CN107959015B - A kind of modified lithium battery positive electrode, preparation method and the lithium battery comprising it - Google Patents

Abstract

The invention discloses a modified lithium battery positive electrode material, a preparation method and a lithium battery containing the same. The positive electrode material is lithium manganese silicate layered and compounded with a fluorine-containing inorganic material, and the fluorine-containing inorganic material is Lithium fluoride, the present invention uses lithium fluoride and lithium manganese silicate for layered compounding, improves the conductivity of the lithium manganese silicate positive electrode, reduces the electrode/electrolyte interface impedance, improves electron mobility, and the lithium fluoride layer structure is stable , can inhibit the deformation and structural collapse of lithium manganese silicate material in lithium ion deintercalation, and improve cycle performance.

Description

A modified lithium battery positive electrode material, preparation method and lithium battery containing the same

technical field

The invention relates to the field of lithium batteries, in particular to a modified lithium battery cathode material, a preparation method and a lithium battery containing the same.

Background technique

The early practical positive electrode material is lithium cobalt oxide. Due to its low resources, high price, and high environmental pollution, it is not suitable as a large-scale power lithium battery energy source. In recent years, lithium iron phosphate and nickel cobalt lithium manganate materials have been studied due to their energy density. The problem has not been completely solved, and it is difficult to meet the needs of large-capacity batteries for the new generation of electric vehicles and electric bicycles. Various new positive electrode materials developed in recent years, such as manganese lithium silicate, have a theoretical number of electrons to be deintercalated and a theoretical specific capacity of 330mAh/g, which is twice that of lithium iron phosphate materials. At the same time, there are a large amount of Si- O bond, strong resistance to electrolyte corrosion, my country's manganese resources are abundant, cheap, non-toxic and non-polluting. Moreover, lithium manganese silicate, etc., as cathode materials for lithium batteries, has the advantages of easy synthesis, high potential, and good safety, and is a new candidate material for cathodes of lithium batteries.

Chinese invention patent 201710458347.4 discloses a functional coating slurry for lithium battery pole pieces and a lithium battery. The functional coating slurry for lithium battery pole pieces of the invention includes coating materials and additives; The coating material includes lithium salt and oxide; the mass ratio of lithium salt to the coating material is 1% to 20%; the oxide includes aluminum oxide, zirconium oxide, amorphous silicon oxide, zinc oxide , one or more of cerium oxide, magnesium oxide, titanium oxide and praseodymium oxide. The invention starts from the point of view of pole piece modification, and coats a layer of functional coating slurry on the surface of the positive and/or negative pole pieces, which can form a layer of functional coating on the surface of the battery pole piece, thereby improving the high energy density at the same time The safety and cycle life of lithium batteries, especially the safety and cycle life of high-energy-density lithium batteries such as high-nickel ternary materials have been significantly improved. However, when the battery is at a high potential, Mn ³⁺ is prone to disproportionation reaction and dissolves from the surface of the active material. Secondly, it is prone to structural distortion during the process of repeated intercalation and delithiation, resulting in rapid capacity decay, especially at higher temperatures. phenomenon is more prominent.

Chinese invention patent 201710081551.9 discloses a positive electrode sheet and a lithium battery. The positive electrode sheet of the invention includes a positive electrode current collector and a positive electrode slurry coated on the surface of the positive electrode current collector; the positive electrode current collector is foamed aluminum foil; the positive electrode slurry includes a mass fraction of 92%-98% positive electrode active material, 0.05%-2% conductive agent, 1%-2.5% PVDF and 0.05%-2% single-wall carbon nanotube. The lithium battery includes a positive electrode sheet and a negative electrode sheet. The positive electrode sheet includes a positive electrode collector and a positive electrode slurry coated on the surface of the positive electrode collector; the negative electrode sheet includes a negative electrode collector and a negative electrode slurry coated on the surface of the negative electrode collector. ; The positive electrode slurry includes a mass fraction of 92%-98% positive active material, 0.05%-2% conductive agent, 1%-2.5% PVDF and 0.05%-2% single-walled carbon nanotubes; negative electrode slurry It includes 93%-96% of positive electrode active material, 1%-3% of conductive agent and 1%-3.5% of LA133. Although this invention improves the rate performance, cycle performance and heat dissipation effect of the positive electrode sheet to a certain extent, it is difficult to improve the electronic conductivity and tap density at the same time.

