Aqueous sodium battery negative electrode active material and preparation method thereof, negative electrode and sodium ion battery

Abstract

The present invention provides an aqueous sodium-ion negative electrode active material and a preparation method thereof, a negative electrode and a sodium ion battery. The aqueous sodium-ion negative electrode active material comprises a core and a coating layer. The core is Na 1+ x Bi x Ti 2‑x (PO4)3, where x ranges from 0 to 0.2 and does not include 0. Compared with the original negative electrode, the aqueous sodium negative electrode active material provided by the present invention has a higher discharge specific capacity, exhibits good rate characteristics and cycle performance, has a better inhibition of negative electrode hydrogen evolution characteristics, and at the same time, the battery has a higher operating voltage during discharge, and has good application prospects in electrochemical energy storage battery technology.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical power sources, and in particular to an aqueous sodium-ion negative electrode active material and a preparation method thereof, a negative electrode and a sodium ion battery. Background Art

[0002] The utilization of energy has further advanced the development of social civilization. Through continuous research and exploration, the development of renewable clean energy sources such as wind and solar energy has received considerable attention and can be widely applied in real life. However, these clean energy sources are significantly affected by factors such as time, season, weather, and region, which can hinder the safe operation of the grid after connection. Electrochemical energy storage continues to achieve significant breakthroughs in safety, energy conversion efficiency, and economics. Aqueous sodium-ion batteries, among them, have attracted increasing research attention and made significant progress due to their advantages such as high safety, low raw material costs, widespread distribution of sodium, and environmental friendliness. Because energy storage and conversion in sodium-ion batteries occur within the positive and negative electrode materials, the key to developing long-life batteries is the preparation of electrode materials that can stably intercalate and deintercalate sodium ions. However, finding anode materials suitable for stable sodium intercalation and deintercalation in such batteries is not easy, and this is one of the key challenges that need to be addressed in the development of aqueous sodium-ion batteries.

[0003] Researchers have explored different electrode materials for sodium-ion batteries, including transition metal layered oxides, Prussian blue compounds, and polyanion compounds. Among them, phosphate-based compounds with sodium as the main component in polyanion compounds are the best choice as negative electrode materials due to their stability, safety, low cost, and structural diversity. Due to their structural stability and structural diversity, phosphate framework materials are not only typical solid ion conductors, but also very suitable low-cost electrode materials for other devices such as sodium-ion batteries. Among these phosphate-based compounds, the sodium superion conductor (NASICON) structure is believed to be able to provide Na + The migration of NASICON provides a highly conductive pathway, thus having a strong sodium storage performance. Among various NASICON structures, sodium titanium phosphate (NaTi2(PO4)3, NTP) has a large theoretical capacity (133 mAh g -1 ), low cost, high structural stability, open channels and smooth charge and discharge platform, and it has attracted increasing attention and is considered to be a promising anode material.

[0004] However, in order to avoid the side reaction of hydrogen evolution at the negative electrode, the Na embedding potential of the negative electrode of the aqueous sodium ion battery should be slightly higher than the hydrogen evolution potential. +The electrode potential for the insertion / extraction reaction is low (-0.581 V vs. NHE), very close to the potential of the hydrogen evolution side reaction at the negative electrode. This makes the hydrogen evolution side reaction more likely to occur during the battery charge and discharge process, thereby affecting the battery's charge and discharge cycling stability. Furthermore, due to the influence of the hydrogen evolution potential, the battery capacity is often low, which greatly affects the application of aqueous sodium-ion batteries under practical conditions. Numerous studies have shown that the incorporation of heteroatoms into NTP anode materials can improve their ionic conductivity and structural stability, thereby improving their cycling stability. For example, partial or complete substitution of Ti in NTP with various elements such as Mn, Mg, V, and Fe can improve the cycling stability of NTP anodes to a certain extent. Furthermore, Fe doping can regulate the Na insertion / extraction potential of the NTP anode and shift it relatively positively, thereby reducing the possibility of overlap with the negative electrode hydrogen evolution side reaction potential during high-rate (>2C) charge and discharge. This can suppress hydrogen evolution at the negative electrode and ultimately improve the coulombic efficiency and cycling stability of the battery at high-rate (>2C) charge and discharge. However, it is worth noting that the increase in the Na insertion / deintercalation potential of the NTP negative electrode after doping can inhibit the occurrence of hydrogen evolution at the negative electrode, but it will also lead to a decrease in the operating voltage of the battery during discharge, thereby reducing the discharge energy density of the battery. If the negative electrode hydrogen evolution overpotential can be increased, so that the negative electrode can be reduced to a lower potential during charging, it can not only inhibit hydrogen evolution at the negative electrode, but also ensure that the battery has a higher operating voltage during discharge, thereby improving the battery's discharge energy density, cycle life and coulombic efficiency.

