Positive electrode lithium supplementing agent, preparation method thereof, positive electrode sheet, lithium ion battery and electric device

Abstract

The present application relates to the field of lithium ion batteries, in particular to a positive electrode lithium supplementing agent, a preparation method thereof, a positive electrode sheet, a lithium ion battery and an electric device. The positive electrode lithium supplementing agent comprises a lithium-containing compound; the lithium-containing compound comprises a chemical composition shown in formula (1-x)Li2FeSiO4·xLiFeBO3, wherein 0 < x < 0.5. The positive electrode lithium supplementing agent has high ion conductivity and high delithiation capacity, excellent charge-discharge performance, and the main structure of the lithium supplementing agent before and after formation basically does not change, and the stability is good, so that the energy density and cycle performance of the lithium ion battery can be improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of lithium ion batteries, in particular to a positive electrode lithium supplementing agent, a preparation method thereof, a positive electrode sheet, a lithium ion battery and an electric device. BACKGROUND

[0002] During the first formation charging process of the lithium ion battery, the decomposition of the electrolyte on the surface of the negative electrode forms a solid electrolyte interface (SEI film) due to the decrease of the negative electrode potential, and the active lithium participates in the formation process of the SEI film, resulting in the decrease of the initial capacity of the battery. The shrinkage and expansion of the negative electrode during the charging and discharging cycle of the lithium ion battery causes the rupture of the SEI film, and the process of forming a new film layer will continuously consume the electrolyte and the active lithium in the positive electrode material. The lithium supplementing technology pre-stores a certain amount of active lithium in the positive electrode or the negative electrode, which can improve the initial capacity and cycle life of the lithium ion battery, and has important significance.

[0003] The common positive electrode lithium supplementing agent Li5FeO4 (LFO) is unstable in air and easy to absorb moisture to form inactive Li x Fe y O z and residual alkali (such as Li2CO3, LiOH), which not only reduces its electrochemical performance, but also causes the battery to produce gas, resulting in safety hazards. In addition, LFO is decomposed into LiFeO2 after the formation process, the structure of the lithium supplementing agent changes significantly, and the decomposition products have the risk of metal dissolution, resulting in the cycle degradation of the battery.

[0004] Therefore, it is of great significance to develop a new type of positive electrode lithium supplementing agent with high stability, good lithium supplementing effect and excellent electrochemical performance. SUMMARY

[0005] The purpose of the present application is to overcome the problems of poor stability and unsatisfactory lithium supplementing effect of the prior art positive electrode lithium supplementing agent, and to provide a positive electrode lithium supplementing agent, a preparation method thereof, a positive electrode sheet, a lithium ion battery and an electric device. Compared with the prior art, the positive electrode lithium supplementing agent provided by the present application has significantly improved structural stability, ionic conductivity and lithium supplementing performance, which can make the lithium ion battery have higher energy density and better cycle performance.

[0006] In order to achieve the above purpose, the first aspect of the present application provides a positive electrode lithium supplementing agent, which comprises a lithium-containing compound.

[0007] The lithium-containing compound comprises a chemical composition represented by the chemical formula (1-x)Li2FeSiO4·xLiFeBO3, wherein 0

[0008] The second aspect of the present application provides a preparation method of the positive electrode lithium supplement agent, comprising:

[0009] The first lithium source, the first silicon source, the first iron source and the first boron source are mixed to obtain a mixture; the mixture is calcined to obtain the positive electrode lithium supplement agent;

[0010] Or

[0011] The second lithium source, the second silicon source, the second iron source, the second boron source and the solvent are mixed to obtain a mixed solution; the mixed solution is subjected to a heating reaction, and the reaction product is sequentially subjected to drying and second calcination to obtain the positive electrode lithium supplement agent;

[0012] The feeding molar ratio of the first lithium source, the first silicon source, the first iron source and the first boron source is such that the lithium-containing compound contained in the prepared positive electrode lithium supplement agent comprises a chemical composition represented by the formula (1-x)Li2FeSiO4·xLiFeBO3, wherein 0

[0013] The feeding molar ratio of the second lithium source, the second silicon source, the second iron source and the second boron source is such that the lithium-containing compound contained in the prepared positive electrode lithium supplement agent comprises a chemical composition represented by the formula (1-x)Li2FeSiO4·xLiFeBO3, wherein 0

[0014] The third aspect of the present application provides the positive electrode lithium supplement agent prepared by the method of the second aspect.

[0015] The fourth aspect of the present application provides a positive electrode tab comprising the positive electrode lithium supplement agent of the first aspect or the third aspect.

[0016] The fifth aspect of the present application provides a lithium ion battery comprising the positive electrode tab of the fourth aspect.

[0017] The sixth aspect of the present application provides an electric device using the lithium ion battery of the fifth aspect.

[0018] By the technical scheme, the positive electrode lithium supplement agent provided by the application contains the lithium-containing compound with the chemical formula (1-x)Li2FeSiO4·xLiFeBO3 (0<x<0.5), and the chemical composition of the lithium-containing compound belongs to a composite material grown in situ. Compared with Li2FeSiO4, the chemical composition of (1-x)Li2FeSiO4·xLiFeBO3 (0<x<0.5) has higher ionic conductivity, and the amount of lithium removed is obviously increased, and the main structure of the lithium-containing compound before and after formation basically does not change. Preferably, the surface of the lithium-containing compound in the positive electrode lithium supplement agent is coated with a carbon coating layer, and the presence of the carbon coating layer can further improve the electronic conductivity of the lithium supplement agent and make the lithium supplement agent have better electrochemical performance. The positive electrode lithium supplement agent provided by the application is applied to a lithium ion battery, and the energy density and cycle life of the battery can be improved. BRIEF DESCRIPTION OF DRAWINGS

[0019] The accompanying drawings are included to provide a further understanding of the application, and constitute a part of the specification, and are used together with the specific embodiments described below to explain the application, but do not constitute a limitation on the application. In the drawings:

[0020] Figure 1 The transmission electron microscope image of the positive electrode lithium supplement agent prepared in Example 1 of the application. DETAILED DESCRIPTION

[0021] The endpoints of the ranges and any values disclosed herein are not limited to the precise values recited as the exact dimensions are not critical to the application. Any numerical values need not be a precision value, provided that these values are treated as approximations. The endpoints of the ranges of values recited are not to be understood as limiting the range of values to the precise values recited. The exact numerical values are not critical to the application. Any numerical value, however, can be expressed as a range by either adding or subtracting a small percentage (e.g., 0.1%) from the precise value. For example, a range of 1.0% can be expressed as 0.9% to 1.1% or 0.11% to 1.09%, either of which is within 0.1% of 1.0%.