Chinese invention patent 201010610221.2 discloses a positive electrode active material and its preparation method, a positive electrode material and a lithium battery. The positive electrode active material of the invention has an inner core and an outer shell, the inner core is lithium manganese silicate, and the outer shell includes carbon and silicon salt; the average particle diameter of the positive electrode active material is 30-60nm. The invention firstly prepares lithium manganese silicate inner core material, and then forms an outer shell including carbon and silicate on the surface, which greatly improves the rate performance of the lithium battery prepared by using the positive electrode active material.

Chinese invention patent 201210591984.6 discloses a lithium battery positive electrode material and its preparation method. The preparation method of the invention includes the following steps: (1) Pretreatment of the positive electrode base material. Calcination; (2) Coating the silicon-containing compound, ultrasonically dispersing the positive electrode material in the silicon-containing compound solution, heating and stirring until dry, and calcining at high temperature; (3) Coating the carbon material, ultrasonically dispersing a layer of coated positive electrode material in the carbon material solution, heated and stirred until dry, and calcined at high temperature. Both the capacity retention rate and the rate performance of the positive electrode material of the lithium battery of the present invention are improved.

However, even if the above-mentioned positive electrode active material is modified by the above-mentioned modification method, the electrochemical performance of lithium manganese silicate is still unsatisfactory, because lithium manganese silicate has a great influence on the lattice structure in the process of electron deintercalation, and The conductivity itself is low, and it has not been widely used in the lithium battery industry. Therefore, it is of great significance to improve the cycle performance and electron mobility of the positive electrode material.

Contents of the invention

The first object of the present invention is to propose a modified lithium battery cathode material for the unsatisfactory electrochemical performance of the existing lithium manganese silicate and its existing problems.

The second object of the present invention is to provide the preparation method of the above-mentioned modified lithium battery cathode material, which uses lithium fluoride and lithium manganese silicate for layered compounding, improves the conductivity of the lithium manganese silicate cathode, and reduces the electrode/electrolyte The interface impedance improves the electron mobility, and the structure of the lithium fluoride layer is stable, which can inhibit the deformation and structural collapse of the lithium manganese silicate material during lithium ion deintercalation, and improve the cycle performance.

The third object of the present invention is to provide a lithium battery positive electrode, a lithium battery and a battery pack comprising the above positive electrode material.

In order to solve the above problems, the present invention adopts the following technical solutions:

A modified lithium battery positive electrode material, the positive electrode material is lithium manganese silicate layered compounded with fluorine-containing inorganic material, and the fluorine-containing inorganic material is lithium fluoride.

Another aspect of the present invention provides a method for preparing a modified lithium battery cathode material, comprising the steps of:

Step A, adding soluble manganese salt to the aqueous solution containing lithium salt, stirring, filtering, and drying to obtain lithium salt-manganese salt solid particles, the molar ratio of lithium salt and manganese salt is 1:2 to 2:1;

Step B, after mixing the lithium salt-manganese salt solid particles obtained in step A with the silicon source at a molar ratio of 3:1, adding a carbon source, and calcining at 850-900°C for 5-8 hours under an inert atmosphere to obtain solid particles ; Pickling to remove unreacted lithium salts and manganese salts, filtering and drying to obtain the lithium manganese silicate;

Step C, weigh lithium hydroxide and ammonium fluoride according to the molar ratio of 1:1.2 to 1:1.5, add an organic solvent to make a mixed solution with a volume ratio of 1:25 to 1:50, and place it on a magnetic stirrer Stir for 2 to 4 hours;

Step D, centrifuging the solution after the reaction in step C to obtain a white precipitate, drying the obtained precipitate at 80-100°C until the water content is less than 5%, to obtain a white powder;

Step E. React the white powder obtained in step D at 200°C for 3 to 4 hours under the protection of an inert gas. After the reaction, raise the temperature of the furnace to 400°C. ammonium fluoride, and the holding time is 3 to 4 hours to obtain the lithium fluoride;

Step F, the lithium manganese silicate obtained in step B and the lithium fluoride obtained in step E are pressed into tablets at 0.5MP and 60-70°C, wherein the thickness of the lithium manganese silicate is 1.5-2.0 mm, the thickness of the tablet of lithium fluoride is 0.5-0.8mm, the two kinds of sheet-shaped green bodies are stacked up and down to form a multi-layer green body, and then moved into an isostatic press to form a whole; finally, after Sintered into a lithium fluoride modified lithium manganese silicate with a layered composite structure.

