Sodium-ion battery positive electrode material precursor as well as preparation method and application thereof

Abstract

The invention provides a sodium ion battery positive electrode material precursor and a preparation method and application thereof. The chemical general formula of the sodium ion battery positive electrode material precursor is NixMgyMz (OH) 2, 0.2 < = x < = 0.4, 0 < y < = 0.1, x / y = (3-5): 1, 0.4 < = z < = 0.7, and M is a transition metal. According to the invention, Mg is introduced to partially replace Ni, on one hand, the cost is greatly reduced, on the other hand, under the synergistic cooperation of the specific ratio of Mg to Ni, Mg is utilized to effectively excite the redox reaction of more active oxygen, so that the reversible capacity of the positive electrode material is further improved, and meanwhile, Mg is utilized to reduce the interlayer spacing of transition metal and improve the interlayer spacing of sodium, so that the reversible capacity of the positive electrode material is improved. The sodium ion diffusion rate is further improved, the rate capability of the positive electrode material is improved, the formation of other impure phases during O3-O3'phase conversion in the charging and discharging process is also remarkably inhibited, and the cycle performance of the positive electrode material is effectively improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials, and in particular relates to a sodium ion battery positive electrode material precursor, a preparation method and an application thereof. Background Art

[0002] Lithium-ion batteries, with their high energy density and long cycle life, are expected to be widely used in energy storage systems to promote the transformation of human energy structure. However, the scarcity, uneven distribution and high price of lithium resources have limited their large-scale application. As a suitable alternative, sodium-ion batteries have become an important development direction in the field of energy storage due to their abundant resource reserves and similar energy storage mechanism to lithium-ion batteries. Like lithium-ion batteries, the energy storage effect of sodium-ion batteries is also mainly affected by the positive electrode material. Therefore, there is an urgent need to find a positive electrode material with high energy density, low cost and long cycle life.

[0003] Sodium-ion battery cathode materials primarily include layered oxides, polyanionic compounds, and Prussian blue compounds. Layered oxides are widely researched and applied due to their low cost and high capacity. Currently developed layered oxide sodium-ion battery cathode materials with excellent electrochemical performance mostly contain around 33% nickel. However, nickel is not only expensive but also toxic.

[0004] Therefore, how to improve the electrochemical performance of the positive electrode material while reducing the nickel content to achieve the effect of reducing costs and increasing efficiency is a technical problem that needs to be solved urgently. Summary of the Invention

[0005] In view of the deficiencies in the prior art, the present invention aims to provide a sodium ion battery cathode material precursor, its preparation method and application. The present invention introduces Mg to partially replace Ni, which greatly reduces the cost on the one hand, and on the other hand, under the synergistic cooperation of the specific ratio of Mg and Ni, Mg is effectively used to stimulate the redox reaction of more active oxygen, thereby improving the reversible capacity of the cathode material. At the same time, Mg is used to reduce the transition metal interlayer spacing and increase the sodium interlayer spacing, thereby increasing the diffusion rate of sodium ions and improving the rate performance of the cathode material. In addition, the synergistic effect of Mg and Ni significantly inhibits the formation of other impurities during the O3-O3' phase transition during the charge and discharge process, effectively improving the cycle performance of the cathode material.

[0006] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0007] In the first aspect, the present invention provides a sodium ion battery positive electrode material precursor, the chemical formula of the sodium ion battery positive electrode material precursor is Ni x Mg y M z(OH)2, wherein 0.2≤x≤0.4, 0<y≤0.1, x / y=(3-5):1, 0.4≤z≤0.7, and M is a transition metal.

[0008] By partially replacing Ni with Mg, the present invention significantly reduces costs. Furthermore, through the synergistic effect of a specific Mg / Ni ratio, Mg effectively stimulates the redox reaction of more active oxygen species, thereby increasing the reversible capacity of the cathode material. Mg also reduces the distance between transition metal layers and increases the distance between sodium layers, thereby increasing the diffusion rate of sodium ions and improving the rate performance of the cathode material. Furthermore, the synergistic effect of Mg and Ni significantly suppresses the formation of other impurities during the O₃-O₃′ phase transition during charge and discharge, effectively improving the cycling performance of the cathode material.

[0009] In the present invention, 0.2≤x≤0.4, for example, it may be 0.2, 0.25, 0.3, 0.35 or 0.4.

[0010] In the present invention, 0<y≤0.1, for example, it can be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09 or 0.1.