[0022] The first aspect of the application provides a positive electrode lithium supplement agent, the positive electrode lithium supplement agent comprising a lithium-containing compound.

[0023] The lithium-containing compound comprises a chemical composition of the chemical formula (1-x)Li2FeSiO4·xLiFeBO3, wherein 0<x<0.5.

[0024] The lithium-containing compound contains a chemical composition of (1-x)Li2FeSiO4·xLiFeBO3, which belongs to in-situ grown composite material, is obtained by doping a small amount of LiFeBO3 in the Li2FeSiO4 crystal, and the lattice stripe of LiFeBO3 doped in the Li2FeSiO4 crystal can be observed by transmission electron microscopy. The composite material is different from the simple physical mixing of Li2FeSiO4 and LiFeBO3 independently. In the chemical composition of (1-x)Li2FeSiO4·xLiFeBO3, LiFeBO3 has good electronic conductivity and ionic conductivity, which can form a network with fast ion and electron conduction in the Li2FeSiO4 grain, which is beneficial to the rapid conduction of lithium ions and electrons in the Li2FeSiO4 grain, and improves the interface dynamic performance of the material, so that the lithium-containing compound has better electronic conductivity and ionic conductivity than Li2FeSiO4 alone, the charge and discharge performance is significantly improved (the specific capacity of more than 270 mAh / g can be released during charging), and the lithium ions can be more fully deintercalated, and the deintercalation capacity is higher.

[0025] According to a preferred embodiment of the present application, for the chemical composition of (1-x)Li2FeSiO4·xLiFeBO3, when 0.01≤x≤0.2, the lithium-containing compound has a higher deintercalation capacity, thereby making the positive electrode lithium supplement agent have a better lithium supplement effect.

[0026] According to a further preferred embodiment of the present application, for the chemical composition of (1-x)Li2FeSiO4·xLiFeBO3, when 0.02≤x≤0.1, the lithium-containing compound has a further improved deintercalation capacity, thereby making the positive electrode lithium supplement agent be able to deintercalate more lithium ions and have a further improved lithium supplement effect.

[0027] According to the present application, preferably, the positive electrode lithium supplement agent can further include a carbon coating layer covering the lithium-containing compound.

[0028] According to the present application, the carbon coating layer in the positive electrode lithium supplement agent tightly covers the surface of the lithium-containing compound, which has the effect of improving the electronic conductivity and ionic conductivity of the positive electrode lithium supplement agent. Preferably, in the positive electrode lithium supplement agent, the weight ratio of the lithium-containing compound to the carbon coating layer is 1:(0.001-0.05), and further preferably 1:(0.01-0.03).

[0029] According to the application, the thickness of the carbon coating layer is 1-5 nm, which can improve the electronic conductivity of the positive electrode lithium supplement agent and does not affect the deintercalation of lithium ions. When the thickness of the carbon coating layer meets the above range, it is beneficial to the positive electrode lithium supplement agent to exert better lithium supplement effect.

[0030] In the application, the thickness of the carbon coating layer is determined by transmission electron microscopy (TEM).

[0031] According to the application, the average particle size of the positive electrode lithium supplement agent is 0.02-5 μm, preferably 0.05-3 μm. When the average particle size of the positive electrode lithium supplement agent meets the above range, on the one hand, it is beneficial to reduce the deintercalation energy barrier of lithium ions, and on the other hand, it is beneficial to subsequent slurry preparation with components such as positive electrode active materials, which can reduce the risk of gelation of the positive electrode slurry and improve the compaction density of the positive electrode sheet.

[0032] In the application, the average particle size refers to the median diameter (D50), which can be determined by a laser particle size analyzer or a scanning electron microscope.

[0033] According to the application, the positive electrode lithium supplement agent can be used as a component of the positive electrode slurry together with the positive electrode active material, the conductive agent, the binder, the solvent and the like to prepare the positive electrode slurry, which is coated on the positive electrode current collector to obtain the positive electrode sheet containing the positive electrode lithium supplement agent.

[0034] The lithium ion battery using the above positive electrode sheet (containing the positive electrode lithium supplement agent provided by the application) can deintercalate a large amount of lithium ions from the positive electrode lithium supplement agent during the first charging process, which participates in the formation process of the SEI film. Since about 80% of the discharge platform of the positive electrode lithium supplement agent is lower than 2.5 V (the above positive electrode sheet is assembled into a button cell with a metal lithium sheet, and a 0.1C small current charging and discharging test is performed on the button cell, the charging and discharging window is 2-4.3 V, and the capacity ratio of the voltage segment lower than 2.5 V is about 80%), which is lower than the discharge cutoff voltage of most positive electrode active materials, most lithium ions will preferentially reintercalate into the positive electrode active material with higher potential during the discharging process, thereby improving the average working voltage and energy density of the lithium ion battery. The positive electrode lithium supplement agent provided by the application has good lithium deintercalation capacity, and the excess lithium ions of the negative electrode will return to the crystal structure of the positive electrode lithium supplement agent during the discharging process. As the lithium ion battery cycles, the active lithium is continuously consumed, the lithium ions stored in the positive electrode lithium supplement agent are released again, and preferentially intercalate into the positive electrode active material with higher potential, which is beneficial to maintaining the charge and discharge capacity and energy density of the lithium ion battery, thereby improving the cycle life of the lithium ion battery.

[0035] The second aspect of the application provides a preparation method of a positive electrode lithium supplement agent, comprising:

[0036] mixing a first lithium source, a first silicon source, a first iron source and a first boron source to obtain a mixture; calcining the mixture to obtain the positive electrode lithium supplement agent;

[0037] or

[0038] mixing a second lithium source, a second silicon source, a second iron source, a second boron source and a solvent to obtain a mixed solution; heating the mixed solution to obtain a reaction product; and drying and calcining the reaction product to obtain the positive electrode lithium supplement agent;

[0039] The molar ratio of the first lithium source, the first silicon source, the first iron source and the first boron source is such that the lithium-containing compound contained in the prepared positive electrode lithium supplement agent comprises a chemical composition represented by the formula (1-x)Li2FeSiO4·xLiFeBO3, wherein 0

[0040] The molar ratio of the second lithium source, the second silicon source, the second iron source and the second boron source is such that the lithium-containing compound contained in the prepared positive electrode lithium supplement agent comprises a chemical composition represented by the formula (1-x)Li2FeSiO4·xLiFeBO3, wherein 0

[0041] According to an embodiment of the present application, the preparation method comprises: mixing a first lithium source, a first silicon source, a first iron source and a first boron source to obtain a mixture; and calcining the mixture to obtain the positive electrode lithium supplement agent. This embodiment adopts a solid phase method, mixes and grinds the solid phase raw materials, and then calcines the mixture to obtain the positive electrode lithium supplement agent.

