Lithium orthosilicate-based lithium supplement additive and preparation method thereof

Abstract

The invention discloses a lithium orthosilicate-based lithium supplement additive and a preparation method thereof. The lithium orthosilicate-based lithium supplement additive is composed of a lithium orthosilicate core, a conductive carbon layer coated outside the lithium orthosilicate core and small molecular sulfur loaded on the conductive carbon layer. The preparation method comprises the following steps: preparing a lithium orthosilicate core coated with a conductive carbon layer by utilizing a sol-gel method and a segmented calcination method, and preparing the lithium orthosilicate-based lithium supplement additive loaded with high-activity small molecular sulfur by utilizing high-temperature activation and a confinement effect of the conductive carbon layer. The lithium orthosilicate-based lithium supplement additive effectively supplements lithium loss of first charge and discharge of a battery, and is beneficial to improving the cycle energy efficiency and prolonging the service life of the battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium batteries, in particular to a lithium silicate-based lithium supplementing additive and a preparation method thereof. BACKGROUND

[0002] During the first charge-discharge process of a lithium ion battery, the solid electrolyte interface film (SEI film) formed at the negative electrode irreversibly consumes a large amount of lithium ions released from the positive electrode, resulting in a loss of irreversible capacity and a reduction in the energy density of the lithium ion battery. In order to ensure the capacity of the battery, the lost lithium needs to be supplemented. This technology is called lithium supplementing, which can compensate for the initial efficiency loss of the positive electrode and help improve the energy density and cycle performance of the lithium ion battery.

[0003] Among various lithium supplementing additives, lithium orthosilicate (Li4SiO4) has become a research hotspot due to its high theoretical lithium supplementing capacity (598 mAh / g) and excellent environmental stability. However, the existing lithium orthosilicate-based lithium supplementing technology still has significant technical bottlenecks, which are as follows: 1. Pure lithium orthosilicate supplementing additive: micron or nanoscale lithium orthosilicate powder is directly used, which has extremely low intrinsic electronic conductivity (≈10-14 S cm -1 ), cannot achieve effective lithium supplementing, and the surface of the lithium orthosilicate particles is prone to form a passivation layer, blocking the diffusion of lithium ions into the particles, resulting in slow reaction kinetics and low lithium supplementing rate, which is difficult to meet the actual battery application requirements.

[0004] 2. Sulfur-modified lithium orthosilicate (Li4SiO4@S) supplementing additive: sulfur single atoms (S8) are physically mixed or attached to the surface of lithium orthosilicate powder by a melting diffusion method or a simple mechanical ball milling method, aiming to release lithium ions by the reaction between sulfur and lithium orthosilicate to achieve lithium supplementing. However, lithium orthosilicate has extremely low intrinsic electronic conductivity (≈10-14 S cm -1 ), and sulfur single atoms (S8) are electronic insulators (conductivity ≈5×10-30 S cm -1 ). The direct contact between the two insulators not only does not improve the conductivity, but also adds an insulating barrier on the already insulating surface of lithium orthosilicate, severely hindering the transmission of electrons and ions, making it difficult to start and conduct electrochemical reactions.

[0005] Therefore, the existing lithium orthosilicate-based lithium supplementing technology still cannot maximize the use of its high theoretical lithium supplementing capacity, and a new lithium orthosilicate-based lithium supplementing additive with high conductivity, high lithium utilization rate, and high stability needs to be developed. SUMMARY

[0006] The present application aims to at least solve one of the technical problems existing in the prior art. To this end, the present application proposes a lithium orthosilicate-based lithium supplement additive and a preparation method thereof, which activates sulfur from insulating S8 into small-molecule sulfur with conductive catalytic function, and cooperates with a conductive carbon layer to solve the self-passivation problem of the lithium orthosilicate-based lithium supplement additive itself and improve the lithium supplement efficiency.

[0007] According to the first aspect of the present application, a lithium orthosilicate-based lithium supplement additive is provided, comprising: a lithium orthosilicate core; a conductive carbon layer coated on the surface of the lithium orthosilicate core; small-molecule sulfur loaded on the conductive carbon layer, the small-molecule sulfur being at least one of disulfide S2, trisulfide S3, and tetrasulfide S4.

[0008] According to some embodiments of the present application, the conductive carbon layer is an acetylene black layer or an activated carbon layer.

[0009] According to some embodiments of the present application, the conductive carbon layer is combined with the lithium orthosilicate core through a C-O-Si covalent bond.

