Mixed-phase-coated sodium ion battery positive electrode material and preparation method thereof, sodium ion battery and electric device

Abstract

The invention discloses a mixed phase coated sodium ion battery positive electrode material. The mixed phase coated sodium ion battery positive electrode material comprises a sodium ion positive electrode material matrix and a layered P2 / O3 mixed phase coating layer NahNiiFejMnkOl coated on the surface of the matrix. The preparation method comprises the following steps: mixing a sodium source, a precursor and an M source by a dry method, and sintering at high temperature to obtain a matrix; adding a sodium source, a nickel source, an iron source and a manganese source into a solvent, stirring and dissolving to obtain a mixed coated raw material solution; and adding the matrix into the mixed coating raw material solution, uniformly stirring and mixing, drying and sintering to obtain the mixed phase coated sodium ion battery positive electrode material. The invention also discloses a sodium ion battery and an electric device comprising the sodium ion battery positive electrode material. According to the mixed-phase-coated sodium ion battery positive electrode material disclosed by the invention, the problems of residual alkali and coating capacity reduction of the material can be effectively solved by coating the mixed phase, meanwhile, the cycle performance and the rate performance of the material are improved, and the mixed-phase-coated sodium ion battery positive electrode material has the advantages of low residual alkali, high capacity, excellent cycle performance and the like.

Description

Technical Field

[0001] The present invention belongs to the field of sodium ion batteries, and in particular relates to a mixed-phase coated sodium ion battery positive electrode material and a preparation method thereof, a sodium ion battery and an electrical device. Background Art

[0002] Sodium-ion batteries, which share the same working principle as lithium-ion batteries, are considered a low-cost complementary system to lithium-ion batteries, especially in low-speed electric vehicles and large-scale energy storage systems. Among the existing sodium-ion battery cathode materials, O3-type layered oxides have the advantages of high theoretical capacity, simple synthesis process, and high compatibility with lithium battery production lines, and have received widespread attention in the industry. However, due to poor air stability, the O3-type layered oxide cathode has a high level of residual alkali on the surface. The presence of residual alkali can cause gelation of the battery slurry, bringing great difficulties to battery production; residual alkali can also affect capacity, leading to severe gas production in the battery and reduced long-cycle performance. This limits the practical application of layered oxide cathodes. On the other hand, sodium-ion batteries themselves still have serious problems such as low energy density and diffusion kinetics that need to be urgently addressed.

[0003] In order to solve this technical problem, the existing technology mainly uses coating treatment to reduce residual alkali. The commonly used coating materials are mainly oxides, such as Al2O3, MgO, ZnO, ZrO2, MnO2, etc. The coating provides a physical barrier layer between the positive electrode and the electrolyte, which inhibits the side reactions between the electrode and the electrolyte to a certain extent, which is beneficial to reduce battery gas production and improve cycle performance, so that the positive electrode material has better electrochemical performance. However, the oxide coating is an electrochemically inert substance, which is not only not conducive to capacity development, but also hinders the transmission of sodium ions and reduces its rate performance. Some researchers have also used sodium electroactive materials for coating, such as P2 type and tunnel type positive electrodes, but the capacity of such chemical substances is relatively low, which also affects the energy density of the active material. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the above background technology and provide a mixed phase coated sodium ion battery positive electrode material and its preparation method, a sodium ion battery and an electrical device.

[0005] In order to solve the above technical problems, the technical solution proposed by the present invention is: A mixed phase coated sodium ion battery positive electrode material, comprising a sodium ion positive electrode material matrix and a layered P2 / O3 mixed phase coating layer wrapped on the surface of the sodium ion positive electrode material matrix, wherein the chemical formula of the layered P2 / O3 mixed phase coating layer is Na h Ni i Fe j Mn k O l, among which, 0.65≤h≤0.85, 0.1≤i≤0.3, 0.2≤j≤0.5, 0.3≤k≤0.6, 1.800≤l≤2.200.

[0006] In the above-mentioned mixed-phase coated sodium-ion battery positive electrode material, preferably, the mass proportion of the P2 phase in the layered P2 / O3 mixed-phase coating layer is 10-50wt%, more preferably 30-50wt%. When the content of the mixed-phase coating layer is too high, the material capacity will be significantly reduced. When it is too low, the residual alkali reduction effect is poor and the long-cycle improvement is small.

[0007] It is noteworthy that the molar ratio of i, j, and l involved in the chemical formula of the layered P2 / O3 mixed phase coating layer can enable the coating layer to effectively consume the residual alkali in the substrate.

[0008] The above-mentioned mixed phase-coated sodium ion battery positive electrode material, preferably, the sodium ion positive electrode material matrix is a sodium nickel iron manganate matrix.