[0042] According to the present application, the first lithium source is at least one selected from lithium silicate, lithium carbonate, lithium acetate and lithium hydroxide, preferably at least one selected from lithium silicate, lithium carbonate and lithium hydroxide.

[0043] According to the present application, the first silicon source is at least one selected from tetraethyl silicate, silicon dioxide and silicic acid, preferably tetraethyl silicate and / or silicic acid.

[0044] According to the present application, the first iron source is at least one selected from ferrous oxalate, ferrous acetate and ferric citrate, preferably ferrous oxalate and / or ferrous acetate.

[0045] According to the present application, the first boron source is at least one selected from boric acid, boron oxide and lithium borate, preferably boric acid and / or boron oxide.

[0046] According to the present application, the first mixing method is not particularly limited, as long as the first lithium source, the first silicon source, the first iron source and the first boron source can be mixed sufficiently to obtain a uniform mixture. Preferably, the first mixing can be performed by ball milling.

[0047] According to the present application, preferably, the average particle size of the mixture is 0.02-5 μm, which is conducive to obtaining better calcination effect. The average particle size in the above range can be obtained by adjusting the particle size of each raw material, or can be obtained by implementing crushing treatment in the process of the first mixing (for example, by using a ball mill).

[0048] According to the present application, the first calcination is implemented at a calcination temperature of 400-800 ℃, preferably 600-750 ℃, and a calcination time of 4-24 h, preferably 8-12 h. By using the above calcination temperature and time, the positive electrode lithium supplementing agent with good crystallinity and uniform composition can be generated.

[0049] According to the present application, the first calcination is implemented in a protective atmosphere, for example, N2 atmosphere, Ar atmosphere, Ar / H2 mixed atmosphere, preferably Ar / H2 mixed atmosphere.

[0050] According to another embodiment of the present application, the sol-gel method is used, and the preparation method comprises: mixing a second lithium source, a second silicon source, a second iron source, a second boron source and a solvent to obtain a mixed solution; and implementing a heating reaction on the mixed solution, and sequentially implementing drying and second calcination on the reaction product to obtain the positive electrode lithium supplementing agent.

[0051] According to the present application, the second lithium source is selected from at least one of lithium acetate, lithium citrate, lithium nitrate and lithium sulfate, and is preferably at least one of lithium acetate, lithium citrate and lithium nitrate.

[0052] According to the present application, the second silicon source is selected from at least one of tetraethyl orthosilicate and / or silicic acid, and is preferably tetraethyl orthosilicate.

[0053] According to the present application, the second iron source is selected from at least one of iron nitrate, iron citrate and iron chloride, and is preferably iron nitrate and / or iron citrate.

[0054] According to the present application, the second boron source is boric acid.

[0055] According to the present application, the solvent is selected from at least one of water, an alcohol solvent (for example, ethanol) and a ketone solvent (for example, acetone).

[0056] According to the present application, the manner of the second mixing is not particularly limited, as long as the second lithium source, the second silicon source, the second iron source, the second boron source and the solvent can be sufficiently mixed to obtain a uniform and stable mixed solution.

[0057] According to the application, the heating reaction conditions include: temperature of 30-85℃, preferably 40-60℃; time of 12-36h, preferably 18-24h. With the above heating reaction temperature and time, the crystal nucleus can be slowly and uniformly grown, which is beneficial to obtain the positive electrode lithium supplement agent with good uniformity in particle size and morphology.

[0058] According to the application, the product obtained by the heating reaction is dried to obtain dry glue. Preferably, the drying conditions include: temperature of 60-120℃; time of 4-12h.

[0059] According to the application, preferably, the dry glue obtained by drying is crushed before the second calcination, and is calcined in the form of powder, which is beneficial to obtain better calcination effect.

[0060] According to the application, the second calcination adopts a calcination temperature of 400-800℃, preferably 600-750℃; and a calcination time of 3-24h, preferably 8-12h. With the above calcination temperature and time, the crystallinity of the (1-x)Li2FeSiO4·xLiFeBO3 (0<x<0.5) schematic chemical composition can be improved, which is beneficial to improve the structural stability of the positive electrode lithium supplement agent before and after delithiation.

[0061] According to the application, the second calcination is carried out in a protective atmosphere, which can be selected according to the protective atmosphere of the aforementioned first calcination, and will not be described here.

[0062] According to the application, preferably, the raw materials for the first mixing further include a first carbon source; or the raw materials for the second mixing further include a second carbon source. By introducing the carbon source, a carbon coating layer can be formed on the surface of the lithium-containing compound. The carbon coating layer has the effect of improving the electronic conductivity of the positive electrode lithium supplement agent itself, and on the other hand, the presence of the carbon coating layer can prevent the mutual contact between lithium-containing compound particles during calcination, inhibit the particle growth, shorten the lithium ion transport path, and further improve the ionic conductivity of the positive electrode lithium supplement agent.

[0063] According to the application, the first carbon source is selected from sucrose, glucose, pitch, ascorbic acid, citric acid and polyvinylpyrrolidone, preferably at least one of sucrose, glucose and polyvinylpyrrolidone.

[0064] According to the application, the second carbon source is selected from at least one of citric acid, ascorbic acid, sucrose and glucose, preferably at least one of citric acid, sucrose and glucose.

[0065] According to the present application, preferably, the feeding amount of the first carbon source or the second carbon source is such that the weight ratio of the lithium-containing compound included in the prepared positive electrode lithium supplement agent to the carbon coating layer coating the lithium-containing compound is 1:(0.001-0.05).

[0066] According to the present application, the two preparation methods described above can be used to obtain positive electrode lithium supplement agents with the same chemical composition and structure. From the perspective of product particle size uniformity and carbon coating effect, the sol-gel method is preferred.

[0067] The third aspect of the present application provides a positive electrode lithium supplement agent prepared by the method of the second aspect.

[0068] According to the present application, the chemical composition, structure, index and performance of the positive electrode lithium supplement agent prepared by the method of the second aspect are the same as those of the positive electrode lithium supplement agent described in the first aspect of the present application, which will not be repeated here.

[0069] The fourth aspect of the present application provides a positive electrode tab containing the positive electrode lithium supplement agent of the first aspect or the third aspect.

[0070] According to the present application, preferably, the positive electrode tab includes a positive electrode current collector and a positive electrode material layer formed by a positive electrode slurry on the surface of the current collector; wherein the positive electrode slurry contains the positive electrode lithium supplement agent of the first aspect or the third aspect.