[0010] According to some embodiments of the present application, the conductive carbon layer is provided with nanoscale micropores with a size comparable to that of the small-molecule sulfur, and the pore wall of the nanoscale micropores and the space steric hindrance effect caused by the narrow space together constitute a confinement effect, the small-molecule sulfur is confined in the nanoscale micropores and directly contacts the conductive carbon layer.

[0011] According to the second aspect of the present application, a preparation method of the above-mentioned lithium orthosilicate-based lithium supplement additive is provided, comprising the following steps: mixing tetraethyl orthosilicate, anhydrous ethanol, and deionized water, adjusting the pH to 3-4 with an acid, and stirring to form a sol; adding conductive carbon layer raw materials to the sol, dispersing, adjusting the pH to >7 with ammonia water, forming a conductive carbon layer coated silica composite gel, and obtaining a dry gel after aging and drying; ball-milling the dry gel and a lithium source in proportion, and performing staged calcination under an inert atmosphere to obtain a conductive carbon layer coated lithium orthosilicate core; grinding and mixing the conductive carbon layer coated lithium orthosilicate core and sulfur single S8, and incubating at 120-180℃ for 4 hours under an inert atmosphere, and then performing a thermal activation reaction at 280-320℃ for 1.5-2.5 hours, so that the sulfur single S8 is ring-broken and generates small-molecule sulfur, the small-molecule sulfur is confined in the nanoscale micropores of the conductive carbon layer, and the lithium orthosilicate-based lithium supplement additive is obtained.

[0012] According to some embodiments of the present application, the staged calcination is specifically: reacting the lithium source with the conductive carbon layer coated silica to generate the conductive carbon layer coated metasilicate lithium by calcining at 250-350 DEG C for 1-3 hours; raising the temperature to 450-650 DEG C, and calcining at 450-650 DEG C for 4-6 hours to further react the conductive carbon layer coated metasilicate lithium with the lithium source to generate the conductive carbon layer coated orthosilicate lithium core.

[0013] According to some embodiments of the present application, the mole ratio of the tetraethyl orthosilicate, the anhydrous ethanol and the deionized water is 1:4:2.

[0014] According to some embodiments of the present application, the mass ratio of the conductive carbon layer raw material and the sol is 1-3:10.

[0015] According to some embodiments of the present application, the lithium source is at least one of LiOH·H2O and LiOH, and the Si / Li mole ratio of the xerogel and the lithium source is 1:4.0-4.5.

[0016] According to some embodiments of the present application, the C / S mole ratio of the conductive carbon layer coated orthosilicate lithium core and the elemental sulfur S8 is 1:0.1-0.4.

[0017] Compared with the prior art, the present application has the following beneficial effects: The orthosilicate lithium based lithium supplementing additive of the present application solves the problems of slow ion and electron conduction and self-passivation of the reaction interface when the orthosilicate lithium is used as a lithium supplementing additive, and realizes the improvement of the lithium supplementing performance and the improvement of the cycle capacity retention rate of the battery by constructing the composite structure of "orthosilicate lithium core-conductive carbon layer-small molecule sulfur loaded on the conductive carbon layer".

[0018] The preparation method of the orthosilicate lithium based lithium supplementing additive of the present application firstly obtains the silica firmly coated with the conductive carbon layer by using the sol-gel method, so that the generation of the silica and the distribution of the conductive carbon layer carbon material are simultaneously performed on the nanometer scale, and the uniform composite of the silica and the carbon material is realized; secondly, the lithium source is added to obtain the conductive carbon layer coated orthosilicate lithium by ball milling and section calcining, so that the firm C-O-Si covalent bond is formed between the functional groups on the surface of the conductive carbon layer carbon material and the orthosilicate lithium, and the long-term stabilization of the structure is realized through chemical bonding; finally, the elemental sulfur is added to obtain the conductive carbon layer coated orthosilicate lithium loaded with high-activity small molecule sulfur through thermal activation and confinement effect, the molten sulfur penetrates into the pores of the carbon material at 280-320 DEG C, at the same time, the elemental sulfur S8 ring is broken and recombined into small molecule sulfur, the small molecule sulfur is captured by the micropores of the carbon material and stabilized through the confinement effect, so that the active center with the dual functions of conductivity and catalysis is formed, the energy barrier of the orthosilicate lithium delithiation is effectively reduced, the lithium supplementing capacity is improved, and then the cycle capacity retention rate of the battery is improved.