Preferably, in step A,

Described lithium salt is the one in lithium hydroxide, lithium carbonate or lithium acetate;

The manganese salt is one of manganese acetate or manganese nitrate;

The concentration of the lithium salt solution is 1.2-2.5 mol/L, and the concentration of the manganese salt solution is 0.8-1.2 mol/L.

Preferably, in step B,

The silicon source is amorphous silicon oxide or tetraethyl orthosilicate;

The carbon source is one of gluconic acid, citric acid or oxalic acid or a mixture thereof.

Preferably, in step D,

The speed of the centrifuge is 5000r/min-6000r/min, and the centrifugation time is 20 minutes.

Preferably, in step F,

The sintering temperature is 400°C, the high-purity inert gas is used as the carrier gas, the heating rate is controlled at 12°C/min, and the sintering time is 3-4 hours. That is, the lithium fluoride-modified manganese silicate lithium battery positive electrode material having a layered composite structure is obtained.

Another aspect of the present invention provides a modified lithium battery positive electrode material positive electrode prepared by the above preparation method.

Still another aspect of the present invention provides a lithium battery including the above positive electrode.

Yet another aspect of the present invention provides a battery pack comprising the above-mentioned lithium battery, the battery pack is used as a power source for medium and large devices, and the medium and large devices are selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles and systems for power storage.

A modified lithium battery positive electrode material, a preparation method and a lithium battery containing the same according to the present invention, compared with the prior art, its outstanding features and excellent effects are:

Use lithium fluoride and lithium manganese silicate for layered composite, improve the conductivity of lithium manganese silicate positive electrode, reduce the electrode/electrolyte interface impedance, improve electron mobility, and the lithium fluoride layer structure is stable, which can inhibit lithium manganese silicate The deformation and structural collapse of the material during lithium ion intercalation improve cycle performance.

Detailed ways

In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be described in detail below. Apparently, the described embodiments are only some of the embodiments of the present invention, but not all of them. Based on the embodiments of the present invention, all other implementations obtained by persons of ordinary skill in the art without making creative efforts fall within the protection scope of the present invention.

In a specific embodiment X, a modified lithium battery positive electrode material provided by the present invention, its preparation method comprises:

Step A, in the aqueous solution containing lithium hydroxide with a concentration of 1.2mol/L, add manganese acetate with a concentration of 1.2mol/L, stir, filter, and dry to obtain lithium salt-manganese salt solid particles, the lithium salt, The molar ratio of manganese salt is 1: 2;

Step B. Mix the lithium salt-manganese salt solid particles obtained in step A with amorphous silicon oxide at a molar ratio of 3:1, add gluconic acid, and calcinate at 850° C. for 8 hours under an inert atmosphere to obtain solid particles; Wash to remove unreacted lithium salt and manganese salt, filter and dry to obtain the lithium manganese silicate;

Step C, weighing lithium hydroxide and ammonium fluoride according to the molar ratio of 1:1.2, adding an organic solvent to prepare a mixed solution with a volume ratio of 1:25, and stirring on a magnetic stirrer for 2 hours;

Step D, centrifuge the solution after the reaction in step C, the speed of the centrifuge is 6000r/min, the centrifugation time is 20 minutes, and a white precipitate is obtained, and the obtained precipitate is dried at 80°C until the water content is less than 5%, and a white precipitate is obtained. Powder;

Step E. React the white powder obtained in step D at 200°C for 3 hours under the protection of an inert gas. After the reaction, raise the temperature of the furnace to 400°C and use a high-purity inert gas as a carrier gas to remove excess fluorine after the reaction. ammonium chloride, and the incubation time was 4 hours to obtain the lithium fluoride;

Step F, the lithium manganese silicate obtained in step B and the lithium fluoride obtained in step E are pressed into tablets at 0.5MP and 60°C by hot pressing, wherein the thickness of the lithium manganese silicate is 2.0 mm. The thickness of the lithium tablet is 0.5mm. The two kinds of sheet-shaped green bodies are stacked up and down to form a multi-layer laminated green body, and then moved into an isostatic press to form a whole; finally, the sintering temperature is 400°C. Using high-purity inert gas as the carrier gas, the heating rate is controlled at 12°C/min, and the sintering time is 4 hours to obtain lithium fluoride-modified lithium manganese silicate with a layered composite structure.

