Sodium-ion battery composite positive electrode material and short-time sintering synthesis method thereof

Abstract

The invention discloses a sodium ion battery composite positive electrode material and a short-time sintering synthesis method thereof.The method comprises the steps that a raw material precursor of a phosphoric acid pyrophosphoric acid polyanion compound is evenly and stably combined to the surfaces of layered oxide particles through a bridging agent, and short-time sintering is conducted after rapid heating is conducted in the argon atmosphere; a phosphoric acid pyrophosphate polyanion compound is effectively and stably grown or adhered to the surface of a layered oxide. Movement of the raw materials between a high-temperature area in the tubular furnace and a normal-temperature area outside the tubular furnace is utilized, synchronous and rapid heating of all parts inside and outside the raw materials to the sintering temperature is promoted, rapid and uniform generation of the material synthesis reaction is promoted, and after short-time sintering, the layered oxide structure and performance are maintained, and meanwhile the material yield is increased. The structure stability of the phosphoric acid pyrophosphate polyanion compound is utilized to improve the cycle stability of the layered oxide positive electrode material, and the composite positive electrode material with high energy density and high cycle stability is synthesized.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery technology, and relates to a sodium-ion battery cathode material and its synthesis method, specifically to a sodium-ion battery composite cathode material and its short-time sintering synthesis method. Background Technology

[0002] Compared with currently commercially available lithium-ion batteries, sodium-ion batteries are safer, have lower production costs, and superior rate performance, making them promising for applications in low-speed transportation and large-scale energy storage.

[0003] Cathode materials are one of the key factors restricting the performance and cost of sodium-ion batteries. Sodium-ion battery cathode materials mainly include layered oxides, Prussian blue analogues, and polyanionic compounds. Among these, layered oxides have high energy density, tunable composition and structure, and a relatively simple synthesis process. Their production technology can be borrowed from ternary cathode materials for lithium-ion batteries. However, they undergo complex irreversible phase transitions and severe interfacial side reactions during cycling, leading to a series of problems such as layered structure deformation and collapse, transition metal dissolution, and rapid capacity and voltage decay. Phosphate pyrophosphate polyanionic compounds contain strong PO covalent bonds, which can participate in the formation of a stable three-dimensional framework and induce regulation of Fe. 3+ / Fe 2+ Due to its high redox potential, the phosphate pyrophosphate polyanionic compound cathode material exhibits excellent cycle stability, thermal stability, safety, and high operating voltage.

[0004] Composite with phosphate pyrophosphate polyanionic compounds is an effective method to improve the cycle stability of layered oxide cathode materials. In traditional synthesis methods, the synthesis of phosphate pyrophosphate polyanionic compounds typically requires sequential low-temperature pre-sintering and high-temperature long-term sintering in an inert gas atmosphere, while the synthesis of layered oxides requires an oxygen or air atmosphere. High-temperature long-term sintering in an inert gas atmosphere easily leads to oxygen loss and transition metal reduction in layered oxides, and even structural collapse, severely affecting their electrochemical performance. Therefore, it is difficult to composite phosphate pyrophosphate polyanionic compounds onto the surface of layered oxides using the aforementioned traditional synthesis methods. Furthermore, traditional multi-step synthesis methods are time-consuming, complex, energy-intensive, and costly. Simultaneously, prolonged high-temperature sintering can easily cause excessive grain growth, thus affecting material properties. Rapid synthesis methods for phosphate pyrophosphate polyanionic compounds can solve the above problems. Joule heating and high-temperature thermal shock can synthesize phosphate pyrophosphate polyanionic compounds on the surface of layered oxides in a very short time. However, these two methods have high requirements for equipment and precursors, and the extremely high heating rate causes significant thermal stress, easily leading to microcracks in particles. The extremely short heating time and extremely rapid cooling rate can result in excessive defects remaining in the final material structure. Therefore, it is necessary to find a short-time sintering method with a gentler heating and cooling process and a more sufficient heating time to composite phosphate pyrophosphate polyanionic compounds on the surface of layered oxides. In the raw material mixing stage, the uniform and stable bonding of the phosphate pyrophosphate polyanionic compound precursor to the surface of the layered oxides is a prerequisite for subsequent short-time sintering to form a structurally stable and high-performance composite material. However, traditional solid-phase and liquid-phase mixing methods usually suffer from weak bonding and poor uniformity. Therefore, it is necessary to find more effective mixing methods to solve these problems. Summary of the Invention