[0005] To this end, it is necessary to further screen out suitable doping atoms to modify the NTP negative electrode bulk material, improve the hydrogen evolution overpotential of the NTP negative electrode, and thus significantly reduce the hydrogen evolution potential of the negative electrode, thereby suppressing the occurrence of negative electrode hydrogen evolution during charge and discharge, and ensuring that the operating voltage of the battery is higher during discharge. There is no relevant report yet. Therefore, the present invention prepares a bismuth-doped sodium titanium phosphate product that can be used for the negative electrode of an aqueous battery, so that the hydrogen evolution potential on the surface of the sodium titanium phosphate negative electrode can be significantly negatively shifted, and at the same time, the negative electrode can be reduced to a lower potential during charging (the discharge cut-off voltage of the negative electrode is lower during the half-cell test), which can ultimately suppress the hydrogen evolution at the negative electrode and ensure that the battery has a higher operating voltage during discharge, thereby improving the discharge energy density, cycle life and coulomb efficiency of the battery, and promoting the commercial application of aqueous sodium ion batteries.

[0006] Therefore, during the charge and discharge process, the surface of the NaTi2(PO4)3 negative electrode is prone to hydrogen evolution side reaction in the aqueous electrolyte, which affects the interface stability of the negative electrode and thus leads to a decrease in the charge and discharge cycle stability of the battery. This has become a technical problem that needs to be urgently solved by technicians in this field. Summary of the Invention

[0007] To solve the above technical problems, the present invention provides an aqueous sodium battery negative electrode active material and a preparation method thereof, a negative electrode and a sodium ion battery. By introducing the Bi element into the aqueous sodium battery negative electrode active material, the hydrogen evolution side reaction at the negative electrode can be suppressed, and the electrochemical performance of the negative electrode active material is improved, which has broad application prospects.

[0008] To achieve this object, the present invention adopts the following technical solutions:

[0009] In the first aspect, the present invention provides an aqueous sodium negative electrode active material, the aqueous sodium negative electrode active material comprising a core and a coating layer, the core being Na 1+x Bi x Ti 2-x (PO4)3, where the value of x ranges from 0 to 0.2 and does not include 0.

[0010] The value range of x can be, for example, 0.005, 0.01, 0.02, 0.03, 0.05, 0.1, 0.15, 0.18 or 0.2, etc., preferably x<0.1.

[0011] It is worth noting that the present invention adopts Bi-doped modified negative electrode, i.e.

[0012] Na 1+x Bi x Ti 2-x (PO4)3(NBTP / C) anode. Bi atoms are doped into the NaTi2(PO4)3 anode material to prepare a bismuth-doped sodium titanium phosphate product that can be used as an anode for aqueous batteries. This can improve the anode's discharge specific capacity to a certain extent. At the same time, the hydrogen evolution potential on the surface of the NaTi2(PO4)3 anode can be significantly shifted negatively, inhibiting the hydrogen evolution side reaction at the anode, thereby improving the battery's charge and discharge rate performance and cycle stability, and resolving the technical issue of poor charge and discharge cycle stability of the NaTi2(PO4)3 anode material. The NBTP / C anode obtained after Bi doping can be used as the working electrode, a platinum sheet as the counter electrode, and saturated calomel (SCE) as the reference electrode, with an aqueous solution as the electrolyte, to construct a three-electrode electrolytic cell device for half-cell charge and discharge testing of the aqueous sodium-ion battery anode.

[0013] It is worth noting that the present invention further prefers that the value of x be less than 0.1. Due to the electrochemical inertness of Bi, it does not participate in the reaction. Therefore, excessive Bi doping to replace Ti will lead to a decrease in theoretical capacity, thereby reducing electrochemical performance. At the same time, excessive Bi doping can easily lead to impurity phases in the formed product phase. When the Bi doping level is too low, the effect of Bi doping is not fully realized, and the electrochemical performance improvement is not significant.

[0014] Preferably, the coating layer is a carbon coating layer.

[0015] Preferably, the carbon content in the aqueous sodium battery negative electrode active material is 0 to 20%, for example, it can be 0.1%, 2.4%, 4.6%, 6.8%, 9%, 11.2%, 13.4%, 15.6%, 17.8% or 20%, etc., and does not include 0.

[0016] Preferably, the aqueous sodium battery negative electrode active material is in granular form.

[0017] Preferably, the particle size of the aqueous sodium negative electrode active material is 0 to 10 μm, and does not include 0, for example, it can be 0.01 μm, 0.1 μm, 0.2 μm, 0.5 μm, 0.8 μm, 0.9 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 0 μm, etc.

[0018] In a second aspect, the present invention provides a method for preparing the aqueous sodium electrolyte negative electrode active material according to the first aspect, the preparation method comprising:

[0019] A sodium source, a bismuth source, a titanium source, a phosphorus source and a carbon source are mixed and dried to prepare a precursor.

[0020] The precursor is sintered to obtain the aqueous sodium negative electrode active material.

[0021] The preparation method of the aqueous sodium negative electrode active material provided by the second aspect of the present invention not only has a simple preparation process, but also can significantly improve the electrochemical performance of the aqueous sodium negative electrode active material.

