Lithium vanadium phosphate-lithium iron phosphate-lithium vanadate composite material, preparation method thereof, positive pole piece and battery

Abstract

The invention belongs to the technical field of battery materials, and particularly relates to a lithium vanadium phosphate-lithium iron phosphate-lithium vanadate composite material, a preparation method thereof, a positive pole piece and a battery. The lithium vanadium phosphate-lithium iron phosphate-lithium vanadate composite material has a general formula of [xLi < 3 > V < 2 > (PO4) < 3-y > Li < 3 > Fe < 2 > (PO4) < 3 >] (z) LiV < 3 > O < 8 >, wherein z / (x + y + z) is equal to 0.1-0.3, and x / y is equal to 2-10. The proportion of the precursor can be freely adjusted, the preparation method of the composite material is simple, the process is relatively mature, the controllability of the product structure and the yield is high, the raw materials used in the method are all bulk chemicals, the raw materials are easy to obtain, large-scale production is easy to achieve, and the application prospect is wide. According to the obtained lithium iron phosphate-lithium vanadate-lithium vanadium phosphate composite material, firstly, balance adjustment between performance and cost can be realized, and the cost, the energy density, the rate and the cycle performance are synergistically improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials, and particularly relates to a lithium vanadium phosphate-lithium iron phosphate-lithium vanadate composite material, a preparation method thereof, a positive electrode sheet and a battery. Background Art

[0002] Lithium vanadium phosphate (Li 3 V 2 (PO 4 ) 3 ) is a cathode material based on phosphate polyanions. It has a relatively large lithium ion diffusion channel, can well realize the insertion and extraction reaction of lithium ions, and has high ionic conductivity; it has three voltage platforms within 3.0 - 4.3V, and the theoretical capacity is 132 mAh / g when two lithium ions are inserted and extracted, and it also has excellent rate performance and cycle stability; however, the overall price of vanadium compounds is relatively high, and the reversible capacity of lithium vanadium phosphate is limited, which restricts the application of lithium vanadium phosphate in cathode materials. Lithium iron phosphate (Li 3 Fe 2 (PO 4 ) 3 ) has the characteristics of low cost, relatively excellent cycle performance and rate performance, but the specific capacity of the lithium iron phosphate cathode material is only 115 mAh / g, and the relatively low specific capacity also restricts its application. Lithium vanadate (LiV 3 O 8 ) is characterized by a relatively high energy density and strong overall adaptability. The disadvantages are that the price of vanadium compounds is relatively high and the rate performance is poor.

[0003] Developing new energy batteries that take into account cost, rate performance and energy density has always been the direction that scientific research personnel strive to develop. Developing a cathode material with good cycle performance and high energy density is the key breakthrough to meet the requirements of power batteries.

[0004] Based on this, the technical solution of the present invention is proposed. Summary of the Invention

[0005] In order to solve the problems existing in the prior art, the present invention provides a lithium vanadium phosphate-lithium iron phosphate-lithium vanadate composite material, which can effectively adjust and balance the preparation cost, energy density, rate and cycle performance.

[0006] The solution of the present invention is to provide a lithium vanadium phosphate-lithium iron phosphate-lithium vanadate composite material, which has the general formula [xLi 3 V 2 (PO 4 ) 3 -yLi 3 Fe 2 (PO 4 ) 3@zLiV 3 O 8 ; wherein:

[0007] z / (x + y + z) = 0.1 - 0.3, x / y = 2 - 10.

[0008] More specifically, lithium vanadium phosphate and lithium iron phosphate have a NASICON structure and form a solid solution ([xLi 3 V 2 (PO 4 ) 3 -yLi 3 Fe 2 (PO 4 ) 3 )), and the solid solution of lithium vanadium phosphate and lithium iron phosphate is coated on the outside ("@" indicates coating) with lithium vanadate ([zLiV 3 O 8 ).

[0009] Preferably, z / (x + y + z) = 0.2 - 0.3, x / y = 4 - 8. The preferred ratio is beneficial to synergistically improve capacity, rate performance, and cycle performance.