[0005] The purpose of this invention is to provide a sodium-ion battery composite cathode material and its short-time sintering synthesis method. A bridging agent is used to uniformly and stably bond the precursor of a phosphoric acid pyrophosphate polyanion compound to the surface of layered oxide particles. Through rapid heating in an argon atmosphere followed by short-time sintering, the phosphoric acid pyrophosphate polyanion compound effectively and stably grows or adheres to the surface of the layered oxide. This invention utilizes the movement of the raw material between the high-temperature region inside the tubular furnace and the ambient temperature region outside the furnace to promote simultaneous and rapid heating of all parts of the raw material to the sintering temperature, promoting rapid and uniform material synthesis reactions. Short-time sintering achieves the composite with the phosphoric acid pyrophosphate polyanion compound while maintaining the structure and performance of the layered oxide, effectively saving energy and time costs. The structural stability of the phosphoric acid pyrophosphate polyanion compound improves the cycle stability of the layered oxide cathode material, synthesizing a composite cathode material with both high energy density and high cycle stability.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A composite cathode material for sodium-ion batteries is a mixture of layered oxide and a polyanionic compound of phosphoric acid pyrophosphate, wherein the chemical formula of the layered oxide is Na. x TMO2, wherein: 0.44≤x≤1, TM is one or more of Fe, Mn, Ni, Ti, Zn, Cu, and Co; the chemical formula of the phosphate pyrophosphate polyanionic compound is Na4M3(PO4)2P2O7, wherein: M is one or more of Fe, Co, Mn, Ni, Ti, Zn, W, Cu, Bi, and Mg; in the composite material, the proportion of Na4M3(PO4)2P2O7 is 0.01~45 wt%.

[0008] A short-time sintering method for the above-mentioned sodium-ion battery composite cathode material includes the following steps:

[0009] Step (1) according to Na x The stoichiometric ratio of each element in TMO2 is determined by weighing the Na source and TM source, with an excess of 5 mol% of the Na source to compensate for sodium loss during the high-temperature sintering process. The Na source and TM source are then thoroughly ground and mixed.

[0010] Step (2) The mixture precursor obtained in step (1) is sintered in air at 400-600℃ for 3-5 h, and then sintered at 800-1000℃ for 12-20 h to obtain Na. x TMO2 cathode material;

[0011] Step (3) According to the proportion of Na4M3(PO4)2P2O7 in the composite material, weigh the Na source, M source, P source and C source according to the stoichiometric ratio of each element in Na4M3(PO4)2P2O7 and mix them by ball milling.

[0012] Step (4) The mixture precursor obtained in step (3) is mixed with the Na obtained in step (2). x The TMO2 cathode material was dispersed and mixed in anhydrous ethanol containing a bridging agent, and then evaporated to dryness by heating in a water bath to obtain a mixture powder.

[0013] Step (5) involves sintering the mixture powder obtained in step (4) at a temperature of 450~1000℃ under an argon atmosphere for a short time to obtain Na4M3(PO4)2P2O7 and Na x Composite cathode material composed of TMO2.

[0014] Compared with the prior art, the present invention has the following advantages:

[0015] (1) The present invention uses a one-step short-time sintering method to composite phosphoric acid pyrophosphate polyanionic compound on the surface of layered oxides. Short-time sintering effectively reduces energy consumption, saves production costs and improves production efficiency.

[0016] (2) The present invention uses a one-step short-time sintering method to synthesize phosphate pyrophosphate polyanionic compound and realize its composite with layered oxide. Compared with the traditional long-time sintering, short-time sintering is beneficial to avoid excessive growth of phosphate pyrophosphate polyanionic compound crystal particles, shorten the sodium ion transport path, improve the reversible capacity of phosphate pyrophosphate polyanionic compound, and thus optimize its electrochemical performance with layered oxide composite material.

[0017] (3) The present invention effectively shortens the time required for the synthesis of phosphate pyrophosphate polyanionic compound, reduces the damage of high temperature inert gas atmosphere to the structure and electrochemical performance of layered oxide, realizes the composite of layered oxide and phosphate pyrophosphate polyanionic compound, and obtains a composite cathode material with high energy density and high cycle stability that combines the advantages of both materials.

[0018] (4) The present invention uses a bridging agent to enable the phosphate pyrophosphate polyanionic compound to grow or attach effectively and stably on the surface of the layered oxide particles, rather than simply physical mixing. One end of this type of bridging agent can combine with the metal (TM-O) or hydroxyl (-OH) on the surface of the layered oxide, and the other end can combine with the polyanionic precursor (phosphate, pyrophosphate), thereby obtaining a composite material with surface coating as the main component.

[0019] (5) Compared with methods such as Joule heating and high-temperature thermal shock, the present invention has lower requirements for equipment, reduces the possibility of local overheating of materials, and the heating and cooling process is relatively gentle, which can avoid a large number of particle cracks and lattice defects caused by instantaneous and drastic temperature changes, and is conducive to obtaining composite cathode materials with better electrochemical performance. Attached Figure Description

[0020] Figure 1 A schematic diagram of a short-time sintering synthesis method for composite cathode materials for sodium-ion batteries;

[0021] Figure 2 The XRD patterns of the cathode materials prepared in the comparative example and Example 4 are shown. Detailed Implementation

[0022] The technical solution of the present invention will be further described below with reference to the accompanying drawings, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention that do not depart from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention.

