Composite lithium supplement and preparation method thereof, secondary battery

Abstract

The application discloses a composite lithium supplement agent, a preparation method thereof, and a secondary battery. The composite lithium supplement agent comprises a main chain and an active lithium unit. The main chain comprises a self-repairing unit, and the self-repairing unit comprises a dynamic sulfide bond. The composite lithium supplement agent can be self-repaired through the dynamic sulfide bond. The active lithium unit is grafted to the main chain, and the active lithium unit comprises lithium ions. The composite lithium supplement agent can avoid microcracks, reduce lithium supplement failure, effectively prolong the service life of lithium supplement, and maintain the stability of lithium supplement.

Description

Technical Field

[0001] This invention relates to the field of secondary battery technology, specifically to a composite lithium replenishing agent and its preparation method, and a secondary battery. Background Technology

[0002] The lithium replenishment agent releases active lithium ions during the first charge and discharge (formation) of the battery, compensating for the irreversible active lithium consumed by the formation of the solid electrolyte interphase (SEI) film at the negative electrode, thereby improving the battery's first coulombic efficiency, usable capacity and cycle life. This technology system is widely applicable to high-energy-density power batteries, energy storage batteries and waste battery repair scenarios.

[0003] However, the positive electrode active material will expand in volume during cycling (expansion rate exceeds 8%). Most existing lithium replenishing agents are rigid structures (such as lithium oxalate, lithium cobalt oxide, etc.), which cannot adapt to the volume change. This makes it easy for microcracks to appear at the interface between the lithium replenishing agent and the positive electrode active material. As a result, the active lithium cannot be effectively transported to the lithium-deficient sites of the positive electrode, resulting in the phenomenon of lithium replenishment failure. Summary of the Invention

[0004] The purpose of this invention is to provide a composite lithium replenishing agent and its preparation method, as well as a secondary battery, to solve the problem that existing lithium replenishing agents are prone to microcracks and cannot be restored.

[0005] To achieve the objectives of this invention, the following technical solution is provided: In a first aspect, the present invention provides a composite lithium replenishing agent, comprising a main chain and active lithium units; the main chain includes self-healing units, the self-healing units including dynamic thioether bonds, and the composite lithium replenishing agent can self-heal through the dynamic thioether bonds; the active lithium units are grafted onto the main chain, and the active lithium units include lithium ions.

[0006] In some implementations, the main chain further includes flexible units connected to the self-healing unit.

[0007] In some embodiments, the self-healing unit is composed of a monomer containing at least two thiol groups.

[0008] In some embodiments, the flexible unit includes one or more of polycaprolactone segments, polylactic acid segments, and poly(δ-valerolactone).

[0009] In some embodiments, the degree of polymerization of the flexible unit is 50 to 80.

[0010] In some embodiments, the main chain further includes a stabilizing end group located at the end of the main chain along its length, the stabilizing end group containing fluorine atoms.

[0011] In some embodiments, the stabilizing end group further comprises a phosphonate group, to which the fluorine atom is attached, and the phosphonate group is used to construct a protective film on the surface of the positive electrode active material.

[0012] In some embodiments, the composite lithium supplement further includes a framework with a porous structure, the main chain being connected to the framework, and the framework forming a mesoporous first ion channel.

[0013] In some embodiments, the main chain and the backbone are connected by covalent bonds, and a second ion channel is formed between the main chain and the backbone. At least a portion of the second ion channel interweaves with and communicates with the first ion channel to form a three-dimensional transport network.

[0014] In some embodiments, the porosity of the skeleton is 25% to 85%.

[0015] In some embodiments, the specific surface area of ​​the skeleton is 1200 m². 2 / g~1500m 2 / g.

[0016] In some embodiments, the aperture of the first ion channel is 15 nm to 20 nm.

[0017] In some implementations, the mass ratio of the main chain to the skeleton is 1:9 to 9:1.

[0018] In some embodiments, the particle size of the composite lithium supplement is 5 μm to 10 μm.

[0019] In a second aspect, the present invention provides a method for preparing a composite lithium supplement, the method being used to prepare the composite lithium supplement as described in the first aspect, the method comprising: adding a first monomer containing a thiol group to a first solvent, and obtaining a prepolymer after reaction; dissolving the prepolymer in a second solvent, and adding a second monomer containing lithium ions to the second solvent, and obtaining the composite lithium supplement after reaction.

[0020] Thirdly, the present invention provides a secondary battery comprising a positive electrode, a negative electrode and an electrolyte, wherein the positive electrode comprises a composite lithium replenishing agent as described in the first aspect, or the positive electrode comprises a composite lithium replenishing agent prepared by the method for preparing the composite lithium replenishing agent as described in the second aspect.

[0021] In some embodiments, the positive electrode comprises a phosphate-based positive electrode active material.

[0022] The composite lithium replenisher provided in this application is based on a main chain with active lithium units grafted onto it. The lithium ions in the active lithium units can be used for lithium replenishment. The self-healing units on the main chain contain dynamic thioether bonds. Relying on the special chemical properties of the dynamic thioether bonds, the composite lithium replenisher can achieve self-repair after being damaged by external forces. In particular, it can avoid the appearance of microcracks at the interface between the composite lithium replenisher and the positive electrode active material, reduce the phenomenon of lithium replenishment failure, and thus effectively extend the service life of the composite lithium replenisher and maintain the stability of lithium replenishment. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0024] Figure 1 This is a schematic diagram of the appearance of a composite lithium supplement agent in one embodiment; Figure 2 This is a schematic diagram of one implementation method in which the main chain is housed within a first ion channel; Figure 3 This is a flowchart illustrating the preparation method of a composite lithium supplement in one embodiment. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used in this invention includes any and all combinations of one or more of the associated listed items.

