A polyanionic sodium-ion battery cathode composite

Abstract

The application relates to a polyanion sodium ion battery positive electrode composite material, and belongs to the technical field of sodium ion batteries. The chemical expression of the positive electrode composite material is sintered by compounding and sintering of specific design carbon-doped potassium pyrophosphate iron powder and a sodium pyrophosphate iron phosphate matrix. The carbon-doped potassium pyrophosphate iron is prepared by a vacuum calcination process by using a structure control agent synthesized by p-ethylphenylthiophenol and triallylamine, and the unique space symmetry structure can chelate iron and potassium ions at the molecular level, form a uniform precursor, and produce an ultra-microstructure wrapped by an edge brittle carbide after calcination. The composite material constructs a continuous three-dimensional electron conductive network and a long-range ion channel in the NFPP matrix, forms an ion conductivity transition zone at the phase interface, significantly improves the ion migration efficiency, and effectively solves the technical bottleneck of poor high-rate performance of the NFPP material.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of sodium ion batteries, and particularly relates to a polyanion sodium ion battery positive electrode composite material. BACKGROUND

[0002] As a new emerging electrochemical energy storage technology, sodium ion batteries have shown great application potential in large-scale energy storage and low-speed electric vehicles due to their advantages of abundant raw material resources, low cost and environmental friendliness. Among the various components of sodium ion batteries, the positive electrode material is the key to determining the energy density, cycle life and safety performance. Among the many positive electrode material systems, polyanion compounds, especially sodium iron pyrophosphates (NFPP for short), have attracted much attention due to their unique advantages. The main elements of NFPP, sodium, iron and phosphorus, have a very high reserve in the earth's crust, and the raw material cost is much lower than that of cobalt and nickel in lithium ion batteries, making it have unparalleled competitiveness in the large-scale energy storage field which is extremely sensitive to cost. In addition, NFPP has a stable three-dimensional framework structure, and the volume change is small during sodium ion deintercalation, which provides it with an ultra-long cycle life. At the same time, its strong P-O covalent bond gives the material excellent thermal stability, strong anti-thermal runaway ability and outstanding safety performance. Therefore, NFPP has achieved a good balance between comprehensive performance and cost, and is praised by the industry as one of the most promising sodium ion battery positive electrode materials for industrialization.

[0003] However, the commercial application of NFPP still faces a key bottleneck: its intrinsic low ion and electron conductivity. This defect seriously limits the performance of the material under high-rate charging and discharging conditions, and the potential of the material in high-power application scenarios cannot be fully realized. To overcome this problem, existing technologies mainly proceed from two aspects: on the one hand, a conductive layer is constructed on the surface of the material by carbon coating, which is the most mature and effective method to improve the electronic conductivity at present, and can effectively reduce the interface charge transfer impedance. On the other hand, the lattice is optimized from the inside by element doping or defect engineering, for example, by introducing hetero-elements to widen the sodium ion migration channel or adjust the energy band structure, so as to improve the ion conductivity and rate performance within a certain range.

[0004] However, the existing technology system still has obvious deficiencies. Carbon coating mainly solves the problem of electronic conduction between particles, and has limited contribution to ion conduction. Traditional phase doping strategies can locally optimize the ion migration path, but it is difficult to construct a long-range and continuous ion conduction network inside the material. More seriously, when the doping concentration is too high, it will destroy the stable primary crystal structure of NFPP and cause the generation of impurities, which will have a negative impact on the capacity and structural stability of the material. Therefore, the existing technology has limited effect on improving the high-rate performance of NFPP, which has become a technical bottleneck restricting the development of NFPP as a high-power positive electrode material. SUMMARY

[0005] In order to solve the technical problems mentioned in the background art, the purpose of this invention is to provide a polyanionic sodium-ion battery cathode composite material.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A polyanionic sodium-ion battery cathode composite material, comprising sodium iron pyrophosphate (NFPP) and specially formulated carbon-doped potassium iron pyrophosphate (NFPP). The chemical formula of the composite sintered body can be represented as: ;

[0008] Therefore, the technical content of this invention includes the following two aspects:

[0009] one, Preparation

[0010] 1.1. Dissolve benzoin dimethyl ether in an ethanol-acetone mixture, add p-ethylthiophenol and triallylamine, mix well, irradiate with a mercury lamp and stir for 8-12 hours, remove the mixed solvent by rotary evaporation after the reaction is complete to obtain the structure control agent.

