Na4Fe x Mn 3-x (PO4)2P2O7 / C composite material, preparation and application thereof in sodium-ion batteries

Abstract

The present invention relates to the field of sodium-ion batteries, specifically to Na4Fe x Mn 3‑x The preparation method of (PO4)2P2O7 / C involves stoichiometric amounts of Fe... x / 3 Mn (3‑x) / 3 The raw materials, including PO4, sodium source, phosphorus source, and carbon source, are mixed to obtain a mixture. The mixture is then calcined to obtain the Na4Fe. x Mn 3‑x (PO4)2P2O7 / C; where x is 1 to 2; wherein the calcination process includes two gradient holding processes, wherein the temperature of the first holding process is 200℃ to 350℃, and the temperature of the second holding process is 460℃ to 550℃. This invention also includes the material obtained by the described preparation method and its applications. The process described in this invention can improve the capacity and wide-temperature-range cycling stability of the prepared material.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of batteries, in particular to the field of sodium-ion battery cathode materials. BACKGROUND

[0002] With the deterioration of global environmental problems and the shortage of fossil energy, the development of clean and renewable energy is imperative and increasingly valued. The development of clean and renewable energy such as solar energy and wind energy requires the support of energy storage devices. Sodium-ion battery cathode material sodium iron manganese pyrophosphate (Na4Fe3(PO4)2P2O7, denoted as NFPP) has the advantages of abundant reserves, wide distribution, low price, and stable structure. This feature is exactly in line with the characteristics of large-scale energy storage devices. Therefore, sodium-ion batteries are considered as potential candidates for large-scale energy storage systems. Sodium iron manganese pyrophosphate NFPP has a high theoretical capacity (~129 mAh / g), a high operating voltage (~3.1 V, Na+ / Na), and a low volume expansion (~4%), and is considered as the most promising sodium-ion battery cathode material. The use of Mn elements to partially replace a portion of Fe elements can improve the platform voltage of NFPP, thereby improving the energy density of the material.

[0003] The prior art reports some preparation processes of sodium iron manganese pyrophosphate, for example, the Chinese patent document with publication number CN116741975A discloses a double-carbon-layer heterogeneous composite cathode material, its preparation and sodium-ion battery. The cathode material is composed of a plurality of heterogeneous composite particles and a double-carbon-layer structure coated on the outside of the heterogeneous composite particles; the heterogeneous composite particles are composite particles of sodium iron manganese pyrophosphate and sodium vanadium manganese phosphate generated in situ at the nanoscale; further disclosed is a preparation process of sintering sodium source, iron source, manganese source, vanadium source, and phosphorus source.

[0004] For another example, the Chinese patent document with publication number CN115312734A discloses a preparation method and application of sodium iron manganese pyrophosphate@C composite material, specifically discloses a method of using iron nitrate Fe(NO3)3·9H2O, citric acid C6H8O7·H2O, sodium dihydrogen phosphate NaH2PO4·2H2O, and manganese acetate C4H6MnO4·4H2O as raw materials to synthesize sodium iron manganese pyrophosphate@C composite material by aqueous solution-sol-gel method.

[0005] In summary, for the preparation of sodium pyrophosphate iron manganese phosphate material, the existing process mostly adopts Na source, manganese source, iron source, phosphoric acid source and the like to be mixed and then sintered to obtain. However, since the sodium pyrophosphate iron manganese phosphate material is prone to mixed phases, the sintering temperature cannot be too high, which will result in difficulty in lattice solid solution of iron and manganese, difficulty in control of mixed phases of the material, and poor consistency of the product, in addition, effective carbonization of carbon is also difficult to achieve under the sintering conditions thereof, which will further affect the electrochemical performance. SUMMARY

[0006] In view of the problems of the existing preparation process of sodium pyrophosphate iron manganese phosphate material, such as difficulty in atomic level lattice matching and solid solution of iron and manganese, poor consistency, many mixed phases, and unsatisfactory capacity and wide temperature range stability, the first object of the present application is to provide a preparation method of Na4Fe x Mn 3-x (PO4)2P2O7 / C composite material, aiming at solving the problems of difficulty in atomic level solid solution matching of iron and manganese, poor consistency, large polarization, and unsatisfactory capacity and wide temperature range stability.

[0007] The second object of the present application is to provide the Na4Fe x Mn 3-x (PO4)2P2O7 / C composite material prepared by the preparation method and the application thereof in sodium ion batteries.