[0009] The above-mentioned mixed phase coated sodium ion battery positive electrode material, preferably, the sodium nickel iron manganese oxide matrix chemical formula is Na a Ni b Fe c Mn d Cu e M f O g , wherein M is at least one of Mg, Zn, Ca, Si, Sb, Mo, Ba, Ti, Sr, Al, and Zr, 0.9≤a≤1.03, 0.1≤b≤0.3, 0.2≤c≤0.4, 0.3≤d≤0.5, 0≤e≤0.2, 0.001≤f≤0.1, b+c+d+e+f=1, and 1.800≤g≤2.200. More preferably, 0.65≤h≤0.8.

[0010] The above-mentioned mixed phase coated sodium ion battery positive electrode material, preferably, the molar ratio of the layered P2 / O3 mixed phase coating layer to the sodium ion positive electrode material matrix is 0.5%~5%, more preferably 1%~3%.

[0011] The mixed phase coated sodium ion battery positive electrode material of the present invention has a matrix Na a Ni b Fe c Mn d Cu e M f O g The material is a typical O3 type material, which shows a high cycle retention rate due to the modification effect of M element. h Ni iFe j Mn k O l It can effectively solve the problem of reduced residual alkali and coating capacity of the material, while improving the material cycle and rate performance, with low residual alkali, high capacity and excellent cycle performance. If only pure P2 phase is used for coating, the sodium content is low, and the unit cell parameters are quite different from those of the matrix, thus affecting the capacity of the matrix; on the contrary, if only pure O3 phase is used for coating, the sodium content is high, and there is no additional sodium vacancy to consume the residual alkali. The material is still in a high residual alkali state, so the battery material shows poor cycle stability. In the coated mixed phase of the present invention, according to the specially designed nickel-iron-manganese content, it can be made to exhibit P2-P2 / O3-O3 when the sodium ratio is from low to high, while controlling a certain range of sodium ratios to ensure the presence of a mixed phase with better electrochemical performance.

[0012] As a general inventive concept, the present invention also provides a method for preparing the above-mentioned mixed-phase coated sodium ion battery positive electrode material, comprising the following steps: (1) Sodium source, Ni b Fe c Mn d Cu e The (OH)2 precursor and the M source are dry-mixed and then sintered at a high temperature to obtain a sodium ion positive electrode material matrix, wherein 0.1≤b≤0.3, 0.2≤c≤0.4, 0.3≤d≤0.5, and 0≤e≤0.2; (2) adding a sodium source, a nickel source, an iron source, and a manganese source into a solvent and stirring and dissolving them to obtain a mixed coating raw material solution; (3) adding the sodium ion positive electrode material matrix to the mixed coating raw material solution obtained in step (2), stirring and mixing until uniform, and drying; (4) Sintering the dried material after step (3) to obtain the mixed phase-coated sodium ion battery positive electrode material.

[0013] In the above preparation method, preferably, in step (1), the high-temperature sintering temperature is 850-1000°C and the sintering time is 10-15h.

[0014] In the above preparation method, preferably, in step (4), the sintering temperature is 800-950°C, and the sintering time is 6-12 h.

[0015] In the above preparation method, preferably, in step (1), the sodium source includes at least one of sodium carbonate, sodium bicarbonate or sodium hydroxide; and the M source is at least one of a metal oxide, carbonate or sulfate containing element M.

[0016] In the above preparation method, preferably, in step (2), the sodium source is at least one of sodium hydroxide, sodium acetate or sodium carbonate; The nickel source is at least one of nickel nitrate, nickel acetate or nickel sulfate; The iron source is at least one of ferric nitrate, ferric acetate or ferric sulfate; The manganese source is at least one of manganese nitrate, manganese acetate or manganese sulfate; The solvent is at least one of water or ethanol; In the mixed coating raw material solution, the metal ion concentration of the transition metal salt is 1-5 mol / L.

[0017] In the above preparation method, preferably, in step (3), the drying is carried out by forced air drying, the drying temperature is 65-90° C., and the drying time is 2-5 h.

[0018] As a general inventive concept, the present invention also provides a sodium ion battery, comprising the above-mentioned mixed-phase-coated sodium ion battery positive electrode material or the mixed-phase-coated sodium ion battery positive electrode material prepared by the above-mentioned preparation method.

[0019] As a general inventive concept, the present invention also provides an electrical device comprising the above-mentioned sodium ion battery.

[0020] Compared with the prior art, the present invention has the following beneficial effects: (1) The mixed phase coated sodium ion battery positive electrode material of the present invention is coated with the mixed phase Na h Ni i Fe j Mn k O l It can effectively solve the problems of residual alkali in materials and reduced coating capacity, while improving the material's cycle and rate performance. It has the advantages of low residual alkali, high capacity and excellent cycle performance.