[0023] This invention provides a composite cathode material for sodium-ion batteries, wherein the composite cathode material is a mixture of layered oxide and a polyanionic compound of phosphoric acid pyrophosphate, and the chemical formula of the layered oxide is Na. x TMO2, wherein: 0.44≤x≤1, TM is one or more of Fe, Mn, Ni, Ti, Zn, Cu, and Co; the chemical formula of the phosphate pyrophosphate polyanionic compound is Na4M3(PO4)2P2O7, wherein: M is one or more of Fe, Co, Mn, Ni, Ti, Zn, W, Cu, Bi, and Mg; in the composite material, the proportion of Na4M3(PO4)2P2O7 is 0.01~45 wt%.

[0024] A short-time sintering synthesis method for the above-mentioned sodium-ion battery composite cathode material utilizes a bridging agent to uniformly and stably bond the precursor of the phosphoric acid pyrophosphate polyanion compound to the surface of layered oxide particles. The raw material is rapidly moved from a room temperature region to a high-temperature region that has reached the target temperature, promoting simultaneous, efficient, and uniform heating inside and outside the raw material particles, accelerating ion migration and synthesis reaction rates. Through a single short-time sintering step, while ensuring the layered oxide structure is not destroyed, the phosphoric acid pyrophosphate polyanion compound is effectively and stably grown or attached to the surface of the layered oxide particles, thereby obtaining a composite cathode material with both high energy density and high cycle stability. The method specifically includes the following steps:

[0025] Step (1) according to Na x The stoichiometric ratio of each element in TMO2 is determined by weighing the Na source and TM source, with an excess of 5 mol% of the Na source to compensate for sodium loss during the high-temperature sintering process. The Na source and TM source are thoroughly ground and mixed. The Na source is one or more of sodium carbonate, sodium acetate, sodium oxalate, and sodium citrate. The TM source is selected from at least one of its oxides, hydroxides, oxalates, acetates, citrates, and sulfates, or is a transition metal mixed hydroxide precursor prepared by a co-precipitation method.

[0026] Step (2) The mixture precursor obtained in step (1) is sintered in air at 400-600℃ for 3-5 h, and then sintered at 800-1000℃ for 12-20 h to obtain Na. x TMO2 cathode material, wherein: during the sintering process, the heating rate is 3~5℃ min. -1 After sintering, the temperature is allowed to drop naturally.

[0027] Step (3) According to the proportion of Na4M3(PO4)2P2O7 in the composite material, weigh the Na source, M source, P source and C source according to the stoichiometric ratio of each element in Na4M3(PO4)2P2O7 and mix them by ball milling. The Na source is one or more of sodium pyrophosphate, disodium dihydrogen pyrophosphate, sodium dihydrogen phosphate, sodium carbonate, and sodium acetate. The M source is selected from at least one of its oxides, oxalates, acetates, citrates, sulfates, and oxyacids. The P source is at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and sodium dihydrogen phosphate. The C source is one or more of citric acid, ascorbic acid, sucrose, and glucose. The ball milling speed is 400~800 rpm and the time is 1~6 h.

[0028] Step (4) The mixture precursor obtained in step (3) is mixed with the Na obtained in step (2). x The TMO2 cathode material is dispersed and mixed in anhydrous ethanol containing a bridging agent, and then evaporated to dryness in a water bath to obtain a powdered mixture. The bridging agent is one or more of the following: organic acids (citric acid, oxalic acid, tartaric acid, malic acid, etc.), surfactants (polyethylene glycol), coupling agents (silane coupling agent KH550, titanate coupling agents), phosphorus-containing organic compounds (phytic acid, aminotrimethylenephosphonic acid, and other phosphonic acid compounds), and polymers (polyethyleneimine, polyacrylic acid), with a content of 0.01~5 wt%. The water bath heating temperature is 60~80℃.

[0029] Step (5) involves sintering the mixture powder obtained in step (4) at a temperature of 450~1000℃ under an argon atmosphere for a short time to obtain Na4M3(PO4)2P2O7 and Na x The composite cathode material composed of TMO2, wherein: during the short-time sintering process, the heating rate is 5~10℃ min. -1 The sintering time is 1~20 min; the method for achieving the short-time sintering is as follows: the mixture powder obtained in step (4) is placed in the room temperature area outside the tube furnace in the quartz tube, and argon gas is introduced to make the mixture powder in the argon atmosphere. The tube furnace is heated at a preset rate. After the tube furnace is heated to the preset sintering temperature, the quartz tube is moved until the mixture precursor reaches the high temperature area within the heating range of the tube furnace, so that the mixture precursor is rapidly heated to the preset sintering temperature. After short-time heat preservation and sintering, the material is moved to the room temperature area to make it cool down rapidly.

