Titanium sodium phosphate coated doped sodium titanate composite material as well as preparation method and application thereof

Abstract

The invention discloses a titanium sodium phosphate coated doped sodium titanate composite material and a preparation method and application thereof, the preparation method comprises the following steps: mixing a titanium source, a sodium source, a doping source and a solvent, ball-milling and calcining to obtain doped sodium titanate Na < 2 > Ti < 3-x > M < x > O7, M is selected from Zr and / or Sn, and x is 0.02-0.08; the preparation method comprises the following steps: mixing doped sodium titanate with a phosphorus source and a solvent, carrying out ball milling, carrying out pretreatment at 300-450 DEG C, carrying out heat treatment at 600-800 DEG C, and constructing a sodium titanium phosphate coating layer on the surface of the doped sodium titanate in situ to obtain the sodium titanium phosphate coated doped sodium titanate composite material. Zr / Sn is introduced into sodium titanate crystal lattices for bulk phase doping, and the crystal framework is stabilized; and a sodium titanium phosphate protective layer which is electrochemically inert and ion-conductive is constructed on the surface of the particle in situ, and direct contact between an active interface and an electrolyte is blocked, so that synchronous optimization of structural stability and interface safety is realized.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, specifically to a sodium titanate-coated doped sodium titanate composite material, its preparation method, and its application. Background Technology

[0002] With rising lithium resource costs and increasingly prominent uneven distribution issues, sodium-ion batteries have become an important development direction for next-generation energy storage systems due to their abundant resources, low cost, and environmental friendliness. Among numerous anode material candidates, layered sodium titanate (Na2Ti3O7) stands out due to its moderate sodium intercalation potential (approximately 0.2 V vs. Na2Ti3O7). + With its high theoretical specific capacity (~200 mAh / g) and good ion diffusion properties, Na₂Ti₃O₇ is considered a promising anode material for sodium-ion batteries. However, Na₂Ti₃O₇ still faces two major bottlenecks in practical applications:

[0003] (1) Poor cycle stability: During the charging and discharging process, Na2Ti3O7 will undergo obvious lattice distortion and phase transition behavior. Especially during deep sodium insertion and extraction, it is easy to cause volume change and structural breakage, resulting in pulverization of active material, contact failure, and rapid decay of cycle capacity.

[0004] (2) Severe interfacial side reactions: Due to its low sodium intercalation potential (close to the sodium deposition potential), and the generation of catalytically active Ti in the sodium intercalation state. 3+ In this state, the material exhibits a strong catalytic decomposition effect on organic electrolytes (such as ethylene carbonate EC, diethyl carbonate DEC, etc.), triggering a continuous electrolyte redox reaction. This results in the generation of a large amount of gas (H2, CO, CO2, low molecular weight hydrocarbons, etc.) inside the battery cell, leading to battery swelling, increased internal resistance, reduced cycle life, and even safety hazards.

[0005] Existing improvement methods mainly include carbon coating, nano-sizing, and elemental doping. While carbon coating can improve conductivity, it cannot effectively suppress Ti... 3+ The catalytic effect on the electrolyte; while single-element doping can stabilize the crystal structure to a certain extent, it is difficult to solve the problem of interfacial side reactions.

[0006] Therefore, there is an urgent need to develop a synergistic modification strategy that combines phase structure strengthening and surface interface passivation functions to simultaneously solve the cycling instability and gas generation problems of sodium titanate materials. Summary of the Invention

[0007] This invention addresses the shortcomings of existing technologies by providing a sodium titanate-coated sodium titanate composite material, its preparation method, and its application. It proposes a design concept of "internal doping and external coating, synergistic enhancement." On one hand, high-valence metal ions (Zr / Sn) are introduced into the Na2Ti3O7 lattice for bulk doping to stabilize its crystal framework. On the other hand, an electrochemically inert and ion-conducting sodium titanate (NaTi2(PO4)3) protective layer is constructed in situ on the surface of the powder particles to block direct contact between the active interface and the electrolyte, thereby achieving simultaneous optimization of structural stability and interface safety.