[0021] (2) The preparation process of the present invention adopts a liquid phase coating process, in which an O3 phase positive electrode matrix material is added to a mixed solution containing nickel, iron, manganese, and sodium, and the mixed phase precursor is evenly distributed on the surface of the O3 phase; then it is dried, and finally heat-treated at a high temperature, so that a uniform layer of mixed phase positive electrode is formed in situ on the surface of the positive electrode material matrix, and finally an O3 phase positive electrode material coated with a mixed phase positive electrode is obtained. The mixed phase material can embed sodium within a certain sodium matching range, so during the high-temperature heat treatment process, the residual sodium in the matrix will be consumed and significantly reduced; because the generated mixed phase material has a similar chemical composition and the same layered structure as the matrix, it also has better air stability and rate performance and higher capacity, so that the coating layer can significantly improve the electrochemical performance of the matrix material. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a SEM image of the sodium ion battery positive electrode material in Example 1 of the present invention; Figure 2 is the XRD pattern of the sodium ion battery positive electrode material in Example 4 of the present invention; Figure 3 1 is a graph showing the charge and discharge cycle performance of the sodium ion battery positive electrode materials in various embodiments and comparative examples of the present invention. DETAILED DESCRIPTION

[0023] To facilitate understanding of the present invention, the present invention will be described in more comprehensive and detailed form below in conjunction with the accompanying drawings and preferred embodiments. However, the protection scope of the present invention is not limited to the following specific embodiments.

[0024] Unless otherwise defined, all technical terms used hereinafter have the same meanings as those generally understood by those skilled in the art. The technical terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0025] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0026] Example 1: A mixed phase coated sodium ion battery positive electrode material of the present invention comprises a sodium ion positive electrode material matrix Na 1.00 Ni 0.24 Fe 0.33 Mn 0.33 Cu 0.098 Sr 0.002 O2 and the layered P2 / O3 mixed phase coating Na wrapped on the surface of the sodium ion positive electrode material matrix 0.70 Ni 0.24 Fe 0.34 Mn 0.42 The molar ratio of the layered P2 / O3 mixed phase coating layer to the sodium ion positive electrode material matrix is 1%, and the mass proportion of the P2 phase is 30wt%.

[0027] The preparation method of the mixed phase-coated sodium ion battery positive electrode material of this embodiment comprises the following steps: (1) Ni 0.24 Fe 0.33 Mn 0.33 Cu 0.098 The (OH)2 precursor material, strontium carbonate and sodium carbonate were dry-mixed for 1 hour at a molar ratio of Sr:Na=1.00:0.002:1.03, and then the obtained mixed powder was sintered in compressed air at 3°C / min to 900°C for 11 hours. After sintering, it was cooled, crushed and sieved to obtain the O3 type sodium ion battery single crystal positive electrode material matrix, with the chemical formula of Na 1.00 Ni0.24 Fe 0.33 Mn 0.33 Cu 0.098 Sr 0.002 O2.

[0028] (2) Sodium hydroxide, nickel acetate, ferric acetate and manganese acetate were added to ethanol at an element molar ratio of Na:Ni:Fe:Mn=0.70:0.24:0.34:0.42 and stirred for 1 hour to obtain a coating raw material solution. The metal ion concentration of the transition metal salt was controlled to be 3 mol / L.

[0029] (3) According to the molar ratio of coating layer to substrate material β=1%, the substrate obtained in step (1) was added to the coating raw material solution in step (2) and stirred for 1 hour, and then dried by forced air at 80°C for 4 hours.

[0030] (4) The powder dried in step (3) was heated to 850°C and sintered for 8 hours under compressed air to obtain a mixed phase coated sodium ion battery positive electrode material, the SEM image of which is shown in FIG. Figure 1 shown.

[0031] In order to confirm the Na 0.70 Ni 0.24 Fe 0.34 Mn 0.42 The proportion of O2 component mixed phase, sodium hydroxide, nickel acetate, iron acetate and manganese acetate were dry mixed according to the element molar ratio of Na:Ni:Fe:Mn=0.70:0.24:0.34:0.42, and the obtained mixed powder was sintered in compressed air at 3℃ / min to 900℃ for 11h. After sintering, it was cooled, crushed and sieved to obtain a layered P2 / O3 mixed phase coating layer with the same components. 0.70 Ni 0.24 Fe 0.34 Mn 0.42 The mass fraction of the P2 phase in the O2 component was determined using the following method: X-ray diffraction data from a powder sample was obtained using an X-ray analyzer (Bruker D8). The X-rays used a copper target, an operating voltage of 40 kV, and a current of 40 mA. The sample scan angle range was 10-80 degrees, with a step size of 0.02 degrees. The XRD pattern was refined using TOPAS to minimize the weighted residual variance factor (Rwp) of the entire spectrum. The mass fraction of the P2 phase was determined to be 30 wt%. The mixed phase fraction in the coating layer in the following examples was determined using the same method, which will not be repeated here.

