Ternary positive electrode material modified by coupling surface and interface modification and bulk phase doping and preparation method thereof

Abstract

The preparation method comprises the following steps: S1, introduction of a titanium source and a tantalum source: dissolving the titanium source and the tantalum source in absolute ethyl alcohol, fully stirring, adding a ternary positive electrode material LiNixCoyMn1-x-yO2 (x is more than or equal to 0.33 and less than or equal to 1), stirring, and carrying out ultrasonic-assisted treatment; s2, hydrolyzing a titanium source and a tantalum source: slowly dropwise adding a small amount of deionized water into the solution, and continuously stirring; s3, adding a lithium source: weighing a corresponding amount of LiOH.H2O, dissolving the LiOH.H2O in absolute ethyl alcohol, and slowly adding the LiOH.H2O into the solution after the LiOH.H2O is completely dissolved; s4, evaporating and drying: heating and stirring the solution at the heating temperature of 40-120 DEG C until the ethanol is completely volatilized to form solid powder, then carrying out vacuum drying on the solid powder, and then carrying out high-temperature sintering treatment. Through grain boundary strengthening and surface coating protection of LiTaO3, a Ti doped stable bulk phase structure is coupled, generation of cracks is effectively inhibited, interface side reaction is slowed down, and the cycle stability of the ternary material is improved.

Description

Technical Field

[0001] The invention relates to the technical field of lithium ion battery positive electrode materials, and in particular to a method for preparing a surface-interface-modified coupled bulk-doped ternary positive electrode material. Background Art

[0002] With the energy crisis and environmental pollution, there is an urgent need to develop efficient and clean energy storage devices. Among the many energy storage devices, lithium-ion batteries have been widely used in the field of mobile energy storage devices due to their high specific energy, long cycle and pollution-free characteristics. The key materials of lithium-ion batteries are positive electrode, negative electrode and electrolyte, among which the positive electrode material determines the capacity and cycle performance of the battery and plays a vital role. x Co y Mn 1-x-y O2(NCM) has become the most promising positive electrode material for lithium-ion batteries due to its high energy density, high operating voltage and long cycle life.

[0003] In order to pursue higher energy density, increasing the nickel content in ternary cathode materials is the only way. However, with the increase of nickel content, the stability of the material structure decreases, and the surface is prone to interfacial side reactions with the electrolyte; more seriously, during the cycle, accompanied by the deintercalation of lithium ions, the expansion and contraction of primary particles intensifies, which leads to the generation of cracks along the grain boundaries (cracks along the grain boundaries refer to the phenomenon that cracks extend along the grain boundaries in the crystal structure of the ternary cathode material. This crack is usually caused by the stress concentration generated by the material during the cyclic charge and discharge process), causing the electrolyte to penetrate into the particles and react with the newly exposed internal surface, aggravating the interface phase change, transition metal dissolution and gas production, and seriously restricting the electrochemical performance of the material. The problem of cracks along the grain boundaries is considered to be the main reason for the performance degradation of ternary cathode materials. Therefore, inhibiting cracks along the grain boundaries and stabilizing the surface interface of the material is the key to improving the electrochemical performance. Summary of the invention

[0004] The present invention aims to provide a method for preparing a ternary positive electrode material with surface interface modification coupled with bulk doping modification, which stabilizes the material structure and surface through grain boundary strength, surface coating and bulk doping, increases the overall strength and surface stability of secondary particles, inhibits the generation of cracks, solves the problem of aggravated interface side reactions caused by cracks during the charge and discharge process, and effectively improves the cycle life.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] A method for preparing a surface-interface-modified coupled bulk-doped ternary cathode material comprises:

[0007] S1. Introduction of titanium source and tantalum source: The titanium source and tantalum source are dissolved in anhydrous ethanol, stirred thoroughly, and the ternary positive electrode material LiNi x Co y Mn 1-x-y O2 (0.33≤x≤1), and stirring and ultrasound-assisted treatment;

[0008] S2. Hydrolysis of titanium source and tantalum source: slowly drop a small amount of deionized water into the above solution and continue stirring;

[0009] S3. Addition of lithium source: weigh a corresponding amount of LiOH·H2O and dissolve it in anhydrous ethanol. After it is completely dissolved, slowly add it to the above solution;

[0010] S4, evaporation and drying: the above solution is heated and stirred at a heating temperature of 40-120°C until the ethanol is completely evaporated and converted into solid powder, and then the obtained solid powder is vacuum dried, and then subjected to high-temperature sintering treatment and then cooled to obtain a modified ternary positive electrode material.