[0008] To address the aforementioned technical problems, the first aspect of this invention provides a method for preparing a sodium titanate-coated doped sodium titanate composite material, comprising the following steps:

[0009] S1. After mixing the titanium source, sodium source, dopant source, and solvent, the mixture is ball-milled and calcined to obtain doped sodium titanate (Na2Ti). 3- x M x O7 is used as the core layer; wherein M is selected from Zr and / or Sn, preferably Zr, and x = 0.02-0.08;

[0010] S2. After mixing the doped sodium titanate with a phosphorus source and a solvent, the mixture is ball-milled, pretreated at 300-450℃, and heat-treated at 600-800℃ to construct an in-situ sodium titanate coating layer on the surface of the doped sodium titanate as a shell layer; thus obtaining the sodium titanate coated doped sodium titanate composite material.

[0011] First, this invention utilizes an internally doped stable structure to select tetravalent metal ions, Zr. 4+ / Sn 4+ Partially replaces Ti 4+ Site; due to Zr 4+ Sn 4+ With a large ionic radius and stronger MO bond energy, it can effectively suppress lattice strain and phase transition during charge and discharge, enhance the structural toughness of the material, and extend cycle life. Secondly, this invention utilizes the sodium and titanium sources provided by the doped sodium titanate itself, combined with an external phosphorus source, to generate a dense and stable NASICON-type sodium titanate phosphate coating layer in situ using a controllable pretreatment and heat treatment process. Compared with existing coating layers, the in-situ generated coating layer has good crystallinity, a tight interface with the core layer matrix, and no obvious cracks or pores; moreover, this in-situ generated coating layer not only possesses excellent Na... + Conductive ability, and can also physically isolate Ti 3+Contact with the electrolyte fundamentally inhibits catalytic decomposition reactions and reduces gas generation. This invention optimizes the function from the entire "bulk phase-interface" dimension, improving both the intrinsic stability of the material and its compatibility with the electrolyte, providing a new path for the development of high-performance sodium-ion battery anode materials.

[0012] Furthermore, in S1, the doping source is ZrO2 and / or SnO2.

[0013] Furthermore, in S1, the solvent is deionized water and / or ethanol.

[0014] Furthermore, in S1, the calcination conditions are: air atmosphere, temperature 800-900℃, and time 10-12h.

[0015] Furthermore, in S2, the phosphorus source is selected from one or more of ammonium dihydrogen phosphate, sodium dihydrogen phosphate, and orthophosphoric acid.

[0016] Furthermore, in S2, the pretreatment conditions are: air atmosphere, time 2-4 hours. This pretreatment is used to remove volatile components and form a preliminary reaction interface.

[0017] Furthermore, in S2, the heat treatment conditions are: a nitrogen and / or argon protective atmosphere, for 4-8 hours. During the heat treatment, the sodium and titanium ions of the core layer itself undergo a solid-phase reaction with the doped phosphorus source, generating an in-situ sodium titanium phosphate coating layer that is tightly bonded to the core layer.

[0018] Furthermore, in S2, the mass of the coating layer is 1-7% of the total mass of the sodium titanate coated doped sodium titanate composite material, preferably 3-6%.

[0019] Furthermore, S2 also includes: natural cooling to room temperature, grinding, and sieving with a mesh size of 200 or larger.

[0020] The second aspect of the present invention provides a sodium titanate composite material coated and doped with sodium titanate by the preparation method described in the first aspect.

[0021] A third aspect of the present invention provides a sodium-ion battery, comprising a positive electrode and a negative electrode, wherein the negative electrode contains the sodium titanate-coated doped sodium titanate composite material described in the second aspect.