[0027] It should be noted that the "range" disclosed in this invention is defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60–120 and 80–110 are listed for specific parameters, it is understood that ranges of 60–110 and 80–120 are also expected. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1–3, 1–4, 1–5, 2–3, 2–4, and 2–5. In this invention, unless otherwise stated, the numerical range "a–b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0028] All steps of the present invention can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0029] The following detailed description of some embodiments of the present invention is provided in conjunction with the accompanying drawings. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0030] This application provides a composite lithium replenishing agent that can be applied to cathode systems, especially when matched with cathode active materials with high voltage systems. The composite lithium replenishing agent can cooperate with the volume expansion of cathode active materials, reduce microcracks through self-repair capabilities, and improve lithium replenishment capacity and battery safety.

[0031] For some implementation methods, please refer to Figure 1 The composite lithium supplement includes a main chain 10 and an active lithium unit. The main chain 10 contains a self-healing unit, which contains a dynamic thioether bond. The composite lithium supplement can self-heal through the dynamic thioether bond. The active lithium unit is grafted onto the main chain 10 and contains lithium ions.

[0032] In some specific embodiments, the main chain 10 is selected from organic polymers with good flexibility, compatibility and chemical stability. Its molecular chain exhibits a linear repeating structure, with repeating self-healing units uniformly distributed on the chain segments. Each self-healing unit contains a dynamic thioether bond (-SS-) functional group, and the dynamic thioether bonds are orderly distributed in the molecular chain of the main chain 10, providing a structural basis for the stable performance of self-healing.

[0033] It should be noted that when the composite lithium supplement is subjected to stress (0.1MPa~0.3MPa), the dynamic thioether bonds on the main chain 10 will break due to stress induction. When the external stress is gradually released, the broken dynamic thioether bond fragments will recombine under the chemical bond force, and the broken main chain 10 can be restored to its integrity. This achieves self-repair of the microstructure and macroscopic properties of the composite lithium supplement, ensuring that its lithium supplementation function is not damaged and can continue to perform stably.

[0034] In some specific embodiments, the self-healing unit is composed of a monomer containing at least two thiol groups (-SH). It is understood that the dynamic thioether bond is formed by the oxidative dehydrogenation of two thiol groups (2R-SH→RSS-R+H2). Therefore, the monomer that polymerizes to form the main chain 10 can be a monomer containing thiol groups, and the monomer contains two thiol groups. Preferably, the monomer of the self-healing unit can be triethylene glycol dithiol (TEG, C6H). 14 O2S2).

[0035] It should be noted that the ether bond structure in triethylene glycol dithiol can also endow the self-healing unit with a certain degree of flexibility, improve the flexibility and deformation ability of the main chain 10. At the same time, triethylene glycol dithiol has good solubility and reactivity, and is easy to polymerize with other monomers to form a structurally regular main chain 10. Moreover, the dynamic thioether bond formed by it has excellent reversibility, which can significantly improve the self-healing efficiency and stability of the composite lithium supplement.

[0036] In some specific embodiments, the active lithium unit can be designed as a branched structure grafted onto the main chain 10 molecular chain, and the active lithium unit is loaded with active lithium ions (Li). + Optionally, the grafting rate of active lithium units on the main chain 10 can be 80% to 90%, thereby providing a stable lithium source and achieving a delithiation-lithiation reversibility of greater than or equal to 98% under high voltage (5V). In other embodiments, the active lithium units can also be designed as repeating units inserted into the main chain 10.

[0037] In existing technologies, conventional organic lithium replenishers rely on carboxylates or alkoxides to provide active lithium. In high-voltage (5V) electrolytes, carboxylates are prone to decarboxylation and alkoxides are easily oxidized to form lithium oxide, resulting in the breakage of the lithium replenisher's main chain. In particular, after multiple cycles, the structural integrity rate decreases, the amount of active lithium remains insufficient, the lithium replenishment efficiency drops sharply, and the lithium replenishment stability deteriorates.

[0038] The composite lithium replenisher provided in this application is based on the main chain 10, on which active lithium units are grafted. The lithium ions in the active lithium units can be used for lithium replenishment. The self-healing units on the main chain 10 contain dynamic thioether bonds. Relying on the special chemical properties of the dynamic thioether bonds, the composite lithium replenisher can achieve self-repair after being damaged by external forces. In particular, it can avoid the appearance of microcracks at the interface between the composite lithium replenisher and the positive electrode active material, reduce the phenomenon of lithium replenishment failure, and thus effectively extend the service life of the composite lithium replenisher and maintain the stability of lithium replenishment.

[0039] In some specific embodiments, relying on the reversible recombination characteristics of dynamic sulfide bonds, the composite lithium replenisher can improve the structural integrity rate by more than 50% and increase the residual active lithium by 55% after 500 cycles at high voltage (5V); at the same time, the structural self-repair efficiency of the composite lithium replenisher reaches 95%, which can adapt to the changes in positive electrode volume in real time, and the capacity retention rate reaches 95% after 1000 cycles, which is more than 10% higher than existing lithium replenishers, thus extending the battery life.

[0040] In some embodiments, the main chain 10 further includes flexible units connected to the self-healing units. Specifically, the flexible units are polymer segments containing flexible groups, wherein the molecular structure of the main chain 10 can be (self-healing unit - flexible unit). n Where n is a positive integer greater than or equal to 2. The flexible unit can give the main chain 10% flexibility to accommodate volume changes of up to 8% during charging and discharging of the positive electrode.