[0011] In the present invention, the appropriate amount of Mg replacing Ni can not only meet the demand of reducing costs, but also fully stimulate the redox reaction of active oxygen and improve the reversible capacity of the material. If the amount of Mg replaced is too much, the number of active sites will be reduced, resulting in a decrease in capacity, and excessive replacement will also cause lattice distortion, increase ion diffusion resistance, reduce the electronic conductivity of the material, and affect the rate performance of the material; In addition, Ni 2+ Although the Jahn-Teller effect (which easily leads to lattice distortion in the low-spin state) may be partially alleviated by Mg substitution, excessive substitution will destroy the integrity of the layered structure and cause structural collapse.

[0012] In the present invention, x / y=(3-5):1, for example, it can be 3:1, 3.5:1, 4:1, 4.5:1 or 5:1.

[0013] In the present invention, the appropriate molar ratio of Mg to Ni helps to stimulate more redox reactions of active oxygen, thereby improving the reversible capacity of the material; helps to further reduce the transition metal interlayer spacing, increase the sodium interlayer spacing, increase the diffusion rate of sodium ions, and improve the rate performance; helps to fully inhibit the formation of other impurities during the O3-O3' phase conversion during the charge and discharge process, thereby improving the cycle performance of the material.

[0014] In the present invention, 0.4≤z≤0.7, for example, it may be 0.4, 0.45, 0.5, 0.55, 0.6, 0.65 or 0.7.

[0015] Preferably, the sodium ion battery positive electrode material precursor is a layered hydroxide.

[0016] Preferably, the value range of y is 0.04-0.06, for example, it can be 0.04, 0.045, 0.05, 0.055 or 0.06.

[0017] Preferably, the x / y=(3.5-4):1, for example, it can be 3.5:1, 3.6:1, 3.7:1, 3.8:1, 3.9:1 or 4:1.

[0018] Preferably, the M includes any one or a combination of at least two of Ti, Zn, Cr, Mn, Fe, Co or Cu.

[0019] In a second aspect, the present invention provides a method for preparing a precursor of a positive electrode material for a sodium ion battery as described in the first aspect, the preparation method comprising the following steps:

[0020] The mixed metal salt solution, the double complexing agent solution and the precipitant solution are mixed and subjected to a coprecipitation reaction to obtain a precursor of a positive electrode material for a sodium ion battery.

[0021] The mixed metal salt solution contains nickel ions, magnesium ions and M ions; and the dual complexing agent solution is a combination of a sodium salt of an organic acid containing a carboxyl group and an inorganic salt containing an ammonium group.

[0022] The preparation method provided by the present invention uses two complexing agents, a sodium salt of an organic acid containing a carboxyl group and an inorganic salt containing an ammonium group, to cooperate with each other, thereby enhancing the complexing ability of different metal ions. The inorganic salt containing an ammonium group has a stronger complexing ability for nickel and a weaker complexing ability for magnesium. At the same time, the introduction of a certain proportion of the sodium salt of an organic acid containing a carboxyl group can solve the problem of weak complexing ability for magnesium ions, so that different metal ions achieve a co-precipitation effect, which is conducive to obtaining a positive electrode material precursor with uniform element distribution, and also increases the utilization rate of active metal atoms in the positive electrode material, which helps to effectively exert the capacity of the positive electrode material.

[0023] Preferably, the total concentration of metal ions in the mixed metal salt solution is 0.5-5 mol / L, for example, 0.5 mol / L, 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L or 5 mol / L.

[0024] Preferably, in the dual complexing agent solution, the concentrations of the two solutes are independently 0.2-2 mol / L, for example, 0.2 mol / L, 0.5 mol / L, 1 mol / L, 1.5 mol / L or 2 mol / L.

[0025] Preferably, in the dual complexing agent solution, the molar ratio of the carboxyl-containing organic acid sodium salt to the ammonium-containing inorganic salt is (0.2-0.8):1, for example, it can be 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1 or 0.8:1.

[0026] In the present invention, a suitable molar ratio helps to make the complexing strengths of different metal ions relatively close, so that different metal ions can achieve a good co-precipitation effect, which is conducive to obtaining a positive electrode material precursor with uniform element distribution.

[0027] Preferably, the concentration of the precipitant solution is 2-15 mol / L, for example, 2 mol / L, 5 mol / L, 7 mol / L, 10 mol / L, 12 mol / L or 15 mol / L, etc., preferably 8-12 mol / L.

[0028] Preferably, the carboxyl-containing organic acid sodium salt includes any one of sodium oxalate, sodium acetate, sodium citrate or EDTA, or a combination of at least two thereof.