[0071] According to the present application, the formation of the positive electrode material layer on the surface of the current collector from the positive electrode slurry can use conventional implementation in the art, preferably using coating method, the positive electrode slurry is uniformly coated on the surface of the positive electrode current collector, after drying, rolling to obtain the positive electrode tab.

[0072] According to the present application, preferably, the positive electrode slurry contains, in addition to the positive electrode lithium supplement agent, a positive electrode active material, a conductive agent, a binder and a solvent; wherein,

[0073] The positive electrode lithium supplement agent is 1-15 parts by weight, the conductive agent is 0.5-5 parts by weight, the binder is 0.5-5 parts by weight and the solvent is 25-75 parts by weight, relative to 100 parts by weight of the positive electrode active material.

[0074] According to the present application, the positive electrode active material in the positive electrode slurry is not particularly limited and any positive electrode active material that can be used in the positive electrode slurry of lithium ion battery can be selected. For example, it can be selected from one or more of lithium-rich manganese-based positive electrode material, lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium manganese iron phosphate.

[0075] According to the present application, the conductive agent in the positive electrode slurry is not particularly limited, and any conductive agent selection that can be used in a lithium ion battery positive electrode slurry can be adopted. For example, it can be selected from one or more of conductive carbon black, carbon nanotubes and graphene.

[0076] According to the present application, the binder in the positive electrode slurry is not particularly limited, and any binder selection that can be used in a lithium ion battery positive electrode slurry can be adopted. For example, it can be selected from one or more of polytetrafluoroethylene, polyvinylidene fluoride, sodium carboxymethyl cellulose and polyvinyl alcohol.

[0077] According to the present application, the solvent in the positive electrode slurry is not particularly limited, and any solvent selection that can be used in a lithium ion battery positive electrode slurry can be adopted. For example, it can be selected from N-methylpyrrolidone and / or water.

[0078] According to a preferred embodiment of the present application, in the positive electrode slurry, the positive electrode lithium supplement agent is 2-10 parts by weight, the conductive agent is 1-3 parts by weight, the binder is 2-4 parts by weight and the solvent is 30-75 parts by weight, relative to 100 parts by weight of the positive electrode active material.

[0079] According to the present application, the positive electrode slurry can be prepared by thoroughly mixing the positive electrode active material, the positive electrode lithium supplement agent, the conductive agent, the binder and the solvent that meet the above-mentioned proportion range.

[0080] According to the present application, the positive electrode current collector can adopt any positive electrode current collector selection that can be used in a lithium ion battery, for example, it can be an aluminum foil, a stainless steel foil.

[0081] The fifth aspect of the present application provides a lithium ion battery comprising the positive electrode tab of the fourth aspect described above.

[0082] The positive electrode tab of the lithium ion battery provided by the present application contains the positive electrode lithium supplement agent of the present application, and has the characteristics of high energy density and long cycle life.

[0083] The sixth aspect of the present application provides an electric device using the lithium ion battery of the fifth aspect described above.

[0084] The present application will be described in detail below through examples. In the following examples and comparative examples, unless otherwise specified, the reagents used are all commercially available.

[0085] Example 1

[0086] (1) 2.01 g of CH3COOLi·2H2O (lithium source), 2.02 g of TEOS (silicon source), 4.04 g of Fe(NO3)3·9H2O (iron source), 0.02 g of H3BO3 (boron source), and 1.92 g of citric acid (carbon source) were added to 80 g of water, and mixed to obtain a mixed solution;

[0087] (2-1) The mixed solution was reacted at 50°C for 24 h under water bath heating, and the obtained reaction product was dried at 80°C for 12 h to obtain a dry gel, which was then ground and crushed to obtain a powder;

[0088] (2-2) The powder was placed in a tube furnace and calcined at 650°C for 10 h under Ar / H2mixed gas (volume ratio of Ar:H2was 95:5), and after natural cooling, the product was ground to obtain a positive electrode lithium supplement (denoted as S1).

[0089] The average particle size of S1 was 1.97 μm, and had a lithium-containing compound and a carbon coating layer covering the lithium-containing compound; the chemical composition of the lithium-containing compound was (1-x)Li2FeSiO4·xLiFeBO3, wherein x = 0.03; the weight ratio of the lithium-containing compound to the carbon coating layer was 1:0.03; and the thickness of the carbon coating layer was 2.53 nm.

[0090] TEM test was performed on S1, and the results are shown in Figure 1 , wherein the region with d 002 = 0.508 nm was LiFeBO3, and the region with d 103 = 0.27 nm was Li2FeSiO4. The lattice fringes of LiFeBO3 appeared inside the Li2FeSiO4lattice, indicating that LiFeBO3 was incorporated into the Li2FeSiO4crystal.

[0091] Example 2

[0092] (1) 2.03 g of CH3COOLi·2H2O (lithium source), 2.06 g of TEOS (silicon source), 4.04 g of Fe(NO3)3·9H2O (iron source), 0.01 g of H3BO3 (boron source), and 1.92 g of citric acid (carbon source) were added to 80 g of water, and mixed to obtain a mixed solution;

[0093] (2-1) The mixed solution was reacted at 50°C for 24 h under water bath heating, and the obtained reaction product was dried at 80°C for 12 h to obtain a dry gel, which was then ground and crushed to obtain a powder;

[0094] (2-2) The above powder was placed in a tube furnace, calcined at 650°C for 10h under Ar / H2mixed gas (volume ratio of Ar:H2was 95:5), and after the calcination was completed, the product was ground to obtain the positive electrode lithium supplement agent (denoted as S2).

[0095] The average particle size of S2 was 2.08 μm, and S2 had a lithium-containing compound and a carbon coating layer coating the lithium-containing compound; the chemical composition of the lithium-containing compound was (1-x)Li2FeSiO4·xLiFeBO3, wherein x=0.01; the weight ratio of the lithium-containing compound to the carbon coating layer was 1:0.028; and the thickness of the carbon coating layer was 2.45 nm.

[0096] Example 3

[0097] (1) 1.84 g of CH3COOLi·2H2O (lithium source), 1.67 g of TEOS (silicon source), 4.04 g of Fe(NO3)3·9H2O (iron source), 0.12 g of H3BO3 (boron source), and 0.96 g of citric acid (carbon source) were added to 80 g of water, and the mixture was mixed to obtain a mixed solution;

[0098] (2-1) The above mixed solution was reacted at 50°C for 24h under water bath heating, and the reaction product was dried at 80°C for 12h to obtain a dry gel, which was then ground to obtain a powder;

[0099] (2-2) The above powder was placed in a tube furnace, calcined at 650°C for 10h under Ar / H2mixed gas (volume ratio of Ar:H2was 95:5), and after the calcination was completed, the product was ground to obtain the positive electrode lithium supplement agent (denoted as S2).