[0010] Preferably, the outer layer of the lithium vanadium phosphate-lithium iron phosphate-lithium vanadate composite material is coated with a carbon layer, and the mass of the carbon layer is 1 - 5% of the mass of the lithium vanadium phosphate-lithium iron phosphate-lithium vanadate composite material. The preferred carbon layer is beneficial to promoting the construction of an ion / electron network transmission channel.

[0011] To facilitate the understanding of the present invention, the lithium vanadium phosphate-lithium iron phosphate-lithium vanadate composite material is explained as follows:

[0012] In this composite material, lithium vanadium phosphate plays a framework role and is partially replaced by lithium iron phosphate in a solid solution form to form a composite framework of lithium vanadium phosphate and lithium iron phosphate. Lithium iron phosphate maintains the stability of the structure within the replacement range. The composite framework ensures high ionic conductivity, excellent rate performance, and cycle stability. Lithium iron phosphate balances the cost of lithium vanadium phosphate and appropriately introduces lattice defects through iron, balancing the problem of low electron mobility caused by the electronic structure of vanadium ions. Lithium vanadate, as a coating layer, embeds on the composite particles of lithium vanadium phosphate and lithium iron phosphate through the sintering process across carbon particles on the surface, forming a certain degree of surface solid solution interface. While further balancing the cost, it further brings an increase in energy density. The coating layer and the surface solid solution interface build an energy density gradient on the outer layer of the composite particles of lithium vanadium phosphate and lithium iron phosphate, which is beneficial to the rapid transmission of ions during the cycling process. The relatively low coating amount of lithium vanadate also brings a synergistic optimization and improvement of capacity and rate performance. The carbon layer (C) on the one hand is beneficial to synergistically improving the electrical conductivity and enhancing the overall electronic conductivity of the material, and on the other hand promotes the stability of the lithium vanadate coating layer.

[0013] Based on the same inventive concept, the present invention further provides a method for preparing a lithium vanadium phosphate-lithium iron phosphate-lithium vanadate composite material, and the preparation method includes the following steps:

[0014] (1) Configure a lithium source, a vanadium source, and a phosphorus source according to a molar ratio of Li:V:P = (3 - 3.1):2:3 to obtain a lithium vanadium phosphate precursor slurry; configure a lithium source, an iron source, and a phosphorus source according to a molar ratio of Li:Fe:P = (3 - 3.05):2:3 to obtain a lithium iron phosphate precursor slurry; mix the lithium vanadium phosphate precursor slurry and the lithium iron phosphate precursor slurry evenly according to the theoretical stoichiometric ratio, grind and dry to obtain a first precursor powder;

[0015] (2) Sinter the first precursor powder for the first time and keep it warm in an inert atmosphere to obtain a first sintered powder;

[0016] (3) Configure a slurry of the first sintered powder with a lithium source and a vanadium source according to the theoretical stoichiometric ratio, and also add an oxidizing agent and a carbon source according to the theoretical stoichiometric ratio and mix evenly, grind and dry to obtain a second precursor powder; wherein, the molar ratio of the lithium source to the vanadium source is Li:V = (3 - 3.1):3;

[0017] (4) Sinter the second precursor powder for the second time and keep it warm in an inert atmosphere to obtain the lithium vanadium phosphate-lithium iron phosphate-lithium vanadate composite material.

[0018] In this step, the lithium source can be selected from lithium dihydrogen phosphate, lithium carbonate, lithium hydroxide, lithium oxide, lithium oxalate, lithium acetate, etc., or a combination of two or more of them; more preferably lithium carbonate; 3 O 8 To provide oxygen ions for the formation of LiV 3 O 8 It should be noted that the vanadium source here must be a 5-valent vanadium ion, which is consistent with the valence state of vanadium in LiV 3 O 8 The main purpose of adding an oxidizing agent here is to inhibit the reduction reaction of 5-valent vanadium ions during the formation of LiV

[0019] Preferably, the lithium source includes one or a combination of two or more of lithium dihydrogen phosphate, lithium carbonate, lithium hydroxide, lithium oxide, lithium oxalate, lithium acetate, etc.; more preferably lithium carbonate;

[0020] And / or, the iron source includes one or a combination of two or more of iron phosphate, iron oxalate, iron oxide, and iron hydroxide; more preferably iron phosphate;

[0021] And / or, the phosphorus source includes one or a combination of two or more of phosphoric acid, ammonium dihydrogen phosphate, and lithium dihydrogen phosphate; more preferably phosphoric acid;

[0022] And / or, the vanadium source includes one or a combination of two or more of vanadium pentoxide, ammonium polyvanadate, ammonium metavanadate, and vanadium trioxide; more preferably vanadium pentoxide;

[0023] And / or, the oxidant includes one or both of oxalic acid and phosphoric acid;

[0024] And / or, the carbon source includes one or a combination of two or more of glucose, sucrose, citric acid, polyethylene glycol, polyvinyl alcohol, graphene, and carbon nanotubes; more preferably glucose.

