Modified preparation method of sodium manganese titanium phosphate cathode material of sodium-ion battery

Abstract

The invention belongs to the field of sodium ion batteries, and discloses a modification preparation method of a sodium manganese titanium phosphate positive electrode material of a sodium ion battery, which comprises the following steps: S1, weighing a metal ion chelating agent to prepare a solution I; s2, weighing a manganese source, a titanium source and a sodium source, and dissolving in the solution I to obtain a solution II; s3, dissolving a Li, Mg or Ca source material in the solution II to obtain a solution III; weighing phosphate to prepare a solution IV; s4, dropwise adding the solution IV into the solution III; and S5, stirring under an oil bath condition, and then drying and calcining to obtain the target modified titanium manganese sodium phosphate positive electrode material. The modified titanium manganese sodium phosphate positive electrode material is obtained by introducing a low-orbital energy level element Li, Mg or Ca into the titanium manganese sodium phosphate Na3MnTi (PO4) 3 positive electrode material and controlling the preparation method at the same time, a Li (Mg, Ca)-O-Mn electron configuration is constructed, the inhibition of antisite defects is realized, and the improvement of electrochemical performance is facilitated.

Description

Technical Field

[0001] The present invention belongs to the field of sodium ion batteries, and more specifically, relates to a method for modifying and preparing a sodium ion battery sodium manganese titanium phosphate positive electrode material. The obtained modified sodium manganese titanium phosphate positive electrode material has the characteristics of suppressing antisite defects and improving the crystal structure, and can optimize and improve the electrochemical performance of the sodium manganese titanium phosphate positive electrode material. Background Art

[0002] In order to adapt to the global trend of green energy and low-carbon economic development, sodium-ion batteries (SIBs) have attracted more and more attention due to their abundant natural sodium resources and low cost. The positive electrode material is an important component of SIBs and largely determines the electrochemical performance of SIBs. Therefore, it is necessary to develop positive electrode materials with fast kinetics and high energy density to meet this growing demand. Sodium superionic conductor (NASICON) phosphate has become a promising positive electrode material for SIBs due to its high safety and good structural stability. Sodium manganese titanium phosphate (Na 3 MnTi(PO 4 ) 3 ) as a typical NASICON positive electrode material, in the voltage range of 1.5-4.3V, accompanied by Mn 4+ / 3+ (≈4.0V vs Na+ / Na), Mn 3+ / 2+ (≈3.6V vs Na+ / Na) and Ti 4+ / 3+ (≈2.1 V vs Na+ / Na) redox couple, which can achieve multi-electron transfer, thus obtaining 178 mAh g -1 High theoretical specific capacity. 3 MnTi(PO 4 ) 3 (NMTP) is composed of PO 4 Tetrahedron and MO 6 (M represents a transition metal element, i.e., Ti and Mn) octahedrons share corners to form a three-dimensional open framework configuration, Na + Located in two independent Na sites, namely (Na1, crystal plane orientation is 6b) and (Na2, crystal plane orientation is 18e), so that they have different Na + coordination environment, and during the charge and discharge process, Na + Ions tend to be reversibly extracted from and inserted into the Na2 site.

[0003] However, Na 3 MnTi(PO 4 ) 3 There are still several problems that need to be solved in positive electrode materials. 3 MnTi(PO 4 ) 3There are quite a lot of Na vacancies in the framework, and Mn 2+ It is easy to occupy these vacancies and form antisite defects. 2+ The offside occupation will not only hinder the diffusion path of Na2-Na1-Na2, but also increase the Na + The diffusion barrier will also destroy the crystal integrity, affecting the electronic conductivity and ion diffusion capacity, which will eventually lead to severe voltage hysteresis and rapid capacity loss of NMTP. Summary of the invention

[0004] In view of the above defects or improvement needs of the prior art, the object of the present invention is to provide a method for modifying and preparing a positive electrode material of a sodium ion battery by adding sodium manganese titanium phosphate to the positive electrode material. 3 MnTi(PO 4 ) 3 Low orbital energy level elements Li, Mg or Ca are introduced into the positive electrode material, and the overall process design of the preparation method and key reaction conditions (such as the amount of low orbital energy level metal elements introduced and the amount of metal ion chelating agent) are controlled to obtain a modified sodium manganese titanium phosphate positive electrode material, construct a Li(Mg, Ca)-O-Mn electronic configuration, achieve the suppression of anti-site defects, and facilitate the improvement of electrochemical performance. The present invention is easy to operate and easy to industrialize. The prepared modified sodium manganese titanium phosphate positive electrode material is easy to control, and the prepared material has excellent cycle performance, rate performance, and structural stability.