[0032] Example 2: A mixed phase coated sodium ion battery positive electrode material of the present invention comprises a sodium ion positive electrode material matrix Na 1.00 Ni 0.24 Fe 0.33Mn 0.33 Cu 0.098 Sr 0.002 O2 and the layered P2 / O3 mixed phase coating Na wrapped on the surface of the sodium ion positive electrode material matrix 0.70 Ni 0.24 Fe 0.34 Mn 0.42 O2, the molar ratio of the layered P2 / O3 mixed phase coating layer to the sodium ion positive electrode material matrix is 2%, and the mass proportion of the P2 phase in the layered P2 / O3 mixed phase coating layer is 30wt%.

[0033] The preparation method of the mixed phase-coated sodium ion battery positive electrode material of this embodiment comprises the following steps: (1) Ni 0.24 Fe 0.33 Mn 0.33 Cu 0.098 The (OH)2 precursor material, strontium carbonate and sodium carbonate were dry-mixed for 1 hour at a molar ratio of Sr:Na=1.00:0.002:1.03, and then the obtained mixed powder was sintered in compressed air at 3°C / min to 900°C for 11 hours. After sintering, it was cooled, crushed and sieved to obtain the O3 type sodium ion battery single crystal positive electrode material matrix, with the chemical formula of Na 1.00 Ni 0.24 Fe 0.33 Mn 0.33 Cu 0.098 Sr 0.002 O2.

[0034] (2) Sodium hydroxide, nickel acetate, ferric acetate and manganese acetate were added to ethanol at an element molar ratio of Na:Ni:Fe:Mn=0.70:0.24:0.34:0.42 and stirred for 1 hour to obtain a coating raw material solution. The metal ion concentration of the transition metal salt was controlled to be 1 mol / L.

[0035] (3) According to the molar ratio of coating layer to substrate material β=2%, the substrate obtained in step (1) was added to the coating raw material solution in step (2) and stirred for 1 hour, and then dried by forced air at 90°C for 2 hours.

[0036] (4) The powder dried in step (3) is heated to 850° C. and sintered for 8 h under compressed air to obtain a mixed phase-coated sodium ion battery positive electrode material.

[0037] Example 3: A mixed phase coated sodium ion battery positive electrode material of the present invention comprises a sodium ion positive electrode material matrix Na 1.00 Ni 0.24 Fe 0.33 Mn 0.33 Cu0.098 Sr 0.002 O2 and the layered P2 / O3 mixed phase coating Na wrapped on the surface of the sodium ion positive electrode material matrix 0.70 Ni 0.24 Fe 0.34 Mn 0.42 O2, the molar ratio of the layered P2 / O3 mixed phase coating layer to the sodium ion positive electrode material matrix is 3%, and the mass proportion of the P2 phase in the layered P2 / O3 mixed phase coating layer is 30wt%.

[0038] The preparation method of the mixed phase-coated sodium ion battery positive electrode material of this embodiment comprises the following steps: (1) Ni 0.24 Fe 0.33 Mn 0.33 Cu 0.098 The (OH)2 precursor material, strontium carbonate and sodium carbonate were dry-mixed for 1 hour at a molar ratio of Sr:Na=1.00:0.002:1.03, and then the obtained mixed powder was sintered in compressed air at 3°C / min to 900°C for 11 hours. After sintering, it was cooled, crushed and sieved to obtain the O3 type sodium ion battery single crystal positive electrode material matrix, with the chemical formula of Na 1.00 Ni 0.24 Fe 0.33 Mn 0.33 Cu 0.098 Sr 0.002 O2.

[0039] (2) Sodium hydroxide, nickel acetate, iron acetate and manganese acetate were added to ethanol at an element molar ratio of Na:Ni:Fe:Mn=0.70:0.24:0.34:0.42 and stirred for 1 hour to obtain a coating raw material solution. The metal ion concentration of the transition metal salt was controlled to be 5 mol / L.

[0040] (3) According to the molar ratio of coating layer to substrate material β=3%, the substrate obtained in step (1) was added to the coating raw material solution in step (2) and stirred for 1 hour, and then dried by forced air at 65°C for 5 hours.

[0041] (4) The powder dried in step (3) is heated to 850° C. and sintered for 8 h under compressed air to obtain a mixed phase-coated sodium ion battery positive electrode material.