[0022] The beneficial effects of this invention are:

[0023] This invention employs a dual mechanism of bulk doping and in-situ surface coating layer generation. High-valence metal ions are introduced into the Na2Ti3O7 lattice for bulk doping to stabilize its crystal framework. An electrochemically inert and ion-conducting sodium titanium phosphate coating layer is constructed in-situ on the surface of the powder particles to block direct contact between the active interface and the electrolyte, thus simultaneously solving the two major problems of structural instability and interfacial gas generation.

[0024] This invention enhances lattice stability through bulk doping and mitigates volume effects through a coating layer, resulting in a capacity retention of ≥92% after 500 cycles at 1C rate. The in-situ generated coating layer effectively isolates Ti. 3+ Contact with the electrolyte reduces the amount of gas generated during battery cycling.

[0025] This invention employs a conventional solid-state method, requiring no complex equipment and suitable for industrial-scale production. It uses no toxic solvents, and the main byproducts are water and ammonia, which are easy to handle. Furthermore, by utilizing the Na and Ti sources of the core matrix itself to generate the coating layer, not only are raw material costs saved, but the generated protective layer also has better adhesion to the matrix material, which is beneficial to the realization of electrochemical capacity. Attached Figure Description

[0026] To more clearly illustrate the technical solution of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a 1C cycle stability test of the battery assembled from the materials obtained in Example 1 and Comparative Example 4 of the present invention. Detailed Implementation

[0028] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] This embodiment relates to a method for preparing a sodium titanate composite material coated with sodium titanate titanium phosphate, comprising the following steps:

[0030] S1. After mixing the titanium source, sodium source, dopant source, and solvent, the mixture is ball-milled and calcined to obtain doped sodium titanate (Na2Ti). 3- x M x O7 is used as the core layer; wherein M is selected from Zr and / or Sn, preferably Zr, and x = 0.02-0.08;

[0031] S2. After mixing the doped sodium titanate with a phosphorus source and a solvent, the mixture is ball-milled, pretreated at 300-450℃, and heat-treated at 600-800℃ to construct an in-situ sodium titanate coating layer on the surface of the doped sodium titanate as a shell layer; thus obtaining the sodium titanate coated doped sodium titanate composite material.

[0032] This embodiment utilizes an internally doped stable structure, selecting tetravalent metal ions Zr. 4+ / Sn 4+ Partially replaces Ti 4+ Site; due to Zr 4+ Sn 4+ With a large ionic radius and stronger MO bond energy, it can effectively suppress lattice strain and phase transition during charge and discharge, enhance the structural toughness of the material, and extend cycle life. This embodiment also utilizes the sodium and titanium sources provided by the doped sodium titanate itself, combined with an external phosphorus source, to generate a dense and stable NASICON-type sodium titanate phosphate coating layer in situ using a controllable pretreatment and heat treatment process. Compared with existing coating layers, the in-situ generated coating layer has good crystallinity, a tight interface with the core layer matrix, and no obvious cracks or pores; moreover, this in-situ generated coating layer not only possesses excellent Na... + Conductive ability, and can also physically isolate Ti 3+ Contact with the electrolyte fundamentally inhibits catalytic decomposition reactions and reduces gas generation. This invention optimizes the function from the entire "bulk phase-interface" dimension, improving both the intrinsic stability of the material and its compatibility with the electrolyte, providing a new path for the development of high-performance sodium-ion battery anode materials.

[0033] In a preferred embodiment, in S1, the doping source is ZrO2 and / or SnO2; the solvent is deionized water and / or ethanol; and the calcination conditions are: air atmosphere, temperature 800-900℃, and time 10-12h.

[0034] In a preferred embodiment, in S2, the phosphorus source is selected from one or more of ammonium dihydrogen phosphate, sodium dihydrogen phosphate, and orthophosphoric acid; the pretreatment conditions are: air atmosphere, time 2-4 hours. This pretreatment is used to remove volatile components and form a preliminary reaction interface; the heat treatment conditions are: nitrogen and / or argon protective atmosphere, time 4-8 hours. During the heat treatment, the sodium and titanium ions of the core layer itself undergo a solid-phase reaction with the doped phosphorus source to generate a sodium titanate phosphate coating layer in situ, which is tightly bonded to the core layer; the mass of the coating layer is 1-7% of the total mass of the sodium titanate phosphate coated doped sodium titanate composite material, preferably 3-6%.