[0022] Preferably, the sodium source comprises any one of sodium carbonate, sodium bicarbonate or sodium acetate, or a combination of at least two thereof, wherein typical but non-limiting combinations are a combination of sodium carbonate and sodium bicarbonate, a combination of sodium acetate and sodium bicarbonate, and a combination of sodium carbonate and sodium acetate.

[0023] Preferably, the bismuth source comprises any one or a combination of at least two of bismuth nitrate, bismuth subcarbonate or bismuth subcarbonate, wherein typical but non-limiting combinations are a combination of bismuth nitrate and bismuth subcarbonate, a combination of bismuth subcarbonate and bismuth subcarbonate, and a combination of bismuth nitrate and bismuth subcarbonate.

[0024] Preferably, the titanium source comprises any one of tetrabutyl titanate, titanium tetraisopropoxide or isopropyl titanate, or a combination of at least two thereof, wherein typical but non-limiting combinations are a combination of tetrabutyl titanate and titanium tetraisopropoxide, a combination of isopropyl titanate and titanium tetraisopropoxide, and a combination of tetrabutyl titanate and isopropyl titanate.

[0025] Preferably, the phosphorus source includes ammonium dihydrogen phosphate and / or diammonium hydrogen phosphate.

[0026] Preferably, the carbon source comprises any one of citric acid, glucose, acetic acid or lactic acid, or a combination of at least two thereof, wherein typical but non-limiting combinations are a combination of citric acid and glucose, a combination of acetic acid and glucose, a combination of citric acid and acetic acid, and a combination of lactic acid and glucose.

[0027] Preferably, a solvent is also added during the mixing.

[0028] Preferably, the solvent includes at least one of anhydrous ethanol and deionized water.

[0029] Preferably, the mixing step includes: first mixing a sodium source, a bismuth source, a phosphorus source, a carbon source and a solvent to obtain a first system; second mixing a titanium source and a solvent to obtain a second system, and then mixing the first system and the second system and stirring to obtain a mixed system.

[0030] Preferably, the mixing of the first system and the second system is adding the second system into the first system.

[0031] Preferably, the sodium source, bismuth source, titanium source and phosphorus source are all raw materials for aqueous sodium negative electrode active materials, and the mass ratio of the carbon in the carbon source to the mass ratio of the sodium, bismuth, titanium and phosphorus in the raw materials for aqueous sodium negative electrode active materials is 0 to 20%, and does not include 0.

[0032] Preferably, the mass ratio of the solvent to the raw material of the aqueous sodium negative electrode active material is (1 to 10):1, for example, it can be 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 5:1, 5.5:1, 6:1, 6.5:1, 7:1, 7.5:1, 8:1, 8.5:1, 9:1 or 10:1, etc.

[0033] Preferably, the sintering includes a first preheating process and a second sintering process.

[0034] The present invention further preferably performs a first preheating treatment before performing a second sintering treatment. This is because the precursor raw material does not undergo thermal decomposition during the first preheating treatment, but can lose crystallization water, which is conducive to better forming the NTP main phase during the second sintering treatment and avoiding the formation of impurity phases.

[0035] Preferably, the temperature of the first preheat treatment is 300-400°C, for example, it can be 300°C, 312°C, 323°C, 334°C, 345°C, 356°C, 367°C, 378°C, 389°C or 400°C.

[0036] Preferably, the time of the first preheating treatment is 3 to 4 hours, for example, it can be 3 hours, 3.2 hours, 3.3 hours, 3.4 hours, 3.5 hours, 3.6 hours, 3.7 hours, 3.8 hours, 3.9 hours or 4 hours.

[0037] Preferably, the temperature of the second sintering treatment is 750-850°C, for example, it can be 750°C, 762°C, 773°C, 784°C, 795°C, 806°C, 817°C, 828°C, 839°C or 850°C.

[0038] Preferably, the second sintering treatment time is 8 to 15 hours, for example, it can be 8 hours, 8.8 hours, 9.6 hours, 10.4 hours, 11.2 hours, 11.9 hours, 12.7 hours, 13.5 hours, 14.3 hours or 15 hours.

[0039] In a third aspect, the present invention provides a negative electrode of an aqueous sodium ion battery, wherein the negative electrode comprises the aqueous sodium negative electrode active material described in the first aspect, and / or the aqueous sodium negative electrode active material prepared by the preparation method of the aqueous sodium negative electrode active material described in the second aspect.

[0040] The negative electrode provided in the third aspect of the present invention contains the aforementioned aqueous sodium battery negative electrode active material, and thus can suppress the negative electrode hydrogen evolution characteristics, thereby improving the electrochemical performance of the battery negative electrode.

[0041] Preferably, the negative electrode comprises a current collector and an active material layer disposed on the current collector, and the active material layer contains aqueous sodium battery negative electrode active material.

[0042] Preferably, the active material layer further contains a conductive agent and a binder.

[0043] Preferably, the mass ratio of the aqueous sodium negative electrode active material, the conductive agent and the binder is: 6-8:1-3:0.5-1.5, wherein the number of parts of the aqueous sodium negative electrode active material can be, for example, 6, 6.3, 6.5, 6.7, 6.9, 7.2, 7.4, 7.6, 7.8 or 8. The number of parts of the conductive agent can be, for example, 1, 1.1, 1.2, 1.5, 1.8, 2.0, 2.2, 2.5, 2.8 or 3.0. The number of parts of the binder can be, for example, 0.5, 0.6, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4 or 1.5, etc., preferably 7:2:1.