[0100] The average particle size of S3 was 2.05 μm, and S3 had a lithium-containing compound and a carbon coating layer coating the lithium-containing compound; the chemical composition of the lithium-containing compound was (1-x)Li2FeSiO4·xLiFeBO3, wherein x=0.2; the weight ratio of the lithium-containing compound to the carbon coating layer was 1:0.015; and the thickness of the carbon coating layer was 1.52 nm.

[0101] Example 4

[0102] (1) 1.73 g of CH3COOLi·2H2O (lithium source), 1.76 g of TEOS (silicon source), 4.04 g of Fe(NO3)3·9H2O (iron source), 0.19 g of H3BO3 (boron source), and 1.92 g of citric acid (carbon source) were added to 80 g of water, and the mixture was mixed to obtain a mixed solution;

[0103] (2-1) The above mixture was reacted at 50°C for 24h under water bath heating, and the reaction product was dried at 80°C for 12h to obtain dry gel, which was then ground and crushed to obtain powder;

[0104] (2-2) The above powder was calcined at 750°C for 10h under Ar / H2mixed gas (volume ratio of Ar:H2was 95:5) in a tube furnace, and the product was ground after natural cooling to obtain positive electrode lithium supplement agent (denoted as S4).

[0105] The average particle size of S4 was 2.33μm, and S4 had lithium-containing compound and carbon coating layer coating the lithium-containing compound; wherein the chemical composition of the lithium-containing compound was (1-x)Li2FeSiO4·xLiFeBO3, wherein x=0.3; the weight ratio of the lithium-containing compound to the carbon coating layer was 1:0.033; and the thickness of the carbon coating layer was 2.63nm.

[0106] Example 5

[0107] (1) 1.73g of CH3COOLi·2H2O (lithium source), 1.76g of TEOS (silicon source), 4.04g of Fe(NO3)3·9H2O (iron source), 0.19g of H3BO3 (boron source), and 2.88g of citric acid (carbon source) were added to 80g of water, and the mixture was mixed to obtain a mixed solution;

[0108] (2-1) The above mixture was reacted at 50°C for 24h under water bath heating, and the reaction product was dried at 80°C for 12h to obtain dry gel, which was then ground and crushed to obtain powder;

[0109] (2-2) The above powder was calcined at 750°C for 10h under Ar / H2mixed gas (volume ratio of Ar:H2was 95:5) in a tube furnace, and the product was ground after natural cooling to obtain positive electrode lithium supplement agent (denoted as S5).

[0110] The average particle size of S5 was 2.28μm, and S5 had lithium-containing compound and carbon coating layer coating the lithium-containing compound; wherein the chemical composition of the lithium-containing compound was (1-x)Li2FeSiO4·xLiFeBO3, wherein x=0.3; the weight ratio of the lithium-containing compound to the carbon coating layer was 1:0.042; and the thickness of the carbon coating layer was 3.52nm.

[0111] Example 6

[0112] (1) 1.63 g of CH3COOLi·2H2O (lithium source), 1.25 g of TEOS (silicon source), 4.04 g of Fe(NO3)3·9H2O (iron source), 0.25 g of H3BO3 (boron source), and 2.88 g of citric acid (carbon source) were added to 80 g of water, and mixed to obtain a mixed solution;

[0113] (2-1) The mixed solution was heated in a water bath at 50°C for 24 h, and the obtained reaction product was dried at 80°C for 12 h to obtain a dry gel. The dry gel was then ground and pulverized to obtain a powder;

[0114] (2-2) The powder was placed in a tube furnace and calcined at 750°C for 10 h under Ar / H2mixed gas (volume ratio of Ar:H2was 95:5). After the calcination was completed, the product was naturally cooled and ground to obtain a positive electrode lithium supplement (denoted as S6).

[0115] The average particle size of S6 was 2.37 μm, and S6 had a lithium-containing compound and a carbon coating layer covering the lithium-containing compound. The chemical composition of the lithium-containing compound was (1-x)Li2FeSiO4·xLiFeBO3, wherein x = 0.4. The weight ratio of the lithium-containing compound to the carbon coating layer was 1:0.039, and the thickness of the carbon coating layer was 3.47 nm.

[0116] Example 7

[0117] (1) 1.73 g of CH3COOLi·2H2O (lithium source), 1.46 g of TEOS (silicon source), 1.8 g of FeC2O4·2H2O (iron source), 0.19 g of H3BO3 (boron source), and 2.88 g of citric acid (carbon source) were placed in a ball mill jar (the weight ratio of the above-mentioned raw materials to the grinding balls was 0.25:1), and 10 g of grinding aid acetone was added. The mixture was ball-milled for 5 h, and the product was dried at 80°C for 12 h to obtain a mixed material (average particle size was 3 μm);

[0118] (2) The mixed material was placed in a tube furnace and calcined at 650°C for 10 h under Ar / H2mixed gas (volume ratio of Ar:H2was 95:5). After natural cooling, a positive electrode lithium supplement (denoted as S7) was obtained.

[0119] The average particle size of S7 was 3.50 μm, and S7 had a lithium-containing compound and a carbon coating layer covering the lithium-containing compound. The chemical composition of the lithium-containing compound was (1-x)Li2FeSiO4·xLiFeBO3, wherein x = 0.3. The weight ratio of the lithium-containing compound to the carbon coating layer was 1:0.035, and the thickness of the carbon coating layer was 3.55 nm.

[0120] Example 8

[0121] (1) 1.54 g of CH3COOLi·2H2O (lithium source), 1.06 g of TEOS (silicon source), 4.04 g of Fe(NO3)3·9H2O (iron source), 0.30 g of H3BO3 (boron source), and 4.23 g of citric acid (carbon source) were added to 80 g of water, and mixed to obtain a mixed solution;

[0122] (2-1) The mixed solution was reacted at 50°C for 24 h under water bath heating, and the obtained reaction product was dried at 80°C for 12 h to obtain a dry gel. Then, the dry gel was ground and crushed to obtain a powder;

[0123] (2-2) The powder was placed in a tube-type atmosphere furnace, calcined at 650°C for 10 h under Ar / H2mixed gas (the volume ratio of Ar:H2was 95:5), and then naturally cooled. The product was ground to obtain a positive electrode lithium supplement (denoted as S8).

[0124] The average particle size of S8 was 0.03 μm, and S8 had a lithium-containing compound and a carbon coating layer covering the lithium-containing compound. The chemical composition of the lithium-containing compound was (1-x)Li2FeSiO4·xLiFeBO3, wherein x = 0.49. The weight ratio of the lithium-containing compound to the carbon coating layer was 1:0.047, and the thickness of the carbon coating layer was 4.95 nm.