In a specific embodiment Y, a modified lithium battery positive electrode material provided by the present invention, its preparation method comprises:

Step A, in the aqueous solution that the concentration of lithium carbonate solution is 2.0mol/L, add the manganese acetate that concentration is 1.0mol/L, obtain lithium salt-manganese salt solid particle after stirring, filtering, drying, described lithium salt, manganese The molar ratio of salt is 1:1;

Step B. Mix the lithium salt-manganese salt solid particles obtained in step A with tetraethyl orthosilicate at a molar ratio of 3:1, add citric acid, and calcinate at 900°C for 5 hours under an inert atmosphere to obtain solid particles ; Pickling to remove unreacted lithium salts and manganese salts, filtering and drying to obtain the lithium manganese silicate;

Step C, weighing lithium hydroxide and ammonium fluoride according to the molar ratio of 1:1.4, adding an organic solvent to prepare a mixed solution with a volume ratio of 1:30, and stirring on a magnetic stirrer for 3 hours;

Step D, centrifuge the solution after the reaction in step C, the speed of the centrifuge is 5000r/min, and the centrifugation time is 20 minutes to obtain a white precipitate, and dry the obtained precipitate at 90°C until the water content is less than 5%, to obtain a white Powder;

Step E. React the white powder obtained in step D at 200°C for 4 hours under the protection of an inert gas. After the reaction, raise the temperature of the furnace to 400°C, and use high-purity inert gas as the carrier gas to remove excess fluorine after the reaction. ammonium chloride, the incubation time was 3 hours to obtain the lithium fluoride;

Step F, the lithium manganese silicate obtained in step B and the lithium fluoride obtained in step E are pressed into tablets at 0.5MP and 65°C by hot pressing, wherein the thickness of the lithium manganese silicate is 1.8 mm, and the fluoride The thickness of the lithium tablet is 0.6mm. The two kinds of sheet-shaped green bodies are stacked up and down to form a multi-layer laminated green body, and then pressed into an isostatic press to form a whole; finally, the sintering temperature is 400°C. Using high-purity inert gas as the carrier gas, the heating rate is controlled at 12°C/min, and the sintering time is 3 hours to obtain lithium fluoride-modified lithium manganese silicate with a layered composite structure.

In a specific embodiment Z, a modified lithium battery positive electrode material provided by the present invention, its preparation method comprises:

Step A, in the aqueous solution that the concentration of lithium acetate solution is 2.5mol/L, add the manganese acetate that concentration is 0.8mol/L, obtain lithium salt-manganese salt solid particle after stirring, filtering, drying, described lithium salt, manganese The molar ratio of salt is 2:1;

Step B, mixing the lithium salt-manganese salt solid particles obtained in step A with tetraethyl orthosilicate in a molar ratio of 3:1, adding oxalic acid, and calcining at 900°C for 6 hours under an inert atmosphere to obtain solid particles; Pickling to remove unreacted lithium salts and manganese salts, filtering and drying to obtain the lithium manganese silicate;

Step C, weighing lithium hydroxide and ammonium fluoride according to the molar ratio of 1:1.5, adding an organic solvent to prepare a mixed solution with a volume ratio of 1:50, and stirring on a magnetic stirrer for 4 hours;

Step D, centrifuge the solution after the reaction in step C, the speed of the centrifuge is 5000r/min, and the centrifugation time is 20 minutes to obtain a white precipitate, which is dried at 100°C until the water content is less than 5%, to obtain a white Powder;

Step E. React the white powder obtained in step D at 200°C for 4 hours under the protection of an inert gas. After the reaction, raise the temperature of the furnace to 400°C, and use high-purity inert gas as the carrier gas to remove excess fluorine after the reaction. ammonium chloride, and the incubation time was 4 hours to obtain the lithium fluoride;

Step F, the lithium manganese silicate obtained in step B and the lithium fluoride obtained in step E are pressed into tablets at 0.5MP and 70°C by hot pressing, wherein the thickness of the lithium manganese silicate is 1.5mm, and the fluoride The thickness of the lithium tablet is 0.8mm. The two kinds of sheet-shaped green bodies are stacked up and down to form a multi-layer laminated green body, and then placed in an isostatic press to form a whole; finally, the sintering temperature is 400°C. Using high-purity inert gas as the carrier gas, the heating rate is controlled at 12°C/min, and the sintering time is 3 hours to obtain lithium fluoride-modified lithium manganese silicate with a layered composite structure.