[0030] Example 1

[0031] This embodiment uses a short-time sintering synthesis method to prepare NaNi. 1 / 3 Fe 1 / 3 Mn 1 / 3A composite cathode material of O2 and Na4Fe3(PO4)2P2O7, wherein Na4Fe3(PO4)2P2O7 accounts for 20 wt%. Figure 1 As shown, the specific preparation steps are as follows:

[0032] Step 1: Prepare Ni according to the co-precipitation method 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2 precursor, Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 The (OH)2 precursor was thoroughly ground and mixed with 5% excess Na2CO3, and then heated in air at 3°C ​​for 1 minute. -1 The temperature was increased at a rate of [missing information], and sintered at 450℃ for 5 h, then sintered at 900℃ for 15 h, followed by natural cooling to obtain NaNi. 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 cathode material.

[0033] Step 2: Based on the proportion of Na4Fe3(PO4)2P2O7, weigh Na4P2O7, NH4H2PO4, FeC2O4·2H2O and anhydrous citric acid into a ball mill jar according to the stoichiometric ratio of each element in Na4Fe3(PO4)2P2O7. Add zirconium dioxide ball milling beads at a ball-to-material ratio of 10:1 and ball mill at 500 rpm for 4 h to obtain precursor powder.

[0034] Step 3: The synthesized NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 was dispersed in anhydrous ethanol, and 3 wt% aminotrimethylenephosphonic acid was added. After stirring and mixing for 6 h, the above-mentioned Na4Fe3(PO4)2P2O7 precursor powder was added, and the mixture was heated and stirred in an 80°C water bath to dryness to obtain a powdered mixture.

[0035] Step 4: Place the mixed powder in a quartz tube outside the tube furnace at room temperature. Pour argon gas into the tube to immerse the precursor in an argon atmosphere. Set the tube furnace to 7°C for [time missing]. -1 The temperature is increased to 650℃ at a certain rate, and the quartz tube is moved until the mixture precursor is in the high-temperature region of the tube furnace heating range. Sintering is carried out for 10 min, and the material is moved to a room-temperature region outside the tube furnace for rapid cooling to obtain NaNi. 1 / 3 Fe 1 / 3 Mn 1 / 3 A composite cathode material with 20 wt% Na4Fe3(PO4)2P2O7 coated on an O2 surface.

[0036] Example 2

[0037] This embodiment uses a short-time sintering synthesis method to prepare Na. 2 / 3 Ni 1 / 3 Mn 2 / 3 O2 and Na4Fe 2.7 Mn 0.3 A composite cathode material of (PO4)2P2O7, in which Na4Fe 2.7 Mn 0.3 The proportion of (PO4)2P2O7 is 30 wt%. For example... Figure 1 As shown, the specific preparation steps are as follows:

[0038] Step 1, according to Na 2 / 3 Ni 1 / 3 Mn 2 / 3 The stoichiometric ratio of each element in O2 is as follows: NiO and MnO2 are weighed and thoroughly ground and mixed with 5% excess Na2C2O4. The mixture is then heated in air at 3°C ​​for 3 min. -1 The temperature was increased at a rate of [missing information], and sintered at 450℃ for 6 h, then sintered at 850℃ for 20 h to obtain Na. 2 / 3 Ni 1 / 3 Mn 2 / 3 O2.

[0039] Step 2, based on Na4Fe 2.7 Mn 0.3 Based on the stoichiometric ratio of (PO4)2P2O7, Na4P2O7, (NH4)2HPO4, FeC2O4·2H2O, Mn(CH3COO)2 and ascorbic acid were weighed into a ball mill jar. Zirconia ball milling beads were added at a ball-to-material ratio of 10:1, and the mixture was ball-milled at 450 rpm for 5 h to obtain the precursor powder.

[0040] Step 3: The synthesized Na... 2 / 3 Ni 1 / 3 Mn 2 / 3 O2 was dispersed in anhydrous ethanol, 5 wt% polyacrylic acid was added, and the mixture was stirred for 8 h before adding the above-mentioned Na4Fe. 2.7 Mn 0.3 (PO4)2P2O7 precursor powder was heated and stirred in a water bath at 70°C until it was evaporated to dryness to obtain a mixed powder.