[0044] Preferably, the conductive agent includes any one or a combination of at least two of SuperP carbon black, acetylene black, carbon nanotubes, graphene or titanium dioxide, wherein typical but non-limiting combinations are a combination of SuperP carbon black and acetylene black, a combination of carbon nanotubes and acetylene black, a combination of SuperP carbon black and carbon nanotubes, a combination of graphene and acetylene black, and a combination of titanium dioxide and acetylene black.

[0045] Preferably, the binder comprises any one or a combination of at least two of PVDF, PTFE, CMC or SBR, wherein typical but non-limiting combinations are a combination of PVDF and PTFE, a combination of CMC and PTFE, a combination of PVDF and CMC, a combination of SBR and PTFE, and a combination of PVDF and SBR.

[0046] Preferably, the current collector comprises any one or a combination of at least two of carbon paper, flexible graphite, aluminum foil, titanium foil, titanium mesh or stainless steel mesh, wherein typical but non-limiting combinations are a combination of carbon paper and flexible graphite, a combination of aluminum foil and flexible graphite, a combination of carbon paper and aluminum foil, and a combination of titanium foil and flexible graphite.

[0047] In a fourth aspect, the present invention provides a sodium ion battery, comprising the negative electrode of the aqueous sodium ion battery according to the third aspect.

[0048] The present invention has no special restrictions on other components, materials and structures in sodium ion batteries. Any other components, materials and structures that can be used in sodium ion batteries and are well known to those skilled in the art can be used, and can also be adjusted according to actual processes.

[0049] Preferably, the sodium ion battery further comprises an electrolyte and a positive electrode.

[0050] Preferably, the electrolyte in the electrolyte includes any one or a combination of at least two of Li2SO4, Na2SO4 or K2SO4, wherein typical but non-limiting combinations are a combination of Li2SO4 and Na2SO4, a combination of K2SO4 and Na2SO4, and a combination of Li2SO4 and K2SO4.

[0051] Preferably, the solvent of the electrolyte includes water.

[0052] Compared with the prior art, the present invention has at least the following beneficial effects:

[0053] (1) The aqueous sodium battery negative electrode active material provided by the present invention is prepared by doping Bi atoms into the NaTi2(PO4)3 negative electrode material and combining the sol-gel method and high-temperature sintering method to prepare the NBTP / C material. The modified negative electrode is then used in an aqueous sodium ion battery, which exhibits a lower hydrogen evolution potential, better charge and discharge rate performance and cycle stability. Under preferred conditions, the 2C first discharge capacity is 94.2 mAh·g -1 Above, the 5C first discharge capacity is 79.9mAh·g -1 Above, the 10C first discharge capacity is 69.1mAh·g -1 Above, the 20C first discharge capacity is 51.6mAh·g -1Above, and the discharge capacity retention rate after 200 cycles at 10C is above 53.3%;

[0054] (2) Compared with the original negative electrode, the aqueous sodium negative electrode active material provided by the present invention has a higher discharge specific capacity, exhibits good rate characteristics and cycle performance, and has a better ability to inhibit negative electrode hydrogen evolution, and ensures that the battery has a higher operating voltage and energy density during discharge, and has good application prospects in electrochemical energy storage battery technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 1 is the X-ray diffraction pattern of the aqueous sodium negative electrode active material in Example 1 and Comparative Example 1.

[0056] Figure 2 This is a surface scanning electron microscope image of the aqueous sodium negative electrode active material in Example 1.

[0057] Figure 3 This is the EDS surface scanning component distribution diagram of the aqueous sodium negative electrode active material in Example 1.

[0058] Figure 4 The charge and discharge performance of the NBTP-0.01 negative electrode in Application Example 1 and the NTP / C negative electrode in Comparative Example 1 at different rates are shown in the test voltage range: -0.5 to -1.0 V vs. SCE.

[0059] Figure 5 The cycling performance of the NBTP-0.01 negative electrode in Application Example 1 and the NTP / C negative electrode in Comparative Example 1 at a rate of 10C is shown in the test voltage range: -0.5 to -1.0 V vs. SCE.

[0060] Figure 6 The charge and discharge curves of the NBTP-0.01 negative electrode in Application Example 1 and the NTP / C negative electrode in Comparative Example 1 at a 1C rate, with a test voltage range of -0.5 to -1.2 V vs. SCE. DETAILED DESCRIPTION

[0061] For the convenience of understanding the present invention, the present invention is given below with examples. It should be understood by those skilled in the art that the examples are only for the purpose of helping to understand the present invention and should not be regarded as specific limitations of the present invention.