[0041] In some specific embodiments, the flexible unit and the self-healing unit are stably connected by chemical bonds, jointly forming the complete molecular skeleton of the main chain 10, achieving a synergistic improvement in "self-healing function" and "structural flexibility". The flexible unit is a polymer segment containing flexible groups, wherein the flexible groups can be methylene chains, ether bonds, ester bonds, or other groups with good molecular chain rotation capabilities. The flexible unit can improve the flexibility and deformation capability of the main chain 10, thereby better buffering external stress and preventing irreversible breakage of the dynamic thioether bonds in the self-healing unit due to stress concentration, providing a more favorable structural environment for the reversible breakage and recombination of the dynamic thioether bonds.

[0042] In some specific embodiments, the flexible unit includes one or more of polycaprolactone segments, polylactic acid segments, and poly(δ-valerolactone), that is, the flexible unit can be a composite flexible segment formed by two or more of them through block copolymerization, random copolymerization, etc. Preferably, the flexible unit is a polycaprolactone segment (PCL, [CH2-(CH2)4-COO]).

[0043] In some specific embodiments, the degree of polymerization of the flexible unit (polycaprolactone segment) is 50 to 80; optionally, the degree of polymerization is 50, 60, 70, 80 or between any two of the above values.

[0044] When the above range is met, the molecular chain length of the polycaprolactone segment is moderate. It will not be too short (degree of polymerization <50) to cause insufficient flexibility and inability to effectively buffer external stress, which would lead to irreversible breakage of the dynamic thioether bond in the self-healing unit due to stress concentration. Nor will it be too long to cause the entanglement between molecular chains to be aggravated, affecting the regularity of the main chain 10 repeating structure. At the same time, it will avoid uneven distribution of grafting sites of active lithium units and reduce lithium replenishment efficiency.

[0045] In some embodiments, the main chain 10 further includes a stabilizing end group located at the end of the main chain 10 along its length, and the stabilizing end group contains a fluorine atom (-CF). x Specifically, the stable end group serves as the end-capping structure of the main chain 10, located at at least one end (i.e., the start and end of the molecular chain) along the length of the main chain 10. The fluorine atom can form a stable coordination with lithium ions in the electrolyte, reducing the oxidative activity of the electrolyte, thereby achieving the dual benefits of stabilizing the main chain 10 structure and optimizing the electrolyte performance.

[0046] In some specific embodiments, the fluorine atoms in the stable end group possess extremely strong electronegativity and coordination ability, a characteristic that enables them to react with lithium ions (Li₂O₃) in the lithium battery electrolyte. + Stable coordination is formed to construct "F-Li + "Coordination system. At the same time, the strong electronegativity of fluorine atoms can also enhance the hydrophobicity of the ends of the main chain 10, reduce the contact between water in the electrolyte and the main chain 10, avoid water from causing hydrolytic breakage of ester groups and dynamic thioether bonds in the main chain 10, and further enhance the structural stability of the main chain 10."

[0047] In some embodiments, the stabilizing end group further includes a phosphonate group (-PO3H2), with fluorine atoms attached to the phosphonate group. The phosphonate group is used to construct a protective film on the surface of the positive electrode active material. Specifically, the phosphonate group can form hydrogen bonds with the hydroxyl groups on the surface of the positive electrode active material. Through the formation of stable hydrogen bonds, the phosphonate group is firmly adsorbed and anchored on the surface of the positive electrode active material, thereby gradually assembling to form a complete interfacial protective film.

[0048] In some specific embodiments, the thickness of the constructed dense interface protective film can be 20nm to 30nm. Optionally, the thickness of the protective film can be 20nm, 22nm, 24nm, 26nm, 28nm, 30nm, or between any two of the above values. The protective film has good density, which can effectively prevent electrolyte molecules from penetrating to the positive electrode surface and reduce the generation of harmful by-products; moreover, the hydrogen bonding is stable and reversible, which ensures the stability of the protective film without hindering the normal migration of lithium ions, ensuring that lithium ions can smoothly pass through the protective film to achieve insertion and extraction, and ensuring that the charge and discharge performance of the battery is not affected.

[0049] In some specific embodiments, the precursor for stabilizing the end group can be trifluoroethyl phosphonate (TFEP, (CF3CH2O)PO(OH)2). The precursor molecule contains both fluorine atoms (fluorine in -CF3) and phosphonate groups (-PO(OH)2), perfectly matching the dual-functional requirement of the stabilizing end group "fluorine atom-phosphonate group".

[0050] It should be noted that using this monomer as a precursor for stabilizing the end group can improve the stability of the composite lithium supplement. Under high-voltage conditions (such as 5V high-energy-density lithium batteries), trifluoroethyl phosphonate itself has an extremely high oxidation decomposition voltage (greater than 5.8V), which ensures that TFEP will not undergo oxidation decomposition during battery charging and discharging, even under high-voltage conditions, and will always maintain molecular structural stability. This effectively isolates the electrolyte from the active sites at the ends of the main chain 10, preventing the main chain 10 from being oxidized and degraded by the electrolyte, thus protecting the main chain 10. The interfacial impedance of the composite lithium supplement after 500 cycles is no greater than 150 Ω·cm. 2 .

[0051] In some specific embodiments, the chemical formula of the backbone 10, composed of triethylene glycol dithiol (TEG), polycaprolactone (PCL) segments, and trifluoroethylphosphonate (TFEP), can be TFEP-[COO-(TEG-SS-TEG)-COO-PCL]. n -COO-CH2CH2-O-PO(OH)(OCH2CF3).

[0052] For some implementation methods, please refer to Figure 1The composite lithium supplement also includes a porous framework 20, with the main chain 10 connected to the framework 20. The framework 20 forms mesoporous first ion channels 21. Specifically, the framework 20 is a three-dimensional structure with continuous pores. The main chain 10 can be firmly connected to the surface of the framework 20 and the inner wall of the pores through chemical bonding, coordination, or intermolecular forces. The main chain 10 can be orderly anchored to the framework 20, avoiding intermolecular entanglement and aggregation, while maximizing the exposure of active lithium units, self-healing units, and stable end groups on the main chain 10, ensuring that each functional site can function efficiently.