[0005] To achieve the above object, according to one aspect of the present invention, a method for preparing a modified sodium manganese titanium phosphate positive electrode material is provided, wherein the molar ratio of the Mn element to the Ti element in the modified sodium manganese titanium phosphate positive electrode material is 1:1, and the preparation method comprises the following steps:

[0006] S1. Weigh a metal ion chelating agent and dissolve it in anhydrous ethanol to obtain a solution I; wherein the ratio of the amount of the metal ion chelating agent contained in the solution I to the total amount of two transition metal elements, Mn and Ti, in the target modified sodium manganese titanium phosphate positive electrode material product is (0.5-3):2;

[0007] S2. According to the Mn element and Ti element in the target modified sodium manganese titanium phosphate positive electrode material product, a manganese source and a titanium source are weighed, and a sodium source is weighed at the same time, so that the molar ratio of the Na element provided by the sodium source to the Mn element provided by the manganese source is greater than 3:1 and less than or equal to 3.05:1; the sodium source, the manganese source and the titanium source are dissolved in solution I to obtain solution II;

[0008] S3, taking any one of Li, Mg and Ca as a low orbital energy level metal element, and weighing a low orbital energy level metal element source material according to a molar ratio of the low orbital energy level metal element to the Na element provided by the sodium source in the solution II of 0.01 to 0.05:3; dissolving the low orbital energy level metal element source material in solution II to obtain solution III;

[0009] At the same time, weigh phosphate and dissolve it in deionized water to obtain solution IV; wherein the molar ratio of the phosphate contained in the phosphate to the Na element provided by the sodium source in the solution II is 1:1;

[0010] S4, add solution IV dropwise into solution III and stir thoroughly to obtain solution V;

[0011] S5. Stir solution V in an oil bath, dry after sufficient reaction, and then calcine at a temperature of 600 to 750° C. for 4 to 6 hours to obtain the target modified sodium manganese titanium phosphate positive electrode material.

[0012] As a further preferred embodiment of the present invention, in step S1, the metal ion chelating agent is selected from tartaric acid, anhydrous citric acid, disodium ethylenediaminetetraacetic acid, and gluconic acid;

[0013] In step S2, the sodium source is selected from sodium acetate and sodium nitrate; the manganese source is selected from manganese acetate and manganese nitrate; the titanium source is selected from tetrabutyl titanate and isopropyl titanate;

[0014] In step S3, the low orbital energy level metal element source material is selected from lithium acetate, lithium nitrate, magnesium acetate, magnesium nitrate, calcium acetate, and calcium nitrate; and the phosphate is diammonium phosphate.

[0015] As a further preferred embodiment of the present invention, in step S3, the concentration of phosphate in the solution IV is 0.345 g / mL;

[0016] In step S4, the dripping rate of the dropwise infusion is 1-5 ml / min; the dropwise infusion is preferably performed using a peristaltic pump; preferably, the dripping speed of the peristaltic pump is 2 ml / min.

[0017] As a further preferred embodiment of the present invention, in step S5, the oil bath is specifically an oil bath with a temperature of 70-85°C, preferably an oil bath with a temperature of 80°C;

[0018] The drying temperature used for the drying is 100-120°C, preferably 110°C; preferably, the drying is carried out using a blast drying oven;

[0019] The calcination is carried out in an Ar atmosphere, the calcination temperature used is 650° C., and the treatment time is 6 to 8 hours.

[0020] As a further preferred embodiment of the present invention, in step S1, the ratio of the amount of the metal ion chelating agent contained in the solution I to the total amount of two transition metal elements, Mn and Ti, in the target modified sodium manganese titanium phosphate positive electrode material product is 1:1.

[0021] As a further preferred embodiment of the present invention, in step S3, the molar ratio of the low orbital energy level metal element to the Na element provided by the sodium source in the solution II is 0.03:3.

[0022] As a further preferred embodiment of the present invention, in step S4, the sufficient stirring is specifically stirring for 20 to 40 minutes after all solution IV is dripped into solution III, and the stirring speed is 200 to 500 r / min.

[0023] According to another aspect of the present invention, the present invention provides a modified sodium manganese titanium phosphate positive electrode material obtained by the above preparation method.

[0024] According to another aspect of the present invention, the present invention provides the use of the modified sodium manganese titanium phosphate positive electrode material as a positive electrode material in a sodium ion battery.

[0025] Through the above technical scheme conceived by the present invention, compared with the prior art, the present invention provides sodium manganese titanium phosphate Na 3 MnTi(PO 4 ) 3 Introducing low orbital energy level Li into the positive electrode material + Mg 2+ , Ca 2+ Replace Na + , constructing Li(Mg, Ca)-O-Mn configuration, suppressing antisite defects, and providing a new modification method and corresponding modified materials for the field of sodium superion conductor (NASICON) phosphate cathode materials. Due to the large orbital energy difference between Li 2s (Mg 3s, Ca 4s) and O 2p, hybridization is limited, which will strengthen the dp orbital hybridization between Mn 3d and O 2p, promote more charge transfer from Mn to O, thereby forming a stronger Mn-O bond, hindering the Mn 2+ Migration to the Na site. Thanks to the strong dp orbital hybridization, the Mn 2+ The offside occupation reduces the anti-site defect, which is directly reflected in the effective control of voltage hysteresis and the improvement of electrochemical performance.