[0019] Additional aspects and advantages of the present application will be made apparent from the following description. DETAILED DESCRIPTION

[0020] In order to make the objects and technical solutions of the present application clearer and more convenient to understand, the present application will be further described in detail below with reference to the embodiments. The specific embodiments described herein are only intended to explain the present application, and not intended to limit the present application.

[0021] In the description of the present application, the meaning of one or more is one or more, the meaning of multiple is two or more, greater than, less than, more than, etc. are understood as not including the number, above, below, etc. are understood as including the number. If it is described as first, second, it is only used for the purpose of distinguishing technical features, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features or the sequence of indicated technical features.

[0022] In the following examples, the raw materials, reagents or devices, if not specifically stated, can be obtained from conventional commercial channels, or can be obtained by existing known methods.

[0023] In a first aspect, the embodiments of the present application provide a lithium orthosilicate-based lithium supplementing additive, characterized in that it comprises: a lithium orthosilicate core; a conductive carbon layer coated on the surface of the lithium orthosilicate core; a small molecule sulfur supported on the conductive carbon layer, the small molecule sulfur being at least one of di-sulfur S2, tri-sulfur S3, and tetra-sulfur S4.

[0024] Specifically, the small molecule sulfur has high reactivity, can efficiently react with the lithium orthosilicate interface, significantly reduces the energy barrier of lithium ion extraction from the lithium orthosilicate lattice, reduces the lithium supplementing reaction activation energy, realizes deep delithiation of the lithium orthosilicate, and makes the actual lithium supplementing energy value close to the theoretical lithium supplementing energy value; the conductive carbon layer provides a three-dimensional electron conduction network for the lithium orthosilicate core, ensures fast conduction of electrons, is conducive to preventing the formation of a dense passivation layer (SiO2) when the high-activity small molecule sulfur continuously and rapidly reacts with the lithium orthosilicate, so that lithium ions can be continuously and rapidly extracted from the inside of the lithium orthosilicate core, thereby solving the problem of low lithium supplementing efficiency caused by termination of lithium ion release. The present application solves the problem of slow ion conduction and self-passivation of the lithium orthosilicate-based lithium supplementing additive by the conductive carbon layer solving the problem of electron conduction and the small molecule sulfur solving the problem of reaction activation, and the two work together to solve the problems of slow ion conduction and self-passivation of the lithium orthosilicate-based lithium supplementing additive in the prior art. The prepared lithium orthosilicate-based lithium supplementing additive has the characteristics of high capacity, high efficiency and long life, and is conducive to enhancing the cycle energy efficiency of the battery.

[0025] Furthermore, the conductive carbon layer has a certain degree of flexibility, which can effectively alleviate the volume change of lithium orthosilicate during the delithiation process, prevent particle pulverization, and extend the material life. At the same time, small molecule sulfur is confined in the nanoscale micropores of the conductive carbon layer, and the spatial constraint effectively prevents the small molecule sulfur from returning to the sulfur elemental S8 ring or transforming into soluble polysulfides, so that the small molecule sulfur can maintain high activity and stability in the electrochemical environment.

[0026] In some embodiments, the conductive carbon layer is an acetylene black layer or an activated carbon layer.

[0027] Specifically, the conductive carbon layer has a porous structure. On the one hand, it can adsorb and store a large amount of electrolyte, effectively optimizing the wetting and ion transport of the electrolyte, ensuring that lithium ions can quickly reach and pass through the reaction interface to complete the lithium replenishment reaction, and improving the activity of the reaction interface. On the other hand, the rich pore structure can effectively load and stabilize highly active small molecule sulfur, effectively preventing small molecule sulfur from agglomerating or turning back into inert elemental sulfur S8 rings.

[0028] Furthermore, the conductive carbon layer is either an acetylene black layer or an activated carbon layer. The acetylene black layer is made from acetylene black, and the activated carbon layer is made from activated carbon. Acetylene black is a carbon black with well-developed chains produced by the thermal decomposition of acetylene. The particles can form a large, stable, and interwoven conductive network, effectively promoting electron transport between the lithium orthosilicate surface and the lithium orthosilicate particles. Activated carbon has a large specific surface area, providing numerous contact points for electron transport. Acetylene black mainly provides mesopores and a small portion of nanopores, while activated carbon is primarily composed of nanopores. The pores of acetylene black and / or activated carbon adsorb molten sulfur through capillary adsorption. In subsequent thermal activation, the confinement effect formed by the adsorption force between the pore walls of the nanopores and the sulfur molecules of small molecules, as well as the steric hindrance effect caused by the narrow space, accommodates and stabilizes highly reactive small-molecule sulfur.