[0042] Example 4: A mixed phase coated sodium ion battery positive electrode material of the present invention comprises a sodium ion positive electrode material matrix Na 1.00 Ni 0.24 Fe 0.33 Mn 0.33 Cu 0.098 Sr0.002 O2 and the layered P2 / O3 mixed phase coating Na wrapped on the surface of the sodium ion positive electrode material matrix 0.70 Ni 0.24 Fe 0.34 Mn 0.42 O2, the molar ratio of the layered P2 / O3 mixed phase coating layer to the sodium ion positive electrode material matrix is 5%, and the mass proportion of the P2 phase in the layered P2 / O3 mixed phase coating layer is 30wt%.

[0043] The preparation method of the mixed phase-coated sodium ion battery positive electrode material of this embodiment comprises the following steps: (1) Ni 0.24 Fe 0.33 Mn 0.33 Cu 0.098 The (OH)2 precursor material, strontium carbonate and sodium carbonate were dry-mixed for 1 hour at a molar ratio of Sr:Na=1.00:0.002:1.03, and then the obtained mixed powder was sintered in compressed air at 3°C / min to 1000°C for 10 hours. After sintering, it was cooled, crushed and sieved to obtain the O3 type sodium ion battery single crystal positive electrode material matrix, with the chemical formula of Na 1.00 Ni 0.24 Fe 0.33 Mn 0.33 Cu 0.098 Sr 0.002 O2.

[0044] (2) Sodium hydroxide, nickel acetate, ferric acetate and manganese acetate were added to ethanol at an element molar ratio of Na:Ni:Fe:Mn=0.70:0.24:0.34:0.42 and stirred for 1 hour to obtain a coating raw material solution. The metal ion concentration of the transition metal salt was controlled to be 3 mol / L.

[0045] (3) According to the molar ratio β of the coating layer to the substrate material = 5%, the substrate obtained in step (1) was added to the coating raw material solution in step (2) and stirred for 1 h, and then dried by forced air at 80 °C for 4 h.

[0046] (4) The powder dried in step (3) was heated to 800°C and sintered for 12 hours under compressed air to obtain a mixed phase coated sodium ion battery positive electrode material, the XRD pattern of which is shown in FIG. Figure 2 shown.

[0047] Example 5: A mixed phase coated sodium ion battery positive electrode material of the present invention comprises a sodium ion positive electrode material matrix Na 1.00 Ni 0.24 Fe 0.33 Mn 0.33 Cu 0.098 Ti0.002 O2 and the layered P2 / O3 mixed phase coating Na wrapped on the surface of the sodium ion positive electrode material matrix 0.70 Ni 0.24 Fe 0.34 Mn 0.42 O2, the molar ratio of the layered P2 / O3 mixed phase coating layer to the sodium ion positive electrode material matrix is 5%, and the mass proportion of the P2 phase in the layered P2 / O3 mixed phase coating layer is 30wt%.

[0048] The preparation method of the mixed phase-coated sodium ion battery positive electrode material of this embodiment comprises the following steps: (1) Ni 0.24 Fe 0.33 Mn 0.33 Cu 0.098 (OH)2 precursor material, titanium dioxide and sodium carbonate were dry-mixed in a molar ratio of Ti:Na=1.00:0.002:1.03 for 1 hour, and then the obtained mixed powder was sintered in compressed air at 3℃ / min to 850℃ for 15 hours. After sintering, it was cooled, crushed and sieved to obtain the O3 type sodium ion battery single crystal positive electrode material matrix, with the chemical formula of Na 1.00 Ni 0.24 Fe 0.33 Mn 0.33 Cu 0.098 Ti 0.002 O2.

[0049] (2) Sodium hydroxide, nickel acetate, ferric acetate and manganese acetate were added to ethanol at an element molar ratio of Na:Ni:Fe:Mn=0.70:0.24:0.34:0.42 and stirred for 1 hour to obtain a coating raw material solution. The metal ion concentration of the transition metal salt was controlled to be 3 mol / L.

[0050] (3) According to the molar ratio β of the coating layer to the substrate material = 5%, the substrate obtained in step (1) was added to the coating raw material solution in step (2) and stirred for 1 h, and then dried by forced air at 80 °C for 4 h.

[0051] (4) The powder dried in step (3) was heated to 950° C. and sintered for 6 h under compressed air to obtain a mixed phase-coated sodium ion battery positive electrode material.

[0052] Comparative Example 1: The sodium ion battery positive electrode material of this comparative example is an O3 type sodium ion battery positive electrode material containing a modifying element M, and its morphology is a single crystal morphology, and its chemical formula is Na 1.00 Ni 0.24 Fe 0.33 Mn 0.33 Cu 0.098 Sr0.002 O2.

[0053] The steps of the preparation method of the sodium ion battery positive electrode material of this comparative example are as follows: Ni 0.24 Fe 0.33 Mn 0.33 Cu 0.098 (OH)2 precursor material, strontium carbonate and sodium carbonate were dry mixed for 1 hour at a molar ratio of Sr:Na=1.00:0.002:1.03, and then the obtained mixed powder was sintered in compressed air at 3℃ / min to 900℃ for 11 hours. After sintering, it was cooled, crushed and sieved to obtain O3 type sodium ion battery single crystal positive electrode material with the chemical formula of Na 1.00 Ni 0.24 Fe 0.33 Mn 0.33 Cu 0.098 Sr 0.002 O2.