[0026] Specifically, the present invention can achieve the following beneficial effects:

[0027] (1) The method of the present invention is to prepare sodium manganese titanium phosphate Na 3 MnTi(PO 4 ) 3The cathode material introduces low orbital energy level elements Li, Mg or Ca. The modification method specifically dissolves various metal source materials (i.e., manganese source, titanium source, sodium source, low orbital energy level metal element source materials; for example, metal salt compounds of corresponding metal elements can be used as source materials) in anhydrous ethanol, coordinates and combines with a chelating agent, and then obtains a site-substituted sodium manganese titanium phosphate cathode material by high-temperature calcination. No strong acid or strong base solvent is used in the whole process, so the method of the present invention is easy to operate and easy to scale industrial production.

[0028] The method of the present invention is to compare the amount of the metal ion chelating agent in solution I with the amount of the total substance containing transition metal elements in the system (i.e., N Ti +N Mn ; Among them, N Ti Indicates the amount of Ti element in the system, N Mn Indicates the amount of Mn in the system, N Ti =N Mn ) is controlled to be (0.5-3):2 (e.g., 1:2), which can avoid the situation that the metal element cannot be fully chelated when there is too little chelating agent, or the solution is acidic when there is too much chelating agent, which is not conducive to the growth of grains and the formation of sol. In addition, the method of the present invention controls the molar ratio of the Na element provided by the sodium source to the Mn element provided by the manganese source and the Ti element provided by the titanium source in solution II to be greater than 3:1:1 and less than or equal to 3.05:1:1 (of course, the molar ratio of the Mn element to the Ti element is 1:1), that is, the sodium source is controlled to be more than the manganese source and the titanium source, so that the loss of sodium salt in the subsequent high-temperature calcination process can be reduced; and by calcining at 600-750°C for 4-6h, it not only avoids the consumption of high-temperature energy, but also ensures the crystallinity during the material growth process.

[0029] (2) The low-orbital energy level Li, Mg or Ca doped modified sodium manganese titanium phosphate positive electrode material prepared by the present invention can realize Na site doping inside the crystal, which can inhibit the Mn 2+ Off-site migration ensures crystal integrity, while increasing the diffusion rate of ions and electrons and optimizing reaction kinetics. Figure 4 As shown in the example, compared with the unmodified NMTP, the modified sodium manganese titanium phosphate obtained by the method of the present invention has higher cycle stability, indicating that the structural stability of the sodium manganese titanium phosphate material after modification is also improved.

[0030] (3) The present invention modifies the sodium manganese titanium phosphate cathode material by doping low-orbital energy level Li, Mg or Ca to construct the Li(Mg, Ca)-O-Mn electronic configuration, promote the strong orbital hybridization of Mn 3d and O 2p, and then strengthen the Mn-O bonding, thereby improving the Mn 2+The off-site migration barrier is reduced, antisite defects are suppressed, voltage hysteresis is reduced, diffusion kinetics and structural stability are improved, and the high-rate and long-cycle electrochemical performance of sodium manganese titanium phosphate is improved.

[0031] (4) The present invention starts from the electronic configuration level and comprehensively strengthens the overall material configuration, which is more suitable for large current and long cycle (5C, 500 cycles, as described later) Figure 4 Actual usage conditions of the examples).

[0032] In summary, the modification method of the present invention is easy to operate and easy to scale up for production. The prepared low-orbital energy level Li (Mg, Ca) doped modified sodium manganese titanium phosphate positive electrode material is easy to control, has good structural stability, and has excellent rate performance and cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is an XRD comparison chart of the modified sodium manganese titanium phosphate positive electrode material (NMTP-Li3) prepared in Example 1 of the present invention and the unmodified sodium manganese titanium phosphate positive electrode material (NMTP) prepared in Comparative Example 1.

[0034] Figure 2 This is a SEM comparison of the modified sodium titanium manganese phosphate positive electrode material prepared in Example 1 of the present invention and the unmodified sodium titanium manganese phosphate positive electrode material prepared in Comparative Example 1; wherein, Figure 2 (a) corresponds to the modified sodium manganese titanium phosphate positive electrode material prepared in Example 1, Figure 2 (b) corresponds to the unmodified sodium manganese titanium phosphate positive electrode material prepared in Example 1, and the scale bars in the figure represent 5 μm.

[0035] Figure 3 The charge and discharge curves of the unmodified sodium titanium manganese phosphate positive electrode material prepared in Comparative Example 1 of the present invention and the modified sodium titanium manganese phosphate positive electrode material prepared in Example 1 are shown; wherein, Figure 3 (a) corresponds to the unmodified sodium manganese titanium phosphate positive electrode material prepared in Example 1, Figure 3 (b) corresponds to the modified sodium manganese titanium phosphate positive electrode material prepared in Example 1.

[0036] Figure 4 This is a comparison chart of the cycle performance of the modified sodium manganese titanium phosphate positive electrode material prepared in Example 1 of the present invention and the unmodified sodium manganese titanium phosphate positive electrode material prepared in Comparative Example 1.