[0025] Preferably, in steps (1) and (3), the particle size D50 of the particles in the slurry after grinding is below 500 nm; the grinding step promotes solid solution and uniform coating between the materials;

[0026] And / or, in steps (1) and (3), the solvent for preparing the slurry is ethanol and / or deionized water, and the solid content of the slurry is 25-40%; which is beneficial to dispersion, reaction, grinding, and drying;

[0027] And / or, in steps (1) and (3), the drying method is spray drying.

[0028] Preferably, in step (2), the temperature of the first sintering is 700-900 °C, and the heat preservation time is 2-20 h; more preferably, the sintering temperature is 800 °C, and the heat preservation time is 10 h;

[0029] And / or, in step (4), the temperature of the second sintering is 250-350 °C, and the heat preservation time is 2-20 h.

[0030] Based on the same technical concept, the present invention further provides a positive electrode sheet, and the positive electrode sheet includes the lithium vanadium phosphate-lithium iron phosphate-lithium vanadate composite material.

[0031] Preferably, the mass ratio of the lithium vanadium phosphate-lithium iron phosphate-lithium vanadate composite material in the positive electrode sheet is 80-95%.

[0032] Based on the same technical concept, the present invention further provides a battery, and the battery includes the lithium vanadium phosphate-lithium iron phosphate-lithium vanadate composite material or the positive electrode sheet.

[0033] The beneficial effects of the present invention are as follows:

[0034] It is possible to freely adjust the proportion of precursors (including lithium vanadium phosphate precursor slurry, lithium iron phosphate precursor slurry, first precursor powder, etc.). This composite material preparation method is simple, the process is relatively mature, the controllability of the product structure and yield is high, and all the chemicals used in this method are bulk chemicals, with strong availability of raw materials, easy to achieve large-scale production, and relatively wide application prospects. The obtained lithium iron phosphate-lithium vanadate-lithium vanadium phosphate composite material can first achieve a balance adjustment between performance and cost, and achieve a synergistic improvement in cost, energy density, rate performance, and cycle performance.

[0035] The positive electrode sheet prepared by using the lithium vanadium phosphate-lithium iron phosphate-lithium vanadate composite material has a specific capacity of 150 - 200 mAh / g when evaluated at a current density of 0.1C in the voltage range of 2 - 4.3V, and a capacity retention rate of 98% after 100 cycles at 1C. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0037] Figure 1 It is the XRD pattern of the composite material obtained in Example 1.

[0038] Figure 2 It is the SEM pattern of the composite material obtained in Example 1.

[0039] Figure 3 It is the charge-discharge curve of the battery obtained in Example 1. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0040] To make the objectives, technical solutions, and advantages of the present invention clearer, the following will describe the technical solutions of the present invention in detail. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

[0041] Example 1

[0042] This example provides a preparation method for a lithium vanadium phosphate-lithium iron phosphate-lithium vanadate composite material. The preparation method includes the following steps:

[0043] (1) Lithium carbonate, ammonium metavanadate, iron oxalate, phosphoric acid, and sucrose are used as the lithium source, vanadium source, iron source, phosphorus source, and carbon source respectively.

[0044] According to the molar ratio Li:V:P = 3.1:2:3, the lithium source, vanadium source, and phosphorus source are configured, and are successively dissolved in deionized water, and stirred at room temperature to obtain a lithium vanadium phosphate precursor slurry with a solid content of 30%.

[0045] According to the molar ratio Li:Fe:P = 3.05:2:3, the lithium source, iron source, and phosphorus source are configured, and are successively dissolved in deionized water and mixed, and stirred at room temperature to obtain a lithium iron phosphate precursor slurry with a solid content of 30%.