[0029] Preferably, the inorganic salt containing ammonium radicals includes any one of ammonium sulfate, ammonium bisulfate, ammonium chloride or ammonium nitrate, or a combination of at least two thereof.

[0030] Preferably, the precipitant solution comprises any one of sodium hydroxide solution, potassium hydroxide solution, sodium carbonate solution, sodium bicarbonate solution or ammonium bicarbonate solution, or a combination of at least two thereof.

[0031] Preferably, the mixing method includes a parallel flow feeding method, and the steps of the parallel flow feeding method include:

[0032] The mixed metal salt solution, the double complexing agent solution and the precipitant solution are added into the prefabricated bottom solution in parallel for mixing.

[0033] In the present invention, the parallel flow feeding method can achieve rapid dispersion at the molecular level, reduce side reactions and impurity generation; secondly, it can accurately adjust the growth particle size and morphology, reduce surface defects, and improve process stability and production efficiency.

[0034] Preferably, the feed rate of the mixed metal salt solution is 4-100 L / h, for example, it can be 4 L / h, 5 L / h, 10 L / h, 20 L / h, 30 L / h, 40 L / h, 50 L / h, 60 L / h, 70 L / h, 80 L / h, 90 L / h or 100 L / h, etc.

[0035] Preferably, the feeding rate of the dual complexing agent solution is 1-20 L / h, for example, 1 L / h, 5 L / h, 10 L / h, 15 L / h or 20 L / h.

[0036] Preferably, the feed rate of the precipitant solution is 0.5-10 L / h, for example, it can be 0.5 L / h, 1 L / h, 2 L / h, 3 L / h, 4 L / h, 5 L / h, 6 L / h, 7 L / h, 8 L / h, 9 L / h or 10 L / h.

[0037] Preferably, the feed rate ratio of the mixed metal salt solution and the dual complexing agent solution is 1:(0.1-0.8), for example, it can be 1:0.1, 1:0.2, 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7 or 1:0.8, etc.

[0038] In the present invention, a suitable feed rate ratio can always maintain a reasonable ratio between metal ions and complexing agent, avoid side reactions such as hydrolysis and polymerization caused by local overconcentration, and ensure the production efficiency of the target product; a suitable feed rate ratio can balance the nucleation and growth processes, obtain products with uniform particle size and regular morphology, which is beneficial to improving the physical and chemical properties of the material; a suitable feed rate ratio can ensure uniform complexation of metal ions and uniform distribution of elements, and ultimately form a positive electrode material precursor with stable structure and uniform interface, which is beneficial to improving the cycle life and rate performance of the battery.

[0039] Preferably, the pH value of the base solution is 8-12, for example, it can be 8, 9, 10, 11 or 12.

[0040] In the present invention, limiting the pH value of the base liquid to 8-12 is conducive to stabilizing the reaction in the early nucleation stage, and the cores of the obtained precursor particles are evenly dispersed and have good sphericity; secondly, controlling the pH value of the base liquid to 8-12 can avoid the problem of precursor particle agglomeration during feeding.

[0041] Preferably, the base liquid comprises a sodium salt of an organic acid containing a carboxyl group and an inorganic salt containing an ammonium group.

[0042] Preferably, the concentrations of the carboxyl-containing organic acid sodium salt and the ammonium-containing inorganic salt in the base solution are each independently 5-100 mmol / L, for example, 5 mmol / L, 10 mmol / L, 20 mmol / L, 30 mmol / L, 40 mmol / L, 50 mmol / L, 60 mmol / L, 70 mmol / L, 80 mmol / L, 90 mmol / L or 100 mmol / L, etc.

[0043] In the present invention, the low concentration of complexing agent solution in the base liquid is helpful for the stable progress of the reaction in the early nucleation stage.

[0044] Preferably, the coprecipitation reaction temperature is 20-70°C, for example, 20°C, 30°C, 40°C, 50°C, 60°C or 70°C.

[0045] Preferably, during the coprecipitation reaction, the pH value of the reaction system is controlled in the range of 8-12, for example, 8, 9, 10, 11 or 12.

[0046] In the present invention, during the coprecipitation reaction, the pH value of the reaction system is controlled in the range of 8-12, which can ensure that the metal ions are completely precipitated and the composition is controllable, promote uniform coprecipitation, obtain product particles with good dispersibility and uniform particle size, avoid side reactions and the introduction of impurities, and improve product purity.

[0047] Preferably, the coprecipitation reaction is carried out under a protective atmosphere, which is an inert atmosphere, for example, a nitrogen atmosphere or an argon atmosphere.