[0037] Figure 5 The first and second cycle charge-discharge curves of the sodium manganese titanium phosphate positive electrode material prepared with excess citric acid metal chelating agent obtained in Comparative Example 4 of the present invention. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0039] Example 1

[0040] A modified preparation method for sodium manganese titanium phosphate positive electrode material for sodium ion batteries. The molar ratio of transition metal elements Ti and Mn in the target modified sodium manganese titanium phosphate positive electrode material for sodium ion batteries is equal to 1:1 (in this embodiment, the amount of Ti and Mn in the target modified sodium manganese titanium phosphate positive electrode material for sodium ion batteries is 1 mmol). The steps of the preparation method described in this embodiment are:

[0041] Step 1: weigh anhydrous citric acid and dissolve it in 80 ml of anhydrous ethanol in a molar ratio of 1:1 to the total transition metal element in the target sodium ion battery sodium manganese titanium phosphate positive electrode material (i.e., weigh 2 mmol of anhydrous citric acid and dissolve it in 80 ml of anhydrous ethanol) to obtain solution I;

[0042] Step 2, weigh 3.02 mmol of sodium acetate, weigh manganese acetate and isopropyl titanate in a molar ratio of 3.02:1:1 and dissolve them in solution I to obtain solution II;

[0043] Step 3, weigh lithium acetate and dissolve it in solution II in a molar ratio of lithium acetate to sodium acetate of 0.03:3 to obtain solution III;

[0044] Step 4: Weigh ammonium dihydrogen phosphate in a molar ratio of 1:1 with sodium acetate and dissolve it in 10 ml of deionized water to obtain solution IV;

[0045] Step 5, after stirring solution III evenly, slowly add solution IV dropwise thereto at a rate of 2 ml / min using a peristaltic pump to obtain solution V;

[0046] Step 6: Place solution V in a constant temperature oil bath at 80°C and stir. After sufficient reaction, dry in a 110°C forced air drying oven;

[0047] Step seven: Grind the dried material into powder and calcine it in a tubular furnace at a high temperature of 650°C for 6 hours in an Ar atmosphere to obtain a low-energy-level Li-doped modified sodium titanium manganese phosphate positive electrode material (which can be naturally cooled to room temperature and then stored in a glove box), recorded as NMTP-Li3 sample.

[0048] The low orbital energy level Li-doped modified sodium titanium manganese phosphate positive electrode material prepared in this embodiment realizes selective site doping of Li element in the crystal to construct a Li-O-Mn electronic configuration. Due to the difference in orbital energy levels between Li 2s and O 2p, Mn3d and O 2p are more strongly orbitally hybridized, Mn-O bonding is strengthened, and Mn is improved. 2+ Migration barrier, suppression of antisite defects, and improvement of crystal structure lead to overall improvement of electrochemical performance.

[0049] Example 2

[0050] A modified preparation method for sodium manganese titanium phosphate positive electrode material for sodium ion batteries. The molar ratio of transition metal elements Ti and Mn in the target modified sodium manganese titanium phosphate positive electrode material for sodium ion batteries is equal to 1:1 (in this embodiment, the amount of Ti and Mn in the target modified sodium manganese titanium phosphate positive electrode material for sodium ion batteries is 1 mmol). The steps of the preparation method described in this embodiment are:

[0051] Step 1: weigh anhydrous citric acid and dissolve it in 80 ml of anhydrous ethanol in a molar ratio of 1:1 to the total transition metal elements in the target sodium-ion battery sodium manganese titanium phosphate positive electrode material to obtain solution I;

[0052] Step 2, weigh 3.02 mmol of sodium acetate, weigh manganese acetate and isopropyl titanate in a molar ratio of 3.02:1:1 and dissolve them in solution I to obtain solution II;

[0053] Step 3, weigh magnesium acetate in a molar ratio of 0.02:3 with sodium acetate and dissolve it in solution II to obtain solution III;

[0054] Step 4: Weigh ammonium dihydrogen phosphate in a molar ratio of 1:1 with sodium acetate and dissolve it in 10 ml of deionized water to obtain solution IV;

[0055] Step 5, after stirring solution III thoroughly, add solution IV dropwise thereto at 2 ml / min using a peristaltic pump to obtain solution V;

[0056] Step 6: Place solution V in a constant temperature oil bath at 80°C and stir. After sufficient reaction, dry in a 110°C forced air drying oven;

[0057] Step 7: Grind the dried material into powder and calcine it in a tubular furnace at a high temperature of 650°C for 6 hours in an Ar atmosphere to obtain a low-orbital energy level Mg-doped modified sodium titanium manganese phosphate positive electrode material (which can be naturally cooled to room temperature and then stored in a glove box).

[0058] The low-orbital energy level Mg-doped modified sodium titanium manganese phosphate positive electrode material prepared in this embodiment: the Mg element is selectively doped in the crystal to construct the Mg-O-Mn electronic configuration. Due to the difference in the orbital energy levels of Mg 3s and O 2p, the orbital hybridization of Mn 3d and O2p is strengthened, the Mn-O bonding is strengthened, and the Mn 2+ Migration barrier, suppression of antisite defects, and improvement of crystal structure lead to overall improvement of electrochemical performance.