[0062] It should be understood that the terms "first," "second," etc. are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature identified with "first," "second," etc. may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0063] Example 1

[0064] This embodiment provides an aqueous sodium-based negative electrode active material, the aqueous sodium-based negative electrode active material comprising a core and a coating layer, the core being Na 1+x Bi x Ti 2-x (PO4)3, wherein the value of x is 0.01. The carbon content of the aqueous sodium negative electrode active material is 10%, and the aqueous sodium negative electrode active material is in a granular form. The average particle size of the aqueous sodium negative electrode active material is 1.0 μm.

[0065] This embodiment also provides a method for preparing an aqueous sodium electrolyte negative electrode active material, the preparation method comprising the following steps:

[0066] First, sodium carbonate, bismuth nitrate, diammonium phosphate, glucose and deionized water are mixed to obtain a first system; second, a titanium source and ethanol are mixed to obtain a second system, wherein the mass ratio of deionized water, ethanol and the raw material of the aqueous sodium negative electrode active material is 4:1:1, and then the second system is added to the first system, stirred to obtain a mixed system, and the mixed system is dried to prepare a precursor;

[0067] The precursor is subjected to a first preheating treatment at 350° C. for 3.5 hours and a second sintering treatment at 800° C. for 9 hours to obtain the aqueous sodium battery negative electrode active material.

[0068] Example 2

[0069] This embodiment provides an aqueous sodium-based negative electrode active material, the aqueous sodium-based negative electrode active material comprising a core and a coating layer, the core being Na 1+x Bi x Ti 2-x (PO4)3, wherein the value of x is 0.02. The carbon content of the aqueous sodium negative electrode active material is 15%, and the aqueous sodium negative electrode active material is in a granular form. The average particle size of the aqueous sodium negative electrode active material is 1.5 μm.

[0070] This embodiment also provides a method for preparing an aqueous sodium electrolyte negative electrode active material, the preparation method comprising the following steps:

[0071] First, sodium carbonate, bismuth nitrate, diammonium phosphate, glucose and deionized water are mixed to obtain a first system; second, a titanium source and ethanol are mixed to obtain a second system, wherein the mass ratio of deionized water, ethanol and the raw material of the aqueous sodium negative electrode active material is 5:2:1, and the second system is added to the first system, stirred to obtain a mixed system, and the mixed system is dried to prepare a precursor;

[0072] The precursor is subjected to a first preheating treatment at 300° C. for 3 hours and a second sintering treatment at 750° C. for 15 hours to obtain the aqueous sodium battery negative electrode active material.

[0073] Example 3

[0074] This embodiment provides an aqueous sodium-based negative electrode active material, the aqueous sodium-based negative electrode active material comprising a core and a coating layer, the core being Na 1+x Bi x Ti 2-x (PO4)3, wherein the value of x is 0.005. The carbon content of the aqueous sodium negative electrode active material is 12.5%, and the aqueous sodium negative electrode active material is in a granular form. The average particle size of the aqueous sodium negative electrode active material is 0.8 μm.

[0075] This embodiment also provides a method for preparing an aqueous sodium electrolyte negative electrode active material, the preparation method comprising the following steps:

[0076] First, sodium carbonate, bismuth nitrate, diammonium phosphate, glucose and deionized water are mixed to obtain a first system; second, a titanium source and ethanol are mixed to obtain a second system, wherein the mass ratio of deionized water, ethanol and the raw material of the aqueous sodium negative electrode active material is 6.5:1.5:1, and then the second system is added to the first system, stirred to obtain a mixed system, and the mixed system is dried to prepare a precursor;

[0077] The precursor is subjected to a first preheating treatment at 400° C. for 4 hours and a second sintering treatment at 850° C. for 8 hours to obtain the aqueous sodium battery negative electrode active material.

[0078] Example 4

[0079] This embodiment provides an aqueous sodium battery negative electrode active material. The aqueous sodium battery negative electrode active material is the same as that of Example 1 except that x is 0.2, and details thereof will not be repeated here.

[0080] Example 5

[0081] This embodiment provides an aqueous sodium battery negative electrode active material. The aqueous sodium battery negative electrode active material is the same as that of Example 1 except that x is 0.002, and details thereof will not be repeated here.

[0082] Example 6

[0083] This embodiment provides an aqueous sodium-ion negative electrode active material. The aqueous sodium-ion negative electrode active material is the same as that in Example 1 except that x is 0.04, and details thereof will not be repeated here.

[0084] Example 7

[0085] This embodiment provides an aqueous sodium-ion negative electrode active material. The aqueous sodium-ion negative electrode active material is the same as that of Example 1 except that the first preheating treatment is not performed, and details thereof will not be repeated here.

[0086] Comparative Example 1

[0087] This comparative example provides an aqueous sodium-based negative electrode active material. The aqueous sodium-based negative electrode active material is the same as Example 1 except that Bi is not added, and details thereof will not be repeated here.

[0088] Comparative Example 2

[0089] This comparative example provides an aqueous sodium battery negative electrode active material. The aqueous sodium battery negative electrode active material is the same as Example 1 except that Bi is replaced by Fe, and the details are not repeated here.