[0011] The molar ratio of p-ethylbenzylthiophenol and triallylamine is 3:1, and the amount of benzoin dimethyl ether is 0.15-0.22 wt% of both. The reaction mechanism is as follows: under ultraviolet irradiation, benzoin dimethyl ether and triallylamine undergo a mercapto-olefin click addition reaction.

[0012] 1.2. Potassium carbonate, ferrous sulfate, and ammonium dihydrogen phosphate are ground and premixed. A structure control agent and dimethylformamide aqueous solution are then added to the premix and ground into a slurry. The mixture is then stirred and homogenized at 60-80℃ for 15-20 hours, vacuum dried to constant weight, calcined in an oxygen-free environment, and finally ground and pulverized to obtain the desired product. .

[0013] The amount of structure control agent is 18-22 wt% of the premix.

[0014] The anaerobic roasting process is divided into two stages. The first stage has a temperature of 320-350℃, a roasting time of 3-3.5h, and a heating rate of 1-5℃ / min. The second stage has a temperature of 600-650℃, a roasting time of 5.5-7h, and a heating rate of 10-15℃ / min.

[0015] II. Preparation of Cathode Composite Materials

[0016] 2.1 Sodium dihydrogen phosphate and ferrous oxalate were mixed in a Na:Fe:P molar ratio of 4:3:4. Glucose was added to the mixture and dry-milled for premixing. Anhydrous ethanol was added and wet-milled until homogeneous. After standing for 24 hours, the mixture was dried to constant weight to prepare the composite precursor.

[0017] The amount of glucose is 3.5-4 wt% of the compound.

[0018] 2.2, the composite precursor and The mixture is mixed by dry ball milling, and after cold isostatic pressing, the mixture is sintered in an argon atmosphere, and after cooling, the mixture is crushed and ground to obtain the positive electrode composite material.

[0019] The amount of glucose is 3.5-4 wt% of the compound. The amount of glucose is 3.5-4 wt% of the compound.

[0020] The cold isostatic pressing pressure is 30-35 MPa.

[0021] The solid phase sintering temperature is 500-550 DEG C, and the time is 8-10 h.

[0022] The beneficial effects of the application are:

[0023] The application introduces an innovative design of carbon composite potassium ferric pyrophosphate (PPF) ) as a functional doping phase, which is successfully combined with the NFPP matrix to solve the inherent bottleneck of the NFPP material in electronic conductivity and ionic conductivity, and realizes the leap of high-rate electrochemical performance.

[0024] The core advantage is first derived from The unique microstructure of the material itself. In the preparation process, we innovatively use a molecule with a spatially centrosymmetric structure as a structure control agent. The sulfur and nitrogen atoms in the center of the molecule have a strong chelation effect on potassium ions and iron ions, achieving precise pre-enrichment of active elements at the molecular scale and ensuring the uniformity of the chemical composition of the final product. In the subsequent calcination process, the benzene ring system on the periphery of the molecule is carbonized to form a kind of edge brittle carbon composite. This structural characteristic makes the final product not need to undergo high-energy consumption and easy-to-introduce-defect strong mechanical crushing, but only needs to be broken by mild grinding to generate a large number of ultrafine particles composed of Crystal nucleus and edge carbon shell. These ultrafine particles not only greatly increase the contact area with the NFPP matrix, but also are more easily dispersed uniformly, laying a foundation for building a continuous conductive network throughout the electrode.

[0025] In terms of ion transmission, the application exhibits a multi-level, cross-scale synergistic enhancement mechanism. First, As a pyrophosphate, it has similar structural units and good lattice matching degree with NFPP, so it can realize excellent interface wetting and combination during solid phase sintering, forming a macroscopically dense composite structure. More importantly, the difference in the radii of potassium ions and iron ions can A large number of micropores and lattice distortions are induced inside the crystal grains. When these ultrafine particles are dispersed in the NFPP matrix, they themselves act as a "ion highway transfer station", and the pores and defects inside them provide a fast migration path for sodium ions, thereby constructing a long-range ion channel network in the NFPP matrix.