[0059] Example 3

[0060] A modified preparation method for sodium manganese titanium phosphate positive electrode material for sodium ion batteries. The molar ratio of transition metal elements Ti and Mn in the target modified sodium manganese titanium phosphate positive electrode material for sodium ion batteries is equal to 1:1 (in this embodiment, the amount of Ti and Mn in the target modified sodium manganese titanium phosphate positive electrode material for sodium ion batteries is 1 mmol). The steps of the preparation method described in this embodiment are:

[0061] Step 1: weigh anhydrous citric acid and dissolve it in 80 ml of anhydrous ethanol in a molar ratio of 1:1 to the total transition metal elements in the target sodium-ion battery sodium manganese titanium phosphate positive electrode material to obtain solution I;

[0062] Step 2, weigh 3.02 mmol of sodium acetate, weigh manganese acetate and isopropyl titanate in a molar ratio of 3.02:1:1 and dissolve them in solution I to obtain solution II;

[0063] Step 3, weigh calcium acetate and dissolve it in solution II in a molar ratio of 0.02:3 with sodium acetate to obtain solution III;

[0064] Step 4: Weigh ammonium dihydrogen phosphate in a molar ratio of 1:1 with sodium acetate and dissolve it in 10 ml of deionized water to obtain solution IV;

[0065] Step 5, after stirring solution III thoroughly, add solution IV dropwise thereto at 2 ml / min using a peristaltic pump to obtain solution V;

[0066] Step 6: Place solution V in a constant temperature oil bath at 80°C, stir and react, and then dry in a forced air drying oven at 110°C;

[0067] Step 7: Grind the dried material into powder and calcine it in a tubular furnace at a high temperature of 650°C for 6 hours in an Ar atmosphere to obtain a low-energy-level Ca-doped modified sodium titanium manganese phosphate positive electrode material (which can be naturally cooled to room temperature and then stored in a glove box).

[0068] The low-orbital energy level Ca-doped modified sodium titanium manganese phosphate positive electrode material prepared in this embodiment realizes selective site doping of Ca element in the crystal to construct a Ca-O-Mn electronic configuration. Due to the difference in the orbital energy levels of Ca 4s and O 2p, the orbital hybridization of Mn3d and O 2p is strengthened, the Mn-O bonding is strengthened, and the Mn 2+ Migration barrier, suppression of antisite defects, and improvement of crystal structure lead to overall improvement of electrochemical performance.

[0069] Example 4

[0070] A modified preparation method for sodium manganese titanium phosphate positive electrode material for sodium ion batteries. The molar ratio of transition metal elements Ti and Mn in the target modified sodium manganese titanium phosphate positive electrode material for sodium ion batteries is equal to 1:1 (in this embodiment, the amount of Ti and Mn in the target modified sodium manganese titanium phosphate positive electrode material for sodium ion batteries is 1 mmol). The steps of the preparation method described in this embodiment are:

[0071] Step 1: weigh anhydrous citric acid and dissolve it in 80 ml of anhydrous ethanol in a molar ratio of 1:1 to the total transition metal element in the target sodium ion battery sodium manganese titanium phosphate positive electrode material (i.e., weigh 2 mmol of anhydrous citric acid and dissolve it in 80 ml of anhydrous ethanol) to obtain solution I;

[0072] Step 2, weigh 3.02 mmol of sodium acetate, weigh manganese acetate and isopropyl titanate in a molar ratio of 3.02:1:1 and dissolve them in solution I to obtain solution II;

[0073] Step 3, weigh lithium acetate and dissolve it in solution II in a molar ratio of lithium acetate to sodium acetate of 0.05:3 to obtain solution III;

[0074] Step 4: Weigh ammonium dihydrogen phosphate in a molar ratio of 1:1 with sodium acetate and dissolve it in 10 ml of deionized water to obtain solution IV;

[0075] Step 5, after stirring solution III evenly, slowly add solution IV dropwise thereto at a rate of 2 ml / min using a peristaltic pump to obtain solution V;

[0076] Step 6: Place solution V in a constant temperature oil bath at 80°C and stir. After sufficient reaction, dry in a 110°C forced air drying oven;

[0077] Step 7: Grind the dried material into powder and calcine it in a tubular furnace at a high temperature of 650°C for 6 hours in an Ar atmosphere to obtain a low-energy-level Li-doped modified sodium titanium manganese phosphate positive electrode material (which can be naturally cooled to room temperature and then stored in a glove box), recorded as NMTP-Li5 sample.

[0078] The low orbital energy level Li-doped modified sodium titanium manganese phosphate positive electrode material prepared in this embodiment realizes selective site doping of Li element in the crystal to construct a Li-O-Mn electronic configuration. Due to the difference in orbital energy levels between Li 2s and O 2p, Mn3d and O 2p are more strongly orbitally hybridized, Mn-O bonding is strengthened, and Mn is improved. 2+ The migration barrier suppresses antisite defects and improves the electrochemical performance (of course, the improvement effect is not as good as that of Example 1 when doping with 0.03 mol).