[0090] In this comparative example, Fe is used to replace Bi. Although the increase in the Na insertion / deintercalation potential of the NTP negative electrode after Fe doping can inhibit the occurrence of hydrogen evolution at the negative electrode, it will also lead to a decrease in the operating voltage of the battery during discharge, thereby reducing the discharge energy density of the battery.

[0091] Application Example 1

[0092] This application example provides a negative electrode of an aqueous sodium ion battery, wherein the negative electrode of the aqueous sodium ion battery comprises the aqueous sodium battery negative electrode active material in Example 1. Specifically, the preparation method thereof is as follows: 1+x Bi x Ti 2-x (PO4)3(NBTP / C) active material (x=0.01), conductive carbon black (SuperP) and binder (PTFE) were dissolved in an appropriate amount of deionized water in a mass ratio of 7:2:1, uniformly mixed and rolled into a film, and then vacuum dried and cut into electrode sheets using a slicer. The sheets were placed on a titanium mesh and pressed into NBTP / C (x=0.01) electrodes. The mass of the active material was weighed and calculated to obtain the NBTP negative electrode sheet.

[0093] Application Example 2

[0094] This application example provides a negative electrode of an aqueous sodium ion battery, wherein the negative electrode of the aqueous sodium ion battery comprises the aqueous sodium battery negative electrode active material in Example 2. Specifically, the preparation method thereof is as follows: 1+x Bi x Ti 2-xThe (PO4)3(NBTP / C) active material, carbon nanotubes and binder (PVDF) were dissolved in an appropriate amount of deionized water in a mass ratio of 6:1:0.5, uniformly mixed and rolled into a film, then vacuum-dried and cut into electrode sheets using a slicer. The sheets were placed on a titanium mesh and pressed into NBTP / C electrodes. The mass of the active material was weighed and calculated to obtain the NBTP negative electrode sheet.

[0095] Application Example 3

[0096] This application example provides a negative electrode of an aqueous sodium ion battery, wherein the negative electrode of the aqueous sodium ion battery comprises the aqueous sodium negative electrode active material in Example 3. Specifically, the preparation method thereof is as follows: 1+x Bi x Ti 2-x The (PO4)3(NBTP / C) active material, graphene and binder (CMC) were dissolved in an appropriate amount of deionized water in a mass ratio of 8:3:1.5, uniformly mixed and rolled into a film, then vacuum-dried and cut into electrode sheets using a slicer. The sheets were placed on a titanium mesh and pressed into NBTP / C electrodes. The mass of the active material was weighed and calculated to obtain the NBTP negative electrode sheet.

[0097] Application Examples 4 to 7 and Comparative Application Example 1

[0098] Application Examples 4 to 7 and Comparative Example 1 provide a negative electrode for an aqueous sodium ion battery. Except for using the aqueous sodium negative electrode active materials in Examples 4 to 7 and Comparative Example 1, the negative electrode of the aqueous sodium ion battery is the same as that in Application Example 1, and will not be repeated here.

[0099] The following is the Na obtained in Application Example 1 1.01 Bi 0.01 Ti 1.99 The (PO4)3 / C(NBTP-0.01) negative electrode is used as an example to illustrate the application. The NBTP-0.01 negative electrode is used as the working electrode, the platinum sheet is used as the counter electrode, and the saturated calomel (SCE) is used as the reference electrode. -1 A Na2SO4 aqueous solution was used as the electrolyte to construct a three-electrode electrolytic cell device, and half-cell charge and discharge tests of the aqueous sodium ion battery negative electrode were carried out.

[0100] The phase composition of the Bi-doped modified NBTP / C negative electrode active material obtained in Example 1 was analyzed by X-ray diffractometer (XRD). The XRD pattern of the original NTP / C negative electrode material and the standard pattern of the NaTi2(PO4)3 material (PDF#84-2012) are also given. Figure 1As shown. It can be seen that the main phase of the Bi-doped NBTP-0.01 negative electrode material has not changed and is still the NaTi2(PO4)3 phase. However, compared with the undoped NTP / C material, the angle of the strongest diffraction peak (113) of the NBTP-0.01 negative electrode material has shifted negatively, which may be due to the Bi 3+ The ionic radius of Ti is larger than that of Ti (1.03 nm). 4+ The incorporation of Bi atoms increases the lattice spacing of NaTi2(PO4)3. The surface of the NBTP-0.01 negative electrode obtained in Example 1 was analyzed by scanning electron microscopy (SEM / EDS) for microscopic morphology and surface scanning composition. Figure 2 and 3 As shown in the figure, the Bi-doped NBTP-0.01 anode material has relatively small (<1 μm) spherical particles, and the presence of Bi can be clearly detected in the sample. This shows that Bi atoms can be successfully incorporated into the NaTi2(PO4)3 material lattice.