[0029] In some embodiments, the conductive carbon layer is bonded to the lithium orthosilicate core via CO-Si covalent bonds.

[0030] Specifically, functional groups (such as carboxyl groups) on the surface of the conductive carbon layer can bind with lithium silicate through CO-Si covalent bonds to form a strong chemical anchor, effectively preventing the separation of the coating layer from the core during charging and discharging, which would further affect the stability and durability of the battery.

[0031] In some embodiments, the conductive carbon layer provides nanoscale micropores with a size comparable to that of the small molecule sulfur. The pore walls of the nanoscale micropores, together with the adsorption force of the sulfur molecules of the small molecule sulfur and the steric hindrance effect caused by the narrow space, constitute a confinement effect. The small molecule sulfur is confined in the nanoscale micropores and directly contacts the conductive carbon layer.

[0032] Specifically, the nanoscale micropores in the conductive carbon layer provide a nanoscale spatial confinement environment comparable to the size of small molecule sulfur. The strong adsorption force between the pore walls and the sulfur molecules of small molecule sulfur, as well as the steric hindrance effect brought about by the narrow space, together constitute the confinement effect, which effectively prevents the reformation and chain lengthening of small molecule sulfur SS bonds, maintains the high activity of small molecule sulfur, and further ensures that the lithium replenishment reaction interface has high catalytic activity, realizing rapid and efficient lithium replenishment.

[0033] Furthermore, small-molecule sulfur is confined in nanoscale micropores, directly contacting the highly conductive carbon layer to form multiple dispersed and efficient micro catalytic reaction centers. Electrons are rapidly injected through the carbon walls, and the activated small-molecule sulfur quickly reacts with the adjacent lithium orthosilicate, greatly reducing the reaction energy barrier of the lithium orthosilicate delithiation reaction and achieving rapid and efficient lithium replenishment.

[0034] Secondly, embodiments of the present invention provide a method for preparing the lithium orthosilicate-based lithium supplementation additive as described above, comprising the following steps: Tetraethyl orthosilicate, anhydrous ethanol, and deionized water were mixed, and the pH was adjusted to 3-4 with acid and stirred to form a sol. Conductive carbon layer raw materials were added to the sol and dispersed. The pH was adjusted to >7 with ammonia water to form a silica composite gel coated with a conductive carbon layer. After aging and drying, a dry gel was obtained. The dry gel was ball-milled and mixed with a lithium source in a certain proportion and calcined in stages under an inert atmosphere to obtain a lithium orthosilicate core coated with a conductive carbon layer. The lithium orthosilicate core coated with the conductive carbon layer is ground and mixed with elemental sulfur S8. The mixture is kept at 120-180°C for 4 hours under an inert atmosphere, and then subjected to a thermal activation reaction at 280-320°C for 1.5-2.5 hours. This causes the elemental sulfur S8 ring to break and generate small molecule sulfur. The small molecule sulfur is confined in the nanoscale micropores of the conductive carbon layer to obtain the lithium orthosilicate-based lithium supplementation additive.

[0035] Specifically, the lithium orthosilicate-based lithium supplementation additive of the present invention obtains a silica composite gel with a solid conductive carbon layer by a sol-gel method, then adds a lithium source and obtains a lithium orthosilicate core with a conductive carbon layer by ball milling and segmented calcination, and finally adds elemental sulfur S8 to obtain lithium orthosilicate with a conductive carbon layer loaded with highly active small molecule sulfur through thermal activation and confinement effect.

[0036] Furthermore, using the sol-gel method, silicon source and conductive carbon layer raw materials (acetylene black / activated carbon) are hydrolyzed and condensed in a fully dispersed system, allowing the generation of silica and the distribution of conductive carbon layer carbon materials to occur simultaneously at the nanoscale, achieving uniform composite of silica and carbon materials. Subsequent segmented calcination enables the functional groups on the surface of the conductive carbon layer carbon material to form strong CO-Si covalent bonds with lithium orthosilicate, achieving long-term structural stabilization through chemical bonding. Through thermal activation and confinement effect, sulfur is transformed from inert elemental sulfur S8 to small molecule sulfur with highly active catalytic function. At 280-320℃, molten sulfur penetrates into the pores of the carbon material, while the elemental sulfur S8 ring breaks and recombines into small molecule sulfur. The small molecule sulfur is captured by the micropores of the carbon material and stabilized through the confinement effect, thus forming active centers with both conductive and catalytic functions. This effectively reduces the energy barrier of lithium orthosilicate core delithiation, improves lithium replenishment capacity, and thus improves the cycle capacity retention rate of the battery.