[0125] Example 9

[0126] (1) 1.54 g of CH3COOLi·2H2O (lithium source), 1.06 g of TEOS (silicon source), 4.04 g of Fe(NO3)3·9H2O (iron source), 0.30 g of H3BO3 (boron source), and 4.23 g of citric acid (carbon source) were added to 80 g of water, and mixed to obtain a mixed solution;

[0127] (2-1) The mixed solution was reacted at 50°C for 24 h under water bath heating, and the obtained reaction product was dried at 80°C for 12 h to obtain a dry gel. Then, the dry gel was ground and crushed to obtain a powder;

[0128] (2-2) The powder was placed in a tube-type atmosphere furnace, calcined at 650°C for 10 h under Ar / H2mixed gas (the volume ratio of Ar:H2was 95:5), and then naturally cooled. The product was ground to obtain a positive electrode lithium supplement (denoted as S8).

[0129] The average particle size of S9 is 4.97 μm, and S9 has a lithium-containing compound and a carbon coating layer covering the lithium-containing compound; the chemical composition of the lithium-containing compound is (1-x)Li2FeSiO4-xLiFeBO3, wherein x = 0.49; the weight ratio of the lithium-containing compound to the carbon coating layer is 1:0.003; and the thickness of the carbon coating layer is 1.05 nm.

[0130] Example 10

[0131] The method of Example 1 is used, except that no citric acid (carbon source) is added in step (1). The other steps and conditions are the same as in Example 1, and a positive electrode lithium supplement (denoted as S10) is obtained.

[0132] The average particle size of S10 is 4.03 μm, and the chemical composition of the lithium-containing compound is (1-x)Li2FeSiO4-xLiFeBO3, wherein x = 0.03.

[0133] Example 11

[0134] The method of Example 2 is used, except that no citric acid (carbon source) is added in step (1). The other steps and conditions are the same as in Example 2, and a positive electrode lithium supplement (denoted as S11) is obtained.

[0135] The average particle size of S11 is 4.25 μm, and the chemical composition of the lithium-containing compound is (1-x)Li2FeSiO4-xLiFeBO3, wherein x = 0.01.

[0136] Example 12

[0137] The method of Example 3 is used, except that no citric acid (carbon source) is added in step (1). The other steps and conditions are the same as in Example 3, and a positive electrode lithium supplement (denoted as S12) is obtained.

[0138] The average particle size of S12 is 4.17 μm, and the chemical composition of the lithium-containing compound is (1-x)Li2FeSiO4-xLiFeBO3, wherein x = 0.2.

[0139] Example 13

[0140] The method of Example 8 is used, except that no citric acid (carbon source) is added in step (1). The other steps and conditions are the same as in Example 8, and a positive electrode lithium supplement (denoted as S13) is obtained.

[0141] The average particle size of S13 is 4.08 μm, and the chemical composition of the lithium-containing compound is (1-x)Li2FeSiO4-xLiFeBO3, wherein x = 0.49.

[0142] Comparative Example 1

[0143] (1) 2.04 g of CH3COOLi·2H2O (lithium source), 2.08 g of TEOS (silicon source), 4.04 g of Fe(NO3)3·9H2O (iron source), and 1.92 g of citric acid (carbon source) were added to 80 g of water, and mixed to obtain a mixed solution;

[0144] (2-1) The mixed solution was reacted at 50°C for 24 h under water bath heating, and the reaction product was dried at 80°C for 12 h to obtain a dry gel. The dry gel was then ground and pulverized to obtain a powder;

[0145] (2-2) The powder was placed in a tube-type atmosphere furnace and calcined at 650°C for 10 h under Ar / H2mixed gas (volume ratio of Ar:H2was 95:5). After the calcination was completed, the product was naturally cooled and ground to obtain a positive electrode lithium supplement (denoted as DS1).

[0146] The average particle size of DS1 was 2 μm, and DS1 had a lithium-containing compound and a carbon coating layer covering the lithium-containing compound. The chemical composition of the lithium-containing compound was Li2FeSiO4 (i.e., (1-x)Li2FeSiO4·xLiFeBO3, where x = 0). The weight ratio of the lithium-containing compound to the carbon coating layer was 1:0.028, and the thickness of the carbon coating layer was 2.52 nm.

[0147] Comparative Example 2

[0148] (1) 2.04 g of CH3COOLi·2H2O (lithium source), 2.08 g of TEOS (silicon source), 4.04 g of Fe(NO3)3·9H2O (iron source), and 1.92 g of citric acid (carbon source) were added to 80 g of water, and mixed to obtain a mixed solution-I;

[0149] (2-1) The mixed solution-I was reacted at 50°C for 24 h under water bath heating, and the reaction product was dried at 80°C for 12 h to obtain a dry gel. The dry gel was then ground and pulverized to obtain a powder-I;

[0150] (2-2) The powder-I was placed in a tube-type atmosphere furnace and calcined at 650°C for 10 h under Ar / H2mixed gas (volume ratio of Ar:H2was 95:5). After the calcination was completed, the product was naturally cooled and ground to obtain a positive electrode lithium supplement A (having a lithium supplement material Li2FeSiO4 and a carbon coating layer covering Li2FeSiO4);

[0151] (3) 1.02 g of CH3COOLi·2H2O (lithium source), 4.04 g of Fe(NO3)3·9H2O (iron source), 0.62 g of H3BO3 (boron source), and 1.92 g of citric acid (carbon source) were added to 80 g of water, and mixed well to obtain a mixed solution-II;

[0152] (4-1) The mixed solution-II was reacted at 50°C for 24 h under water bath heating, and the obtained reaction product was dried at 80°C for 12 h to obtain a dry gel. Then, the dry gel was ground and pulverized to obtain a powder-II;

[0153] (4-2) The powder-II was calcined at 650°C for 10 h under Ar / H2mixed gas (volume ratio of Ar:H2was 95:5) in a tube furnace, and then naturally cooled. The product was ground to obtain a positive electrode lithium supplement B (having a lithium supplement material LiFeBO3and a carbon coating layer covering the LiFeBO3).

[0154] (5) The positive electrode lithium supplement A and the positive electrode lithium supplement B were mixed by grinding in a molar ratio of 0.97:0.03 to obtain a positive electrode lithium supplement (denoted as DS2).

[0155] The average particle size of the DS2 was 2.33 μm, and the DS2 had a lithium supplement material and a carbon coating layer covering the lithium supplement material. In the positive electrode lithium supplement A, the weight ratio of the lithium supplement material to the carbon coating layer was 1:0.037, and the thickness of the carbon coating layer was 2.35 nm. In the positive electrode lithium supplement B, the weight ratio of the lithium supplement material to the carbon coating layer was 1:0.035, and the thickness of the carbon coating layer was 2.27 nm.