[0053] In some specific embodiments, the framework 20 includes, but is not limited to, porous carbon materials (such as mesoporous carbon, cross-linked carbon nanotube frameworks, and graphene aerogels), inorganic non-metallic ceramic materials (such as mesoporous silica and lithium titanium phosphate porous frameworks), or highly stable organic polymer aerogels (such as polyvinylidene fluoride porous frameworks and polyimide porous frameworks). These materials not only provide stable physical support for the composite lithium supplement, but also exhibit good compatibility with battery electrolytes and electrode materials, avoiding interfacial side reactions.

[0054] It should be noted that the mesoporous first ion channel 21 refers to the pore size of the first ion channel 21 meeting the standard for mesopore size. Mesopores are porous structures with pore sizes between 2 nm and 50 nm, so the pore size of the first ion channel 21 can also meet this range. Furthermore, the first ion channel 21 serves as a "fast transport channel" for transporting lithium ions. The lithium-ion migration activation energy is reduced to below 0.3 eV, and the ionic conductivity at -40℃ is ≥5 × 10⁻⁶. -4 S / cm.

[0055] For some implementation methods, please refer to Figure 2 The backbone 20 contains siloxane. The main chain 10 and the backbone 20 are covalently connected, and a second ion channel 22 is formed between the main chain 10 and the backbone 20. At least a portion of the second ion channel 22 interweaves and connects with the first ion channel 21 to form a three-dimensional transport network. Specifically, the main chain 10 can be connected to the backbone 20 through a silane coupling agent. The silane coupling agent forms covalent bonds with the abundant hydroxyl functional groups on the main chain 10, thereby constructing a three-dimensional structure with the main chain 10 and the backbone 20. The three-dimensional transport network consists of spatial channels existing in the three-dimensional structure for the movement of lithium ions. At the same time, the main chain 10 molecules and the surface of the silica backbone 20 are not completely tightly adhered. A series of tiny, uniformly distributed gaps naturally form between them. These gaps are interconnected, forming the second ion channel 22, which is complementary to the first ion channel 21.

[0056] In some specific embodiments, the siloxane may include silicon dioxide and organosilane linked by chemical bonds; wherein, the silicon dioxide can be precisely prepared into a mesoporous structure with uniform pore size and continuous pores through mature processes such as template method and sol-gel method; preferably, the framework 20 can be prepared by siloxane combined with template method, so the framework 20 can have a large number of silanol groups (-Si-OH), which serve as active reaction sites, providing a natural structural basis for achieving covalent bond connection between the main chain 10 and the three-dimensional framework 20, without the need for additional complex surface modification treatment of the framework 20, thus simplifying the preparation process.

[0057] In existing technologies, conventional organic lithium replenishers rely on the linear lithium transport channels of the conductive polymer backbone 10. During cycling, backbone 10 breakage or branch aggregation can lead to channel blockage, causing the lithium-ion transference number to drop from 0.6 to below 0.2. Especially at low temperatures (-40°C), the activation energy for lithium-ion migration in the linear channels rises above 0.8 eV, and the ionic conductivity decreases to 1 × 10⁻⁶. -5 When the discharge capacity retention rate is below S / cm, it is less than 50%, which cannot meet the requirements for low-temperature start-up.

[0058] This invention combines a porous framework 20 with the main chain 10 and provides a first ion channel 21 and a second ion channel 22, enabling multi-dimensional and efficient lithium transfer based on the main chain 10. The framework 20 and the main chain 10 construct a dual transport channel of "pores" and "interfaces", which not only avoids the risk of blockage of a single channel and increases the lithium-ion migration number by more than 0.7, but also increases the ionic conductivity at -40℃ by 5 times; it can also improve the capacity retention rate at high rates.

[0059] In some embodiments, the porosity of the skeleton 20 is 25% to 85%. Optionally, the porosity of the skeleton 20 can be 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, or between any two of the above values.

[0060] With the porosity of the framework 20 within the aforementioned range, the framework 20 can maintain a good rigid structure while retaining sufficient pore space. This avoids insufficient mechanical strength due to the framework 20 being too porous, which would prevent it from being unable to withstand the mechanical stress and electrode volume deformation during battery assembly and cycling. At the same time, sufficient pore space can ensure the continuous connection between the first ion channel 21 and the second ion channel 22, providing a sufficient space basis for rapid lithium ion transport and full electrolyte wetting, and avoiding problems such as pore blockage or obstructed mass transfer paths.

[0061] In some embodiments, the specific surface area of ​​the skeleton 20 is 1200 m². 2 / g~1500m 2 / g. Optionally, the specific surface area of ​​the skeleton 20 can be 1200m². 2 / g、1250m 2 / g、1300m 2 / g, 1350m 2 / g, 1400m 2 / g, 1450m 2 / g, 1500m 2 / g or any two of the above values.

[0062] If the specific surface area of ​​the framework 20 is within the above range, it can provide sufficient covalent bond grafting sites for the main chain 10, significantly increase the loading of the main chain 10, increase the interfacial contact area between the electrolyte and the framework 20 and the main chain 10, improve the wetting rate and wetting uniformity of the electrolyte, and avoid mass transfer obstruction caused by excessive pore density, so that the migration of lithium ions in the first ion channel 21 and the second ion channel 22 is smoother.