[0037] In some embodiments, the segmented calcination specifically refers to: Calcination at 250℃~350℃ for 1 to 3 hours allows the lithium source to react with the conductive carbon-coated silicon dioxide to generate conductive carbon-coated lithium metasilicate. The temperature is raised to 450℃~650℃ and calcined at 450℃~650℃ for 4~6 hours, so that the lithium metasilicate coated with conductive carbon layer and the lithium source can react further to generate lithium orthosilicate core coated with conductive carbon layer.

[0038] Specifically, calcination at 250℃~350℃ for 1~3 hours allows the lithium source to react with the conductive carbon-coated silicon dioxide to generate conductive carbon-coated lithium metasilicate. This stage has a relatively mild temperature, which is conducive to the stable progress of the reaction and the initial construction of the structure. Calcination at 450℃~650℃ for 4~6 hours allows the conductive carbon-coated lithium metasilicate and the lithium source to further react to generate conductive carbon-coated lithium orthosilicate cores. This stage has a higher temperature, allowing the conductive carbon-coated lithium metasilicate and the remaining lithium source to further react to generate the final conductive carbon-coated lithium orthosilicate core. At the same time, the surface functional groups of the conductive carbon layer can form strong CO-Si covalent bonds with lithium orthosilicate, ensuring the structural stability of the conductive carbon layer during long-term charge-discharge cycles of the battery, which is beneficial to the stability and durability of the battery.

[0039] In some embodiments, the molar ratio of tetraethyl orthosilicate, anhydrous ethanol, and deionized water is 1:4:2.

[0040] Specifically, four molar amounts of anhydrous ethanol provide a suitable reaction medium. Too little anhydrous ethanol leads to excessively high system viscosity, uneven local concentrations of reactants, and the formation of large, irregular silica particles. Too much anhydrous ethanol, on the other hand, causes over-dilution, slowing the reaction rate, increasing costs, and reducing efficiency. Two molar amounts of water control the hydrolysis of tetraethyl orthosilicate to be controllable and gradual, while simultaneously promoting the subsequent gelation process, which is mainly characterized by polycondensation. This facilitates the formation of a continuous, dense three-dimensional network structure, resulting in silica gels with ideal pore size and mechanical strength.

[0041] Furthermore, by controlling the molar ratio of tetraethyl orthosilicate, anhydrous ethanol, and deionized water, a silica gel with ideal pore size and mechanical strength is obtained, ensuring efficient subsequent composite with carbon materials and lithium sources.

[0042] In some embodiments, the mass ratio of the conductive carbon layer raw material to the sol is 1-3:10.

[0043] Specifically, after adjusting the pH to alkaline, the sol forms a uniformly structured gel, providing carbon materials with a huge specific surface area and abundant anchoring points for composite formation, thereby obtaining a strong carbon coating layer. This ensures the high efficiency and stability of the electron conduction network, which is the fundamental prerequisite for lithium supplementation agents to have high first-time efficiency and long cycle life.

[0044] In some embodiments, the lithium source is at least one of LiOH·H2O and LiOH, and the Si / Li molar ratio of the dry gel and the lithium source is 1:4.0-4.5.

[0045] Specifically, the lithium sources chosen, LiOH·H2O and LiOH, both exhibit high reactivity and can undergo a complete solid-phase reaction with silicon dioxide during calcination. Compared to other lithium salts (such as lithium carbonate), they have lower decomposition temperatures, effectively preventing the formation of impurity phases due to incomplete lithium source reaction. Controlling the Si / Li molar ratio to 1:4.0-4.5 effectively avoids the formation of impurity phases (such as SiO2 and Li2SiO3), ensuring the high purity of Li4SiO4. At the same time, an appropriate excess of lithium source helps compensate for lithium volatilization during high-temperature calcination and ensures that there is always sufficient lithium in the reaction system to drive the reaction to completion, preventing the formation of electrochemically inert SiO2 or Li2SiO3 residues due to insufficient local lithium concentration.

[0046] In some embodiments, the C / S molar ratio of the conductive carbon-coated lithium orthosilicate core to the elemental sulfur S8 is 1:0.1-0.4.

[0047] Specifically, the C / S molar ratio of the conductive carbon-coated lithium orthosilicate core to elemental sulfur S8 is 1:0.1-0.4, ensuring sufficient sulfur to deeply activate lithium orthosilicate. At the same time, the sulfur loading matches the carbon carrying capacity, maximizing catalytic activity without sacrificing conductivity.

