liquid or solid lithium supplementing agent with a high decomposition voltage to prepare a composite lithium supplementing material, the voltage can be reduced by introducing a catalyst. Of course, in other embodiments, the selected liquid lithium supplementing agent or solid lithium supplementing agent itself can be decomposed at a low decomposition voltage, and there is no need to add a catalyst.

[0155] From the test results of Example 1, Example 8 and Example 9 in Table 2, it can be seen that when the mass ratio of the packaging shell is too small, it will lead to imperfect packaging, resulting in decreased stability in the air and a significant decrease in capacity; when the mass ratio of the packaging shell is too large, the conductivity of the lithium supplement material will be too poor, the overpotential and decomposition voltage will increase, and the capacity will be relatively reduced. Therefore, it is necessary to control the mass ratio of the packaging shell within an appropriate range.

[0156] It can be seen from the test results of Example 1, Example 10 and Example 11 in Table 2 that when the thickness of the bottom of the packaging shell is too small, it will lead to imperfect packaging, resulting in reduced stability in the air and a significant reduction in capacity. When the thickness of the packaging shell is too large, the conductivity of the lithium supplement material will be too poor, the overpotential and decomposition voltage will increase, and the capacity will decrease relatively.

[0157] It can be seen from the test results of Example 1, Example 12 and Example 13 in Table 2 that when the particle size of the lithium supplement material is too small, the packaging effect of the lithium supplement material is poor, resulting in a decrease in the capacity and the air stability of the lithium supplement material. When the particle size of the lithium supplement material is too large, the conductivity of the lithium supplement material will decrease, and the overpotential and decomposition voltage of the material will increase.

[0158] From the test results of Example 1 and Example 14 in Table 2, it can be seen that the role of the dispersant and the stabilizer is mainly to improve the stability of the composite lithium supplement material during the preparation process, that is, to improve the dispersibility of the liquid lithium supplement in the saturated solution and to avoid the compatibility of the two. However, a composite lithium supplement material with a core-shell dual-phase structure can be obtained without adding a dispersant and a stabilizer, and the material performance is significantly improved compared to the liquid lithium supplement in the prior art.

[0159] In the description of the embodiments of the present invention, it should be noted that the orientation or positional relationship of terms such as "center", "up", "down", "left", "right", "vertical", "horizontal", "inside" and "outside" are based on the orientation or positional relationship described in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0160] What is disclosed above is only a preferred embodiment of the present invention, and it certainly cannot be used to limit the scope of rights of the present invention. Ordinary technicians in this field can understand that all or part of the processes of the above embodiment and equivalent changes made according to the claims of the present invention still fall within the scope covered by the present invention.

Claims

1. A composite lithium supplement material, characterized in that: The invention comprises a packaging shell and a liquid lithium supplement, wherein the packaging shell encloses a cavity, the liquid lithium supplement is contained in the cavity, and the packaging shell is used for controlling the lithium ions in the liquid lithium supplement to release lithium.

2. The composite lithium supplement material according to claim 1, characterized in that: The liquid lithium supplement contains a lithium-rich compound, and the lithium-rich compound is liquid at room temperature; or, the liquid lithium supplement contains a lithium-rich compound and a solvent, and the lithium-rich compound is dissolved in the solvent.

3. The composite lithium supplement material according to claim 2, characterized in that: The lithium-rich compound includes an organic lithium-rich compound and / or an inorganic lithium-rich compound.

4. The composite lithium supplement material according to claim 1, characterized in that: The packaging shell contains one or more of a solid lithium supplement, an ion conductor material, an ion-electron dual-conducting material, and a dissociation material, and the dissociation material can be decomposed in the internal environment of the secondary battery.

5. The composite lithium supplement material according to claim 4, characterized in that: The solid lithium supplement comprises at least one of an organic lithium salt and an inorganic lithium salt; The ion conductor material includes at least one of an organic solid electrolyte and an inorganic solid electrolyte; The ionic-electronic dual-conductive material comprises at least one of an organic ionic-electronic dual-conductive composite material and an inorganic ionic-electronic dual-conductive composite material; The dissociation material includes at least one of an organic dissociation material and an inorganic dissociation material.

6. The composite lithium supplement material according to claim 1, characterized in that: The composite lithium supplement material further includes a functional additive, which is dispersed in the liquid lithium supplement agent. The functional additive includes one or more of a catalyst, a dispersant and a stabilizer.

7. The composite lithium supplement material according to claim 6, characterized in that: The mass ratio of the catalyst, the dispersant and the stabilizer is (50-98):(1-25):(1-25).

8. The composite lithium supplement material according to any one of claims 1 to 7, characterized in that: The mass ratio of the liquid lithium supplement to the packaging shell is 100:(20-100); and / or The shell layer thickness of the encapsulation shell is 200nm-2μm; and / or The particle size of the composite lithium supplement material is 1 μm to 10 μm.

9. A method for preparing a composite lithium supplement material, characterized in that: include: The liquid lithium supplement is made into a microemulsion; preparing an encapsulation material into an encapsulation solution, and spraying the microemulsion into the encapsulation solution; The mixed solution of the microemulsion and the encapsulation solution is filtered and dried to obtain a composite lithium supplement material.

10. A secondary battery, characterized in that: It comprises a positive electrode, a negative electrode and an electrolyte, wherein the positive electrode comprises the composite lithium supplement material according to any one of claims 1 to 8, or the positive electrode comprises the composite lithium supplement material prepared by the preparation method of the composite lithium supplement material according to claim 9.

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