[0156] Comparative Example 3

[0157] (1) 1.43 g of CH3COOLi·2H2O (lithium source), 0.83 g of TEOS (silicon source), 1.80 g of Fe(NO3)3·9H2O (iron source), 0.37 g of H3BO3 (boron source), and 1.92 g of citric acid (carbon source) were added to 80 g of water, and mixed well to obtain a mixed solution;

[0158] (2-1) The mixed solution was reacted at 50°C for 24 h under water bath heating, and the obtained reaction product was dried at 80°C for 12 h to obtain a dry gel. Then, the dry gel was ground and pulverized to obtain a powder;

[0159] (2-2) The powder was calcined at 650°C for 10 h under Ar / H2mixed gas (volume ratio of Ar:H2was 95:5) in a tube furnace, and then naturally cooled. The product was ground to obtain a positive electrode lithium supplement (denoted as DS3).

[0160] The average particle size of the DS3 is 2.09 μm, and the DS3 has a lithium-containing compound and a carbon coating layer coating the lithium-containing compound; wherein the chemical composition of the lithium-containing compound is (1-x)Li2FeSiO4·xLiFeBO3, wherein x = 0.6; the weight ratio of the lithium-containing compound to the carbon coating layer is 1:0.033; and the thickness of the carbon coating layer is 2.63 nm.

[0161] Comparative Example 4

[0162] According to the method of Comparative Example 1, except that no citric acid (carbon source) is added in step (1). Other steps and conditions are the same as those in Comparative Example 1, and a positive electrode lithium supplement (denoted as DS4) is obtained.

[0163] The average particle size of the DS4 is 4.13 μm, and the chemical composition of the lithium-containing compound is Li2FeSiO4 (i.e., (1-x)Li2FeSiO4·xLiFeBO3, wherein x = 0).

[0164] Comparative Example 5

[0165] According to the method of Comparative Example 2, except that no citric acid (carbon source) is added in steps (1) and (3). Other steps and conditions are the same as those in Comparative Example 2, and a positive electrode lithium supplement (denoted as DS5) is obtained.

[0166] The DS5 is a mixture of Li2FeSiO4 and LiFeBO3 physically mixed at a molar ratio of 0.97:0.03, and the average particle size of the DS5 is 4.33 μm.

[0167] Comparative Example 6

[0168] According to the method of Comparative Example 3, except that no citric acid (carbon source) is added in step (1). Other steps and conditions are the same as those in Comparative Example 3, and a positive electrode lithium supplement (denoted as DS6) is obtained.

[0169] The average particle size of the DS6 is 4.25 μm, and the chemical composition of the lithium-containing compound is (1-x)Li2FeSiO4·xLiFeBO3, wherein x = 0.6.

[0170] Test Example

[0171] 1. Preparation of the positive electrode slurry and the positive electrode tab:

[0172] Polyvinylidene fluoride (binder) was added to N-methylpyrrolidone (solvent) and stirred to dissolve, after which conductive carbon black (conductive agent), lithium iron phosphate (positive active material), and positive electrode lithium supplement (positive electrode lithium supplements S1-S13 and DS1-DS6 prepared in Examples 1-13 and Comparative Examples 1-6 described above were added, and kneaded well (the above raw materials were added in the following amounts: 100 parts by weight of positive active material, 5 parts by weight of positive electrode lithium supplement, 3 parts by weight of conductive agent, 3 parts by weight of binder, and 65 parts by weight of solvent), to obtain positive electrode slurry (denoted as F1-F13 and DF1-DF6, respectively);

[0173] The above positive electrode slurries F1-F13 and DF1-DF6 were uniformly coated on aluminum foil under the same process parameters, and were baked and rolled to prepare positive electrode electrodes (denoted as P1-P13 and DP1-DP6, respectively).

[0174] 2. Preparation of lithium ion battery:

[0175] The above positive electrode electrodes P1-P13 and DP1-DP6 were assembled into soft pack batteries (denoted as B1-B13 and DB1-DB6, respectively) with negative electrodes and electrode sheets (negative electrode slurry prepared by mixing 100 parts by weight of graphite, 3 parts by weight of binder, 3 parts by weight of conductive carbon black, and 80 parts by weight of N-methylpyrrolidone, uniformly coated on copper foil, and baked and rolled to prepare negative electrode sheets) and electrolyte (LiPF6 concentration of 1 mol / L, with solvent being a mixture of EC and EMC in a volume ratio of 1:2).

[0176] 3. Battery charge-discharge performance test and high-temperature cycle performance test

[0177] The above soft pack batteries B1-B13 and DB1-DB6 were charged at a current of 0.6 A to 4.0 V at room temperature, and then discharged at a current of 0.6 A to 2.0 V, and the initial charge capacity and initial discharge capacity of the batteries were recorded, and the initial coulombic efficiency of the batteries was calculated (initial coulombic efficiency = initial discharge capacity / initial charge capacity x 100%), and the results are shown in Table 1.

[0178] The above soft pack batteries B1-B13 and DB1-DB6 were charged at a current of 1C (about 1.8 A) to 3.8 V at 45°C, and then discharged at a current of 1.8 A to 2.0 V, and the initial charge capacity and initial discharge capacity of the batteries were recorded; this was repeated for 500 cycles, and the discharge capacity at the 500th cycle was recorded, and the cycle capacity retention rate of the batteries was calculated (cycle capacity retention rate = discharge capacity at the 500th cycle / initial discharge capacity x 100%), and the results are shown in Table 2.

[0179] Table 1

[0180] Table 2

[0181] Table 2

[0182]

[0183]

[0184] As can be seen from Table 1 and Table 2, the positive electrode lithium supplementing agent S1-S13 provided by the present application can make the lithium supplementing battery B1-B13 have higher first charge capacity and first discharge capacity, and higher energy density, and the cycle capacity retention rate is greater than 85% after 500 cycles of charging and discharging under the above test conditions, showing good cycle performance, wherein the positive electrode lithium supplementing agent S1-S3 prepared in Examples 1-3 has a significant performance advantage. The positive electrode lithium supplementing agent S1-S9 provided by the present application has a carbon coating layer, in this case, when the value of x in the chemical composition of (1-x)Li2FeSiO4·xLiFeBO3 contained in the lithium-containing compound falls within the preferred range of the present application, the lithium supplementing battery has higher first charge capacity, indicating that more lithium ions are transferred from the positive electrode side to the negative electrode during the charging process, more lithium ions are pre-stored in the negative electrode, and higher cycle capacity retention rate is promoted. In addition, the positive electrode lithium supplementing agent S10-S13 provided by the present application does not have a carbon coating layer, in this case, when the value of x in the chemical composition of (1-x)Li2FeSiO4·xLiFeBO3 contained in the lithium-containing compound in S10-S13 falls within the preferred range of the present application, the preferred scheme also shows better results.