[0008] The third object of the present application is to provide a sodium ion battery comprising the Na4Fe x Mn 3-x (PO4)2P2O7 / C composite material, and a positive electrode and a positive electrode material thereof.

[0009] Unlike lithium pyrophosphate iron manganese phosphate material, sodium pyrophosphate iron manganese phosphate material has poorer electrical conductivity and is more prone to problems of mixed phases at iron sites, manganese sites, phosphoric acid sites, and pyrophosphate sites, and needs to be prepared by sintering at a lower temperature. However, this will result in difficulty in atomic level solid solution matching of iron and manganese, and in addition, the lower synthesis temperature will also affect the carbonization of carbon material. Therefore, for the preparation of sodium pyrophosphate iron manganese phosphate material, it needs to solve the problems of difficulty in atomic level solid solution of iron and manganese, difficulty in control of mixed phases, and difficulty in considering electronic and ionic conductivity, and these problems have not been well solved, which will make it difficult to meet the application requirements under some harsh conditions such as wide temperature range. However, for the preparation of sodium pyrophosphate iron manganese phosphate material, the existing technology mostly synchronously sinters raw materials containing sodium, iron, manganese and phosphorus and the like to prepare, which is difficult to solve the problems faced by the preparation of sodium pyrophosphate iron manganese phosphate material. In view of the current situation in the industry, the present application provides the following improved scheme:

[0010] A preparation method of Na4Fe x Mn 3-xA preparation method of Fe x / 3 Mn (3-x) / 3 PO4, a sodium source, a phosphorus source, and a carbon source are mixed to obtain a mixture, and the mixture is calcined to obtain the Na4Fe x Mn 3-x (PO4)2P2O7 / C; wherein x is 1-2;

[0011] The calcination process includes two-stage gradient holding processes, wherein the temperature of the first-stage holding process is 200-350 DEG C, and the temperature of the second-stage holding process is 460-550 DEG C.

[0012] The present application innovatively provides a preparation method of sintering after fusing iron and manganese in the early stage, which fuses iron and manganese to form Fe x / 3 Mn (3-x) / 3 PO4 in advance, and then participates in the subsequent two-stage calcination, which unexpectedly significantly improves the Na4Fe x Mn 3-x (PO4)2P2O7 / C, improves the atomic lattice matching of iron and manganese, and cooperatively improves the electrochemical performance such as the capacity and wide-temperature-range stability of the prepared material.

[0013] In the present application, the Fe x / 3 Mn (3-x) / 3 The obtaining step of Fe x / 3 Mn (3-x) / 3 PO4 includes the following steps: firstly, a mixed solution containing ferrous source and manganese source is prepared, then a phosphorus source and hydrogen peroxide are added, and a co-precipitation reaction is carried out under the condition that the pH is 2.5-5.5, then solid-liquid separation, water washing, and heat treatment at a temperature of 500 DEG C or higher (preferably 550-1050 DEG C, and further 600-1000 DEG C) are carried out, and the Fe x / 3 Mn (3-x) / 3 PO4 is obtained.

[0014] Preferably, the pH is 3-5.

[0015] Preferably, the heat treatment time is 1 h or higher, and preferably 4-8 h.

[0016] The temperature of the co-precipitation reaction is not particularly limited, for example, it is 20 DEG C or higher, and further can be 40-50 DEG C.

[0017] Preferably, gas is blown during the co-precipitation reaction, and the gas pressure in the reaction stage is controlled to be 8-12 MPa, and preferably 9.5-10.5 MPa. The present application shows that the pressure treatment in the co-precipitation stage unexpectedly improves the Fe x / 3 Mn (3-x) / 3The physicochemical characteristics of PO4 are adapted to the subsequent sintering process, thereby improving the capacity and wide temperature range stability of the prepared material.

[0018] Preferably, the gas is at least one of nitrogen and inert gas.

[0019] Preferably, the time of the co-precipitation reaction is 6-12h, preferably 8-10h.

[0020] In the present application, the sodium source includes but is not limited to at least one of sodium acetate, sodium carbonate, sodium bicarbonate, trisodium phosphate, sodium dihydrogen phosphate, sodium hydrogen phosphate, sodium pyrophosphate, and sodium citrate.

[0021] The phosphorus source includes but is not limited to at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, trisodium phosphate, sodium dihydrogen phosphate, sodium hydrogen phosphate, and sodium pyrophosphate.