[0035] As a preferred embodiment, S2 further includes: natural cooling to room temperature, grinding, and sieving with a mesh size of 200 or larger.

[0036] Another embodiment provides a sodium titanate composite material coated and doped with sodium titanate phosphate prepared by the preparation method described in the above embodiments.

[0037] Another embodiment provides a sodium-ion battery, including a positive electrode and a negative electrode, wherein the negative electrode contains the sodium titanate-coated doped sodium titanate composite material described in the above embodiment.

[0038] Example 1

[0039] This embodiment relates to a method for preparing a sodium titanate-coated doped sodium titanate composite material, comprising the following steps:

[0040] (1) Using TiO2 as the titanium source, Na2CO3 as the sodium source, and ZrO2 as the dopant source, they were mixed in ethanol at a molar ratio of Na / Ti / Zr = 2:2.95:0.05, ball-milled for 6 h, and calcined in air at 850℃ for 12 h to obtain Zr-doped sodium titanate Na2Ti. 2.95 Zr 0.05 O7.

[0041] (2) Take Zr-doped sodium titanate, add ammonium dihydrogen phosphate (NH4H2PO4) at 5wt% of the coating layer, ball mill with ethanol for 3h, pre-treat at 400℃ for 3h in air atmosphere, then calcine at 700℃ for 6h in argon atmosphere, grind after natural cooling, and sieve with 200 mesh to obtain sodium titanate coated doped sodium titanate composite material.

[0042] Example 2

[0043] The difference between this embodiment and embodiment 1 is that the doping source in step (1) is replaced with SnO2, while the other steps and parameters remain unchanged.

[0044] Example 3

[0045] The difference between this embodiment and embodiment 1 is that the doping source in step (1) is SnO2 and ZrO2 with a molar ratio of 3:2, while the other steps and parameters remain unchanged.

[0046] Example 4

[0047] The difference between this embodiment and embodiment 1 is that the molar ratio of Na / Ti / Zr in step (1) is 2:2.97:0.03, while the other steps and parameters remain unchanged.

[0048] Example 5

[0049] The difference between this embodiment and embodiment 1 is that the molar ratio of Na / Ti / Zr in step (1) is 2:2.93:0.07, while the other steps and parameters remain unchanged.

[0050] Comparative Example 1

[0051] The difference between this comparative example and Example 1 is that the molar ratio of Na / Ti / Zr in step (1) is 2:2.99:0.01, while other steps and parameters remain unchanged.

[0052] Comparative Example 2

[0053] The difference between this comparative example and Example 1 is that the molar ratio of Na / Ti / Zr in step (1) is 2:2.9:0.1, while other steps and parameters remain unchanged.

[0054] Comparative Example 3

[0055] The difference between this comparative example and Example 1 is that no doping source is added in step (1), and Na2Ti3O7 is prepared using TiO2 as the titanium source and Na2CO3 as the sodium source. Other steps and parameters remain unchanged.

[0056] Comparative Example 4

[0057] The difference between this comparative example and Example 1 is that step (2) is omitted and sodium titanium phosphate is not coated, while other steps and parameters remain unchanged.

[0058] Comparative Example 5

[0059] The difference between this comparative example and Example 1 is that, in preparing Zr-doped sodium titanate Na2Ti 2.95 Zr 0.05 After O7, it was mixed with sodium titanate powder and ball-milled with ethanol for 3 hours, and then dried and cooled to obtain sodium titanate coated and doped sodium titanate composite material.

[0060] Test case

[0061] Step 1: Place the raw material powder into a high vacuum oven, first evacuate to -0.09MPa, then fill with nitrogen, repeat 3 times, heat the oven to 80℃, bake for 24 hours, and perform gas replacement every 2 hours during the process to control the moisture content of the powder to ≤1000ppm.