[0011] Working principle and beneficial effects of the present invention:

[0012] Through liquid phase pre-coating and high-temperature sintering, the Ti element diffuses into the bulk phase, and the Ta element generates LiTaO3 at the grain boundaries and surfaces. Through the grain boundary strengthening and surface coating protection of LiTaO3, coupled with Ti doping to stabilize the bulk phase structure, the generation of cracks is effectively inhibited, the interface side reactions are slowed down, and the cyclic stability of the ternary material is improved.

[0013] Furthermore, the S2 is continuously stirred for more than 0.5 h.

[0014] Furthermore, the vacuum drying has a drying temperature of 80-120° C. and a drying time of more than 6 hours.

[0015] Further, the amount of the titanium source added is based on the molar ratio of Ti / LiNi x Co y Mn 1-x-y O2 = 0.5% - 3%; the amount of tantalum source added is based on the molar ratio of Ta / LiNi x Co y Mn 1-x-y O2=0.5%-5%.

[0016] Furthermore, the titanium source includes tetrabutyl titanate, isopropyl titanate, titanium n-propoxide, titanium isooctoxide, tetraethyl titanate, titanium tert-butoxide, and titanium isopropoxide.

[0017] Furthermore, the tantalum source includes tantalum ethoxide, tantalum methanol, tantalum pentachloride, tantalum butoxide, and tantalum penta(dimethylamino).

[0018] Furthermore, the high temperature sintering treatment is carried out in a tube furnace by heating to 550-850° C. at a heating rate of 3-10° C. / min, keeping the temperature for 2-6 hours, and the oxygen flow rate is 40-100 mL / min.

[0019] Furthermore, the LiNi x Co y Mn 1-x-y O2, wherein x is 0.33-0.95, y is 0.025-0.33, and 0<1-xy<1.

[0020] Furthermore, the heating rate is 3-10°C / min, and the cooling rate of the cooling treatment is 3-5°C / min or natural cooling. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a SEM morphology image of the ternary cathode material particles of Example 1;

[0022] Figure 2 This is a screenshot of the EDS spectrum of the ternary cathode material of Example 1;

[0023] Figure 3 The 1C cycle performance of the ternary positive electrode materials of the comparative example and the embodiment in the voltage range of 2.8 to 4.5V. DETAILED DESCRIPTION

[0024] The following is further described in detail through specific implementation methods:

[0025] Embodiment 1:

[0026] A method for preparing a surface-interface-modified coupled bulk-doped ternary cathode material comprises the following steps:

[0027] (1) Weigh 0.17 g of tetrabutyl titanate and 0.2 g of tantalum ethoxide and dissolve them in 100 mL of anhydrous ethanol. Stir evenly and add 5 g of LiNi 0.8 Co 0.1 Mn 0.1 O2 cathode powder, stirring and ultrasound-assisted treatment;

[0028] (2) Slowly add 2.5 ml of deionized water, stir for 0.5 h to fully hydrolyze, and then add 15 ml of 0.05 mol / L LiOH·H2O ethanol solution;

[0029] (3) heating the solution obtained in step 2 at 80° C. with stirring until the ethanol is completely evaporated;

[0030] (4) vacuum drying the solid powder obtained in step 3 for 12 h;

[0031] (5) The dried solid powder was placed in a tube furnace and heated to 700°C at a heating rate of 5°C / min, kept at this temperature for 4 h, with an oxygen flow rate of 60 mL / min, and then cooled to room temperature at a cooling rate of 5°C / min to obtain LiTaO3 grain boundary and surface modified coupled Ti bulk doped LiNi 0.8 Co 0.1 Mn 0.1 O2 ternary positive electrode material. Figure 1 and Figure 2 As shown, the Ta element is enriched at the grain boundaries and surfaces to form LiTaO3, which performs grain boundary strengthening and surface coating modification.