[0101] Figure 4 The charge and discharge curves of the NTP / C negative electrode in Comparative Example 1 and the NBTP-0.01 negative electrode in Application Example 1 at different rates are given. It can be seen that the discharge specific capacity of the NBTP-0.01 negative electrode at different rates is higher than that of the original NTP / C electrode, which indicates that Bi doping can significantly improve the discharge specific capacity of the NTP negative electrode material. Figure 5 The charge-discharge cycle curves of the NTP / C negative electrode in comparative example 1 and the NBTP-0.01 negative electrode in application example 1 at a rate of 10C are given. It can be seen that the discharge capacity of the NBTP-0.01 negative electrode is about 70 mAh g after 200 cycles. -1 , which is still higher than that of the original NTP / C negative electrode (about 48 mAhg -1 ), and the capacity retention rate of the NBTP-0.01 negative electrode can reach about 80% after 200 cycles. This shows that Bi doping can improve the charge-discharge cycle performance of NTP negative electrode materials. Figure 6 The charge-discharge curves of NTP / C and NBTP-0.01 negative electrodes at a discharge cut-off voltage of -1.2 V vs. SCE are further given. The change in the slope of the charge-discharge curves shows that the charge-discharge curves of the original NTP / C negative electrode have two obvious platforms, which indicates that the original negative electrode surface undergoes Na + At the same time as the ion insertion and extraction reaction, an obvious hydrogen evolution side reaction also occurred; the charge and discharge curve of the modified NBTP-0.01 negative electrode showed only one obvious platform, indicating that only Na +Ion insertion and extraction reactions occur without significant hydrogen evolution side reactions. This shows that Bi doping can significantly shift the hydrogen evolution potential of the NTP negative electrode negatively, which is beneficial for directly inhibiting the occurrence of hydrogen evolution side reactions at the negative electrode, thereby improving the cycle stability of the negative electrode during charge and discharge. At the same time, the negative shift of the negative electrode discharge cut-off voltage is also beneficial for the battery to have a higher operating voltage, actual capacity, and energy density during discharge.

[0102] The test results of the above application examples and comparative application examples are shown in Table 1.

[0103] Table 1

[0104]

[0105]

[0106] From Table 1 we can see the following points:

[0107] (1) Comprehensive application examples 1 to 3 show that the negative electrode of the aqueous sodium ion battery provided by the present invention can improve the discharge capacity, cycle performance and rate performance of the battery material by doping Bi element in the negative electrode active material, wherein the 2C first discharge capacity is 94.2 mAh·g -1 Above, the 5C first discharge capacity is 79.9mAh·g -1 Above, the 10C first discharge capacity is 69.1mAh·g -1 Above, the 20C first discharge capacity is 51.6mAh·g -1 Above, and the discharge capacity retention rate after 200 cycles at 10C is above 53.3%;

[0108] (2) From the perspective of Application Example 1 and Application Examples 4 to 6, it can be seen that in Application Example 1, x is 0.01, and in Application Example 6, x is 0.04. Compared with Application Examples 4 to 5, where x is 0.2 and 0.002, respectively, the 2C first discharge capacity in Application Example 1 and Application Example 6 is as high as 104.8 mAh·g, respectively. -1 and 101.8 mAh g -1 , and the 10C first discharge capacity is 88.6mAh·g -1 and 86.7 mAh g -1 , and the 200-cycle discharge capacity retention rates at 10C were 69.1% and 68.5% respectively, while the 2C first discharge capacity in Application Examples 4 and 5 was only 80.6 mAh·g -1 and 81.3 mAh g -1 , and the 10C first discharge capacity is only 54.2mAh·g -1 and 53.1 mAh g -1, and the discharge capacity retention rates after 200 cycles at 10C were only 49.8% and 50.3%, respectively. This shows that the present invention can better improve the electrochemical performance of the negative electrode material by preferably controlling the Bi doping amount within a specific range;

[0109] (3) From the perspective of Application Example 1 and Application Example 7, it can be seen that in Application Example 1, the preheating treatment is performed before the sintering treatment. Compared with Application Example 7, which does not perform the preheating treatment and directly performs the sintering treatment, the 2C first discharge capacity in Application Example 1 is as high as 104.8 mAh g -1 , and the 10C first discharge capacity is 88.6mAh·g -1 , and the discharge capacity retention rate after 200 cycles at 10C is 69.1%, while the first discharge capacity at 2C in Application Example 7 is only 85.6 mAh·g -1 , and the 10C first discharge capacity is only 54.5mAh·g -1 , and the discharge capacity retention rate after 200 cycles at 10C is only 52.6%, which shows that the present invention can cooperate with Bi doping to improve the electrochemical performance of the negative electrode material by preferably preheating before sintering.

[0110] (4) It can be seen from the comprehensive application example 1 and the application comparative example 1 that the use of Bi doping in the application example 1 can better suppress the negative electrode hydrogen evolution side reaction, and the discharge capacity and cycle stability are significantly improved compared with the application comparative example 1 without Bi doping.

[0111] In summary, the discharge specific capacity and cycle stability of the NBTP / C negative electrode obtained after Bi doping modification of the present invention are significantly better than those of the original electrode. At the same time, the doped negative electrode can better inhibit the hydrogen evolution side reaction, and further help to improve the actual discharge specific capacity and charge-discharge cycle stability of the negative electrode. This may be mainly due to the enhanced ionic conductivity and structural stability of the Bi-doped negative electrode, while having better inhibition of negative electrode hydrogen evolution properties, improving the interface stability of the negative electrode, and ultimately helping to improve the charge-discharge rate characteristics and cycle performance of the negative electrode, while ensuring that the battery has a higher operating voltage and energy density during discharge.