[0048] Preferably, at the end of the coprecipitation reaction, the average particle size of the product particles is 5-10 μm, for example, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 10 μm.

[0049] Preferably, after the coprecipitation reaction is completed, post-processing is further performed, and the post-processing steps include:

[0050] The coprecipitated product is aged, washed and dried.

[0051] In a third aspect, the present invention provides a sodium ion battery positive electrode material, which is obtained by mixing and sintering the sodium ion battery positive electrode material precursor as described in the first aspect and a sodium source.

[0052] Preferably, the sodium ion battery positive electrode material is a layered oxide.

[0053] Preferably, the sintering temperature is 800-1400°C, for example, 800°C, 900°C, 1000°C, 1100°C, 1200°C, 1300°C or 1400°C.

[0054] Preferably, the sintering time is 10-25 hours, for example, 10 hours, 15 hours, 20 hours or 25 hours.

[0055] In a fourth aspect, the present invention provides a sodium ion battery, wherein the positive electrode sheet of the sodium ion battery comprises the sodium ion battery positive electrode material as described in the third aspect.

[0056] The numerical range described in the present invention includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0057] Compared with the prior art, the present invention has the following beneficial effects:

[0058] (1) The present invention introduces Mg to partially replace Ni, significantly reducing costs. Furthermore, with the synergistic effect of a specific ratio of Mg to Ni, Mg effectively stimulates the redox reaction of more active oxygen, thereby increasing the reversible capacity of the positive electrode material. Mg also reduces the distance between transition metal layers and increases the distance between sodium layers, thereby increasing the diffusion rate of sodium ions and improving the rate performance of the positive electrode material. Furthermore, the synergistic effect of Mg and Ni significantly inhibits the formation of other impurities during the O3-O3' phase transition during charge and discharge, effectively improving the cycle performance of the positive electrode material.

[0059] (2) The preparation method provided by the present invention uses two complexing agents, a sodium salt of an organic acid containing a carboxyl group and an inorganic salt containing an ammonium group, to cooperate with each other, thereby enhancing the complexing ability of different metal ions, so that different metal ions can achieve the effect of co-precipitation, which is beneficial to obtaining a positive electrode material precursor with uniform element distribution, and also increases the utilization rate of active metal atoms in the positive electrode material, which helps to effectively exert the capacity of the positive electrode material.

[0060] (3) The sodium ion battery prepared based on the positive electrode material precursor provided by the invention has the advantages of high energy density, good safety and low production cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 This is an SEM image of the positive electrode material precursor prepared in Example 1 of the present invention.

[0062] Figure 2 This is a cross-sectional EPMA image of the Ni element in the positive electrode material precursor prepared in Example 1 of the present invention.

[0063] Figure 3 This is a cross-sectional EPMA image of the Mg element in the positive electrode material precursor prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0064] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0065] Example 1

[0066] This embodiment provides a sodium ion battery cathode material precursor, the chemical formula of which is Ni x Mg y M z (OH)2, wherein x=0.25, y=0.05, x / y=5:1, z=0.7, and M comprises Fe and Mn in a molar ratio of 4:3.

[0067] This embodiment also provides a method for preparing the above-mentioned sodium ion battery positive electrode material precursor, the preparation method comprising the following steps:

[0068] (1) A mixed metal salt solution, a double complexing agent solution, and a precipitant solution are added to a reactor containing a prefabricated bottom solution in parallel and mixed, and the pH value of the reaction system is controlled to be in the range of 9.6-9.8. A coprecipitation reaction is carried out at a temperature of 45° C. under a nitrogen atmosphere for 50 hours. When the average particle size of the product particles reaches 5 μm, the reaction is stopped to obtain a coprecipitation reaction product.

[0069] The mixed metal salt solution contains nickel ions, magnesium ions, iron ions and manganese ions in a molar ratio of 0.25:0.05:0.4:0.3, and the total concentration of metal ions is 2 mol / L; the double complexing agent solution is a combination of sodium oxalate and ammonium sulfate, the concentration of sodium oxalate is 0.3 mol / L, the concentration of ammonium sulfate is 0.5 mol / L, and the molar ratio of sodium oxalate to ammonium sulfate is 0.6:1; the concentration of the precipitant solution is 10 mol / L, and the precipitant solution is a sodium hydroxide solution.