[0062] Step 2: Positive electrode homogenization: Take the main material (sodium iron pyrophosphate), conductive agent 1 (acetylene black), conductive agent 2 (carbon nanotubes), and binder in a mass ratio of 95.0:2.0:1.0:2.0 and add them to the mixing machine in a certain order. Add an appropriate amount of NMP as a solvent, control the solid content to 55%, and disperse at high speed for 200 min. During the process, control the vacuum degree to -0.09MPa.

[0063] Negative electrode homogenization: Take the main material (the material obtained in the examples and comparative examples), acetylene black, carbon nanotubes and binder in a mass ratio of 94.5:2.0:1.5:2.0 and add them to the mixing machine in a certain order. Add an appropriate amount of NMP as a solvent, control the solid content to 52%, and disperse at high speed for 210 min. During the process, control the vacuum degree to -0.09MPa.

[0064] Step 3: Transfer the well-mixed slurry to the coating machine. Turn on the coating machine oven beforehand and control the oven temperature to 90℃. The surface density of the double-sided dry film coated on the positive electrode is 18.0 mg / cm³. 2 The density of the double-sided dry film coated on the negative electrode is 16.0 mg / cm³. 2 .

[0065] Step 4: Roll the coated electrode rolls at 25°C and 10.0% RH. Control the positive electrode compaction density to 2.0 g / cm³. 3 The negative electrode compaction density is 1.7 g / cm³. 3 The corresponding thickness is 100μm for the positive electrode and 110μm for the negative electrode.

[0066] Step 5: Select electrode sheets of different roll-pressed thicknesses according to the capacity ratio of the battery design, and then die-cut and group them. The positive and negative electrodes are stacked in a Z-shaped stacking form to form a core package and assembled into a square battery.

[0067] Specific capacity test: The battery is charged / discharged at a rate of 0.1 C within a voltage range of 1.5 V to 4.2 V. The specific capacity of the active material is calculated according to the formula C=QD / M, where QD is the discharge capacity and M is the mass of the active material.

[0068] Battery Deformation: The change in battery thickness, or deformation, is used to assess the amount of gas produced by the battery. Gas production increases the internal pressure, causing a slight expansion of the casing. This change in battery thickness is measured using a high-precision displacement sensor. The battery is clamped in a stainless steel fixture and subjected to charge-discharge tests in a constant temperature chamber. A high-precision dial indicator or LVDT displacement sensor (resolution 0.1–1 μm) is used to measure the change in casing thickness ΔT%=(T t -T0) / T0*100%; where T0 is the initial thickness, T t The thickness is after 50 cycles.

[0069] Cyclic stability: First, a 1C capacity calibration was performed and the discharge capacity was recorded as C0. Then, a 1C charge-discharge cycle (charged to 3.9V, discharged to 1.5V) was used to record the discharge capacity C after the 500th cycle. 500 Capacity retention ratio R=C 500 / C0*100% was used to evaluate the cycle stability of sodium-ion batteries after 500 cycles.

[0070] Figure 1 The 1C cycle stability tests of the composite material batteries obtained in Example 1 and Comparative Example 4 show that the uncoated Comparative Example 1 exhibits poor cycle stability. Performance test data for the composite material assembled batteries obtained in the examples and comparative examples are shown in Table 1.

[0071] Table 1

[0072]

[0073] As shown in Table 1, the assembled batteries obtained from Examples 1-5 exhibit good specific capacity, battery deformation rate, and capacity retention rate after 500 cycles at 1C. Among them, Example 1 has the best performance. Example 2 uses a Sn-doped stable structure, but the larger ion radius results in a slightly lower specific capacity than the best Example 1, although the cycle performance is stable. Example 3 uses dual-element doping, balancing structural stability and kinetic performance. Example 4 uses a slightly lower doping amount, while Example 5 uses a slightly higher doping amount, resulting in slightly lower performance than the best Example 1.