[0079] Comparative Example 1

[0080] The present comparative example synthesizes an unmodified sodium titanium manganese phosphate positive electrode material (the molar ratio of transition metal elements Ti and Mn in the sodium titanium manganese phosphate positive electrode material is also equal to 1:1; in the present comparative example, the amount of Ti and Mn in the target unmodified sodium ion battery sodium titanium manganese phosphate positive electrode material is 1 mmol), comprising the following steps:

[0081] Step 1: weigh anhydrous citric acid and dissolve it in 80 ml of anhydrous ethanol in a molar ratio of 1:1 to the total transition metal elements in the target sodium-ion battery sodium manganese titanium phosphate positive electrode material to obtain solution I;

[0082] Step 2, weigh 3.02 mmol of sodium acetate, weigh manganese acetate and isopropyl titanate in a molar ratio of 3.02:1:1 and dissolve them in solution I to obtain solution II;

[0083] Step 3, weigh ammonium dihydrogen phosphate in a molar ratio of 1:1 with sodium acetate and dissolve it in 10 ml of deionized water to obtain solution III;

[0084] Step 4: After stirring solution II thoroughly, add solution III dropwise thereto at 2 ml / min using a peristaltic pump to obtain solution IV;

[0085] Step 5, placing solution IV in a constant temperature oil bath at 80°C, stirring for reaction, and drying in a forced air drying oven at 110°C;

[0086] Step 6: Grind the dried material into powder and calcine it in a tubular furnace at a high temperature of 650°C for 6 hours in an Ar atmosphere to obtain an unmodified sodium manganese titanium phosphate positive electrode material (which can be naturally cooled to room temperature and then stored in a glove box), recorded as the NMTP sample.

[0087] Comparative Example 2

[0088] A modified preparation method for a sodium ion battery sodium titanium manganese phosphate positive electrode material. The molar ratio of transition metal elements Ti and Mn in the target modified sodium ion battery sodium titanium manganese phosphate positive electrode material is equal to 1:1 (in this comparative example, the amount of Ti and Mn in the target modified sodium ion battery sodium titanium manganese phosphate positive electrode material is 1 mmol). The steps of the preparation method described in this comparative example are:

[0089] Step 1: weigh anhydrous citric acid and dissolve it in 80 ml of anhydrous ethanol in a molar ratio of 1:1 to the total transition metal elements in the target sodium-ion battery sodium manganese titanium phosphate positive electrode material to obtain solution I;

[0090] Step 2, weigh 3.02 mmol of sodium acetate, weigh manganese acetate and isopropyl titanate in a molar ratio of 3.02:1:1 and dissolve them in solution I to obtain solution II;

[0091] Step 3, weigh lithium acetate in a molar ratio of 0.1:3 with sodium acetate and dissolve it in solution II to obtain solution III;

[0092] Step 4: Weigh ammonium dihydrogen phosphate in a molar ratio of 1:1 with sodium acetate and dissolve it in 10 ml of deionized water to obtain solution IV;

[0093] Step 5, after stirring solution III thoroughly, add solution IV dropwise thereto at 2 ml / min using a peristaltic pump to obtain solution V;

[0094] Step 6: Place solution V in a constant temperature oil bath at 80°C, stir and react, and then dry in a forced air drying oven at 110°C;

[0095] Step 7: Grind the dried material into powder and calcine it in a tubular furnace at a high temperature of 650°C for 6 hours in an Ar atmosphere to obtain a low-energy-level Li-doped modified sodium titanium manganese phosphate positive electrode material (which can be naturally cooled to room temperature and then stored in a glove box).

[0096] The low orbital energy level Li doped modified sodium titanium manganese phosphate positive electrode material prepared in this comparative example: selective site doping of Li element is achieved in the crystal to construct the Li-O-Mn electronic configuration. Due to the difference in the orbital energy levels of Li 2s and O 2p, Mn3d and O 2p are more strongly hybridized, and Mn-O bonding is strengthened. However, due to excessive doping, the lattice is severely damaged, which hinders the Na + The diffusion capacity of the electrochemical performance is reduced.

[0097] Comparative Example 3

[0098] A modified preparation method for a sodium ion battery sodium titanium manganese phosphate positive electrode material. The molar ratio of transition metal elements Ti and Mn in the target modified sodium ion battery sodium titanium manganese phosphate positive electrode material is equal to 1:1 (in this comparative example, the amount of Ti and Mn in the target modified sodium ion battery sodium titanium manganese phosphate positive electrode material is 1 mmol). The steps of the preparation method described in this comparative example are:

[0099] Step 1: weigh anhydrous citric acid and dissolve it in 80 ml of anhydrous ethanol in a molar ratio of 1:1 to the total transition metal elements in the target sodium-ion battery sodium manganese titanium phosphate positive electrode material to obtain solution I;

[0100] Step 2, weigh 3.02 mmol of sodium acetate, weigh manganese acetate and isopropyl titanate in a molar ratio of 3.02:1:1 and dissolve them in solution I to obtain solution II;

[0101] Step 3, weigh calcium acetate and dissolve it in solution II in a molar ratio of 0.03:3 with sodium acetate to obtain solution III;

[0102] Step 4: Weigh ammonium dihydrogen phosphate in a molar ratio of 1:1 with sodium acetate and dissolve it in 10 ml of deionized water to obtain solution IV;

[0103] Step 5, after stirring solution III thoroughly, add solution IV dropwise thereto at 2 ml / min using a peristaltic pump to obtain solution V;

[0104] Step 6: Place solution V in a constant temperature oil bath at 80°C, stir and react, and then dry in a forced air drying oven at 110°C;

[0105] Step 7: Grind the dried material into powder and calcine it in a tubular furnace at a high temperature of 750°C for 8 hours in an Ar atmosphere to obtain a low-energy-level Ca-doped modified sodium titanium manganese phosphate positive electrode material (which can be naturally cooled to room temperature and then stored in a glove box).