[0048] Furthermore, when the sulfur ratio is too low, there are not enough catalytically active sites for the delithiation reaction, and the reaction terminates prematurely inside the lithium orthosilicate particles. This results in a large amount of lithium being trapped in the unreacted lithium orthosilicate core, making the actual lithium replenishment capacity far lower than the theoretical value. When the sulfur ratio is too high, there is not enough conductive carbon layer to support the lithium, and sulfur deposits on the surface of the conductive carbon layer, severely reducing the conductivity of the final lithium replenishment additive. Therefore, when the C / S molar ratio of the conductive carbon-coated lithium orthosilicate core to elemental sulfur S8 is 1:0.1 to 0.4, in the molten state, sulfur can fully wet and fill the pores of the conductive carbon layer. During thermal activation, the confinement effect is utilized to convert sulfur into highly active small molecule sulfur to a large extent, achieving the best balance between electron conduction and interfacial catalysis.

[0049] Example 1 S01, Lithium orthosilicate core precursor coated with conductive carbon layer: Tetraethyl orthosilicate, anhydrous ethanol, and deionized water were mixed in a molar ratio of 1:4:2. 0.1M hydrochloric acid was added dropwise to adjust the pH to 3-4, and the mixture was stirred continuously until a transparent sol was formed. The sol and acetylene black powder were mixed in a mass ratio of 5:1 and ultrasonically treated at 40 kHz for 2 hours to achieve nanoscale dispersion of the acetylene black particles. 25wt% ammonia was slowly added dropwise to adjust the pH to 9, forming a SiO2@C composite gel. The gel was aged at 60℃ for 12 hours and dried to obtain a dry gel. The dry gel and LiOH·H2O were mixed at a Si / Li molar ratio of 1:4.2 and treated in a ball mill at 400 rpm for 4 hours to obtain a conductive carbon-coated lithium orthosilicate core precursor.

[0050] SO2, lithium orthosilicate core coated with conductive carbon layer: Under a nitrogen atmosphere, the lithium orthosilicate core precursor coated with a conductive carbon layer was calcined at 300°C for 2 hours; the temperature was then increased to 500°C at a rate of 5°C / min and held for 5 hours to obtain the lithium orthosilicate core coated with a conductive carbon layer.

[0051] SO3, introduces elemental sulfur and activates it into small molecule sulfur: The conductive carbon-coated lithium orthosilicate core and elemental sulfur S8 were thoroughly ground in an agate mortar for 30 minutes at a C / S molar ratio of 1:0.1. The uniformly mixed powder was transferred to a reaction vessel and sealed. The sealed reaction vessel was then placed in an oven and heated to 155°C at 3°C / min under a nitrogen atmosphere and held for 4 hours. The temperature was then increased to 300°C at 2°C / min and held for 2 hours. The mixture was then naturally cooled to room temperature to obtain a lithium orthosilicate-based lithium supplementation additive.

[0052] Example 2 The difference between Example 2 and Example 1 is that the conductive carbon layer coated lithium orthosilicate core and sulfur element S8 in step S03 are adjusted to a C / S molar ratio of 1:0.4.