[0022] The carbon source includes but is not limited to at least one of glucose, sucrose, starch, fructose, maltose, cyclodextrin, citric acid, polyethylene glycol, polyvinyl alcohol, polyglycerol, graphene, and carbon nanotube.

[0023] The carbon source is Na4Fe x Mn 3-x 2-10wt% of (PO4)2P2O7 by weight;

[0024] In the present application, the raw materials and the carbon source can be mixed in solid phase to obtain the mixture, or mixed in liquid phase and then subjected to desolventization to obtain the mixture.

[0025] The liquid phase mixing process is carried out with mechanical assistance, for example, sand milling.

[0026] The rotation speed of sand milling is for example 1000-2000rpm, the sand milling time is for example 0.5-6h, preferably 2-4h, and the average particle size of the slurry obtained by sand milling is for example 100-300nm.

[0027] The solvent in the liquid phase mixing stage can be water and / or an organic solvent. The organic solvent is for example alcohol, acetone, etc.

[0028] The desolventization mode can be spray drying.

[0029] In the spray drying granulation process, the temperature of the air inlet is 105-200℃, and the temperature of the air outlet is 70-105℃.

[0030] In the present application, in the mixture, the molar ratio of Na:Fe:Mn:P is 4:x:3-x:4; preferably, the x is 1-2.

[0031] In the present application, the atmosphere in the calcination stage is a protective atmosphere.

[0032] Preferably, the temperature in the first stage of heat preservation is 250-300℃.

[0033] Preferably, the time in the first stage of heat preservation is 1-5h, preferably 3-4h.

[0034] Preferably, the temperature in the second stage of heat preservation is 480-520℃.

[0035] Preferably, the time in the second stage of heat preservation is 8-20h, preferably 10-14h.

[0036] The present application also shows that the pressure in the calcination process is controlled to be 0.01-0.02Mpa. The present application shows that, under the preferred calcination mechanism, the capacity and the wide-temperature-range stability of the Fe x / 3 Mn (3-x) / 3 PO4 are unexpectedly further improved.

[0037] The present application also provides a Na4Fe x Mn 3-x (PO4)2P2O7 / C prepared by the preparation method.

[0038] The preparation method of the present application can endow the prepared material with special physicochemical characteristics, and the material prepared by the preparation method unexpectedly exhibits excellent capacity and wide-temperature-range performance.

[0039] The present application also provides a positive electrode material, comprising a positive electrode active material, a binder and a conductive agent, wherein the positive electrode active material comprises the Na4Fe x Mn 3-x (PO4)2P2O7 / C of the present application.

[0040] In the present application, the content of the Na4Fe x Mn 3-x (PO4)2P2O7 / C in the positive electrode active material is more than 20wt.%, preferably more than 60wt.%, and further preferably more than 90wt.%, and more preferably the Na4Fe x Mn 3-x (PO4)2P2O7 / C.

[0041] In the present application, the content of the positive electrode active material in the positive electrode material is more than 60wt.%, and preferably 70-90wt.%.

[0042] In the present application, the content of the conductive agent and the binder is less than 15wt.%, and preferably 5-10wt.%.

[0043] The application also provides a positive electrode, comprising a current collector and a positive electrode material compounded on the surface of the current collector, wherein the positive electrode material is the positive electrode material according to the application.

[0044] The application also provides a sodium ion battery comprising the positive electrode according to the application.

[0045] Compared with the prior art, the application has the following beneficial effects:

[0046] The application innovatively provides a preparation idea of sintering after fusing iron and manganese in the front stage, which fuses iron and manganese in advance to form Fe x / 3 Mn (3-x) / 3 PO4, and then participates in subsequent calcination, so that the preparation of Na4Fe x Mn 3-x (PO4)2P2O7 / C can be unexpectedly and significantly improved, the atomic lattice matching of iron and manganese is improved, and the capacity, wide temperature range stability and other electrochemical properties of the prepared material can be synergistically improved.

[0047] In the application, Fe x / 3 Mn (3-x) / 3 PO4 is prepared by using an optimal gas compression process, and / or a micro-pressure calcination process, which can be further combined with the above-mentioned fusing idea in the front stage, so that the capacity and wide temperature range stability of the prepared material can be unexpectedly and further improved. BRIEF DESCRIPTION OF DRAWINGS

[0048] Figure 1 : Rate performance of Na4Fe 1.5 Mn 1.5 (PO4)2P2O7 / C pyrophosphoric acid sodium iron material at room temperature 25 DEG C.