[0106] The low orbital energy level Ca-doped modified sodium titanium manganese phosphate positive electrode material prepared in this comparative example: the selective site doping of Ca element in the crystal is realized to construct the Ca-O-Mn electronic configuration. Due to the difference in the orbital energy levels of Ca 4s and O 2p, the orbital hybridization of Mn3d and O 2p is strengthened, and the Mn-O bonding is strengthened. However, due to the long calcination time, the grain growth is broken, resulting in reduced electrochemical performance.

[0107] Comparative Example 4

[0108] A modified preparation method for a sodium ion battery sodium titanium manganese phosphate positive electrode material. The molar ratio of transition metal elements Ti and Mn in the target modified sodium ion battery sodium titanium manganese phosphate positive electrode material is equal to 1:1 (in this comparative example, the amount of Ti and Mn in the target modified sodium ion battery sodium titanium manganese phosphate positive electrode material is 1 mmol). The steps of the preparation method described in this comparative example are:

[0109] Step 1: weigh anhydrous citric acid and dissolve it in 80 ml of anhydrous ethanol in a molar ratio of 5:2 to the total transition metal element in the target sodium-ion battery sodium manganese titanium phosphate positive electrode material to obtain solution I;

[0110] Step 2, weigh 3.02 mmol of sodium acetate, weigh manganese acetate and isopropyl titanate in a molar ratio of 3.02:1:1 and dissolve them in solution I to obtain solution II;

[0111] Step 3, weigh magnesium acetate in a molar ratio of 0.03:3 with sodium acetate and dissolve it in solution II to obtain solution III;

[0112] Step 4: Weigh ammonium dihydrogen phosphate in a molar ratio of 1:1 with sodium acetate and dissolve it in 10 ml of deionized water to obtain solution IV;

[0113] Step 5, after stirring solution III thoroughly, add solution IV dropwise thereto at 2 ml / min using a peristaltic pump to obtain solution V;

[0114] Step 6: Place solution V in a constant temperature oil bath at 80°C, stir and react, and then dry in a forced air drying oven at 110°C;

[0115] Step 7: Grind the dried material into powder and calcine it in a tubular furnace at a high temperature of 750°C for 8 hours in an Ar atmosphere to obtain a low-energy-level Mg-doped modified sodium titanium manganese phosphate positive electrode material (which can be naturally cooled to room temperature and then stored in a glove box).

[0116] The low orbital energy level Mg-doped modified sodium titanium manganese phosphate positive electrode material prepared in this comparative example: the Mg element is selectively doped in the crystal to construct the Mg-O-Mn electronic configuration. Due to the difference in the orbital energy levels of Mg 3s and O 2p, Mn 3d and O2p are more strongly hybridized, and Mn-O bonding is strengthened. However, due to the excessive amount of metal chelating agent citric acid, the solution is acidic, which is not conducive to the bonding of metal elements, resulting in an incomplete crystal structure of the synthesized sodium titanium manganese phosphate, a weakened sodium storage performance of the main material, and a reduced electrochemical performance.

[0117] Performance testing:

[0118] Figure 1 The XRD comparison diagram of the modified sodium manganese titanium phosphate positive electrode material (NMTP-Li3) prepared in Example 1 of the present invention and the unmodified sodium manganese titanium phosphate positive electrode material (NMTP) prepared in Comparative Example 1 is shown in FIG. Figure 1 It can be seen that compared with the unmodified sample, there is no difference in the peak shape of the modified sodium manganese titanium phosphate positive electrode material.

[0119] Figure 2 This is a SEM comparison of the modified sodium manganese titanium phosphate positive electrode material prepared in Example 1 of the present invention and the unmodified sodium manganese titanium phosphate positive electrode material prepared in Comparative Example 1. Figure 2 It can be seen that both the modified samples and the unmodified samples present micrometer-sized polyhedral particles with almost no change in morphology.

[0120] Figure 3 The charge and discharge curves of the modified sodium titanium manganese phosphate positive electrode material prepared in Example 1 of the present invention and the unmodified sodium titanium manganese phosphate positive electrode material prepared in Comparative Example 1 at a current density of 0.1C and a voltage range of 1.5-4.3V are shown in FIG. Figure 3 It can be seen that the discharge capacity is improved (compared with the unmodified sample prepared in Comparative Example 1, its discharge capacity is 154 mAh g -1 The discharge capacity of the modified sample obtained by the method of the present invention is increased to 163 mAh g -1 ), the voltage hysteresis at 4.0V and 2.6V is significantly suppressed, effectively alleviating the problem of voltage hysteresis.