[0041] Step 4: Place the mixed powder in a room temperature area outside the tube furnace, purge the air from the quartz tube with argon gas, and allow the tube furnace to operate at 8°C for 1 minute. -1 The temperature is increased to 800℃ at a certain rate, the precursor is moved to the high-temperature region within the heating range of the tube furnace, sintered for 1 min, and then the material is moved to a room-temperature region outside the tube furnace for rapid cooling to obtain Na. 2 / 3 Ni 1 / 3 Mn2 / 3 O2 surface composite with 30wt% Na4Fe 2.7 Mn 0.3 (PO4)2P2O7 composite cathode material.

[0042] Example 3

[0043] This embodiment uses a short-time sintering synthesis method to prepare Na. 0.7 Mn 0.7 Ni 0.2 Co 0.1 O2 and Na4Fe 2.8 Ni 0.2 A composite cathode material of (PO4)2P2O7, in which Na4Fe 2.8 Ni 0.2 The proportion of (PO4)2P2O7 is 40 wt%. For example... Figure 1 As shown, the specific preparation steps are as follows:

[0044] Step 1, according to Na 0.7 Mn 0.7 Ni 0.2 Co 0.1 The stoichiometric ratio of each element in O2 is as follows: NiO, Mn2O3, and Co3O4 are weighed and thoroughly ground and mixed with 5% excess CH3COONa. The mixture is then heated in air at 5°C for [time missing]. -1 The temperature was increased at a rate of [missing information], and sintered at 500℃ for 4 h, then sintered at 950℃ for 12 h, followed by natural cooling to obtain Na. 0.7 Mn 0.7 Ni 0.2 Co 0.1 O2.

[0045] Step 2, based on Na4Fe 2.8 Ni 0.2 Based on the stoichiometric ratio of (PO4)2P2O7, NaH2PO4, FeC2O4·2H2O, Ni(CH3COO)2 and glucose were weighed into a ball mill jar, and zirconium dioxide ball milling beads were added at a ball-to-material ratio of 10:1. The mixture was ball-milled at 450 rpm for 3 h to obtain the precursor powder.

[0046] Step 3: The synthesized Na... 0.7 Mn 0.7 Ni 0.2 Co 0.1 O2 was dispersed in anhydrous ethanol, and 2 wt% silane coupling agent KH550 was added. After stirring and mixing for 6 h, the above-mentioned Na4Fe was added. 2.8 Ni 0.2 (PO4)2P2O7 precursor powder was heated and stirred in a water bath at 75°C until it was evaporated to dryness to obtain a mixed powder.

[0047] Step 4: Place the mixed powder in a room temperature area outside the tube furnace, and purge the air from the quartz tube with argon gas, allowing the tube furnace to operate at 10°C / min. -1 The temperature is rapidly increased to 550℃, and the precursor is moved to the high-temperature region within the heating range of the tube furnace. Sintering is performed for 5 minutes. The material is then moved to a room-temperature region outside the tube furnace for rapid cooling, thus obtaining Na. 0.7 Mn 0.7 Ni 0.2 Co 0.1 O2 surface composite with 40 wt% Na4Fe 2.8 Ni 0.2 (PO4)2P2O7 composite cathode material.

[0048] Example 4

[0049] The difference between this embodiment and Embodiment 1 is that the proportion of Na4Fe3(PO4)2P2O7 is 1 wt%, the short-time sintering temperature is 650℃, and the time is 8 min. During the composite process, in the NaNi... 1 / 3 Fe 1 / 3 Mn 1 / 3 A thin Na4Fe3(PO4)2P2O7 coating layer forms on the O2 surface.

[0050] Example 5

[0051] This embodiment uses a short-time sintering synthesis method to prepare NaNi. 2 / 9 Mn 1 / 3 Cu 2 / 9 Ti 2 / 9 O2 and Na4Ti 2.7 Cu 0.3 A composite cathode material of (PO4)2P2O7, in which Na4Fe 2.7 Mn 0.3 The proportion of (PO4)2P2O7 is 10 wt%. For example... Figure 1 As shown, the specific preparation steps are as follows:

[0052] Step 1, according to NaNi 2 / 9 Mn 1 / 3 Cu 2 / 9 Ti 2 / 9 The stoichiometric ratio of each element in O2 is as follows: NiO, MnO2, CuO, and TiO2 are weighed and thoroughly ground and mixed with 5% excess Na2CO3. The mixture is then in air at 3°C ​​for [time missing]. -1 The temperature was increased at a rate of [missing information], and sintered at 400℃ for 6 h, then sintered at 1000℃ for 10 h, followed by natural cooling to obtain NaNi. 2 / 9 Mn 1 / 3 Cu 2 / 9Ti 2 / 9 O2.