[0063] In some embodiments, the aperture of the first ion channel 21 is 15 nm to 20 nm. Optionally, the aperture of the first ion channel 21 can be 15 nm, 16 nm, 17 nm, 18 nm, 19 nm, 20 nm, or between any two of the above values.

[0064] The pore size of the first ion channel 21 is within the above range, which can meet the requirements of rapid lithium-ion transport. This pore size range can provide sufficient migration space for lithium-ions, effectively reduce the diffusion resistance of lithium-ions in the channel, and avoid the entanglement of the main chain 10 caused by the channel being too dense. This ensures that the molecular chain of the main chain 10 is distributed in an orderly manner in the channel, providing sufficient space for the reversible breaking and recombination of dynamic thioether bonds, and ensuring the efficient performance of self-healing properties.

[0065] In some embodiments, the mass ratio of the main chain 10 to the backbone 20 is 1:9 to 9:1. Optionally, the mass ratio of the main chain 10 to the backbone 20 can be 1:9, 2:8, 3:7, 4:6, 5:5, 6:4, 7:3, 8:2, 9:1 or between any two of the above values.

[0066] The mass ratio of the main chain 10 to the backbone 20 is within the above range. The mass ratio of the main chain 10 can ensure that there are sufficient active lithium units, self-healing units and stable end groups, and ensure the lithium replenishment capacity of the composite lithium replenishing agent. At the same time, it balances the load of the main chain 10 and the support of the backbone 20. Relying on the high rigidity of silicon dioxide, it provides stable physical support for the polymer main chain 10.

[0067] In some embodiments, the particle size of the composite lithium supplement is 5 μm to 10 μm, and D90 ≤ 10 μm. Optionally, the particle size of the composite lithium supplement can be 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, or between any two of the above values.

[0068] Meeting the particle size requirement of the composite lithium replenisher within the above-mentioned range ensures that the composite lithium replenisher can be well adapted to the positive electrode active material particles, with a suitable electron-lithium ion transport distance, resulting in higher lithium replenishment efficiency and battery rate performance. At the same time, the preparation difficulty of the composite lithium replenisher is reduced, and the particles can be uniformly dispersed, making them less prone to agglomeration.

[0069] In some embodiments, the room temperature ionic conductivity of the composite lithium supplement is greater than or equal to 2 × 10⁻⁶. -4 S / cm. Optionally, the room temperature ionic conductivity of the composite lithium supplement can be 2 × 10⁻⁶. -4 S / cm, 4×10 -4 S / cm, 6×10 -4 S / cm, 8×10 -4 S / cm, 2×10 -3 S / cm.

[0070] The composite lithium replenisher provided by this invention includes a main chain 10 and a framework 20. The main chain 10 contains self-healing dynamic thioether bonds and end groups with high voltage stability. During battery cycling, the dynamic thioether bonds can self-repair structural defects and prevent the main chain 10 from breaking. The stable end groups containing fluorophosphonates enhance high voltage stability and suppress side reactions. The framework 20 has a three-dimensional network, which ensures unobstructed lithium transport channels and adapts to a wide temperature range. The three components work together to achieve a comprehensive performance improvement in "structural stability, efficient lithium transport, and wide temperature adaptability".

[0071] Meanwhile, the composite lithium replenishing agent provided by this invention has higher safety, can reduce gas production by 60%, and reduce the risk of battery swelling; the composite lithium replenishing agent has strong stability and good compatibility with high-voltage high-nickel cathodes and silicon-based anodes, without the need to adjust existing battery manufacturing processes, and has strong adaptability.

[0072] In some embodiments, the present invention also provides a method for preparing a composite lithium supplement, please refer to [reference needed]. Figure 3 The method for preparing the composite lithium supplement is used to prepare the composite lithium supplement provided in the above embodiments. The preparation method specifically includes the following steps: Step S100: The first monomer containing thiol groups is added to the first solvent, and a prepolymer is obtained after reaction. In step S200, the prepolymer is dissolved in a second solvent, and a second monomer containing lithium ions is added to the second solvent. After reaction, a main chain containing active lithium units is obtained.

[0073] In a specific embodiment, in step S100, the first monomer containing a thiol group can be triethylene glycol dithiol (TEG) provided in the above-described embodiments, and the first solvent can be anhydrous toluene. Of course, in other embodiments, the first monomer containing a thiol group can also be diethylene glycol dithiol (C4H... 10 O2S2), tetraethylenedithiol (C8H) 18 O3S2), 1,6-hexanedithiol (C6H) 14 S2), etc.; it is understood that monomers containing two thiol groups (-SH, which can be used to form dynamic thioether bonds) at both ends of the molecule can be used in the technical solutions provided in this application.

[0074] In some specific embodiments, the prepolymer further includes flexible units, and step S100 further includes: adding a first monomer containing thiol groups, a third monomer, and a catalyst to a first solvent, and reacting to obtain the prepolymer. The third monomer is used to polymerize and obtain the flexible units.

[0075] In some specific embodiments, in step S100, the third monomer may be ε-caprolactone (ε-CL, C6H). 10 One or more of the following: O2), δ-valerol (δ-VL, C5H8O2), and lactide (LA, C6H8O4). The catalyst may be stannous octoate. Optionally, the reaction temperature may be 100℃~120℃, and the reaction time may be 6h~48h.

[0076] In some specific embodiments, in step S200, the second solvent can be N,N-dimethylformamide (DMF); the second monomer can be a mixture of 3-lithiumoxypropionic acid and 1-ethyl-(3-dimethylaminopropyl)carbodiimide. Optionally, the reaction temperature can be 20°C to 80°C, and the reaction time can be 6 h to 24 h.