[0121] Figure 4 This is a comparison chart of the cycle performance of the modified sodium titanium manganese phosphate positive electrode material prepared in Example 1 of the present invention and the unmodified sodium titanium manganese phosphate positive electrode material prepared in Comparative Example 1 under 5C conditions and a voltage range of 1.5-4.3V. Figure 4 It can be seen that the cycle stability and discharge specific capacity of the modified sodium manganese titanium phosphate positive electrode material prepared in Example 1 are improved, and the rapid loss of capacity can be avoided (as analyzed above, this is attributed to the more perfect crystal structure).

[0122] Figure 5 The charge and discharge curve of the sodium manganese titanium phosphate positive electrode material added with excess citric acid prepared in Comparative Example 4 of the present invention at a current density of 0.1C and a voltage range of 1.5-4.3V is shown in FIG. Figure 5 It can be seen that the discharge capacity is greatly reduced, which is attributed to the destruction of the crystal structure by excessive metal chelating agent.

[0123] The above embodiments are merely examples. For example, in addition to the Ar gas atmosphere, other protective atmospheres (such as nitrogen or other inert gases) may also be used for calcination.

[0124] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a modified sodium manganese titanium phosphate positive electrode material, characterized in that: The molar ratio of Mn element to Ti element in the modified sodium manganese titanium phosphate positive electrode material is 1:1, and the preparation method comprises the following steps: S1. Weigh a metal ion chelating agent and dissolve it in anhydrous ethanol to obtain a solution I; wherein the ratio of the amount of the metal ion chelating agent contained in the solution I to the total amount of two transition metal elements, Mn and Ti, in the target modified sodium manganese titanium phosphate positive electrode material product is (0.5-3):2; S2. According to the Mn element and Ti element in the target modified sodium manganese titanium phosphate positive electrode material product, a manganese source and a titanium source are weighed, and a sodium source is weighed at the same time, so that the molar ratio of the Na element provided by the sodium source to the Mn element provided by the manganese source is greater than 3:1 and less than or equal to 3.05:1; the sodium source, the manganese source and the titanium source are dissolved in solution I to obtain solution II; S3, taking any one of Li, Mg and Ca as a low orbital energy level metal element, and weighing a low orbital energy level metal element source material according to a molar ratio of the low orbital energy level metal element to the Na element provided by the sodium source in the solution II of 0.01 to 0.05:3; dissolving the low orbital energy level metal element source material in solution II to obtain solution III; At the same time, weigh phosphate and dissolve it in deionized water to obtain solution IV; wherein the molar ratio of the phosphate contained in the phosphate to the Na element provided by the sodium source in the solution II is 1:1; S4, add solution IV dropwise into solution III and stir thoroughly to obtain solution V; S5. Stir solution V in an oil bath, dry after sufficient reaction, and then calcine at a temperature of 600 to 750° C. for 4 to 6 hours to obtain the target modified sodium manganese titanium phosphate positive electrode material.

2. The preparation method according to claim 1, characterized in that: In step S1, the metal ion chelating agent is selected from tartaric acid, anhydrous citric acid, disodium ethylenediaminetetraacetic acid, and gluconic acid; In step S2, the sodium source is selected from sodium acetate and sodium nitrate; the manganese source is selected from manganese acetate and manganese nitrate; the titanium source is selected from tetrabutyl titanate and isopropyl titanate; In step S3, the low orbital energy level metal element source material is selected from lithium acetate, lithium nitrate, magnesium acetate, magnesium nitrate, calcium acetate, and calcium nitrate; and the phosphate is diammonium phosphate.

3. The preparation method according to claim 1, characterized in that: In step S3, the concentration of phosphate in the solution IV is 0.345 g / mL; In step S4, the dripping rate of the dropwise infusion is 1-5 ml / min; the dropwise infusion is preferably performed using a peristaltic pump; preferably, the dripping speed of the peristaltic pump is 2 ml / min.

4. The preparation method according to claim 1, characterized in that: In step S5, the oil bath is specifically an oil bath with a temperature of 70-85°C, preferably an oil bath with a temperature of 80°C; The drying temperature used for the drying is 100-120°C, preferably 110°C; preferably, the drying is carried out using a blast drying oven; The calcination is carried out in an Ar atmosphere, the calcination temperature used is 650° C., and the treatment time is 6 to 8 hours.

5. The preparation method according to claim 1, characterized in that: In step S1, the ratio of the amount of the metal ion chelating agent contained in the solution I to the total amount of two transition metal elements, Mn and Ti, in the target modified sodium manganese titanium phosphate positive electrode material product is 1:

1.

6. The preparation method according to claim 1, characterized in that: In step S3, the molar ratio of the low orbital energy level metal element to the Na element provided by the sodium source in the solution II is 0.03:

3.

7. The preparation method according to claim 1, characterized in that: In step S4, the sufficient stirring specifically includes stirring for 20 to 40 minutes after all solution IV is dripped into solution III, and the stirring speed is 200 to 500 r / min.

8. A modified sodium manganese titanium phosphate positive electrode material is obtained by the preparation method according to any one of claims 1 to 7.

9. Use of the modified sodium manganese titanium phosphate positive electrode material as claimed in claim 8 as a positive electrode material in a sodium ion battery.

Images