[0053] Step 2, based on Na4Ti 2.7 Cu 0.3 Based on the stoichiometric ratio of (PO4)2P2O7, Na4P2O7, NH4H2PO4, TiO2, (CH3COO)2Cu·H2O and ascorbic acid were weighed into a ball mill jar, and zirconium dioxide ball milling beads were added at a ball-to-material ratio of 10:1. The precursor powder was obtained by ball milling at 450 rpm for 6 h.

[0054] Step 3: The synthesized NaNi 2 / 9 Mn 1 / 3 Cu 2 / 9 Ti 2 / 9 O2 was dispersed in anhydrous ethanol, 3 wt% tartaric acid was added, and the mixture was stirred for 8 h before adding the above-mentioned Na4Ti. 2.7 Cu 0.3 (PO4)2P2O7 precursor powder was heated and stirred in an 80°C water bath until it was evaporated to dryness to obtain a mixed powder.

[0055] Step 4: Place the mixed powder in a room temperature area outside the tube furnace, and purge the air from the quartz tube with argon gas, allowing the tube furnace to operate at 10°C / min. -1 The temperature is increased to 750℃ at a certain rate, and the precursor is moved to the high-temperature region within the heating range of the tube furnace. Sintering is performed for 3 minutes, and then the material is moved to a room-temperature region outside the tube furnace for rapid cooling to obtain NaNi. 2 / 9 Mn 1 / 3 Cu 2 / 9 Ti 2 / 9 O2 surface composite with 10 wt% Na4Ti 2.7 Cu 0.3 (PO4)2P2O7 composite cathode material.

[0056] Example 6

[0057] This embodiment uses a short-time sintering synthesis method to prepare Na. 0.67 Mn 0.9 Zn 0.1 O2 and Na4Co 2.9 Mg 0.1 (PO4)2P2O7 composite cathode material, in which Na4Co 2.9 Mg 0.1 The proportion of (PO4)2P2O7 is 15 wt%. For example... Figure 1 As shown, the specific preparation steps are as follows:

[0058] Step 1, according to Na 0.67 Mn 0.9 Zn0.1 The stoichiometric ratio of each element in O2 is as follows: MnO2 and ZnO are weighed and thoroughly ground and mixed with 5% excess CH3COONa. The mixture is then heated in air at 3°C ​​for [time missing]. -1 The temperature was increased at a rate of [missing information], and sintered at 600℃ for 3 h, then sintered at 900℃ for 12 h to obtain Na. 0.67 Mn 0.9 Zn 0.1 O2.

[0059] Step 2, based on Na4Co 2.9 Mg 0.1 Based on the stoichiometric ratio of (PO4)2P2O7, Na4P2O7, (NH4)2HPO4, MgC2O4, CoC2O4·2H2O and anhydrous citric acid were weighed into a ball mill jar. Zirconia ball milling beads were added at a ball-to-material ratio of 10:1, and the mixture was ball-milled at 500 rpm for 2 h to obtain the precursor powder.

[0060] Step 3: The synthesized Na... 0.67 Mn 0.9 Zn 0.1 O2 was dispersed in anhydrous ethanol, 5 wt% ethylene glycol was added, and the mixture was stirred for 4 h before adding the above-mentioned Na4Co. 2.9 Mg 0.1 (PO4)2P2O7 precursor powder was heated and stirred in a water bath at 75°C until it was evaporated to dryness to obtain a mixed powder.

[0061] Step 4: Place the mixed powder in a room temperature area outside the tube furnace, and purge the air from the quartz tube with argon gas, allowing the tube furnace to operate at 10°C / min. -1 The temperature is increased to 600℃ at a rate that allows the precursor to be moved to the high-temperature region within the heating range of the tube furnace and sintered for 15 minutes. The material is then moved to a room-temperature region outside the tube furnace for rapid cooling to obtain Na. 0.67 Mn 0.9 Zn 0.1 O2 surface composite with 15 wt% Na4Co 2.9 Mg 0.1 (PO4)2P2O7 composite cathode material.

[0062] Example 7

[0063] This embodiment uses a short-time sintering synthesis method to prepare Na. 0.67 Mn 0.8 Cu 0.1 Zn 0.1 O2 and Na4Mn 2.9 Zn 0.05 Bi 0.05 (PO4)2P2O7 composite cathode material, in which Na4Mn2.9 Zn 0.05 Bi 0.05 The proportion of (PO4)2P2O7 is 25 wt%. For example... Figure 1 As shown, the specific preparation steps are as follows:

[0064] Step 1, according to Na 0.67 Mn 0.8 Cu 0.1 Zn 0.1 The stoichiometric ratio of each element in O2 is as follows: MnO2, CuO, and ZnO are weighed and thoroughly ground and mixed with 5% excess Na2CO3. The mixture is then in an air atmosphere at 5℃ for [time missing]. -1 The temperature was increased at a rate of [missing information], and sintered at 550℃ for 5 h, then sintered at 1000℃ for 12 h to obtain Na. 0.67 Mn 0.8 Cu 0.1 Zn 0.1 O2.