[0070] The feeding rate of the mixed metal salt solution is 20 L / h, the feeding rate of the dual complexing agent solution is 3 L / h, the feeding rate of the precipitant solution is 7 L / h, and the feeding rate ratio of the mixed metal salt solution to the dual complexing agent solution is 1:0.15; the pH value of the base liquid is 11, and the base liquid includes sodium oxalate with a concentration of 30 mmol / L and ammonium sulfate with a concentration of 50 mmol / L.

[0071] (2) The coprecipitation reaction product was aged for 12 h, centrifuged and washed, and then dried at 130° C. to obtain a powdered sodium ion battery positive electrode material precursor.

[0072] This embodiment also provides a sodium ion battery positive electrode material, the chemical formula of which is NaNi 0.25 Mg 0.05 Fe 0.40 Mn 0.30 O2.

[0073] The sodium ion battery positive electrode material is obtained by mixing and sintering the sodium ion battery positive electrode material precursor as described above with a sodium source, and the specific steps include:

[0074] Sodium carbonate and the sodium ion battery positive electrode material precursor were weighed and evenly mixed in a molar ratio of 1.03:1, and then calcined at 900° C. for 18 hours. After grinding and screening, the sodium ion battery positive electrode material was obtained.

[0075] Figure 1The SEM image of the positive electrode material precursor prepared in this embodiment is shown. It can be seen from the figure that the sodium electrode precursor particles prepared in this embodiment have uniform particle size distribution and good sphericity.

[0076] Figure 2 The cross-sectional EPMA diagram of the Ni element in the positive electrode material precursor prepared in this embodiment is shown. It can be seen from the figure that the nickel element is evenly distributed inside the sodium electrode precursor particles prepared in this embodiment.

[0077] Figure 3 The cross-sectional EPMA diagram of the Mg element in the positive electrode material precursor prepared in this embodiment is shown. As can be seen from the figure, the magnesium element is evenly distributed inside the sodium electrode precursor particles prepared in this embodiment.

[0078] Example 2

[0079] This embodiment provides a sodium ion battery cathode material precursor, the chemical formula of which is Ni x Mg y M z (OH)2, wherein x=0.3, y=0.06, x / y=5:1, z=0.64, and M is Mn.

[0080] This embodiment also provides a method for preparing the above-mentioned sodium ion battery positive electrode material precursor, the preparation method comprising the following steps:

[0081] (1) A mixed metal salt solution, a double complexing agent solution, and a precipitant solution are added to a reactor containing a prefabricated bottom solution in parallel and mixed, and the pH value of the reaction system is controlled to be in the range of 10-10.2. A coprecipitation reaction is carried out at a temperature of 52° C. under a nitrogen atmosphere for 90 hours. When the average particle size of the product particles reaches 9 μm, the reaction is stopped to obtain a coprecipitation reaction product.

[0082] The mixed metal salt solution contains nickel ions, magnesium ions and manganese ions in a molar ratio of 0.3:0.06:0.64, and the total concentration of metal ions is 2 mol / L; the double complexing agent solution is a combination of sodium citrate and ammonium sulfate, the concentration of sodium citrate is 0.2 mol / L, the concentration of ammonium sulfate is 0.5 mol / L, and the molar ratio of sodium citrate to ammonium sulfate is 0.4:1; the concentration of the precipitant solution is 10 mol / L, and the precipitant solution is a sodium hydroxide solution.

[0083] The feed rate of the mixed metal salt solution is 40 L / h, the feed rate of the dual complexing agent solution is 8 L / h, the feed rate of the precipitant solution is 10 L / h, and the feed rate ratio of the mixed metal salt solution to the dual complexing agent solution is 1:(0.2); the pH value of the base liquid is 11.2, and the base liquid includes sodium citrate with a concentration of 20 mmol / L and ammonium sulfate with a concentration of 50 mmol / L.

[0084] (2) The coprecipitation reaction product was aged for 8 h, centrifuged and washed, and then dried at 150° C. to obtain a powdered sodium ion battery positive electrode material precursor.

[0085] This embodiment also provides a sodium ion battery positive electrode material, the chemical formula of which is NaNi 0.3 Mg 0.06 Mn 0.64 O2.

[0086] The sodium ion battery positive electrode material is obtained by mixing and sintering the sodium ion battery positive electrode material precursor as described above with a sodium source, and the specific steps include:

[0087] Sodium carbonate and the sodium ion battery positive electrode material precursor were weighed and evenly mixed in a molar ratio of 1.05:1, and then calcined at 1000° C. for 16 hours. After grinding and screening, the sodium ion battery positive electrode material was obtained.