[0046] The lithium vanadium phosphate precursor slurry and the lithium iron phosphate precursor slurry are mixed according to the molar ratio V:Fe = 6:1 and stirred for more than 30 minutes, and then ground by a sand mill. After grinding, the particle size D50 in the slurry is controlled to be below 500 nm. Finally, the slurry is spray-dried to obtain a first precursor powder.

[0047] (2) The first precursor powder is placed under an inert gas (such as nitrogen) and sintered at 800 °C for 10 h to obtain a first sintered powder.

[0048] (3) According to the molar ratio, the first sintered powder:Li:V = 7:3.1:3, the precursor first-sintered powder, lithium source, and vanadium source are configured, and oxalic acid is added according to the theoretical composite material mass (the addition amount is calculated according to twice the number of hydrogen ions in oxalic acid corresponding to the number of oxygen atoms in the lithium source and vanadium source, and the purpose is to avoid oxygen atoms participating in the reduction of vanadium lithium ions. If the addition amount of oxalic acid is inappropriate, the purity of lithium vanadate may be reduced), and sucrose is added at 5% of the theoretical mass of the composite material. The above raw materials are successively dissolved in deionized water and mixed, stirred evenly at room temperature, then ground by a sand mill. After grinding, the particle size D50 in the slurry is controlled to be below 500 nm and spray-dried to obtain a second precursor powder.

[0049] (4) The second precursor powder is placed under an inert gas and sintered at 500 °C for 5 h, and finally naturally cooled to obtain [0.6Li 3 V 2 (PO4) 3 -0.1Li 3 Fe 2 (PO 4 ) 3 @0.3LiV 3 O 8 。

[0050] Based on the same technical concept, this embodiment further provides a method for preparing a positive electrode plate. The specific method is as follows: Take [0.6Li 3 V 2(PO4) 3 -0.1Li 3 Fe 2 (PO 4 ) 3 @0.3LiV 3 O 8 , using conductive carbon black SP as the conductive agent and NMP as the binder, and mixing them in a ratio of 90:5:5. After uniform mixing, the positive electrode sheet is made on the aluminum foil.

[0051] Based on the same technical concept, this embodiment further provides a method for preparing a battery. The specific method is as follows: After the positive electrode sheet is prepared, then use a lithium sheet as the negative electrode, PP as the separator, and 1mol / L LiPF 6 / EC:DMC (volume ratio 1:1) as the electrolyte, and assemble it into a CR2016 coin cell.

[0052] Example 2

[0053] Prepare the relevant solutions according to Example 1. The difference is that [0.5Li 3 V 2 (PO 4 ) 3 -0.25Li 3 Fe 2 (PO 4 ) 3 @0.25LiV 3 O 8 composite material is obtained according to different raw material ratios.

[0054] Example 3

[0055] Prepare the relevant solutions according to Example 1. The difference is that [0.67Li 3 V 2 (PO 4 ) 3 -0.07Li 3 Fe 2 (PO 4 ) 3 @0.26LiV 3 O 8 composite material is obtained according to different raw material ratios.

[0056] Comparative Example 1

[0057] Prepare the relevant solutions according to Example 1. The difference is that [0.3Li 3 V 2 (PO 4 ) 3 -0.3Li 3Fe 2 (PO 4 ) 3 -[0.4LiV 3 O 8 @C composite material.

[0058] Comparative Example 2

[0059] Prepare the relevant solution according to Example 1, the difference is that, according to different raw material ratios, [0.2Li 3 V 2 (PO 4 ) 3 -0.2Li 3 Fe 2 (PO 4 ) 3 -[0.6LiV 3 O 8 @C composite material.

[0060] Comparative Example 3

[0061] Prepare the relevant solution according to Example 1, the difference is that, according to different raw material ratios, [0.3Li 3 V 2 (PO 4 ) 3 -0.4Li 3 Fe 2 (PO 4 ) 3 -[0.3LiV 3 O 8 @C composite material.

[0062] Comparative Example 4

[0063] Prepare the relevant solution according to Example 1, the difference is that, according to different raw material ratios, [0.4Li 3 V 2 (PO 4 ) 3 -0.3Li 3 Fe 2 (PO 4 ) 3 -[0.3LiV 3 O 8 @C composite material.