[0049] Figure 2 : Cycle performance of Na4Fe 1.5 Mn 1.5 (PO4)2P2O7 / C pyrophosphoric acid sodium iron material at room temperature 25 DEG C.

[0050] Figure 3 : Cycle performance of Na4Fe 1.5 Mn 1.5 (PO4)2P2O7 / C pyrophosphoric acid sodium iron material at high temperature and low temperature.

[0051] Figure 4 : Scanning electron microscope image of Na4Fe 1.5 Mn 1.5 (PO4)2P2O7 / C pyrophosphoric acid sodium iron material. DETAILED DESCRIPTION

[0052] An optional Na4Fe x Mn 3-x The preparation method of the Na4Fe

[0053] Step (1): Fe x / 3 Mn (3-x) / 3 PO4 preparation

[0054] First, configure ferrous sulfate A solution, manganese sulfate B solution, then pour A, B metal solution into the reaction kettle together, add phosphoric acid C solution, then add hydrogen peroxide D solution as oxidant, and add ammonia E solution as pH regulator, by controlling the reaction temperature, time and stirring temperature, to get the precipitate by co-precipitation, filter, wash, dry, calcine the precipitate to get Fe x / 3 Mn (3-x) / 3 PO4, x is 1-2. In the present application, the pH of the co-precipitation stage is controlled between 3-5, the co-precipitation temperature is between 40-50℃, the co-precipitation reaction time is between 6-12h, preferably between 8-10h, the stirring speed is controlled between 500-600r / min, the calcination temperature is controlled between 600-1000℃, and the calcination time is 4-8h. The co-precipitation stage is preferably carried out under the pressure of 9.5-10.5MPa.

[0055] Step (2): Na4Fe x Mn 3-x (PO4)2P2O7 / C(x=1-2) preparation

[0056] Step 2-1, add sodium source, Fe x / 3 Mn (3-x) / 3 PO4, phosphorus source, carbon source to deionized water, stir and disperse to get a suspension;

[0057] Step 2-2, pour the suspension into a sand mill, and get the sand mill slurry after sand milling;

[0058] Step 2-3, spray granulation of the slurry to get the sprayed precursor material;

[0059] Step 2-4, the sintering conditions are:

[0060] The precursor material is subjected to secondary calcination to obtain Na4Fe x Mn 3-xPO4)2P2O7 / C cathode material, wherein the first pre-sintering temperature is 200-350℃, preferably, the pre-sintering temperature is 250-300℃, and the holding time is 3-4h; the second calcination temperature is 460-550℃; preferably, the second calcination temperature is 480-520℃, and the holding time is 10-14h; the inert reducing atmosphere is one or more than two mixtures of nitrogen, argon, hydrogen, preferably argon-hydrogen mixed gas, and the hydrogen volume percentage is 1-10% (in the following cases, unless otherwise stated, the hydrogen / argon mixed gas atmosphere refers to the mixed gas with hydrogen content of 4-6v%).

[0061] In step (2-1), the molar ratio of the elements in Na, Fe, Mn and P satisfies: 4: x: 3-x: 4, wherein x is 1-2.

[0062] In the present application, the sodium source is at least one of sodium acetate, sodium carbonate, sodium bicarbonate, trisodium phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium pyrophosphate, and sodium citrate.

[0063] In the present application, the phosphorus source is at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, trisodium phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, and sodium pyrophosphate.

[0064] The carbon source is at least one of glucose, sucrose, starch, fructose, maltose, cyclodextrin, citric acid, polyethylene glycol, polyvinyl alcohol, polyglycerol, graphene, and carbon nanotube, and further can be sucrose and polyethylene glycol. The addition amount of the carbon source is controlled to make the carbon content in the sodium pyrophosphate iron phosphate material be 2-10wt%.

[0065] In step (2-2), the rotation speed of the sand mill is 1000-2000rpm, preferably 1500rpm, the sand milling time is 0.5-6h, preferably 3h, and the average particle size of the slurry obtained by sand milling is 100-300nm.

[0066] In step (2-3), the inlet temperature of the spray drying granulation process is 105-200℃, and the outlet temperature is 70-105℃.