[0088] Example 3

[0089] The difference between this embodiment and embodiment 1 is that the content of magnesium ions in the mixed metal salt solution in step (1) is adjusted so that in the sodium ion battery positive electrode material precursor, y=0.06, x=0.24, and x / y=4:1.

[0090] The rest of the preparation methods and parameters remained the same as in Example 1.

[0091] Example 4

[0092] The difference between this embodiment and embodiment 1 is that the content of magnesium ions in the mixed metal salt solution in step (1) is adjusted so that in the sodium ion battery positive electrode material precursor, y=0.0625, x=0.2375, and x / y=3.8:1.

[0093] The rest of the preparation methods and parameters remained the same as in Example 1.

[0094] Example 5

[0095] The difference between this embodiment and embodiment 1 is that the molar ratio of sodium oxalate to ammonium sulfate in step (1) is 0.1:1.

[0096] The rest of the preparation methods and parameters remained the same as in Example 1.

[0097] Example 6

[0098] The difference between this embodiment and embodiment 1 is that the molar ratio of sodium oxalate to ammonium sulfate in step (1) is 1.5:1.

[0099] The rest of the preparation methods and parameters remained the same as in Example 1.

[0100] Example 7

[0101] The difference between this embodiment and embodiment 1 is that the feed rate ratio of the mixed metal salt solution and the dual complexing agent solution in step (1) is 1:0.05.

[0102] The rest of the preparation methods and parameters remained the same as in Example 1.

[0103] Example 8

[0104] The difference between this embodiment and embodiment 1 is that the feed rate ratio of the mixed metal salt solution and the dual complexing agent solution in step (1) is 1:1.

[0105] The rest of the preparation methods and parameters remained the same as in Example 1.

[0106] Example 9

[0107] The difference between this embodiment and embodiment 1 is that no base liquid is provided.

[0108] The rest of the preparation methods and parameters remained the same as in Example 1.

[0109] Example 10

[0110] The difference between this embodiment and embodiment 1 is that the temperature of the coprecipitation reaction in step (1) is 100°C.

[0111] The rest of the preparation methods and parameters remained the same as in Example 1.

[0112] Comparative Example 1

[0113] The difference between this comparative example and Example 1 is that the metal ions in the mixed metal salt solution in step (1) do not contain magnesium ions, and the molar ratio of the metal elements in the sodium ion battery positive electrode material precursor is Ni:Fe:Mn=0.25:0.4:0.3.

[0114] The rest of the preparation methods and parameters remained the same as in Example 1.

[0115] Comparative Example 2

[0116] The difference between this comparative example and Example 1 is that the ammonium sulfate in the double complexing agent solution and the base solution in step (1) is replaced by an equimolar amount of sodium oxalate.

[0117] The rest of the preparation methods and parameters remained the same as in Example 1.

[0118] Comparative Example 3

[0119] This comparative example differs from Example 2 in that the metal ions in the mixed metal salt solution in step (1) do not contain magnesium ions, and the ammonium sulfate in both the double complexing agent solution and the base solution in step (1) is replaced with an equimolar amount of sodium citrate. This results in a metal element molar ratio of Ni:Mn in the sodium ion battery positive electrode material precursor of 0.3:0.64.

[0120] The rest of the preparation methods and parameters remained the same as in Example 2.

[0121] Comparative Example 4

[0122] The difference between this comparative example and Example 1 is that the content of magnesium ions in the mixed metal salt solution in step (1) is adjusted so that in the sodium ion battery positive electrode material precursor, y=0.1, x=0.2, and x / y=2:1.

[0123] The rest of the preparation methods and parameters remained the same as in Example 1.

[0124] Comparative Example 5

[0125] The difference between this comparative example and Example 1 is that the content of magnesium ions in the mixed metal salt solution in step (1) is adjusted so that in the sodium ion battery positive electrode material precursor, y=0.045, x=0.255, and x / y=5.67:1.

[0126] The rest of the preparation methods and parameters remained the same as in Example 1.

[0127] Comparative Example 6

[0128] The difference between this comparative example and Example 1 is that the content of magnesium ions in the mixed metal salt solution in step (1) is adjusted so that y=0.3 and x=0 in the sodium ion battery positive electrode material precursor.

[0129] The rest of the preparation methods and parameters remained the same as in Example 1.

[0130] Performance Testing

[0131] At 25° C., the positive electrode materials prepared in the above examples and comparative examples were used as the positive electrode main material to prepare positive electrode sheets, and the metal sodium sheet was used as the negative electrode sheet to assemble into CR2032 button batteries.

[0132] Cyclic performance test: In the voltage range of 2-4V, the discharge current density is 10mA·g -1 Repeat 5 times.