[0112] The present invention uses the above-described embodiments to illustrate the detailed features of the present invention. However, the present invention is not limited to the above-described detailed features, which does not mean that the present invention must rely on the above-described detailed features to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent replacements for the selected technical features of the present invention, additions to auxiliary technical features, and selections of specific methods, etc., fall within the scope of protection and disclosure of the present invention.

Claims

1. An aqueous sodium negative electrode active material, characterized in that The aqueous sodium negative electrode active material comprises a core and a coating layer, wherein the core is Na 1+x Bi x Ti 2-x (PO4)3, where the value of x ranges from 0.005 to 0.2; The coating layer is a carbon coating layer; The carbon content of the aqueous sodium negative electrode active material is 0.1-20%; The aqueous sodium negative electrode active material is in granular form; The particle size of the aqueous sodium negative electrode active material is 0.01-10 μm.

2. A method for preparing the aqueous sodium negative electrode active material according to claim 1, characterized in that: The preparation method comprises: A sodium source, a bismuth source, a titanium source, a phosphorus source, and a carbon source are mixed and dried to prepare a precursor; The precursor is sintered to obtain the aqueous sodium negative electrode active material; The mixing step comprises: first mixing a sodium source, a bismuth source, a phosphorus source, a carbon source and a solvent to obtain a first system; second mixing a titanium source and a solvent to obtain a second system; and then mixing the first system and the second system and stirring to obtain a mixed system; The sintering includes a first preheating process and a second sintering process; The temperature of the first preheating treatment is 300-400°C; The temperature of the second sintering treatment is 750-850°C.

3. The preparation method according to claim 2, characterized in that The sodium source includes any one of sodium carbonate, sodium bicarbonate or sodium acetate, or a combination of at least two of them.

4. The preparation method according to claim 2, characterized in that The bismuth source includes any one of bismuth nitrate, bismuth subcarbonate or bismuth subcarbonate, or a combination of at least two of them.

5. The preparation method according to claim 2, characterized in that The titanium source includes any one of tetrabutyl titanate, titanium tetraisopropoxide or isopropyl titanate, or a combination of at least two thereof.

6. The preparation method according to claim 2, characterized in that The phosphorus source includes ammonium dihydrogen phosphate and / or diammonium hydrogen phosphate.

7. The preparation method according to claim 2, characterized in that The carbon source includes any one of citric acid, glucose, acetic acid or lactic acid, or a combination of at least two of them.

8. The preparation method according to claim 2, characterized in that The solvent includes at least one of anhydrous ethanol and deionized water.

9. The preparation method according to claim 2, characterized in that Mixing the first system and the second system is adding the second system into the first system.

10. The preparation method according to claim 2, characterized in that The sodium source, bismuth source, titanium source and phosphorus source are all raw materials for aqueous sodium negative electrode active materials, and the mass ratio of carbon in the carbon source to the mass ratio of sodium, bismuth, titanium and phosphorus in the raw materials for aqueous sodium negative electrode active materials is 0.1-20%.

11. The preparation method according to claim 2, characterized in that The mass ratio of the solvent to the raw material of the aqueous sodium negative electrode active material is (1-10):

1.

12. The preparation method according to claim 2, characterized in that The first preheating treatment lasts for 3 to 4 hours.

13. The preparation method according to claim 2, characterized in that The second sintering treatment time is 8 to 15 hours.

14. A negative electrode for an aqueous sodium ion battery, characterized in that: The negative electrode comprises the aqueous sodium-ion negative electrode active material according to claim 1, and / or the aqueous sodium-ion negative electrode active material prepared by the preparation method of the aqueous sodium-ion negative electrode active material according to any one of claims 2 to 13.

15. The negative electrode according to claim 14, characterized in that The negative electrode comprises a current collector and an active material layer arranged on the current collector, wherein the active material layer contains aqueous sodium negative electrode active material.

16. The negative electrode according to claim 15, characterized in that The active material layer also contains a conductive agent and a binder.

17. The negative electrode according to claim 16, characterized in that The mass ratio of the aqueous sodium negative electrode active material, the conductive agent and the binder is: 6-8:1-3:0.5-1.

5.

18. The negative electrode according to claim 16, characterized in that The conductive agent includes any one of SuperP carbon black, acetylene black, carbon nanotubes, graphene or titanium dioxide, or a combination of at least two thereof.

19. The negative electrode according to claim 16, characterized in that The binder includes any one of PVDF, PTFE, CMC or SBR, or a combination of at least two of them.

20. The negative electrode according to claim 15, characterized in that The current collector includes any one of carbon paper, flexible graphite, aluminum foil, titanium foil, titanium mesh or stainless steel mesh, or a combination of at least two of them.

21. A sodium ion battery, characterized in that: The sodium ion battery comprises the negative electrode of the aqueous sodium ion battery according to any one of claims 14 to 20.

Images