[0077] In some specific embodiments, in step S200, the reaction solution after the reaction is further subjected to precipitation and drying to obtain a main chain containing active lithium units. Specifically, the reaction solution is poured into anhydrous diethyl ether to precipitate, and then vacuum dried after centrifugation. The active lithium loading on the obtained main chain is greater than or equal to 18 wt%.

[0078] In some embodiments, the preparation method of the composite lithium supplement further includes: Step S300: Dissolve the framework precursor and template agent in a third solvent, and remove the template agent after reaction to obtain a framework with a porous structure. In step S400, the main chain and framework containing active lithium units are dissolved in a fourth solvent and dispersed to form a mixture. A fourth monomer for end capping is added to the mixture, and a composite lithium supplement is obtained after reaction.

[0079] In some specific embodiments, in step S300, the framework precursor can be tetraethyl orthosilicate (TEOS), the template agent can be hexadecyltrimethylammonium bromide (CTAB), and the third solvent can be a mixture of ethanol and water. Optionally, the pH of the third solvent can be adjusted to alkaline, the reaction temperature can be 50°C to 100°C, and the reaction time can be 12h to 48h; the removal of the template agent includes calcination, and the calcination temperature can be 400°C to 600°C. After removing the template agent, mesoporous silica is obtained.

[0080] In some specific embodiments, step S300 further includes: mixing and reacting mesoporous silica with a silane coupling agent to graft the epoxy groups of the silane coupling agent onto the surface of the mesoporous silica, thereby obtaining a framework. It is understood that the silane coupling agent forms covalent bonds with the abundant hydroxyl functional groups on the main chain, thereby constructing a three-dimensional lithium transport network from the main chain and the framework.

[0081] In some specific embodiments, in step S400, the fourth solvent can be N,N-dimethylformamide (DMF); the fourth monomer can be trifluoroethylphosphonate (TFEP); and TFEP is grafted to the end of the main chain through a ring-opening reaction of the epoxy groups on the flexible unit. Optionally, the reaction temperature can be 20°C to 80°C, and the reaction time can be 6 h to 24 h.

[0082] The method for preparing the composite lithium replenishing agent provided by this invention uses conventional solvents and equipment, requires no special or harsh conditions, and has a cost that is 30% lower than that of existing high-voltage lithium replenishing agents, making it easy to scale up production. During the preparation process, a freeze-drying process can be used to ensure the integrity of the material's mesoporous structure.

[0083] In some embodiments, the present invention also provides a positive electrode sheet, the positive electrode sheet comprising a current collector and an active material layer disposed on the current collector, the active material layer comprising the composite lithium supplement agent of any of the above embodiments. Alternatively, the active material layer comprises a composite lithium supplement agent obtained by the preparation method of the composite lithium supplement agent in the above embodiments.

[0084] In some embodiments, the positive electrode active layer includes components such as a positive electrode active material, a composite lithium supplement, a conductive agent, and a binder. The positive electrode active material includes a phosphate-based positive electrode active material. Exemplarily, the positive electrode active material includes lithium iron phosphate (LiFePO4, LFP), lithium manganese phosphate (LiMnPO4, LMP), and lithium manganese iron phosphate (LiMn... x Fe 1-x PO4, LMFP, etc.

[0085] In specific embodiments, the positive electrode 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 electrode active layer is 3wt%~5wt%. The binder includes one or more of 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 electrode active layer is 2wt%~4wt%.

[0086] In some embodiments, the present invention also provides a secondary battery, which includes a negative electrode, a positive electrode, and an electrolyte. The positive electrode can be the positive electrode sheet described above, and the positive electrode includes the composite lithium replenishing agent provided in the above embodiments. The electrolyte can be a liquid electrolyte or a solid electrolyte.

[0087] The technical solution of the present invention will be described in detail below through specific embodiments.

[0088] Example 1 This embodiment provides a composite lithium supplement agent, which includes a main chain (TFEP-[COO-(TEG-SS-TEG)-COO-PCL]). n -COO-CH2CH2-O-PO(OH)(OCH2CF3)), active lithium units (LiS(CH2)3COOLi), and a framework (silicon dioxide). The framework has mesoporous first ion channels.

[0089] The porosity of the skeleton is 70%; the specific surface area of ​​the skeleton is 1350 m². 2 / g; the pore size of the first ion channel is 18nm; the mass ratio of the main chain to the framework is 1:1; the particle size D50 of the composite lithium supplement is 7μm.

[0090] The preparation method of this composite lithium supplement includes the following steps: (1) Triethylene glycol dithiol (TEG-SH, 10 mmol), ε-caprolactone (PCL, 50 mmol) and stannous octoate (0.1 mmol) were added to anhydrous toluene and stirred at 120 °C under a nitrogen atmosphere for 24 h to form a prepolymer (P(TEG-PCL)). (2) Dissolve the prepolymer in N,N-dimethylformamide (DMF), add 3-lithiumoxypropionic acid (20 mmol) and 1-ethyl-(3-dimethylaminopropyl)carbodiimide (EDC, 5 mmol), stir at 60 °C for 12 h, and introduce LiS(CH2)3COOLi active lithium units into the main chain. (3) Pour the reaction solution into anhydrous diethyl ether to precipitate, centrifuge (10000 r / min, 15 min), and then vacuum dry (50℃, -0.09 MPa) for 24 h to obtain the main chain grafted with active lithium units; (4) Tetraethyl orthosilicate (TEOS, 20 mmol) and hexadecyltrimethylammonium bromide (CTAB, 2 mmol) were dissolved in an ethanol-water mixture (volume ratio 1:1), the pH was adjusted to 10, stirred at 80°C for 24 h, centrifuged, and calcined at 550°C for 6 h to remove the template, thus obtaining mesoporous silica (MSN). (5) Add MSN (1g) and KH-560 (3mmol) to anhydrous ethanol and reflux at 70°C for 8h to graft the epoxy group of KH-560 onto the surface of MSN to obtain a framework with the first ion channel (MSN-KH560). (6) Dissolve the dynamic thioether bond backbone (0.8g) and MSN-KH560 (0.2g) in DMF and ultrasonically disperse for 30min (power 500W) to form a homogeneous mixture; (7) Add trifluoroethyl phosphonate (TFEP, 1 mmol), stir at 50 °C for 6 h, and graft TFEP onto the end of the main chain through an epoxy ring-opening reaction; (8) The reaction solution was poured into anhydrous ethanol to precipitate, and then freeze-dried (-50℃, -0.1MPa) for 48h to obtain a dynamic thioether bond-mesoporous siloxane composite organic lithium supplement material.