[0067] Example 1

[0068] Step (1):

[0069] Firstly, a ferrous sulfate solution A with a concentration of 1 mol / L and a manganese sulfate solution B with a concentration of 1 mol / L are configured, then the metal solutions A and B are poured into a reaction kettle, a phosphoric acid solution C with a concentration of 85% is added, a hydrogen peroxide solution D with a concentration of 30% is added as an oxidant, and an ammonia water solution E with a concentration of 25% is added to adjust the pH to 4, and then stirring reaction is carried out (reaction temperature 40℃, reaction time 8h, stirring speed 600r / min), the pressure of the reaction kettle is controlled at 10MPa (pressure P, pressurized by nitrogen), the reaction liquid is filtered, washed with deionized water three times and dried in an oven at 80℃, and then calcined at 800℃ (marked as T1) for 5h to obtain Fe 1.5 / 3Mn 1.5 / 3 PO4.

[0070] Step (2):

[0071] Sodium acetate CH3COONa, Fe 1.5 / 3 Mn 1.5 / 3 PO4, ammonium dihydrogen phosphate NH4H2PO4 materials, according to the molar ratio of Na, Fe, Mn, P elements in pyrophosphate manganese iron sodium phosphate 4:1.5:1.5:4, sucrose and polyethylene glycol (mass ratio 1:1) are added as carbon sources, the weight is 5% of the theoretical mass of sodium pyrophosphate iron phosphate, deionized water (liquid-solid ratio 1.6-1.8ml / g) is added, and sand grinding is carried out at a speed of 1500rpm for 3 hours to obtain a slurry after sand grinding. The obtained slurry is spray dried at an inlet temperature of 150℃ and an outlet temperature of 87.2℃ to obtain sodium pyrophosphate iron phosphate precursor powder; the sodium pyrophosphate iron phosphate precursor powder is placed in a tube furnace, heated to 250℃ (marked as T2) at a heating rate of 2℃ / min in a hydrogen / argon mixed atmosphere, and then heated to 480℃ (marked as T3) and kept for 14h, and the T2 / T3 heating and keeping stages maintain a micro-pressure of 0.015MPa in the tube furnace, and then the Na4Fe 1.5 Mn 1.5 (PO4)2P2O7 / C pyrophosphate iron phosphate sodium material is obtained after cooling with the furnace.

[0072] Example 2

[0073] Firstly, a ferrous sulfate A solution with a concentration of 1 mol / L and a manganese sulfate B solution with a concentration of 2 mol / L are prepared, and then the A and B metal solutions are poured into a reaction kettle, an 85% phosphoric acid C solution is added, a 30% hydrogen peroxide D solution is added as an oxidizing agent, a 25% ammonia water E solution is added to adjust the pH to 5, and the reaction is stirred (reaction temperature 45°C, reaction time 10h, stirring speed 500r / min), and the reaction kettle pressure is controlled at 9.5MPa (pressurized by nitrogen). After the reaction liquid is filtered, washed with deionized water three times, and dried in an oven at 80°C, Fe 1 / 3 Mn 2 / 3 PO4.

[0074] Sodium carbonate Na2CO3, Fe 1 / 3 Mn 2 / 3 PO 4， Ammonium dihydrogen phosphate NH4H2PO4 material, according to the molar ratio of Na, Fe, Mn, P elements in pyrophosphate manganese iron sodium phosphate, the corresponding materials are weighed, sucrose and polyethylene glycol (mass ratio 1:1) are added as carbon sources, the weight is 8% of the theoretical mass of pyrophosphate sodium iron phosphate, deionized water (liquid-solid ratio 1.6-1.8ml / g) is added, and sand grinding is carried out at a speed of 1500rpm for 3 hours to obtain a slurry after sand grinding. The obtained slurry is spray dried at an inlet temperature of 130°C and an outlet temperature of 78.9°C to obtain pyrophosphate sodium iron phosphate precursor powder; the pyrophosphate sodium iron phosphate precursor powder is placed in a tube furnace, heated to 300°C (T2) at a heating rate of 2°C / min under a hydrogen / argon mixed atmosphere, kept for 3h, and then heated to 500°C (T3) and kept for 12h, and the T2 / T3 heating and keeping stages maintain a micro-pressure of 0.02MPa in the tube furnace. After cooling with the furnace, Na4FeMn2(PO4)2P2O7 / C pyrophosphate sodium iron phosphate material is obtained.