[0053] Application Example 1 A battery containing a lithium orthosilicate-based lithium supplementation additive is a square aluminum-cased battery with a thickness of 50 mm, a width of 160 mm, a height of 118 mm, and a capacity of 100 Ah. It includes a positive electrode, a negative electrode, an electrolyte, and a separator, specifically comprising: 1. Preparation of the positive electrode: 1.1 The lithium orthosilicate-based lithium supplementation additive prepared in Example 1 was placed at 25°C and 30% humidity for 24 hours; 1.2 Lithium iron phosphate, lithium orthosilicate-based lithium supplementation additive, conductive additive (Super-P), and binder (PVDF) were dissolved in 1-methyl-2-pyrrolidone (NMP) at a mass ratio of 93:1:4:2 and mixed evenly using a 60L dual planetary mixer. The resulting cathode slurry had a viscosity of 7500±1500 mPas and a solid content of 61±2%. 1.3 The positive electrode slurry was coated using an extrusion coating machine onto a (12+1+1) μm thick double-sided carbon-coated aluminum foil, with a single-sided areal density of 173 g / m³. 2 The coated positive electrode sheet is then rolled on a roller press to achieve a compaction density of 2.5 g / cm³. 3 The positive electrode sheet is obtained by drying. 2. Preparation of the negative electrode: 2.1 Graphite, conductive carbon black, sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) were mixed evenly using a 60L dual planetary mixer at a weight ratio of 95.5:1:1.5:2. The resulting negative electrode slurry had a viscosity of 4000±1000 mPas and a solid content of 50±2%. 2.2 The negative electrode slurry was coated onto a 6μm thick copper foil using an extrusion coating machine, resulting in an areal density of 89 g / m². 2 The coated negative electrode sheet is then rolled on a roller press, and the compacted density of the negative electrode sheet is 1.5 g / cm³. 3 The negative electrode sheet is obtained by drying. 3. Preparation of electrolyte: Lithium hexafluorophosphate, vinylene carbonate, ethylene glycol and solvent were mixed evenly in a weight ratio of 10:2:2:86 to obtain an electrolyte; wherein the solvent was obtained by mixing ethylene carbonate, ethyl methyl carbonate and ethyl propionate in a volume ratio of 1:1:1. 4. Diaphragm: The diaphragm is a single-sided ceramic-coated diaphragm with a specification of (9+3+1)μm*109mm; 5. Battery fabrication: The positive electrode, negative electrode, and separator are wound and baked using a multi-tab winding method. After the cell is packaged, the above-mentioned electrolyte is used to inject the cell into the cell once, place it for wetting, form, age, inject it into the cell a second time, and then perform capacity testing to obtain the finished battery.

[0054] Application Example 2-10 As shown in Table 1, the difference between Application Example 2-10 and Application Example 1 is that the formulation of the positive electrode is adjusted.

[0055] Comparative Example 1 The formulation of the positive electrode was adjusted to lithium iron phosphate, conductive additive (Super-P), and binder (PVDF) in a mass ratio of 93:5:2. The rest was the same as the method of assembling the battery in Application Example 1, resulting in a positive electrode without lithium supplementation additive and a battery assembled from it.

[0056] The batteries obtained from Application Examples 1-10 and Comparative Example 1 were subjected to performance tests, and the performance test results are shown in Table 1.

[0057] Table 1 shows the formulations of the positive electrode sheets for Application Examples 1-10, the initial coulombic efficiency of the batteries obtained from Application Examples 1-10 and Comparative Example 1, and the capacity retention after 1000 cycles. By comparing Application Examples 1-10 and Comparative Example 1, the use of the lithium orthosilicate-based lithium replenishment additive of the present invention significantly improves the cycle life of lithium batteries, with a capacity retention rate of 95.0% to 99.2% after 1000 cycles, which is significantly higher than the 94.8% of Comparative Example 1 without the lithium orthosilicate-based lithium replenishment additive. Meanwhile, comparing the initial coulombic efficiency, it was found that the addition of the lithium orthosilicate-based lithium replenishment additive had little effect on the initial coulombic efficiency, indicating that the role of the lithium orthosilicate-based lithium replenishment additive is mainly to compensate for the loss of active lithium in subsequent cycles due to the SEI film.

[0058] By comparing application examples 1-10, it was found that the battery performance of the lithium orthosilicate-based lithium replenishment additive prepared in Example 2 was better. This is because the acetylene black used in Example 1 has mesopores and a small number of micropores. In contrast, Example 2 used activated carbon with more microporous structures. Micropores are the main space in which activated small molecule sulfur can be stably stored through the confinement effect. Example 2 can hold more highly active small molecule sulfur than Example 1, which can better reduce the energy barrier, promote the delithiation of lithium orthosilicate to release lithium ions and achieve lithium replenishment, and further improve the cycle life and cycle efficiency of the battery.

[0059] By comparing application examples 1-10, it can be seen that with the addition of lithium orthosilicate-based lithium replenishing additives, the amount of conductive agent added also decreases, but the initial coulombic efficiency remains above 95%. This is because lithium orthosilicate-based lithium replenishing additives are both lithium replenishing additives and conductive agents, and can completely replace the conductive agent Super-P. The lithium orthosilicate-based lithium replenishing additives of the present invention not only improve the initial coulombic efficiency by providing an additional lithium source, but also replace the traditional conductive agent Super-P by constructing a conductive network, thereby significantly improving the long-term cycle stability of the battery while simplifying the formulation.