[0032] (6) The modified ternary cathode material and metal lithium were combined into a button cell, and the electrochemical performance was tested in the voltage range of 2.8-4.5V. Figure 3 As shown, the synergistically modified material has excellent cycle performance. The first discharge capacity at 1C current density is 202.6mAh / g, and the capacity retention rate after 100 cycles is as high as 86%. The first discharge capacity of the unmodified ternary positive electrode material is 195.2mAh / g, and the capacity retention rate is only 68.4% (comparative example), indicating that the cycle stability of the modified material is significantly improved.

[0033] Example 2: Using different titanium and tantalum sources for mutual comparison experiments

[0034] A method for preparing a surface-interface-modified coupled bulk-doped ternary cathode material comprises the following steps:

[0035] (1) Weigh 0.142 g of isopropyl titanate and 0.547 g of tantalum butanol and dissolve them in 150 mL of anhydrous ethanol. Stir well and add 5 g of LiNi 0.8 Co 0.1 Mn 0.1 O2 cathode powder, stirring and ultrasound-assisted treatment;

[0036] (2) Slowly add 3 ml of deionized water, stir for 0.5 h to fully hydrolyze, and then add 20 ml of 0.05 mol / L LiOH·H2O ethanol solution;

[0037] (3) heating the solution obtained in step 2 at 90° C. with stirring until the ethanol is completely evaporated;

[0038] (4) vacuum drying the solid powder obtained in step 3 for 10 h;

[0039] (5) The dried solid powder was placed in a tube furnace and heated to 700°C at a heating rate of 5°C / min, kept at this temperature for 4 h, with an oxygen flow rate of 60 mL / min, and then cooled to room temperature at a cooling rate of 5°C / min to obtain LiTaO3 grain boundary and surface modified coupled Ti bulk doped LiNi 0.8 Co 0.1 Mn 0.1 O2 ternary positive electrode material.

[0040] (6) The modified ternary cathode material and metal lithium were combined into a button cell, and the electrochemical performance was tested in the voltage range of 2.8-4.5V. Figure 3 As shown, the synergistic modified material has excellent cycle performance, with an initial discharge capacity of 199.2 mAh / g at a current density of 1C and a capacity retention rate of up to 86.4% after 100 cycles.

[0041] Embodiment 3:

[0042] A method for preparing a surface-interface-modified coupled bulk-doped ternary cathode material comprises the following steps:

[0043] (1) Weigh 0.17 g of tetrabutyl titanate and 0.2 g of tantalum ethoxide and dissolve them in 100 mL of anhydrous ethanol. Stir evenly and add 5 g of LiNi 0.8 Co 0.1 Mn 0.1 O2 cathode powder, stirring and ultrasound-assisted treatment;

[0044] (2) Slowly add 2.5 ml of deionized water, stir for 0.5 h to fully hydrolyze, and then add 15 ml of 0.05 mol / L LiOH·H2O ethanol solution;

[0045] (3) heating the solution obtained in step 2 at 90° C. with stirring until the ethanol is completely evaporated;

[0046] (4) The solid powder obtained in step 3 is vacuum dried for 12 h to obtain a pre-coated LiNi 0.8 Co 0.1 Mn 0.1 O2 ternary positive electrode material.

[0047] (6) The modified ternary cathode material without high temperature treatment was combined with metal lithium to form a button cell, and the electrochemical performance was tested in the voltage range of 2.8-4.5V. Figure 3 As shown, the first discharge capacity at 1C current density is 196.5mAh / g, and the capacity retention rate after 100 cycles is 68.3%. This shows that without high temperature treatment, the material performance has not been improved, which means that only high temperature treatment can form an effective surface interface modification layer and bulk doping.