[0026] Secondly, in the sintering process, Controllable potassium-sodium ion mutual diffusion and solid-phase ion exchange occur at the phase and NFPP phase interface. Since the radius of potassium ions is larger than that of sodium ions, after diffusing into the near-surface region of the NFPP lattice, the potassium ions can effectively support the interlayer spacing of the sodium layer like "pillars", widening the migration channel of sodium ions. However, unlike traditional high-concentration bulk doping, the present application forms a potassium concentration gradient "ion conductivity transition zone" in the local area of the NFPP adjacent to the second phase by means of second phase compounding. The existence of the transition zone makes the conduction ability of sodium ions from the NFPP bulk phase with low intrinsic mobility to the composite phase interface with high ion mobility change smoothly and continuously, rather than steeply and abruptly. This ingenious design effectively reduces the interface ion accumulation effect caused by the large difference in ion conductivity between the heterogeneous materials, significantly reduces the interface ion transmission impedance, and enables sodium ions to achieve more smooth and efficient global transport from the bulk phase to the interface.

[0027] In terms of electron conduction, The in-situ carbonized layer at the edge of the particles plays a crucial role. These carbon layers are firmly combined with the core and, after compounding with the NFPP, can act as "conductive bridges" to connect individual isolated NFPP particles, forming a continuous and stable three-dimensional electron conduction network inside the entire electrode. This network and the above-mentioned ion channel network interweave and complement each other, together solving the "double low" conduction problem of NFPP materials. This effectively overcomes the limitations of existing single carbon coating or bulk doping technology, greatly improves the rate performance of the NFPP materials without sacrificing their high capacity, long life and high safety, and provides strong technical support for promoting the industrialization process of high-performance sodium ion batteries. DETAILED DESCRIPTION

[0028] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of the present application.

[0029] ​Example 1, preparation of positive electrode composite material, the specific implementation method as follows:

[0030] One, Preparation of

[0031] 1.1, according to the 3:1 mole ratio of raw materials p-ethyl benzene thiophenol and triallylamine, 0.15wt% of photoinitiator benzoin dimethyl ether, mixed with anhydrous ethanol and acetone as mixed solvent and take 3 times the mass of raw materials according to 1:1 volume ratio; first, benzoin dimethyl ether is added to the mixed solvent, then p-ethyl benzene thiophenol and triallylamine are added and mixed, irradiated with a 100W 365nm ultraviolet mercury lamp, stirred for 12h, and then the mixed solvent is removed by rotary evaporation to prepare the structure control agent.

[0032] 1.2, preparation powder, with x=0.5, using potassium carbonate, ferrous sulfate and ammonium dihydrogen phosphate as raw materials, according to K:Fe:P mole ratio of 3:0.5:2 for batching and grinding pre-mixing, then adding 18wt% of the structure control agent and 2 times the mass of dimethylformamide aqueous solution (volume fraction of 45%) to the pre-mixed material, grinding to make uniform slurry, then heating to 60℃ and stirring for 20h, then vacuum drying the slurry to constant weight, then sending it to a nitrogen atmosphere furnace for oxygen-free calcination, the calcination process parameters are set as follows: the first stage, the heating rate is 3℃ / min, the temperature reaches 320℃ and calcines for 3.5h, the second stage, the heating rate is 10℃ / min, the temperature reaches 600℃ and calcines for 7h; after cooling, the material is ground and crushed by air jet mill to prepare powder.

[0033] Two, preparation of positive electrode composite material

[0034] 2.1, with sodium dihydrogen phosphate and ferrous oxalate as raw materials, according to Na:Fe:P mole ratio of 4:3:4 for batching, then adding 3.5wt% of glucose to the mixture for dry grinding pre-mixing, then adding 1.2 times the mass of anhydrous ethanol to the mixture for wet grinding and mixing uniformly, drying to constant weight after standing for 24h, to prepare the composite precursor.

[0035] 2.2, adding 13.2wt% of powder to the composite precursor, sending it to a ball mill for dry ball milling, mixing the mixture into a tablet in a cold isostatic press at 30MPa, then sending it to an argon atmosphere furnace for solid phase sintering at 500℃ for 10h, crushing and grinding after cooling to obtain the positive electrode composite material.