[0054] Comparative Example 2: The sodium ion battery positive electrode material of this comparative example is an O3 type sodium ion battery positive electrode material that does not contain the modifying element M, and its morphology is a single crystal morphology, and its chemical formula is Na 1.00 Ni 0.24 Fe 0.33 Mn 0.33 Cu 0.1 O2.

[0055] The steps of the preparation method of the sodium ion battery positive electrode material of this comparative example are as follows: Ni 0.24 Fe 0.33 Mn 0.33 Cu 0.1 The (OH)2 precursor material and sodium carbonate were dry-mixed in a molar ratio of precursor: Na=1.00:1.03 for 1 hour, and then the obtained mixed powder was sintered in compressed air at 3°C / min to 900°C for 11 hours. After sintering, it was cooled, crushed, and sieved to obtain the O3 type sodium ion battery single crystal positive electrode material with the chemical formula of Na 1.00 Ni 0.24 Fe 0.33 Mn 0.33 Cu 0.1 O2.

[0056] Comparative Example 3: The sodium ion battery positive electrode material of this comparative example includes a matrix material Na 1.00 Ni 0.24 Fe 0.33 Mn 0.33 Cu 0.098 Sr 0.002O2 and pure P2 phase coating layer Na 0.60 Ni 0.24 Fe 0.34 Mn 0.42 O2, wherein the amount ratio of the coating layer to the base material is 3%.

[0057] The preparation method of the sodium ion battery positive electrode material of this comparative example comprises the following steps: (1) Ni 0.24 Fe 0.33 Mn 0.33 Cu 0.098 The (OH)2 precursor material, strontium carbonate and sodium carbonate were dry-mixed for 1 hour at a molar ratio of Sr:Na=1.00:0.002:1.03, and then the obtained mixed powder was sintered in compressed air at 3°C / min to 900°C for 11 hours. After sintering, it was cooled, crushed and sieved to obtain the O3 type sodium ion battery single crystal positive electrode material matrix, with the chemical formula of Na 1.00 Ni 0.24 Fe 0.33 Mn 0.33 Cu 0.098 Sr 0.002 O2.

[0058] (2) Sodium hydroxide, nickel acetate, ferric acetate and manganese acetate were added to ethanol at an element molar ratio of Na:Ni:Fe:Mn=0.60:0.24:0.34:0.42 and stirred for 1 hour to obtain a coating raw material solution. The metal ion concentration of the transition metal salt was controlled to be 3 mol / L.

[0059] (3) According to the molar ratio of coating layer to substrate material β=3%, the substrate obtained in step (1) was added to the coating raw material solution in step (2) and stirred for 1 hour, and then dried by forced air at 65°C for 5 hours.

[0060] (4) The powder dried in step (3) was heated to 850° C. and sintered for 8 h under compressed air to obtain a pure P2 phase-coated sodium ion battery positive electrode material.

[0061] Comparative Example 4: The sodium ion battery positive electrode material of this comparative example includes a matrix material Na 1.00 Ni 0.24 Fe 0.33 Mn 0.33 Cu 0.098 Sr 0.002 O2 and pure O3 phase coating NaNi 0.24 Fe 0.34 Mn 0.42 O2, wherein the amount ratio of the coating layer to the base material is 3%, and the morphology of the positive electrode material is a single crystal morphology.

[0062] The preparation method of the sodium ion battery positive electrode material of this comparative example comprises the following steps: (1) Ni 0.24 Fe 0.33 Mn 0.33 Cu 0.098 The (OH)2 precursor material, strontium carbonate and sodium carbonate were dry-mixed for 1 hour at a molar ratio of Sr:Na=1.00:0.002:1.03, and then the obtained mixed powder was sintered in compressed air at 3°C / min to 900°C for 11 hours. After sintering, it was cooled, crushed and sieved to obtain the O3 type sodium ion battery single crystal positive electrode material matrix, with the chemical formula of Na 1.00 Ni 0.24 Fe 0.33 Mn 0.33 Cu 0.098 Sr 0.002 O2.

[0063] (2) Sodium hydroxide, nickel acetate, ferric acetate and manganese acetate were added to ethanol at an element molar ratio of Na:Ni:Fe:Mn=1.00:0.24:0.34:0.42 and stirred for 1 hour to obtain a coating raw material solution. The metal ion concentration of the transition metal salt was controlled to be 3 mol / L.