In comparative example M, its preparation method comprises:

Step A, in the aqueous solution containing lithium hydroxide with a concentration of 1.2mol/L, add manganese acetate with a concentration of 1.2mol/L, stir, filter, and dry to obtain lithium salt-manganese salt solid particles, the lithium salt, The molar ratio of manganese salt is 1: 2;

Step B. Mix the lithium salt-manganese salt solid particles obtained in step A with amorphous silicon oxide at a molar ratio of 3:1, add gluconic acid, and calcinate at 850° C. for 8 hours under an inert atmosphere to obtain solid particles; Wash to remove unreacted lithium salt and manganese salt, filter and dry to obtain the lithium manganese silicate;

Step C. The lithium manganese silicate obtained in step B is pressed into a tablet under the condition of 0.5MP and 60°C by hot pressing, wherein the thickness of the lithium manganese silicate is 2.0mm. Layered to form a multi-layer green body, and then moved to an isostatic press to form a whole; finally, the sintering temperature is 400°C, with high-purity inert gas as the carrier gas, and the heating rate is controlled at 12°C/min. The sintering time 4 hours is the layered lithium manganese silicate.

In comparative example N, its preparation method comprises:

Step A, in the aqueous solution containing lithium hydroxide with a concentration of 1.2mol/L, add manganese acetate with a concentration of 1.2mol/L, stir, filter, and dry to obtain lithium salt-manganese salt solid particles, the lithium salt, The molar ratio of manganese salt is 1: 2;

Step B. Mix the lithium salt-manganese salt solid particles obtained in step A with amorphous silicon oxide at a molar ratio of 3:1, add gluconic acid, and calcinate at 850° C. for 8 hours under an inert atmosphere to obtain solid particles; Wash to remove unreacted lithium salt and manganese salt, filter and dry to obtain the lithium manganese silicate;

Step C, weighing lithium hydroxide and ammonium fluoride according to the molar ratio of 1:1.2, adding an organic solvent to prepare a mixed solution with a volume ratio of 1:25, and stirring on a magnetic stirrer for 2 hours;

Step D, centrifuge the solution after the reaction in step C, the speed of the centrifuge is 6000r/min, the centrifugation time is 20 minutes, and a white precipitate is obtained, and the obtained precipitate is dried at 80°C until the water content is less than 5%, and a white precipitate is obtained. Powder;

Step E. React the white powder obtained in step D at 200°C for 3 hours under the protection of an inert gas. After the reaction, raise the temperature of the furnace to 400°C and use a high-purity inert gas as a carrier gas to remove excess fluorine after the reaction. ammonium chloride, and the incubation time was 4 hours to obtain the lithium fluoride;

Step F, the lithium manganese silicate obtained in step B and the lithium fluoride obtained in step E are uniformly mixed according to the mass ratio that the tablet thickness of lithium manganese silicate is 2.0mm, and the tablet thickness of lithium fluoride is 0.5mm. MP, tablet molding under the condition of 60°C, the sheet-shaped green body is laminated up and down to form a multi-layer laminated green body, and then moved into an isostatic press to form a whole; finally, the sintering temperature is 400°C, with High-purity inert gas is used as the carrier gas, the heating rate is controlled at 12°C/min, and the sintering time is 4 hours to become a composite cathode material of lithium fluoride and manganese lithium silicate with a layered structure.

In addition, Example X, Example Y and Example Z and Comparative Example M and Comparative Example N in this application were prepared into electrode sheets and assembled for battery testing. The test results of various indicators are shown in the table below.

Table 1 is the first Coulombic efficiency index comparison of Example X, Example Y and Example Z and Comparative Example M and Comparative Example N prepared into electrode sheets and assembled into batteries:

project Comparative Example M Comparative example N Example X Example Y Example Z first coulombic efficiency 81.7% 87.5% 93.1% 91.3% 89.6%

From the data analysis in Table 1, it can be seen that the lithium fluoride-modified lithium manganese silicate with a layered composite structure prepared in Example X has the best cycle performance of electrode sheets and assembled batteries. Example Y and Example Z is equivalent to its performance, but comparative example M, comparative example N are quite different from the performance test results of the present invention.