[0133] Rate performance test: at discharge current density of 140 mA g -1 and 14 mA·g -1 A discharge test was carried out under the same conditions, and the discharge capacities were compared to obtain the 1C / 0.1C capacity retention rate.

[0134] The test results are shown in Table 1

[0135] Table 1

[0136]

[0137]

[0138] analyze:

[0139] It can be seen from Examples 1-2 that the button battery prepared from the cathode material precursor provided by the present invention has excellent cycle performance and rate performance.

[0140] From the comparison of Example 1, Examples 3-4 and Comparative Examples 4-5, it can be seen that the appropriate molar ratio of Mg and Ni helps to stimulate the redox reaction of more active oxygen, thereby improving the reversible capacity of the material; helps to further reduce the distance between transition metal layers, increase the distance between sodium layers, increase the diffusion rate of sodium ions, and improve the rate performance; helps to fully inhibit the formation of other impurities during the O3-O3' phase transition during the charge and discharge process, and improve the cycle performance of the material. If the molar ratio of x / y is too small, the amount of Mg substitution is too much, which will reduce the number of active sites and lead to a decrease in capacity, and excessive substitution will also cause lattice distortion, increase ion diffusion resistance, reduce the electronic conductivity of the material, and affect the rate performance of the material; in addition, Ni 2+ While the Jahn-Teller effect (lattice distortion in the low-spin state) can be partially alleviated by Mg substitution, excessive substitution can damage the integrity of the layered structure and cause structural collapse. If the x / y molar ratio is too large, too little Mg will not only fail to achieve the cost-effectiveness effect, but will also lead to a decrease in battery capacity performance.

[0141] From the comparison between Example 1 and Examples 5-6, it can be seen that a molar ratio of sodium oxalate to ammonium sulfate that is too small or too large is not conducive to the co-precipitation of different metal ions to obtain a precursor with uniform element distribution, which in turn leads to a significant decrease in the electrochemical performance of the final positive electrode material.

[0142] By comparing Example 1 with Examples 7-8, it can be seen that if the feed rate ratio of the mixed metal salt solution and the dual complexing agent solution is too small, the complexing ability will be too strong and the precipitation rate will be too slow, which will affect the morphology of the precursor and thus affect the electrical properties of the positive electrode material; if the feed rate ratio of the mixed metal salt solution and the dual complexing agent solution is too large, it will be unfavorable for the complexing agent to fully complex the metal ions, resulting in a faster precipitation rate, poor morphology of the obtained precursor, and ultimately poor performance of the sintered positive electrode material.

[0143] From the comparison between Example 1 and Example 9, it can be seen that if the base liquid is not provided, precursor particles with regular morphology cannot be obtained, and the particle size distribution of the positive electrode material after sintering is also uneven and the morphology is irregular, which affects the performance of its capacity during the charge and discharge process.

[0144] From the comparison between Example 1 and Example 10, it can be seen that if the coprecipitation reaction temperature is too high, more impurities will be formed during the coprecipitation process. After calcination, the impurities cannot form an electrochemically active layered oxide positive electrode material, which ultimately leads to a low capacity of the positive electrode material.

[0145] From the comparison between Example 1 and Comparative Example 1, it can be seen that if magnesium ions are not introduced to replace part of the nickel ions, the sodium interlayer spacing of the obtained positive electrode material is small, the capacity is low, and the rate performance is poor.

[0146] From the comparison between Example 1 and Comparative Example 2, it can be seen that if only sodium oxalate is used as the complexing agent, the co-precipitated elements will be unevenly distributed, and thus a positive electrode material with uniform element distribution cannot be obtained, and the performance of the positive electrode material will be significantly reduced.

[0147] From the comparison between Example 2 and Comparative Example 3, it can be seen that if only sodium citrate is used as a complexing agent and magnesium ions are not introduced to replace part of the nickel ions, the elements of the obtained positive electrode material are evenly distributed and the sodium interlayer spacing is small, resulting in poor performance.

[0148] From the comparison between Example 1 and Comparative Example 6, it can be seen that if magnesium ions completely replace nickel ions, the active metal element content of the positive electrode material will be significantly reduced, and both the capacity and rate performance will drop significantly.

[0149] It should be noted that while the present invention illustrates the process method through the above-described embodiments, the present invention is not limited to the above-described process steps, and does not necessarily rely on the above-described process steps for implementation. Those skilled in the art will appreciate that any improvements to the present invention, equivalent replacements for the raw materials used, additions of auxiliary components, and selection of specific methods, etc., fall within the scope of protection and disclosure of the present invention.