[0036] Example 2, preparation of positive electrode composite material, the specific implementation method as follows:

[0037] One, Preparation of the structure control agent

[0038] 1.1, accurately measure the raw materials p-ethylbenzenethiol and triallylamine according to a 3:1 molar ratio, measure 0.18wt% of the photoinitiator benzoin dimethyl ether of the raw materials, mix anhydrous ethanol and acetone according to a 1:1 volume ratio as mixed solvents and take 3 times the mass of the raw materials for standby; first add benzoin dimethyl ether to the mixed solvent for dissolution, then add p-ethylbenzenethiol and triallylamine for mixing, irradiate with a 100W 365nm ultraviolet mercury lamp, stir for 10h, remove the mixed solvent by rotary evaporation after the reaction is complete, and prepare the structure control agent.

[0039] 1.2, preparation of the composite precursor The powder, with x=0.7, is prepared by taking potassium carbonate, ferrous sulfate and ammonium dihydrogen phosphate as raw materials, and preparing according to a K:Fe:P molar ratio of 2.6:0.7:2 and grinding for pre-mixing, then adding 20wt% of the structure control agent and 2 times the mass of dimethylformamide aqueous solution (volume fraction of 45%) to the pre-mixed material, grinding to form a uniform slurry, then heating to 70℃ and stirring for 18h, then vacuum drying the slurry to a constant weight, then sending it to a nitrogen atmosphere furnace for anaerobic calcination, with the calcination process parameters set as: first stage, heating rate of 5℃ / min, temperature reaches 320℃ for 3.2h, second stage, heating rate of 12℃ / min, temperature reaches 620℃ for 6.5h; after cooling, grinding and crushing with an air jet mill to prepare K 4-2x Fe x P2O7 / C powder.

[0040] II. Preparation of the positive electrode composite material

[0041] 2.1, take sodium dihydrogen phosphate and ferrous oxalate as raw materials, prepare according to a Na:Fe:P molar ratio of 4:3:4, then add 3.8wt% of glucose to the mixture for dry grinding and pre-mixing, then add 1.4 times the mass of anhydrous ethanol to the mixture for wet grinding and mixing, let stand for 24h, then dry to a constant weight to prepare the composite precursor.

[0042] 2.2, add 11.5wt% of the powder to the composite precursor, send it to a ball mill for dry ball milling and mixing, send the mixture to a cold isostatic press for tabletting at 32MPa, then send it to an argon atmosphere furnace for solid phase sintering at 510℃ for 9.5h, then crush and grind after cooling to obtain the positive electrode composite material.

[0043] Example 3, preparation of the positive electrode composite material, the specific implementation method is as follows:

[0044] I. Preparation of the structure control agent

[0045] 1.1, Accurately measure raw materials p-ethylbenzenethiol and triallylamine according to a 3:1 molar ratio, measure 0.22wt% of the photoinitiator benzoin dimethyl ether of the raw materials, mix anhydrous ethanol and acetone according to a 1:1 volume ratio as mixed solvents and take 3 times the mass of the raw materials for standby; first add benzoin dimethyl ether to the mixed solvent for dissolution, then add p-ethylbenzenethiol and triallylamine and mix well, irradiate with a 100W 365nm ultraviolet mercury lamp, stir for 8h, remove the mixed solvent by rotary evaporation after the reaction is complete, and prepare the structure control agent.

[0046] 1.2, Preparation of powder, measure the ingredients with x=1.0, use potassium carbonate, ferrous sulfate, and ammonium dihydrogen phosphate as raw materials, and mix and grind the pre-mixture according to a K:Fe:P molar ratio of 2:1:2, then add 22wt% of the structure control agent to the pre-mixture and 2.5 times the mass of dimethylformamide aqueous solution (45% by volume) to the mixture, grind to form a uniform slurry, then heat to 80℃ and stir for 15h, then vacuum dry the slurry to constant weight, then send it to a nitrogen atmosphere furnace for oxygen-free calcination, with the following process parameters: first stage, heating rate 2℃ / min, temperature reaches 350℃, calcination for 3h, second stage, heating rate 15℃ / min, temperature reaches 650℃, calcination for 5.5h; after cooling, grind and crush with an air jet mill to obtain powder.