[0065] Step 2, based on Na4Mn 2.9 Zn 0.05 Bi 0.05 Based on the stoichiometric ratio of (PO4)2P2O7, NaH2PO4, Mn(CH3COO)2, ZnC2O4·2H2O, C6H5BiO7 and glucose were weighed into a ball mill jar, and zirconium dioxide ball milling beads were added at a ball-to-material ratio of 10:1. The mixture was ball-milled at 400 rpm for 5 h to obtain the precursor powder.

[0066] Step 3: The synthesized Na... 0.67 Mn 0.8 Cu 0.1 Zn 0.1 O2 was dispersed in anhydrous ethanol, 3 wt% phytic acid was added, and the mixture was stirred for 8 h before adding the above-mentioned Na4Mn. 2.9 Zn 0.05 Bi 0.05 (PO4)2P2O7 precursor powder was heated and stirred in a water bath at 70°C until it was evaporated to dryness to obtain a mixed powder.

[0067] Step 4: Place the mixed powder in a room temperature area outside the tube furnace, and purge the air from the quartz tube with argon gas, allowing the tube furnace to operate at 10°C / min. -1 The temperature is increased to 850℃ at a certain rate, the precursor is moved to the high-temperature region within the heating range of the tube furnace, sintered for 1 min, and then the material is moved to a room-temperature region outside the tube furnace for rapid cooling to obtain Na. 0.67 Mn 0.8 Cu 0.1 Zn 0.1 O2 surface composite with 25 wt% Na4Mn2.9 Zn 0.05 Bi 0.05 (PO4)2P2O7 composite cathode material.

[0068] Example 8

[0069] The difference between this embodiment and Embodiment 2 is that in Na 2 / 3 Ni 1 / 3 Mn 2 / 3 O2 surface composite with 35 wt% Na4Fe 2.7 Mn 0.2 W 0.1 (PO4)2P2O7, W source is (NH4). 10 H2(W2O7)6, short sintering time is 2 min.

[0070] Comparative Example

[0071] NaNi was prepared by solid-state sintering. 1 / 3 Fe 1 / 3 Mn 1 / 3 The specific steps for producing O2 layered oxide cathode material are as follows:

[0072] Ni was prepared by coprecipitation method 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2 precursor, Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 The (OH)2 precursor was thoroughly ground and mixed with 5% excess Na2CO3, and sintered at 450℃ for 5 h in air atmosphere, followed by sintering at 900℃ for 15 h to obtain NaNi. 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 cathode material, tube furnace heating rate 3℃ min -1 The temperature will drop naturally.

[0073] The cathode materials prepared in the above embodiments and comparative examples were tested.

[0074] Half-cell assembly: Using the positive electrode material from each embodiment and comparative example as the active material, it was mixed with the conductive agent Super P and the binder polyvinylidene fluoride (PVDF) at a mass ratio of 7:2:1. N-methylpyrrolidone (NMP) solvent was added, and the mixture was stirred for 10 h. The resulting uniformly mixed slurry was coated onto an aluminum foil current collector and vacuum dried at 120°C for 10 h to prepare a positive electrode sheet with a diameter of 14 mm. A sodium metal sheet was used as the negative electrode. The electrolyte consisted of propylene carbonate (PC) and ethylene carbonate (EC) in a volume ratio of 1:1, dissolved in 1 mol L... -1NaClO4 was used, and glass fiber was used as the battery separator to assemble CR2025 coin cells in a glove box.

[0075] Charge / discharge test: The charge / discharge voltage range of the coin cell half-cell is 2~4.2 V. Before cycling, it is first charged at 0.1C (15 mA g). -1 Activation was performed by cycling three times at a certain rate, followed by cycling at a rate of 1C at room temperature.

[0076] Electrochemical performance tests were conducted on the half-cells assembled from the materials of Examples 1-4 and the comparative examples. The results of the initial discharge capacity at 0.1C and 1C rates and the capacity retention rate after 100 cycles at 1C rate are shown in Table 1.

[0077]

[0078] Figure 2 The XRD patterns of the cathode materials prepared in the comparative example and Example 4 are shown. The cathode material synthesized in Example 4 retains NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 The O3-type structure of O2 demonstrates that the short-time sintering method is beneficial for reducing the impact of high-temperature argon atmosphere on NaNi. 1 / 3 Fe 1 / 3 Mn 1 / 3 The destruction of the O2 structure.