[0064] Comparative Example 5

[0065] Prepare the first sintered powder according to the method of Example 1.

[0066] Lithium source and vanadium source were configured according to the molar ratio of lithium:vanadium = 3.1:3, the amount of oxalic acid added was calculated theoretically, and the carbon source was added in an amount of 5% of the theoretically obtained mass of lithium vanadate. The above raw materials were successively dissolved in deionized water and mixed, stirred at room temperature to obtain a slurry, and then the slurry was ground by a sand mill. After grinding, the particle size D50 was controlled to be below 500 nm. Then the slurry was spray-dried to obtain precursor powder, and the precursor powder was sintered at 500 °C for 5 h under an inert gas to obtain lithium vanadate sintered powder.

[0067] The first sintered powder and the lithium vanadate sintered powder were mixed according to the molar ratio of lithium iron phosphate-lithium vanadate phosphate-lithium vanadate in Example 1 to obtain a composite material, and the battery was assembled by the same method as in Example 1.

[0068] Verification example

[0069] The above examples and comparative examples were subjected to constant current charge and discharge tests at a voltage of 3 - 4.3 V with a current of 0.1 C, and the capacity retention rate was measured at 1 C for 50 cycles. The results are shown in Table 1.

[0070] Table 1 Electrical property results

[0071]

[0072]

[0073] Figure 1 ,, Figure 2 and Figure 3 are respectively the XRD pattern, SEM pattern and charge-discharge curve of Example 1. It can be seen from the XRD that the material contains lithium iron phosphate, lithium vanadate phosphate and lithium vanadate phases. The phases of lithium vanadate phosphate and lithium iron phosphate have overlapping diffraction peaks, indicating that they have a basic crystal form and unit cell structure, and the two form a solid solution framework. The diffraction peaks in the XRD results are relatively high, indicating that the synthesized crystal material shows good crystallinity; from the scanning electron microscope image, the composite material is small balls with a size of 2 - 10 μm, and the crystalline phase is generally uniform. From Figure 3 the charge-discharge curve, it can be seen that the material has three voltage platforms at 3.5, 3.6 and 4.1 V respectively, its charge specific capacity reaches 175 mAh / g, and the first efficiency also reaches more than 93%.

[0074] It can be seen from Examples 1, 2, 3 and Comparative Examples 1, 2 in Table 1 that as the relative content of lithium vanadate phosphate and lithium iron phosphate decreases, lithium vanadate contributes more charge and discharge capacity, but too much lithium vanadate leads to a significant decrease in rate performance.

[0075] Comparing Comparative Example 3 with Comparative Example 4 against the previous groups, it can be seen that as the amount of lithium iron phosphate increases, the overall cycling performance decreases significantly, and the capacity retention rate drops to about 90%; the main reason is that in the lithium vanadium phosphate system, the valence states of vanadium and iron are different. When the addition amount of lithium iron phosphate is too large, the incompatibility of the whole system will occur due to the different valence states between lithium iron phosphate and lithium vanadium phosphate and lithium vanadate; when the doping amount of lithium iron phosphate is relatively small compared to lithium vanadium phosphate in general, it is more conducive to the improvement of performance and effectively reduces the synthesis cost of the overall composite material.

[0076] According to Comparative Example 5, after obtaining the solid solution framework structure of lithium iron phosphate and lithium vanadium phosphate, it is difficult to form the coated surface solid solution interface of lithium vanadate on the surface of the composite particles of lithium iron phosphate and lithium vanadium phosphate of the present invention by directly mixing with lithium vanadate particles through powder. It is impossible to build a stable gradient structure and a good transmission channel, and it is impossible to effectively improve the performance.

[0077] The above is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of changes or substitutions, which should all be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the said claims.

Claims

1. A lithium vanadium phosphate-lithium iron phosphate-lithium vanadate composite material, characterized in that: It has the general formula [xLi3V2(PO4)3-yLi3Fe2(PO4)3]@zLiV3O8; wherein: z / (x+y+z)=0.1~0.3, x / y=2~10.