Claims

1. A sodium ion battery cathode material precursor, characterized in that: The chemical formula of the sodium ion battery cathode material precursor is Ni x Mg y M z (OH)2, wherein 0.2≤x≤0.4, 0<y≤0.1, x / y=(3-5):1, 0.4≤z≤0.7, and M is a transition metal.

2. The sodium ion battery cathode material precursor according to claim 1, characterized in that The precursor of the sodium ion battery cathode material is a layered hydroxide; Preferably, the value range of y is 0.04-0.06; Preferably, x / y=(3.5-4):1; Preferably, the M includes any one or a combination of at least two of Ti, Zn, Cr, Mn, Fe, Co or Cu.

3. A method for preparing a sodium ion battery cathode material precursor according to claim 1 or 2, characterized in that: The preparation method comprises the following steps: The mixed metal salt solution, the double complexing agent solution and the precipitant solution are mixed to carry out a coprecipitation reaction to obtain a precursor of a positive electrode material for a sodium ion battery; The mixed metal salt solution contains nickel ions, magnesium ions and M ions; and the dual complexing agent solution is a combination of a sodium salt of an organic acid containing a carboxyl group and an inorganic salt containing an ammonium group.

4. The preparation method according to claim 3, characterized in that In the mixed metal salt solution, the total concentration of metal ions is 0.5-5 mol / L; Preferably, in the dual complexing agent solution, the concentrations of the two solutes are independently 0.2-2 mol / L; Preferably, in the dual complexing agent solution, the molar ratio of the carboxyl-containing organic acid sodium salt to the ammonium-containing inorganic salt is (0.2-0.8):1; Preferably, the concentration of the precipitant solution is 2-15 mol / L, preferably 8-12 mol / L.

5. The preparation method according to claim 3 or 4, characterized in that The carboxyl-containing organic acid sodium salt includes any one of sodium oxalate, sodium acetate, sodium citrate or EDTA, or a combination of at least two thereof; Preferably, the inorganic salt containing ammonium radicals comprises any one or a combination of at least two of ammonium sulfate, ammonium bisulfate, ammonium chloride or ammonium nitrate; Preferably, the precipitant solution comprises any one of sodium hydroxide solution, potassium hydroxide solution, sodium carbonate solution, sodium bicarbonate solution or ammonium bicarbonate solution, or a combination of at least two thereof.

6. The preparation method according to any one of claims 3 to 5, characterized in that The mixing method includes a parallel flow feeding method, and the steps of the parallel flow feeding method include: Adding the mixed metal salt solution, the double complexing agent solution and the precipitant solution into the pre-made base solution in parallel for mixing; Preferably, the feed rate of the mixed metal salt solution is 4-100 L / h; Preferably, the feeding rate of the dual complexing agent solution is 1-20 L / h; Preferably, the feed rate of the precipitant solution is 0.5-10 L / h; Preferably, the feed rate ratio of the mixed metal salt solution and the dual complexing agent solution is 1:(0.1-0.8); Preferably, the pH value of the base liquid is 8-12; Preferably, the base liquid includes a sodium salt of an organic acid containing a carboxyl group and an inorganic salt containing an ammonium group; Preferably, the concentrations of the carboxyl-containing organic acid sodium salt and the ammonium-containing inorganic salt in the base solution are independently 5-100 mmol / L.

7. The preparation method according to any one of claims 3 to 6, characterized in that The temperature of the coprecipitation reaction is 20-70°C; Preferably, during the coprecipitation reaction, the pH value of the reaction system is controlled in the range of 8-12; Preferably, the coprecipitation reaction is carried out under a protective atmosphere, which is an inert atmosphere; Preferably, at the end of the coprecipitation reaction, the average particle size of the product particles is 5-10 μm; Preferably, after the coprecipitation reaction is completed, post-processing is further performed, and the post-processing steps include: The coprecipitated product is aged, washed and dried.

8. A sodium ion battery cathode material, characterized in that The sodium ion battery positive electrode material is obtained by mixing and sintering the sodium ion battery positive electrode material precursor according to claim 1 or 2 and a sodium source.

9. The sodium ion battery cathode material according to claim 8, characterized in that The sodium ion battery positive electrode material is a layered oxide; Preferably, the sintering temperature is 800-1400°C; Preferably, the sintering time is 10-25 hours.

10. A sodium ion battery, characterized in that: The positive electrode sheet of the sodium ion battery includes the sodium ion battery positive electrode material according to claim 8 or 9.

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