[0075] Example 3

[0076] Firstly, a ferrous sulfate A solution with a concentration of 2 mol / L and a manganese sulfate B solution with a concentration of 1 mol / L are prepared, and then the A and B metal solutions are poured into a reaction kettle, an 85% phosphoric acid C solution is added, a 30% hydrogen peroxide D solution is added as an oxidizing agent, a 25% ammonia water E solution is added to adjust the pH to 3, and the reaction is stirred (reaction temperature 50°C, reaction time 8h, stirring speed 600r / min), and the reaction kettle pressure is controlled at 10.5MPa (pressurized by nitrogen). After the reaction liquid is filtered, washed with deionized water three times, and dried in an oven at 80°C, Fe 2 / 3 Mn 1 / 3 PO4.

[0077] Sodium bicarbonate NaHCO3, Fe 2 / 3 Mn 1 / 3 PO4, ammonium dihydrogen phosphate NH4H2PO4, according to the molar ratio of Na, Fe, Mn, P elements in pyrophosphate sodium manganese phosphate iron 4:2:1:4, sucrose and polyethylene glycol (mass ratio 1:1) were added as carbon source, the weight was 4% of the theoretical mass of sodium pyrophosphate iron phosphate, deionized water (liquid-solid ratio 1.6-1.8 ml / g) was added, and sand grinding was carried out at a speed of 2000 rpm for 2.5 hours to obtain a slurry after sand grinding. The obtained slurry was spray dried at an inlet temperature of 110°C and an outlet temperature of 70.7°C to obtain sodium pyrophosphate iron phosphate precursor powder; the sodium pyrophosphate iron phosphate precursor powder was placed in a tube furnace, heated to 250°C (T2) at a heating rate of 2°C / min under a hydrogen / argon mixed atmosphere, and kept for 4h, and then heated to 520°C (T3) and kept for 10h, the T2 / T3 heating and keeping stages maintained a micro pressure of 0.01 MPa in the tube furnace, and after cooling with the furnace, Na4Fe2Mn(PO4)2P2O7 / C sodium pyrophosphate iron phosphate material was obtained.

[0078] Example 4

[0079] Compared with Example 1, the only difference is that in step (1), no air pressure treatment is carried out, that is, the pressure P is atmospheric pressure. Other operations and parameters are the same as in Example 1.

[0080] Example 5

[0081] Compared with Example 1, the only difference is that in step (2), no micro pressure treatment is carried out, that is, the T2 / T3 heating and keeping stages maintain atmospheric pressure in the tube furnace.

[0082] Comparative Example 1

[0083] Compared with Example 1, the only difference is that no step 1 treatment is carried out, and in step 2, iron phosphate FePO4 with the same molar ratio of iron / manganese is used instead of the Fe 4， Manganese phosphate MnPO4 instead of the Fe 1.5 / 3 Mn 1.5 / 3 PO4 involved in step (2) treatment, and other operations and parameters are the same as in Example 1.

[0084] Comparative Example 2

[0085] Compared with Example 1, the only difference is that the temperature T3 of step (2) is changed to 600°C, and other operations and parameters are the same as in Example 1.

[0086] Comparative Example 3

[0087] Compared with Example 1, the only difference is that the temperature T3 of step (2) is changed to 400°C, and other operations and parameters are the same as in Example 1.

[0088] Comparative Example 4

[0089] Compared with Example 1, the only difference is that x in step (1) is set to 0.5; the finally prepared material is Na4Fe 0.5 Mn 2.5 (PO4)2P2O7 / C pyrophosphate sodium iron phosphate material.

[0090] Comparative Example 5

[0091] Compared with Example 1, the only difference is that x in step (1) is set to 2.5; the finally prepared material is Na4Fe 2.5 Mn 0.5 (PO4)2P2O7 / C pyrophosphate sodium iron phosphate material.

[0092] Comparative Example 6

[0093] Compared with Example 1, the only difference is that in step (2), the temperature T2 is omitted, and other operations and parameters are the same as those in Example 1.