[0074] Compared to Example 1, the doping amount in Comparative Example 1 was too low, which could not effectively suppress the phase transition stress during the charging and discharging process, resulting in significant cycle decay; the doping amount in Comparative Example 2 was too high, which destroyed the layered ordered structure of sodium titanate and hindered the development of Na+. + Intercalation / de-intercalation leads to a decrease in both specific capacity and cycling performance; although Comparative Example 3 has a coating layer to alleviate interfacial reactions, it lacks bulk doping, making its structure prone to collapse during cycling. Irreversible phase transitions still occur during long-term cycling, resulting in severe swelling with a swelling rate of 3.5% and rapid capacity decay; Comparative Example 4 has only Zr doping without coating, resulting in a relatively stable structure, but the surface Ti... 3+ The continuous catalytic decomposition of the electrolyte produces a large amount of H2 / CO gas, resulting in severe swelling (4.2%) and capacity decay. Although Comparative Example 5 is coated with sodium titanium phosphate material, the coating effect is poor because sodium titanium phosphate is not generated in situ, and the test results are similar to those of the comparative example.

[0075] The present invention has been described in detail above with reference to specific embodiments and exemplary examples; however, these descriptions should not be construed as limiting the present invention. Those skilled in the art will understand that various equivalent substitutions, modifications, or improvements can be made to the technical solutions and embodiments of the present invention without departing from the spirit and scope of the invention, and all such modifications and improvements fall within the scope of the present invention. The scope of protection of the present invention is defined by the appended claims.

Claims

1. A method for preparing a sodium titanate composite material coated with sodium titanate phosphate, characterized in that, Includes the following steps: S1. After mixing the titanium source, sodium source, dopant source, and solvent, the mixture is ball-milled and calcined to obtain doped sodium titanate (Na2Ti). 3-x M x O7, where M is selected from Zr and / or Sn, x = 0.02-0.08; S2. After mixing the doped sodium titanate with a phosphorus source and a solvent, the mixture is ball-milled, pretreated at 300-450℃, and heat-treated at 600-800℃ to construct a sodium titanate coating layer in situ on the surface of the doped sodium titanate, thereby obtaining the sodium titanate coated doped sodium titanate composite material.

2. The method for preparing sodium titanate-coated doped sodium titanate composite material as described in claim 1, characterized in that, In S1, the doping source is ZrO2 and / or SnO2.

3. The preparation method of sodium titanate-coated doped sodium titanate composite material as described in claim 1, characterized in that, In S1, the calcination conditions are: air atmosphere, temperature 800-900℃, and time 10-12h.

4. The preparation method of sodium titanate-coated doped sodium titanate composite material as described in claim 1, characterized in that, In S2, the phosphorus source is selected from one or more of ammonium dihydrogen phosphate, sodium dihydrogen phosphate, and orthophosphoric acid.

5. The method for preparing sodium titanate-coated doped sodium titanate composite material as described in claim 1, characterized in that, In S2, the pretreatment conditions are: air atmosphere and time 2-4 hours.

6. The method for preparing sodium titanate-coated doped sodium titanate composite material as described in claim 1, characterized in that, In S2, the heat treatment conditions are: nitrogen and / or argon protective atmosphere, for 4-8 hours.

7. The method for preparing sodium titanate-coated doped sodium titanate composite material as described in claim 1, characterized in that, In S2, the mass of the coating layer is 1-7% of the total mass of the sodium titanate coated doped sodium titanate composite material.

8. The method for preparing sodium titanate-coated doped sodium titanate composite material as described in claim 1, characterized in that, S2 also includes: natural cooling to room temperature, grinding, and sieving with a mesh size of 200 or larger.

9. A sodium titanate composite material coated with sodium titanate phosphate prepared by the preparation method according to any one of claims 1-8.

10. A sodium-ion battery, characterized in that, It includes a positive electrode and a negative electrode, wherein the negative electrode contains the sodium titanate-coated doped sodium titanate composite material as described in claim 9.

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