[0091] Example 2 This embodiment provides a composite lithium supplement. The difference between this embodiment and Embodiment 1 is that trifluoroethyl phosphonate (TFEP) is not used as an end group for capping the main chain.

[0092] Example 3 This embodiment provides a composite lithium supplement. The difference between this embodiment and Embodiment 1 is that the composite lithium supplement includes a main chain and active lithium units.

[0093] Example 4 This embodiment provides a composite lithium supplement. The difference between this embodiment and Embodiment 1 is that the framework is made of conventional porous silica with a porosity of 40%.

[0094] Example 5 This embodiment provides a composite lithium supplement. The difference between this embodiment and Embodiment 1 is that the porosity of the framework is 25%.

[0095] Example 6 This embodiment provides a composite lithium supplement. The difference between this embodiment and Embodiment 1 is that the porosity of the framework is 85%.

[0096] Example 7 This embodiment provides a composite lithium supplement. The difference between this embodiment and Embodiment 1 is that the specific surface area of ​​the framework is 1200 m². 2 / g.

[0097] Example 8 This embodiment provides a composite lithium supplement. The difference between this embodiment and Embodiment 1 is that the specific surface area of ​​the skeleton is 1500 m². 2 / g.

[0098] Example 9 This embodiment provides a composite lithium supplement. The difference between this embodiment and Embodiment 1 is that the pore size of the first ion channel is 15 nm.

[0099] Example 10 This embodiment provides a composite lithium supplement. The difference between this embodiment and Embodiment 1 is that the pore size of the first ion channel is 20 nm.

[0100] Example 11 This embodiment provides a composite lithium supplement. The difference between this embodiment and Embodiment 1 is that the mass ratio of the main chain to the backbone is 9:1.

[0101] Example 12 This embodiment provides a composite lithium supplement. The difference between this embodiment and Embodiment 1 is that the mass ratio of the main chain to the backbone is 1:9.

[0102] Example 13 This embodiment provides a composite lithium supplement. The difference between this embodiment and Embodiment 1 is that the particle size D50 of the composite lithium supplement is 5 μm.

[0103] Example 14 This embodiment provides a composite lithium supplement. The difference between this embodiment and Embodiment 1 is that the particle size D50 of the composite lithium supplement is 10 μm.

[0104] Comparative Example 1 This comparative example provides a lithium supplement, which includes LiS(CH2)3COOLi.

[0105] The parameters of the composite lithium supplement provided in Examples 1-14 and Comparative Example 1 are shown in Table 1: Table 1. Parameters of the composite lithium supplement provided in the examples and comparative examples.

[0106] The composite lithium replenishing agents provided in Examples 1-14 and the composite lithium replenishing agent provided in Comparative Example 1 were assembled into positive electrode sheets and lithium-ion batteries respectively according to the following methods: Positive electrode sheet: The composite lithium supplement, 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. Negative electrode: Lithium sheet; Electrolyte: Ethyl carbonate and ethyl methyl carbonate are mixed in a volume ratio of 3:7, and LiPF6 is added to form an electrolyte with a concentration of 1 mol / L. Diaphragm: Polypropylene microporous diaphragm; Lithium-ion battery assembly: Assemble button-type lithium-ion full cells in an inert atmosphere glove box according to the assembly sequence of negative electrode plate-separator-electrolyte-positive electrode plate.

[0107] The batteries provided in Examples 1-14 and Comparative Example 1 were tested as follows: under room temperature conditions, constant current-constant voltage charging was performed at 0.066C, the charging voltage was 2.0V~3.75V, and the cutoff current was 0.01C.

[0108] The test results for the above batteries are shown in Table 2 below: Table 2. Test results of the examples and comparative examples

[0109] As can be seen from the test results of Example 1 and Comparative Example 1 in Table 1, a composite lithium replenisher with higher lithium replenishment capacity can be obtained by grafting active lithium units onto the main chain with dynamic thioether bonds. Thanks to the self-healing units on the main chain containing dynamic thioether bonds, the composite lithium replenisher can achieve self-repair after being damaged by external forces, thereby reducing the phenomenon of lithium replenishment failure and improving the specific capacity of the composite lithium replenisher.

[0110] As can be seen from the test results of Examples 1 and 2 in Table 1, by grafting end groups onto the main chain and using the end groups to cap the main chain, the electrochemical performance of the composite lithium replenisher can be improved, ultimately increasing the lithium replenishment capacity of the composite lithium replenisher. This is because the fluorine atoms in the stable end groups have extremely strong electronegativity and coordination ability, enabling them to form stable coordination with lithium ions, thereby further reducing lithium loss.

[0111] As can be seen from the test results of Examples 1, 3 and 4 in Table 1, the performance of the composite lithium replenisher can be further improved by loading both the main chain and the active lithium unit onto the framework. Both the main chain and the active lithium unit can be orderly anchored on the framework, and the porous structure of the framework provides abundant ion channels for the active lithium unit, thereby improving the lithium ion migration efficiency and increasing the lithium replenishment capacity.