[0094] Test Example: The finally prepared pyrophosphate sodium iron phosphate in Examples 1-5 and Comparative Examples 1-6 is used as an active material, and Super-P and PVDF are dispersed in NMP according to a mass ratio of 8:1:1. After grinding and dispersing uniformly, the positive electrode sheet is prepared by coating on an aluminum foil, drying in a vacuum oven at 100°C, taking metallic sodium as the negative electrode sheet, taking glass fiber membrane as the separator, and taking NaClO4 / EC+DEC (EC:DEC=1:1 by volume) as the electrolyte, and additionally adding 5% fluoroethylene carbonate (FEC) as an additive. The button cell is assembled in a glove box. In the process of electrochemical performance test, the charge and discharge temperature is room temperature, the test voltage range is 1.7V-4.2V, the high temperature performance is tested at 60°C under 1C for 500 cycles, and the low temperature performance is tested at-40°C under 1C for 500 cycles. The results are shown in Table 1.

[0095] The charge and discharge current is 0.1C, and the current 1C is 129mA / g. The test results are shown in Table 1.

[0096] Table 1

[0097]

[0098] By the method of the present application, the problems of difficult doping and phase preparation caused by low preparation temperature of sodium battery can be solved, and the wide temperature range stability of the prepared material at high temperature and low temperature can be significantly improved.

[0099] The above presents a preferred embodiment of the present application, but the present application should not be limited to the disclosed embodiment. Any equivalent or modification made without departing from the disclosed principles falls into the scope of the present application.

Claims

1. Na₄Fe x Mn 3-x The preparation method of (PO4)2P2O7 / C is characterized by, stoichiometric Fe x / 3 Mn (3-x) / 3 The raw materials, including PO4, sodium source, phosphorus source, and carbon source, are mixed to obtain a mixture. The mixture is then calcined to obtain the Na4Fe. x Mn 3-x (PO4)2P2O7 / C; where x is 1~2; The calcination process includes two stages of gradient heat preservation. The temperature of the first stage heat preservation is 200℃~350℃, and the temperature of the second stage heat preservation is 460~550℃. The Fe x / 3 Mn (3-x) / 3 The steps for obtaining PO4 are as follows: First, a mixed solution containing ferrous and manganese sources is prepared. Then, a phosphorus source and hydrogen peroxide are added, and a co-precipitation reaction is carried out under conditions of pH 2.5-5.

5. Following solid-liquid separation, washing with water, and heat treatment at above 500°C, the Fe is obtained. x / 3 Mn (3-x) / 3 PO4.

2. The Na4Fe as described in claim 1 x Mn 3-x The preparation method of (PO4)2P2O7 / C is characterized by, pH is 3-5.

3. The Na4Fe as described in claim 1 x Mn 3-x The preparation method of (PO4)2P2O7 / C is characterized by, The heat treatment time is more than 1 hour.

4. The Na4Fe as described in claim 3 x Mn 3-x The preparation method of (PO4)2P2O7 / C is characterized by, The heat treatment time is 4~8 hours.

5. The Na4Fe as described in claim 1 x Mn 3-x The preparation method of (PO4)2P2O7 / C is characterized by, Gas is bubbled into the coprecipitation reaction process, and the gas pressure during the reaction stage is controlled at 8~12MPa.

6. The Na4Fe as described in claim 5 x Mn 3-x The preparation method of (PO4)2P2O7 / C is characterized by, Gas is bubbled into the coprecipitation reaction process, and the gas pressure during the reaction stage is controlled at 9.5~10.5MPa.

7. The Na4Fe as described in claim 5 x Mn 3-x The preparation method of (PO4)2P2O7 / C is characterized by, The gas is at least one of nitrogen or an inert gas.

8. The Na4Fe as described in claim 1 x Mn 3-x The preparation method of (PO4)2P2O7 / C is characterized by, The coprecipitation reaction takes 6 to 12 hours.

9. The Na4Fe as described in claim 8 x Mn 3-x The preparation method of (PO4)2P2O7 / C is characterized by, The coprecipitation reaction takes 8-10 hours.

10. The Na4Fe as described in claim 1 x Mn 3-x The preparation method of (PO4)2P2O7 / C is characterized by, The sodium source includes at least one of sodium acetate, sodium carbonate, sodium bicarbonate, trisodium phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium pyrophosphate, and sodium citrate.

11. The Na4Fe as described in claim 1 x Mn 3-x The preparation method of (PO4)2P2O7 / C is characterized by, The phosphorus source includes at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, trisodium phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, and sodium pyrophosphate.

12. The Na4Fe as described in claim 1 x Mn 3-x The preparation method of (PO4)2P2O7 / C is characterized by, The carbon source includes at least one of glucose, sucrose, starch, fructose, maltose, cyclodextrin, citric acid, polyethylene glycol, polyvinyl alcohol, glycerol, graphene, and carbon nanotubes.