[0060] In summary, the lithium orthosilicate-based lithium replenishment additive of the present invention solves the problems of slow ion and electron conduction and self-passivation of reaction interface when lithium orthosilicate is used as a lithium replenishment additive by constructing a composite structure of "lithium orthosilicate core-conductive carbon layer-small molecule sulfur supported on conductive carbon layer". At 280-320°C, molten sulfur penetrates into the carbon material pores of the conductive carbon layer, while the S8 ring of elemental sulfur breaks and recombines into small molecule sulfur. The small molecule sulfur is captured by the micropores of the carbon material and stabilized by the confinement effect, thereby forming an active center with both conductive and catalytic functions. This effectively reduces the energy barrier of lithium delithiation of the lithium orthosilicate core, improves the lithium replenishment capacity, and thus improves the lithium replenishment performance and the cycle capacity retention rate of the battery.

[0061] The above description is only a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made based on the content of the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A lithium orthosilicate-based lithium supplementation additive, characterized in that, include: Lithium orthosilicate core; A conductive carbon layer coating the surface of the lithium orthosilicate core; Small molecule sulfur loaded on the conductive carbon layer, wherein the small molecule sulfur is at least one of disulfide S2, trisulfide S3, and tetrasulfide S4.

2. The lithium orthosilicate-based lithium supplementation additive according to claim 1, characterized in that, The conductive carbon layer is an acetylene black layer or an activated carbon layer.

3. The lithium orthosilicate-based lithium supplementation additive according to claim 1, characterized in that, The conductive carbon layer is bonded to the lithium orthosilicate core via CO-Si covalent bonds.

4. The lithium orthosilicate-based lithium supplementation additive according to claim 1, characterized in that, The conductive carbon layer provides nanoscale micropores with a size comparable to that of the small molecule sulfur. The pore walls of the nanoscale micropores, the adsorption force of the sulfur molecules of the small molecule sulfur, and the steric hindrance effect caused by the narrow space together constitute a confinement effect. The small molecule sulfur is confined in the nanoscale micropores and directly contacts the conductive carbon layer.

5. A method for preparing a lithium orthosilicate-based lithium supplementing additive as described in any one of claims 1-4, characterized in that, Includes the following steps: Tetraethyl orthosilicate, anhydrous ethanol, and deionized water were mixed, and the pH was adjusted to 3-4 with acid and stirred to form a sol. Conductive carbon layer raw materials were added to the sol and dispersed. The pH was adjusted to >7 with ammonia water to form a silica composite gel coated with a conductive carbon layer. After aging and drying, a dry gel was obtained. The dry gel was ball-milled and mixed with a lithium source in a certain proportion and calcined in stages under an inert atmosphere to obtain a lithium orthosilicate core coated with a conductive carbon layer. The lithium orthosilicate core coated with the conductive carbon layer is ground and mixed with elemental sulfur S8. The mixture is kept at 120-180°C for 4 hours under an inert atmosphere, and then subjected to a thermal activation reaction at 280-320°C for 1.5-2.5 hours. This causes the elemental sulfur S8 ring to break and generate small molecule sulfur. The small molecule sulfur is confined in the nanoscale micropores of the conductive carbon layer to obtain the lithium orthosilicate-based lithium supplementation additive.

6. The method for preparing the lithium orthosilicate-based lithium supplementation additive according to claim 5, characterized in that, The segmented calcination specifically refers to: Calcination at 250℃~350℃ for 1 to 3 hours allows the lithium source to react with the conductive carbon-coated silicon dioxide to generate conductive carbon-coated lithium metasilicate. The temperature is raised to 450℃~650℃ and calcined at 450℃~650℃ for 4~6 hours, so that the lithium metasilicate coated with conductive carbon layer and the lithium source can react further to generate lithium orthosilicate core coated with conductive carbon layer.

7. The method for preparing the lithium orthosilicate-based lithium supplementation additive according to claim 5, characterized in that, The molar ratio of tetraethyl orthosilicate, anhydrous ethanol, and deionized water is 1:4:

2.

8. The method for preparing the lithium orthosilicate-based lithium supplementation additive according to claim 5, characterized in that, The mass ratio of the conductive carbon layer raw material to the sol is 1-3:

10.

9. The method for preparing the lithium orthosilicate-based lithium supplementation additive according to claim 5, characterized in that, The lithium source is at least one of LiOH·H2O and LiOH, and the Si / Li molar ratio of the dry gel and the lithium source is 1:4.0-4.

5.

10. The method for preparing the lithium orthosilicate-based lithium supplementation additive according to claim 5, characterized in that, The C / S molar ratio of the lithium orthosilicate core coated with the conductive carbon layer to the elemental sulfur S8 is 1:0.1-0.4.

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