[0047] II. Preparation of positive electrode composite material

[0048] 2.1, Use sodium dihydrogen phosphate and ferrous oxalate as raw materials, mix according to a Na:Fe:P molar ratio of 4:3:4, then add 4wt% of glucose to the mixture for dry grinding and pre-mixing, then add 1.5 times the mass of anhydrous ethanol to the mixture for wet grinding and mixing, let stand for 24h, then dry to constant weight to prepare the composite precursor.

[0049] 2.2, Add 8.5wt% of powder to the composite precursor, send it to a ball mill for dry ball milling and mixing, press the mixture into a tablet in a cold isostatic press at 35MPa, then send it to an argon atmosphere furnace for solid phase sintering at 550℃ for 8h, then crush and grind after cooling to obtain the positive electrode composite material.

[0050] Example 4, preparation of positive electrode composite material, the specific implementation method is as follows:

[0051] I, preparation of

[0052] 1.1, Accurately measure raw materials p-ethylbenzenethiol and triallylamine according to a 3:1 molar ratio, measure 0.20wt% of the photoinitiator benzoin dimethyl ether, mix anhydrous ethanol and acetone according to a 1:1 volume ratio as mixed solvents and take 3 times the mass of the raw materials for standby; first add benzoin dimethyl ether to the mixed solvent for dissolution, then add p-ethylbenzenethiol and triallylamine and mix well, irradiate with a 100W 365nm ultraviolet mercury lamp, stir for 11h, remove the mixed solvent by rotary evaporation after the reaction is complete, and prepare the structure control agent.

[0053] 1.2, Preparation The powder is prepared by measuring the ingredients with x=0.8, using potassium carbonate, ferrous sulfate, and ammonium dihydrogen phosphate as raw materials, and preparing the ingredients according to a K:Fe:P molar ratio of 2.4:0.8:2 and grinding for pre-mixing, then adding 21wt% of the structure control agent to the pre-mixed material and 2 times the mass of dimethylformamide aqueous solution (volume fraction of 45%) to the pre-mixed material, grinding to form a uniform slurry, then heating to 75°C and stirring for 16h, then vacuum drying the slurry to a constant weight, then placing it in a nitrogen atmosphere furnace for oxygen-free calcination, with the calcination process parameters set as follows: first stage, heating rate of 3°C / min, temperature reaches 330°C, calcination for 3.5h, second stage, heating rate of 12°C / min, temperature reaches 630°C, calcination for 6.5h; after cooling, grinding and crushing with an air jet mill to prepare powder.

[0054] II. Preparation of positive electrode composite material

[0055] 2.1, Using sodium dihydrogen phosphate and ferrous oxalate as raw materials, prepare the ingredients according to a Na:Fe:P molar ratio of 4:3:4, then add 3.8wt% of glucose to the mixture for dry grinding and pre-mixing, then add 1.4 times the mass of anhydrous ethanol to the mixture for wet grinding and mixing, let stand for 24h, then dry to a constant weight to prepare the composite precursor.

[0056] 2.2, Add 10.8wt% of the powder to the composite precursor, place it in a ball mill for dry ball milling, then place the mixture in a cold isostatic press to press into a tablet at 33MPa, then place it in an argon atmosphere furnace for solid phase sintering at 530°C for 9h, then crush and grind after cooling to obtain the positive electrode composite material.

[0057] Comparative example, using NFPP as the positive electrode material, to avoid the influence of the process on the product, strictly refer to the implementation method of Example 4, do not add during the preparation process, the rest is the same.

[0058] Electrode sheet preparation: The above prepared positive electrode composite, conductive acetylene black, and polyvinylidene fluoride binder were mixed in a mass ratio of 8:1:1 in N-methylpyrrolidone solvent, stirred until a uniform slurry was formed. Subsequently, the slurry was uniformly coated on an aluminum foil current collector using a doctor blade, dried in a 100°C vacuum oven for 12 hours, and finally, the electrode sheet was punched into a round sheet using a sheet punching machine.