13. The Na4Fe as described in claim 1 x Mn 3-x The preparation method of (PO4)2P2O7 / C is characterized by, The carbon source is theoretically Na₄Fe. x Mn 3-x 2-10 wt% of (PO4)2P2O7.

14. The Na4Fe as described in claim 1 x Mn 3-x The preparation method of (PO4)2P2O7 / C is characterized by, In the mixture, the molar ratio of Na:Fe:Mn:P is 4:x:3-x:

4.

15. The Na4Fe as described in claim 14 x Mn 3-x The preparation method of (PO4)2P2O7 / C is characterized by, The value of x is 1 to 2.

16. The Na4Fe as described in claim 1 x Mn 3-x The preparation method of (PO4)2P2O7 / C is characterized by, The raw materials and carbon source are mixed in a solid phase to obtain the mixture, or the mixture is mixed in a liquid phase and then desolventized to obtain the mixture.

17. The Na4Fe as described in claim 16 x Mn 3-x The preparation method of (PO4)2P2O7 / C is characterized by, The liquid phase mixing process is subjected to sand milling.

18. The Na4Fe as described in claim 17 x Mn 3-x The preparation method of (PO4)2P2O7 / C is characterized by, The milling speed is 1000-2000 rpm, the milling time is 0.5-6 h, and the average particle size of the slurry obtained by milling is 100 nm-300 nm.

19. The Na4Fe as described in claim 16 x Mn 3-x The preparation method of (PO4)2P2O7 / C is characterized by, The solvent removal method is spraying.

20. The Na4Fe as described in claim 19 x Mn 3-x The preparation method of (PO4)2P2O7 / C is characterized by, During the spray drying granulation process, the inlet temperature is 105°C to 200°C, and the outlet temperature is 70°C to 105°C.

21. The Na4Fe as described in claim 1 x Mn 3-x The preparation method of (PO4)2P2O7 / C is characterized by, The temperature during the first stage of heat preservation is 250~300℃.

22. The Na4Fe as described in claim 21 x Mn 3-x The preparation method of (PO4)2P2O7 / C is characterized by, The first insulation period is 1-5 hours.

23. The Na4Fe as described in claim 1 x Mn 3-x The preparation method of (PO4)2P2O7 / C is characterized by, The temperature for the second stage of insulation is 480~520℃.

24. The Na4Fe as described in claim 1 x Mn 3-x The preparation method of (PO4)2P2O7 / C is characterized by, The second insulation period is 8–20 hours.

25. The Na4Fe as described in claim 1 x Mn 3-x The preparation method of (PO4)2P2O7 / C is characterized by, The pressure during the calcination process is controlled at 0.01~0.02 MPa.

26. A Na₄Fe₄ prepared by the method according to any one of claims 1 to 25 x Mn 3-x (PO4)2P2O7 / C.

27. A positive electrode material, comprising a positive electrode active material, a binder, and a conductive agent, characterized in that, The positive electrode active material comprises the Na4Fe as described in claim 26. x Mn 3-x (PO4)2P2O7 / C.

28. The cathode material as described in claim 27, characterized in that, In the aforementioned positive electrode active material, the Na4Fe x Mn 3-x The content of (PO4)2P2O7 / C is above 20wt%.

29. The cathode material as described in claim 28, characterized in that, In the aforementioned positive electrode active material, the Na4Fe x Mn 3-x The content of (PO4)2P2O7 / C is above 60wt%.

30. The cathode material as described in claim 28, characterized in that, In the aforementioned positive electrode active material, the Na4Fe x Mn 3-x The content of (PO4)2P2O7 / C is above 90wt%.

31. The cathode material according to any one of claims 27 to 30, characterized in that, The content of the positive electrode active material in the positive electrode material is above 60 wt.%.

32. The cathode material as described in claim 31, characterized in that, The content of the positive electrode active material in the positive electrode material is 70~90 wt.%.

33. The cathode material as described in claim 27, characterized in that, The content of conductive agent and binder is below 15 wt.%.

34. The cathode material as described in claim 33, characterized in that, The content of conductive agent and binder is 5~10 wt.%.

35. A positive electrode, comprising a current collector and a positive electrode material composited thereon, characterized in that, The cathode material is the cathode material according to any one of claims 27 to 34.

36. A sodium-ion battery, characterized in that, It includes the positive electrode as described in claim 35.

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