2. The lithium vanadium phosphate-lithium iron phosphate-lithium vanadate composite material according to claim 1, characterized in that: z / (x+y+z)=0.2~0.3, x / y=4~8.

3. The lithium vanadium phosphate-lithium iron phosphate-lithium vanadate composite material according to claim 1, characterized in that: The outer layer of the lithium vanadium phosphate-lithium iron phosphate-lithium vanadate composite material is coated with a carbon layer, and the mass of the carbon layer is 1-5% of the mass of the lithium vanadium phosphate-lithium iron phosphate-lithium vanadate composite material.

4. The method for preparing the lithium vanadium phosphate-lithium iron phosphate-lithium vanadate composite material according to any one of claims 1 to 3, characterized in that: The preparation method comprises the following steps: (1) a lithium source, a vanadium source, and a phosphorus source are configured according to a molar ratio of Li:V:P=(3-3.1):2:3 to obtain a lithium vanadium phosphate precursor slurry; a lithium source, an iron source, and a phosphorus source are configured according to a molar ratio of Li:Fe:P=(3-3.05):2:3 to obtain a lithium iron phosphate precursor slurry; the lithium vanadium phosphate precursor slurry and the lithium iron phosphate precursor slurry are uniformly mixed, and the first precursor powder is obtained after grinding and drying; (2) sintering the first precursor powder for the first time under an inert atmosphere and keeping the temperature to obtain a first sintered powder; (3) preparing a slurry with the first sintered powder, a lithium source and a vanadium source, adding an oxidant and a carbon source, mixing evenly, grinding and drying to obtain a second precursor powder; wherein the molar ratio of the lithium source to the vanadium source is Li:V=(3-3.1):3; (4) Sintering the second precursor powder for the second time in an inert atmosphere and keeping the temperature constant to obtain the lithium vanadium phosphate-lithium iron phosphate-lithium vanadate composite material.

5. The method for preparing the lithium vanadium phosphate-lithium iron phosphate-lithium vanadate composite material according to claim 4, characterized in that: The lithium source includes one or a combination of two or more of lithium dihydrogen phosphate, lithium carbonate, lithium hydroxide, lithium oxide, lithium oxalate, and lithium acetate; And / or, the iron source includes one or a combination of two or more of ferric phosphate, ferric oxalate, ferric oxide, and ferric hydroxide; And / or, the phosphorus source includes one or a combination of two or more of phosphoric acid, ammonium dihydrogen phosphate, and lithium dihydrogen phosphate; And / or, the vanadium source includes one or a combination of two or more of vanadium pentoxide, ammonium polyvanadate, ammonium metavanadate, and vanadium trioxide; And / or, the oxidant comprises one or both of oxalic acid and phosphoric acid; And / or, the carbon source includes one or a combination of two or more of glucose, sucrose, citric acid, polyethylene glycol, polyvinyl alcohol, graphene, and carbon nanotubes.

6. The method for preparing the lithium vanadium phosphate-lithium iron phosphate-lithium vanadate composite material according to claim 4, characterized in that: In step (1) and step (3), the particle size D50 of the particles in the slurry after grinding is less than 500 nm; And / or, in step (1) and step (3), the solvent for preparing the slurry is ethanol and / or deionized water, and the solid content of the slurry is 25-40%; And / or, in step (1) and step (3), the drying method is spray drying.

7. The method for preparing the lithium vanadium phosphate-lithium iron phosphate-lithium vanadate composite material according to claim 4, characterized in that: In step (2), the temperature of the first sintering is 700-900° C., and the holding time is 2-20 hours; And / or, in step (4), the temperature of the second sintering is 250-350° C., and the insulation time is 2-20 hours.

8. A positive electrode sheet, characterized in that: The positive electrode plate comprises the lithium vanadium phosphate-lithium iron phosphate-lithium vanadate composite material according to any one of claims 1 to 3.

9. The positive electrode sheet according to claim 8, characterized in that: The mass proportion of the lithium vanadium phosphate-lithium iron phosphate-lithium vanadate composite material in the positive electrode plate is 80-95%.

10. A battery, characterized in that: The battery comprises the lithium vanadium phosphate-lithium iron phosphate-lithium vanadate composite material according to any one of claims 1 to 3 or the positive electrode sheet according to claims 8 to 9.

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