[0059] Battery assembly: In an argon-filled glove box, a CR2032 type button cell was assembled with a metal sodium sheet as the counter electrode, a glass fiber membrane as the separator, 1M NaClO4 solution in EC / PC (volume ratio 1:1) and 5% FEC added as the electrolyte.

[0060] Constant current charge-discharge tests were performed on all assembled button cells, with a voltage range of 1.7-4.3V. The rate performance tests were all carried out in a constant temperature environment of 25°C, and the specific test data are shown in Table 1:

[0061] Table 1

[0062] 0.2C first cycle discharge capacity (mAh / g) 5C rate capacity retention (%) 20C rate capacity retention (%) 50C rate capacity retention (%) Example 1 112 93.3 87.5 70.3 Example 2 118.9 91.2 84.2 66.5 Example 3 106.3 91.8 81.7 72.8 Example 4 121.5 92.5 85.9 69.4 Comparative Example 103.7 79.1 55.4 26.2

[0063] Note: The capacity retention in the data is the percentage relative to the discharge capacity at 0.2C.

[0064] As can be seen from the test results in Table 1, the capacity retention of the example at 5C rate is above 90% relative to the capacity at 0.2C, and the capacity retention at high rates of 20C and 50C is significantly higher than that of the comparative example, indicating that the positive electrode composite material of the present application has extremely excellent rate performance.

[0065] In the description of the specification, the description of the reference terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are contained in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0066] The above is only an example and description of the present application, and those skilled in the art can make various modifications or supplements to the described specific embodiments or use similar ways to replace them, as long as they do not deviate from the invention or exceed the scope defined by the present claims, which shall fall within the protection scope of the present application.

Claims

1. A polyanionic sodium-ion battery cathode composite material, characterized in that, The chemical formula for this cathode composite material is: NFPP-K 4-2x Fe x P2O7 / C, x=0.5-1.0; The K 4-2x Fe x P2O7 / C is prepared by the following method: Step A1: Dissolve benzoin dimethyl ether in an ethanol-acetone mixed solvent, add p-ethylthiophenol and triallylamine, mix well, and carry out a click addition reaction under ultraviolet irradiation to prepare a structure control agent. The molar ratio of p-ethylthiophenol to triallylamine is 3:1, and the amount of benzoin dimethyl ether is 0.15-0.22 wt% of the two. Step A2: Potassium carbonate, ferrous sulfate, and ammonium dihydrogen phosphate are ground and premixed. Then, a structure control agent and dimethylformamide aqueous solution are added to the premix and ground into a slurry. After homogenization, the slurry is dried to constant weight, and then subjected to anaerobic calcination and grinding to obtain K. 4- 2x Fe x P2O7 / C; wherein the amount of structure control agent is 18-22 wt% of the premix; the anaerobic calcination process is divided into two stages: the first stage temperature is 320-350℃, the calcination time is 3-3.5h, and the heating rate is 1-5℃ / min; the second stage temperature is 600-650℃, the calcination time is 5.5-7h, and the heating rate is 10-15℃ / min.

2. The polyanionic sodium-ion battery cathode composite material according to claim 1, characterized in that, The positive electrode composite material is prepared by the following method: Step B1: Sodium dihydrogen phosphate and ferrous oxalate are mixed in a Na:Fe:P molar ratio of 4:3:

4. Glucose is added to the mixture and dry-milled for premixing. Anhydrous ethanol is added and wet-milled until homogeneous. After standing for 24 hours, the mixture is dried to constant weight to prepare the composite precursor. Step B2: Combine the composite precursor and K 4-2x Fe x P2O7 / C was dry ball-milled and mixed. The mixture was then cold isostatically pressed into sheets and solid-state sintered in an argon atmosphere. After cooling, the sheets were pulverized and ground to obtain the positive electrode composite material. The solid-state sintering temperature was 500-550℃ and the time was 8-10h.

3. The polyanionic sodium-ion battery cathode composite material according to claim 2, characterized in that, K 4- 2x Fe x The amount of P2O7 / C used is 8.5-13.2 wt% of the composite precursor.

4. The polyanionic sodium-ion battery cathode composite material according to claim 3, characterized in that, The pressure for cold isostatic pressing is 30-35 MPa.

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