Table 2 is the comparison of the test indicators of the prepared electrode sheets and assembled batteries of Example X, Example Y and Example Z and Comparative Example M and Comparative Example N:

project Comparative Example M Comparative example N Example X Example Y Example Z First discharge specific capacity 230mAh/g 230mAh/g 238mAh/g 235mAh/g 230mAh/g Capacity retention after 50 cycles 78.9% 86.1% 96.9% 96.2% 95.3% Capacity retention after 200 cycles 70.5% 78.3% 92.2% 92.5% 91.6% magnification 1C 1C 1C 1C 1C

From the data analysis in Table 2, it can be seen that the lithium fluoride-modified lithium manganese silicate with a layered composite structure prepared in Example X has the best cycle performance of electrode sheets and assembled batteries. Z is equivalent to its performance, but comparative example M, comparative example N are quite different from the performance test results of the present invention.

The above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Anyone skilled in the art can easily think of changes or substitutions within the technical scope disclosed in the present invention. Should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be determined by the protection scope of the claims.

Claims (9)

1. A modified lithium battery positive electrode material, characterized in that, the positive electrode material is lithium manganese silicate that uses a fluorine-containing inorganic material to carry out layered compounding, and the fluorine-containing inorganic material is lithium fluoride; The positive electrode material is prepared by the following preparation method: Step A, adding soluble manganese salt to the aqueous solution containing lithium salt, stirring, filtering, and drying to obtain lithium salt-manganese salt solid particles, the molar ratio of lithium salt and manganese salt is 1:2 to 2:1; Step B, after mixing the lithium salt-manganese salt solid particles obtained in step A with the silicon source at a molar ratio of 3:1, adding a carbon source, and calcining at 850-900°C for 5-8 hours under an inert atmosphere to obtain solid particles ; Pickling to remove unreacted lithium salts and manganese salts, filtering and drying to obtain the lithium manganese silicate; Step C, weigh lithium hydroxide and ammonium fluoride according to the molar ratio of 1:1.2 to 1:1.5, add an organic solvent to prepare a mixed solution with a volume ratio of 1:25 to 1:50, and stir on a magnetic stirrer for 2 ~4 hours; Step D, centrifuging the solution after the reaction in step C to obtain a white precipitate, drying the obtained precipitate at 80-100°C until the water content is less than 5%, to obtain a white powder; Step E. React the white powder obtained in step D at 200°C for 3 to 4 hours under the protection of an inert gas. After the reaction, raise the temperature of the furnace to 400°C. ammonium fluoride, and the holding time is 3 to 4 hours to obtain the lithium fluoride; In step F, the lithium manganese silicate obtained in step B and the lithium fluoride obtained in step E are pressed into tablets at 0.5 MP and 60-70° C., wherein the thickness of the lithium manganese silicate is 1.5-2.0 mm, the thickness of the tablet of lithium fluoride is 0.5-0.8mm, the two kinds of sheet-shaped green bodies are stacked up and down to form a multi-layer green body, and then moved into an isostatic press to form a whole; Sintered into a lithium fluoride modified lithium manganese silicate with a layered composite structure. 2. The modified lithium battery cathode material according to claim 1, characterized in that, in step A, Described lithium salt is the one in lithium hydroxide, lithium carbonate or lithium acetate; The manganese salt is one of manganese acetate or manganese nitrate; The concentration of the lithium salt solution is 1.2-2.5 mol/L, and the concentration of the manganese salt solution is 0.8-1.2 mol/L. 3. The modified lithium battery cathode material according to claim 1, characterized in that, in step B, The silicon source is amorphous silicon oxide or tetraethyl orthosilicate; The carbon source is one of gluconic acid, citric acid or oxalic acid or a mixture thereof. 4. The modified lithium battery cathode material according to claim 1, characterized in that, in step D, The speed of the centrifuge is 5000r/min-6000r/min, and the centrifugation time is 20 minutes. 5. The modified lithium battery cathode material according to claim 1, characterized in that, in step F, The sintering temperature is 400°C, the high-purity inert gas is used as the carrier gas, the heating rate is controlled at 12°C/min, and the sintering time is 3 to 4 hours, the lithium fluoride modified silicic acid with a layered composite structure is obtained Manganese lithium battery cathode material. 6. A lithium battery positive electrode, said positive electrode comprising the modified lithium battery positive electrode material according to claim 1. 7. A lithium battery comprising the positive electrode of claim 6. 8. A lithium battery pack comprising the battery of claim 7. 9. The battery pack according to claim 8, which is used as a power source for a medium to large device selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles and system.