[0064] (3) According to the molar ratio of coating layer to substrate material β=3%, the substrate obtained in step (1) was added to the coating raw material solution in step (2) and stirred for 1 hour, and then dried by forced air at 65°C for 5 hours.

[0065] (4) The powder dried in step (3) was heated to 850° C. and sintered for 8 h under compressed air to obtain a pure O3 phase-coated sodium ion battery positive electrode material.

[0066] Comparative Example 5: The sodium ion battery material of this comparative example is a mixed phase material Na 0.70 Ni 0.24 Fe 0.34 Mn 0.42 O2, its preparation steps are as follows: Sodium hydroxide, nickel acetate, manganese acetate and manganese acetate were dry mixed in an element molar ratio of 0.70:0.24:0.34:0.42 for 1 hour, and then the obtained mixed powder was heated to 900 ° C in compressed air at 3 ° C / min and sintered for 11 hours. After sintering, it was cooled, crushed and sieved to obtain a sodium ion mixed phase positive electrode material with a chemical formula of Na 0.70 Ni 0.24 Fe 0.34 Mn 0.42 O2.

[0067] The sodium ion battery positive electrode materials prepared in each embodiment and comparative example were prepared into CR2032 button batteries and their electrochemical properties were studied. The test results are shown in Table 1. The charge and discharge cycle diagrams of each embodiment and comparative example are shown in Table 1. Figure 3 As shown, the test method is as follows: The positive electrode material, conductive carbon black (SP), and polyvinylidene fluoride (PVDF) were stirred and dispersed in a 93:5:2 mass ratio with the solvent NMP. The mixture was then coated onto an aluminum foil substrate and roller-pressed to produce the positive electrode. A sodium metal sheet was used as the negative electrode. The electrolyte was a 1 mol / L NaPF6 solution, and the solvent was a mixture of EC and PC in a 1:1 volume ratio, with 1% FEC added as an additive. The above components were assembled into CR2032 button cells for battery testing. A 0.1C first cycle activation test profile was established with a charge cutoff voltage of 4.0 V, a discharge cutoff voltage of 2.0 V, and an [XY1] current density of 140 mA / g.

[0068] The residual alkali results of the sodium-ion battery cathode materials for each example and comparative example are shown in Table 2. The pH and sodium carbonate test methods are as follows: 10 g of each sample was dissolved in 100 mL of water, stirred for 10 minutes, and the supernatant was collected. The pH value was directly read using a pH meter. For the residual alkali test, a 0.2 mol / L HCl solution was prepared and placed in an automatic potentiometric titrator. Titration was performed using the equivalence point method, and the volume of HCl consumed at the break point was recorded. The residual sodium content of the sample was calculated. This was repeated three times, and the average value of the test was taken.

[0069] Table 1 Electrochemical test results of sodium ion battery cathode materials prepared in various examples and comparative examples

[0070] As can be seen from Table 1, the difference between Comparative Example 1 and Comparative Example 2 is the presence or absence of doping with the modifying element M. In Comparative Example 1, due to the presence of Sr 2+ The ion radius is 118 pm. Doping with Sr elements can effectively expand the sodium ion channel, increase the sodium ion migration rate, and give full play to the charging capacity. At the same time, Sr, as a flux, can ensure that the high-temperature reaction is fully carried out and the layered structure is more complete. Therefore, Comparative Example 1 shows a higher capacity than Comparative Example 2.

[0071] As can be seen from Table 1, the molar β values selected for the coating layers of Examples 1-3 are all within the preferred range of 1% to 3%, so the discharge capacity is extremely close to that of the base O3 material. Due to the effect of the mixed phase coating layer, the rate performance and cycle performance are significantly improved compared to the base material. In Examples 4 and 5, the mixed phase coating layer is relatively thick, and the β value is 5%, and the 0.1C discharge capacity is significantly reduced. This may be because when the mixed phase content is high, it will affect the number of sodium ions that can be intercalated and deintercalated in the overall positive electrode material, and ultimately have a greater impact on the first discharge of the battery, so it is necessary to control the β value. In Example 5, Ti 4+ Can effectively alleviate Mn 3+ Other types of modifying elements M are also crucial for preparing high-capacity matrices.

[0072] As can be seen from Table 1, the comparative example shows that the pure mixed phase material has excellent cycle performance, but the capacity is 20 mAh / g lower than that of the O3 phase material, which is equivalent to a 15% lower capacity. In addition, the coating layers of Comparative Examples 3 and 4 use 3% pure P2 phase and O3 phase respectively. Compared with Example 3, the coating layer chemical formula is different; Compared with Example 3, the buckling capacity of Comparative Example 3 is too low, which is attributed to the lower sodium content of the P2 phase itself. The unit cell parameters are quite different from those of the matrix, thus affecting the capacity of the matrix; Compared with Example 3, the rate performance of Comparative Example 4 is worse, and the cycle performance is worse, which is attributed to the higher sodium content of the O3 phase. There are no additional sodium vacancies to consume the high residual alkali of the matrix. The material is still in a high residual alkali state, so the battery material exhibits poor cycle stability, which is confirmed by the results in Table 2.