[0112] As can be seen from the test results of Examples 1, 5 and 6 in Table 1, the porosity of the framework has an impact on the performance of the composite lithium supplement. By controlling its porosity within a suitable range, the framework can maintain a good rigid structure while retaining sufficient pore space, thus ensuring the structural stability of the composite lithium supplement. The framework can also provide sufficient pore space to ensure the continuous connection between the first ion channel and the second ion channel, providing a basis for lithium ion movement.

[0113] As can be seen from the test results of Examples 1, 7 and 8 in Table 1, the specific surface area of ​​the skeleton has an impact on the performance of the composite lithium supplement. This is because the skeleton provides sufficient covalent bond grafting sites for the main chain, and its larger specific surface area can increase the main chain loading and also increase the interfacial contact area of ​​the electrolyte. Controlling the upper limit of the specific surface area can ensure the structural stability of the skeleton and prevent the skeleton from collapsing during processing.

[0114] As can be seen from the test results of Examples 1, 9, and 10 in Table 1, the pore size of the first ion channel affects the performance of the composite lithium supplement. Controlling the pore size of the first ion channel can provide sufficient migration space for lithium ions and effectively reduce the diffusion resistance of lithium ions in the channel. If the pore size of the first ion channel is too small, it will hinder the movement of lithium ions and lead to a decrease in capacity; if the pore size is too large, it will affect the structural stability of the framework.

[0115] As can be seen from the test results of Examples 1, 11 and 12 in Table 1, the mass ratio of the main chain to the framework has an impact on the performance of the composite lithium replenisher. Since the main chain is the basis for the dynamic repair of the composite lithium replenisher and can provide binding sites for active lithium units to ensure the lithium replenishment capacity of the composite lithium replenisher, while the framework provides stable physical support for the main chain based on its own rigidity, the ratio of the two should be controlled within an appropriate range.

[0116] As can be seen from the test results of Examples 1, 13 and 14 in Table 1, the particle size of the composite lithium replenisher has an impact on its performance. Ensuring that the particle size of the composite lithium replenisher is within a suitable range can ensure that the composite lithium replenisher can be well adapted to the positive electrode active material particles, the electron-lithium ion transport distance is appropriate, and the lithium replenishment efficiency and battery rate performance are higher. At the same time, the preparation difficulty of the composite lithium replenisher is reduced, the particles can be uniformly dispersed, and it is not easy for agglomeration to occur.

[0117] In the description of the embodiments of the present invention, it should be noted that the orientation or positional relationship of the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer" and other indicators are based on the orientation or positional relationship of the accompanying drawings, and are only for the convenience of describing the present invention 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, and therefore should not be construed as a limitation of the present invention.

[0118] The above description discloses only one preferred embodiment of the present invention, and should not be construed as limiting the scope of the present invention. Those skilled in the art will understand that all or part of the processes of the above embodiments can be implemented, and equivalent changes made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. A composite lithium supplement, characterized in that, include: The main chain contains self-healing units, each containing dynamic thioether bonds, and the composite lithium supplement can self-heal through these dynamic thioether bonds. An active lithium unit is grafted onto the main chain, and the active lithium unit contains lithium ions.

2. The composite lithium supplement agent according to claim 1, characterized in that, The main chain also includes flexible units, which are connected to the self-healing units.

3. The composite lithium supplement agent according to claim 2, characterized in that, The self-healing unit is composed of monomers containing at least two thiol groups; and / or The flexible unit includes one or more of polycaprolactone segments, polylactic acid segments, and poly(δ-valerol); and / or The degree of polymerization of the flexible unit is 50~80.

4. The composite lithium supplement agent according to claim 1, characterized in that, The main chain also includes a stabilizing end group located at the end of the main chain along its length, and the stabilizing end group contains fluorine atoms.

5. The composite lithium supplement agent according to claim 4, characterized in that, The stabilizing end group further includes a phosphonate group, to which the fluorine atom is attached, and the phosphonate group is used to construct a protective film on the surface of the positive electrode active material.

6. The composite lithium supplement agent according to claim 1, characterized in that, The composite lithium supplement also includes a porous framework, the main chain being connected to the framework, and the framework forming a mesoporous first ion channel.

7. The composite lithium supplement agent according to claim 6, characterized in that, The main chain and the backbone are connected by covalent bonds, and a second ion channel is formed between the main chain and the backbone. At least a portion of the second ion channel interweaves with and connects with the first ion channel to form a three-dimensional transport network.

8. The composite lithium supplement agent according to claim 6, characterized in that, The porosity of the skeleton is 25%~85%; and / or The specific surface area of ​​the skeleton is 1200 m². 2 / g~1500m 2 / g; and / or The pore size of the first ion channel is 15 nm to 20 nm; and / or The mass ratio of the main chain to the skeleton is 1:9 to 9:1; and / or The particle size of the composite lithium supplement is 5μm~10μm.

9. A method for preparing a composite lithium supplement, characterized in that, The method for preparing the composite lithium supplement is used to prepare the composite lithium supplement as described in any one of claims 1-8, and the preparation method includes: A first monomer containing a thiol group is added to a first solvent, and a prepolymer is obtained after reaction. The prepolymer is dissolved in a second solvent, and a second monomer containing lithium ions is added to the second solvent. After reaction, a composite lithium supplement is obtained.

10. A secondary battery, characterized in that, It includes a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode includes the composite lithium supplement as described in any one of claims 1-8, or the positive electrode includes the composite lithium supplement prepared by the method for preparing the composite lithium supplement as described in claim 9.

11. The secondary battery according to claim 10, characterized in that, The positive electrode includes a phosphate-based positive electrode active material.

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