Claims

1. A sodium-ion battery composite cathode material, characterized in that... The composite cathode material is a mixture of layered oxide and phosphate pyrophosphate polyanionic compound, wherein the chemical formula of the layered oxide is Na. x TMO2, wherein: 0.44≤x≤1, TM is one or more of Fe, Mn, Ni, Ti, Zn, Cu, and Co; the chemical formula of the phosphate pyrophosphate polyanionic compound is Na4M3(PO4)2P2O7, wherein: M is one or more of Fe, Co, Mn, Ni, Ti, Zn, W, Cu, Bi, and Mg; in the composite material, the proportion of Na4M3(PO4)2P2O7 is 0.01~45 wt%.

2. A short-time sintering method for the sodium-ion battery composite cathode material according to claim 1, characterized in that... The method includes the following steps: Step (1) according to Na x The stoichiometric ratio of each element in TMO2 is determined by weighing the Na source and TM source, with an excess of 5 mol% of the Na source to compensate for sodium loss during the high-temperature sintering process. The Na source and TM source are then thoroughly ground and mixed. Step (2) The mixture precursor obtained in step (1) is sintered in air at 400-600℃ for 3-5 h, and then sintered at 800-1000℃ for 12-20 h to obtain Na. x TMO2 cathode material; Step (3) According to the proportion of Na4M3(PO4)2P2O7 in the composite material, weigh the Na source, M source, P source and C source according to the stoichiometric ratio of each element in Na4M3(PO4)2P2O7 and mix them by ball milling. Step (4) The mixture precursor obtained in step (3) is mixed with the Na obtained in step (2). x The TMO2 cathode material was dispersed and mixed in anhydrous ethanol containing a bridging agent, and then evaporated to dryness by heating in a water bath to obtain a mixture powder. Step (5) involves sintering the mixture powder obtained in step (4) at a temperature of 450~1000℃ under an argon atmosphere for a short time to obtain Na4M3(PO4)2P2O7 and Na x Composite cathode material composed of TMO2.

3. The short-time sintering method for sodium-ion battery composite cathode material according to claim 2, characterized in that... In step (1), the Na source is one or more of sodium carbonate, sodium acetate, sodium oxalate, and sodium citrate; the TM source is selected from at least one of their oxides, hydroxides, oxalates, acetates, citrates, and sulfates, or is a transition metal mixed hydroxide precursor prepared by a co-precipitation method.

4. The short-time sintering method for sodium-ion battery composite cathode material according to claim 2, characterized in that... In step (2), the heating rate is 3~5℃ min. -1 After sintering, the temperature is allowed to drop naturally.

5. The short-time sintering method for sodium-ion battery composite cathode material according to claim 2, characterized in that... In step (3), the Na source is one or more of sodium pyrophosphate, disodium dihydrogen pyrophosphate, sodium dihydrogen phosphate, sodium carbonate, and sodium acetate; the M source is selected from at least one of its oxides, oxalates, acetates, citrates, sulfates, and oxyacids; the P source is at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and sodium dihydrogen phosphate; and the C source is one or more of citric acid, ascorbic acid, sucrose, and glucose.

6. The short-time sintering method for sodium-ion battery composite cathode material according to claim 2, characterized in that... In step (3), the ball milling speed is 400~800 rpm and the time is 1~6 h.

7. The short-time sintering method for sodium-ion battery composite cathode material according to claim 2, characterized in that... In step (4), the bridging agent is one or more of organic acids, surfactants, coupling agents, phosphorus-containing organic compounds, and polymers, with a content of 0.01~5 wt%; the water bath heating temperature is 60~80℃.

8. The short-time sintering method for sodium-ion battery composite cathode material according to claim 7, characterized in that... The organic acid is one or more of citric acid, oxalic acid, tartaric acid, and malic acid; the surfactant is polyethylene glycol; the coupling agent is one or two of silane coupling agent KH550 and titanate coupling agent; the phosphorus-containing organic compound is one or two of phytic acid and aminotrimethylenephosphonic acid; and the polymer is one or two of polyethyleneimine and polyacrylic acid.

9. The short-time sintering method for sodium-ion battery composite cathode material according to claim 2, characterized in that... In step (5), the heating rate for short-time sintering is 5~10℃ min. -1 The sintering time is 1~20 min.

10. The short-time sintering method for sodium-ion battery composite cathode material according to claim 2, characterized in that... In step (5), the method for achieving short-time sintering is as follows: the mixture powder obtained in step (4) is placed in a quartz tube outside the tube furnace at room temperature, and argon gas is introduced to make the mixture powder in an argon atmosphere. The tube furnace is heated at a preset rate. After the tube furnace is heated to the preset sintering temperature, the quartz tube is moved until the mixture precursor reaches the high-temperature area within the heating range of the tube furnace, so that the mixture precursor is rapidly heated to the preset sintering temperature. After short-time heat preservation and sintering, the material is moved to the room temperature area to rapidly cool down.

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