[0073] Table 2 Results of residual alkali in the positive electrode materials of sodium ion batteries of various embodiments and comparative examples

[0074] As can be seen from Table 2, the residual sodium carbonate and pH value of the matrix coated with the mixed phase coating layer are significantly reduced compared with the matrix sample alone, which indicates that the mixed phase coating layer improves the air stability of the O3 layered sample.

Claims

1. A mixed phase coated sodium ion battery positive electrode material, characterized in that: It comprises a sodium ion positive electrode material matrix and a layered P2 / O3 mixed phase coating layer wrapped on the surface of the sodium ion positive electrode material matrix, wherein the chemical formula of the layered P2 / O3 mixed phase coating layer is Na h Ni i Fe j Mn k O l , among which, 0.65≤h≤0.85, 0.1≤i≤0.3, 0.2≤j≤0.5, 0.3≤k≤0.6, 1.800≤l≤2.

200.

2. The mixed phase coated sodium ion battery positive electrode material according to claim 1, characterized in that In the layered P2 / O3 mixed phase coating layer, the mass proportion of the P2 phase is 10-50wt%.

3. The mixed phase coated sodium ion battery positive electrode material according to claim 1, characterized in that The sodium ion positive electrode material matrix is a sodium nickel iron manganate matrix.

4. The mixed phase coated sodium ion battery positive electrode material according to claim 3, characterized in that The sodium nickel iron manganate matrix chemical formula is Na a Ni b Fe c Mn d Cu e M f O g , wherein M is at least one of Mg, Zn, Ca, Si, Sb, Mo, Ba, Ti, Sr, Al, and Zr, 0.9≤a≤1.03, 0.1≤b≤0.3, 0.2≤c≤0.4, 0.3≤d≤0.5, 0≤e≤0.2, 0.001≤f≤0.1, b+c+d+e+f=1, and 1.800≤g≤2.

200.

5. The mixed phase-coated sodium ion battery positive electrode material according to any one of claims 1 to 4, characterized in that The molar ratio of the layered P2 / O3 mixed phase coating layer to the sodium ion positive electrode material matrix is 0.5% to 5%.

6. A method for preparing a mixed-phase coated sodium ion battery cathode material according to any one of claims 1 to 5, characterized in that: The following steps are involved: (1) Sodium source, Ni b Fe c Mn d Cu e The (OH)2 precursor and the M source are dry-mixed and then sintered at a high temperature to obtain a sodium ion positive electrode material matrix, wherein 0.1≤b≤0.3, 0.2≤c≤0.4, 0.3≤d≤0.5, and 0≤e≤0.2; (2) adding a sodium source, a nickel source, an iron source, and a manganese source into a solvent and stirring and dissolving them to obtain a mixed coating raw material solution; (3) adding the sodium ion positive electrode material matrix obtained in step (1) to the mixed coating raw material solution obtained in step (2), stirring and mixing until uniform, and drying; (4) Sintering the dried material after step (3) to obtain the mixed phase-coated sodium ion battery positive electrode material.

7. The preparation method according to claim 6, wherein In step (1), the high temperature sintering temperature is 850-1000°C and the sintering time is 10-15h.

8. The preparation method according to claim 6, wherein In step (4), the sintering temperature is 800-950°C, and the sintering time is 6-12 h.

9. The preparation method according to claim 6, wherein In step (1), the sodium source includes at least one of sodium carbonate, sodium bicarbonate or sodium hydroxide; the M source is at least one of a metal oxide, carbonate or sulfate containing element M; In step (2), the sodium source is at least one of sodium hydroxide, sodium acetate or sodium carbonate; the nickel source is at least one of nickel nitrate, nickel acetate or nickel sulfate; the iron source is at least one of ferric nitrate, ferric acetate or ferric sulfate; the manganese source is at least one of manganese nitrate, manganese acetate or manganese sulfate; the solvent is at least one of water or ethanol; and the metal ion concentration of the transition metal salt in the mixed coating raw material solution is 1-5 mol / L.

10. The preparation method according to claim 6, wherein In step (3), the drying is carried out by forced air drying, the drying temperature is 65-90° C., and the drying time is 2-5 h.

11. A sodium ion battery, characterized in that: A sodium ion battery positive electrode material comprising the mixed phase coated material according to any one of claims 1 to 5 or a sodium ion battery positive electrode material prepared by the preparation method according to any one of claims 6 to 10.

12. An electrical device, characterized in that: Including the sodium ion battery as claimed in claim 11.

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