[0048] Compare columns:

[0049] The following is further described in detail through specific implementation methods:

[0050] A method for preparing a ternary positive electrode material comprises the following steps:

[0051] (1) Weigh 5g LiNi 0.8 Co 0.1 Mn 0.1 The O2 cathode powder was added into 100 mL of anhydrous ethanol and stirred and ultrasonically assisted;

[0052] (2) heating the solution obtained in step 1 at 80° C. with stirring until the ethanol is completely evaporated;

[0053] (3) vacuum drying the solid powder obtained in step 2 for 12 h;

[0054] (4) The dried solid powder was placed in a tube furnace and heated to 700°C at a heating rate of 5°C / min, kept at this temperature for 4 h, with an oxygen flow rate of 60 mL / min, and then cooled to room temperature at a cooling rate of 5°C / min to obtain unmodified LiNi 0.8 Co 0.1 Mn 0.1 O2 ternary positive electrode material.

[0055] (5) The obtained unmodified ternary cathode material and metallic lithium were combined into a button cell, and the electrochemical performance was tested in the voltage range of 2.8-4.5V. Figure 3 As shown, the first discharge capacity is 196.5 mAh / g at 1C current density, and the capacity retention rate is 68.3% after 100 cycles.

Claims

1. A method for preparing a surface-interface-modified coupled bulk-doped ternary cathode material, characterized in that: include: S1. Introduction of titanium source and tantalum source: The titanium source and tantalum source are dissolved in anhydrous ethanol, stirred thoroughly, and the ternary positive electrode material LiNi x Co y Mn 1-x-y O2 (0.33≤x≤1), and stirring and ultrasound-assisted treatment; S2. Hydrolysis of titanium source and tantalum source: slowly drop a small amount of deionized water into the above solution and continue stirring; S3. Addition of lithium source: weigh a corresponding amount of LiOH·H2O and dissolve it in anhydrous ethanol. After it is completely dissolved, slowly add it to the above solution; S4, evaporation and drying: the above solution is heated and stirred at a heating temperature of 40-120°C until the ethanol is completely evaporated and converted into solid powder, and then the obtained solid powder is vacuum dried, and then subjected to high-temperature sintering treatment and then cooled to obtain a modified ternary positive electrode material.

2. The method for preparing the surface-interface-modified coupled body-phase-doped ternary cathode material according to claim 1, characterized in that: The S2 was stirred continuously for more than 0.5 h.

3. The method for preparing the surface-interface-modified coupled bulk-doped ternary cathode material according to claim 2, characterized in that: The vacuum drying has a drying temperature of 80-120° C. and a drying time of more than 6 hours.

4. The method for preparing the surface-interface-modified coupled bulk-doped ternary cathode material according to claim 1, characterized in that: The amount of titanium source added is based on the molar ratio Ti / LiNi x Co y Mn 1-x-y O2 = 0.5% - 3%; the amount of tantalum source added is based on the molar ratio of Ta / LiNi x Co y Mn 1-x-y O2=0.5%-5%.

5. The method for preparing the surface-interface-modified coupled bulk-doped ternary cathode material according to claim 1, characterized in that: The titanium source includes tetrabutyl titanate, isopropyl titanate, titanium n-propoxide, titanium isooctoxide, tetraethyl titanate, titanium tert-butoxide, and titanium isopropoxide.

6. The method for preparing the surface-interface-modified coupled body-phase doped ternary cathode material according to claim 1, characterized in that: The tantalum source includes tantalum ethoxide, tantalum methanol, tantalum pentachloride, tantalum butoxide, and tantalum penta(dimethylamino).

7. The method for preparing the surface-interface-modified coupled body-phase doped ternary cathode material according to claim 1, characterized in that: The high temperature sintering treatment is carried out in a tube furnace at a heating rate of 3-10°C / min to 550-850°C, and the temperature is kept for 2-6h with an oxygen flow rate of 40-100mL / min.

8. The method for preparing the surface-interface-modified coupled bulk-doped ternary cathode material according to claim 1, characterized in that: The LiNi x Co y Mn 1-x-y O2, wherein x is 0.33-0.95, y is 0.025-0.33, and 0<1-xy<1.

9. The method for preparing the surface-interface-modified coupled bulk-doped ternary cathode material according to claim 7, characterized in that: The heating rate is 3-10°C / min, and the cooling rate of the cooling treatment is 3-5°C / min or natural cooling.

10. A surface-interface modified coupled body-phase doping-modified ternary positive electrode material, obtained according to the preparation method according to any one of claims 1 to 9.

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