[0185] The positive electrode lithium supplementing agent provided by the present application has higher electronic conductivity in the case of carbon coating of the lithium-containing compound (such as S1-S3, S8 corresponding to S10-S13 respectively) compared to the case without carbon coating (such as S10-S13), which can further improve the first charge capacity and cycle capacity retention rate of the lithium supplementing battery, wherein the weight ratio of the lithium-containing compound:carbon coating layer is preferably 1:(0.01-0.03), which can make the lithium supplementing battery have higher first charge capacity and higher cycle capacity retention rate.

[0186] Particularly, the positive electrode lithium supplementing agent DS1 prepared in Comparative Example 1 uses single Li2FeSiO4 as the lithium supplementing material, lithium ions in Li2FeSiO4 are difficult to be smoothly released, and the lithium supplementing effect is limited, resulting in that the initial charge-discharge capacity and the cycle capacity retention rate of the lithium supplementing battery DB1 are relatively low; the positive electrode lithium supplementing agent S2 prepared in Comparative Example 2 uses the form of physical mixing of Li2FeSiO4 / C and LiFeBO3 / C, the amount of lithium ions released is not high, the supplementing effect on the battery capacity attenuation caused by the loss of active lithium in the cycle process is not ideal, resulting in that the initial charge-discharge capacity and the cycle capacity retention rate of the lithium supplementing battery DB2 are lower than those of B1-B9. For the positive electrode lithium supplementing agent DS3 prepared in Comparative Example 3, the value of x in the schematic chemical composition (1-x)Li2FeSiO4·xLiFeBO3 contained in the lithium-containing compound does not meet the limitation of the present application, the lithium supplementing effect is not ideal, and the initial discharge capacity and the cycle capacity retention rate of the lithium supplementing battery DB3 are lower than those of B1-B9. DS4-DS6 respectively give up the carbon coating layer compared with DS1-DS3, and the performance further decreases.

[0187] The above describes the preferred embodiments of the present application in detail, but the present application is not limited thereto. Within the technical concept of the present application, various simple modifications can be made to the technical solutions of the present application, including that various technical features are combined in any other suitable manner, and these simple modifications and combinations should also be considered as the disclosed content of the present application, and all fall within the protection scope of the present application.

Claims

1. A positive electrode lithium supplement, characterized in that: The positive electrode lithium supplement comprises a lithium-containing compound; The lithium-containing compound comprises a chemical composition represented by a chemical formula (1-x)Li2FeSiO4·xLiFeBO3, wherein 0<x<0.

5.

2. The positive electrode lithium supplement according to claim 1, wherein 0.01≤x≤0.2。 3. The positive electrode lithium supplement according to claim 2, wherein 0.02≤x≤0.1。 4. The positive electrode lithium supplement according to any one of claims 1 to 3, wherein: The positive electrode lithium supplement further includes a carbon coating layer coating the lithium-containing compound.

5. The positive electrode lithium supplement according to claim 4, wherein The weight ratio of the lithium-containing compound to the carbon coating layer is 1:(0.001-0.05); And / or, the carbon coating layer has a thickness of 1-5 nm.

6. The positive electrode lithium supplement according to claim 5, wherein The weight ratio of the lithium-containing compound to the carbon coating layer is 1:(0.01-0.03).

7. The positive electrode lithium supplement according to any one of claims 1 to 3, 5 to 6, wherein: The average particle size of the positive electrode lithium supplement agent is 0.02-5 μm.

8. The positive electrode lithium supplement according to claim 7, wherein: The average particle size of the positive electrode lithium supplement is 0.05-3 μm.

9. The positive electrode lithium supplement according to claim 4, wherein The average particle size of the positive electrode lithium supplement agent is 0.02-5 μm.

10. The positive electrode lithium supplement according to claim 9, wherein The average particle size of the positive electrode lithium supplement is 0.05-3 μm.

11. A method for preparing a positive electrode lithium supplement, characterized in that: include: performing a first mixing of a first lithium source, a first silicon source, a first iron source, and a first boron source to obtain a mixture; and performing a first calcination of the mixture to obtain a positive electrode lithium supplement; or A second lithium source, a second silicon source, a second iron source, a second boron source and a solvent are mixed for a second time to obtain a mixed solution; the mixed solution is heated to react, and the reaction product is dried and calcined for a second time in sequence to obtain a positive electrode lithium supplement; The molar ratio of the first lithium source, the first silicon source, the first iron source, and the first boron source is such that the lithium-containing compound included in the prepared positive electrode lithium supplement comprises a chemical composition represented by the chemical formula (1-x)Li2FeSiO4·xLiFeBO3, wherein 0<x<0.5; The molar ratio of the second lithium source, the second silicon source, the second iron source and the second boron source is such that the lithium-containing compound included in the prepared positive electrode lithium supplement comprises a chemical composition represented by the chemical formula (1-x)Li2FeSiO4·xLiFeBO3, wherein 0<x<0.

5.

12. The method according to claim 11, wherein The average particle size of the mixture is 0.02-5 μm; And / or, the conditions of the first calcination include: carrying out under a protective atmosphere, a temperature of 400-800° C., and a time of 4-24 hours; And / or, the conditions of the heating reaction include: temperature of 30-85° C., time of 12-36 h; And / or, the conditions for the second calcination include: being carried out under a protective atmosphere, at a temperature of 400-800° C., and for a time of 3-24 hours.

13. The method according to claim 12, wherein: The conditions of the first calcination include: carrying out under a protective atmosphere, a temperature of 600-750° C., and a time of 8-12 hours; And / or, the heating reaction conditions include: temperature of 40-60° C., time of 18-24 h; And / or, the second calcination conditions include: being carried out under a protective atmosphere, at a temperature of 600-750° C., and for 8-12 hours.

14. The method according to any one of claims 11 to 13, wherein: The raw materials for the first mixing also include a first carbon source; or The raw materials for the second mixing also include a second carbon source; The amount of the first carbon source or the second carbon source is such that the prepared positive electrode lithium supplement contains The weight ratio of the lithium-containing compound to the carbon coating layer coating the lithium-containing compound is 1:(0.001-0.05).

15. A positive electrode lithium supplement prepared by the method according to any one of claims 11 to 14.

16. A positive electrode plate comprising the positive electrode lithium supplement according to any one of claims 1 to 10 and 15.

17. A lithium-ion battery comprising the positive electrode sheet according to claim 16.

18. An electrical device using the lithium-ion battery according to claim 17.

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