Magnesium-lanthanum co-modified high-nickel ternary positive electrode material and preparation method thereof

Abstract

The invention discloses a magnesium-lanthanum co-modified high-nickel ternary positive electrode material and a preparation method thereof, and belongs to the field of lithium ion battery positive electrode materials. The material composition is LiMgmNixCoyMnzLanO2, x is larger than or equal to 0.8 and smaller than or equal to 0.92, y is larger than or equal to 0 and smaller than or equal to 0.1, z is larger than or equal to 0 and smaller than or equal to 0.1, m is larger than or equal to 0.00125 and smaller than or equal to 0.005, n is larger than or equal to 0.00125 and smaller than or equal to 0.005, lanthanum exists in a La4NiLiO8 phase form, generation of oxygen vacancies can be inhibited, and lithium-nickel mixed discharge in the initial charging stage or the final discharging stage is further inhibited; magnesium occupies a lithium site, and Ni < 2 + > is prevented from entering a lithium layer by utilizing an electrostatic repulsion effect, so that lithium-nickel mixed discharge at the end of charging or the initial stage of discharging is inhibited. The two doping elements have a synergistic effect, so that lithium-nickel mixing of the high-nickel ternary positive electrode material in the whole charging and discharging process is inhibited, and the electrochemical cycle stability of the high-nickel ternary positive electrode material is remarkably improved. In addition, the preparation method is simple in process, high in controllability and easy for large-scale production.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion battery positive electrode materials and their preparation, and in particular relates to a magnesium-lanthanum co-modified high-nickel ternary positive electrode material and a preparation method thereof. Background Art

[0002] Lithium-ion batteries are currently the most widely used and promising batteries for electric vehicles. Compared with nickel-metal hydride and nickel-cadmium batteries, they have higher energy density advantages and do not contain toxic substances, so they have broad application prospects. The performance of the positive electrode material directly determines the overall performance of the battery. The high nickel ternary positive electrode material lithium nickel cobalt manganese oxide LiNi 1-x-y Co x Mn y (0.8≤1-xy≤1) has attracted widespread attention due to its high specific capacity and has become one of the most promising cathode materials in lithium-ion batteries.

[0003] As the nickel content increases, although its energy density is improved, it also brings about structural instability problems, among which lithium-nickel mixing is the key reason for structural instability. In addition to the lithium-nickel mixing caused during the material synthesis process, the degree of lithium-nickel mixing will gradually increase with the progress of the charge and discharge process, thereby affecting the electrochemical cycle stability of the material. At the beginning of charging or at the end of discharging, that is, in the lithiated state, due to the low lithium vacancy concentration, Ni 2+ It mainly enters the Li layer through oxygen vacancies. In the literature (1) Nature, 2022, 611(7934): 61-67, Wang et al. introduced the perovskite phase La4[LiTM]O8 into the high nickel ternary material, which inhibited the generation of oxygen vacancies. The reduction of oxygen vacancies can inhibit the Ni 2+ From the octahedral position of the transition metal layer, it enters the Li layer through oxygen vacancies, thereby suppressing the lithium-nickel mixing at the beginning of charging or the end of discharging. At the end of charging or the beginning of discharging, that is, in the lithium-free state, there are enough Li vacancies and Ni 2+ It will migrate from the octahedral position of the transition metal layer to the nearest tetrahedral vacancy, and then enter the octahedral vacancy of the lithium layer. In the literature (2) Journal of Power Sources, 2019, 438: 227017, Liu et al. synthesized a magnesium-doped ternary cathode material. Due to the Mg 2+ He Li + The ionic radius of Mg is similar to that of 2+ More inclined to occupy the Li site in the Li layer, because the Mg 2+ The charge of Ni is higher. 2+ The electrostatic repulsion is large, which can inhibit the Ni 2+Migration to the Li layer, thereby suppressing lithium-nickel mixing at the end of charge or the beginning of discharge. Summary of the Invention

[0004] As mentioned above, single-element doping can only improve the lithium-nickel mixing problem in a local stage during the charge-discharge process. In order to suppress the lithium-nickel mixing problem throughout the charge-discharge process, the present invention proposes a multi-element co-modification strategy.

[0005] One of the purposes of the present invention is to provide a magnesium-lanthanum co-modified high nickel ternary cathode material, the chemical composition of which is LiMg m Ni x Co y Mn z La n O2, where 0.8≤x≤0.92, 0≤y≤0.1, 0≤z≤0.1, 0.00125≤m≤0.005, 0.00125≤n≤0.005. La exists in the form of La4NiLiO8 phase, which can inhibit the generation of oxygen vacancies and thus inhibit the lithium-nickel mixing at the beginning of charge or the end of discharge; magnesium occupies the lithium site and uses electrostatic repulsion to prevent Ni 2+ Enter the lithium layer, thereby inhibiting the mixing of lithium and nickel at the end of charge or the beginning of discharge.

[0006] The second object of the present invention is to provide a method for preparing a magnesium-lanthanum co-modified high-nickel ternary positive electrode material, that is, a magnesium compound, a lanthanum compound, a nickel-cobalt-manganese hydroxide precursor and a lithium compound are uniformly mixed by ball milling, and then lithiated and calcined to obtain a finished material. The specific synthesis steps are as follows:

[0007] (1) Magnesium compound, lanthanum compound and nickel cobalt manganese hydroxide precursor are weighed and mixed with lithium compound in the ratio of n(Li):n(Ni+Co+Mn)=1.01:1~1.05:1, n(Mg):n(Ni+Co+Mn)=0.00125:1~0.005:1, n(La):n(Ni+Co+Mn)=0.00125:1~0.005:1 to obtain mixed powder. The ball milling speed is 100~300rpm and the ball milling time is 1~3h. The magnesium compound is one or more of magnesium oxide, magnesium hydroxide and magnesium chloride, the lanthanum source is one or more of lanthanum oxide, lanthanum hydroxide and lanthanum chloride, and the nickel cobalt manganese hydroxide precursor is Ni x Co y Mn z (OH)2, wherein 0.8≤x≤0.92, 0≤y≤0.1, 0≤z≤0.1, and the lithium compound is a mixture of lithium hydroxide and lithium nitrate, with n(lithium hydroxide):n(lithium nitrate)=1:1~2:3.

[0008] (2) Pre-sintering and sintering the mixed materials in an oxygen atmosphere, wherein the first pre-sintering temperature is 200-300°C, the pre-sintering time is 5-8h, the second pre-sintering temperature is 450-550°C, the pre-sintering time is 5-8h, and the sintering temperature is 690-750°C, and the sintering time is 15-20h.

[0009] (3) Grinding and crushing the product after calcination in step (2), and then passing it through a 400-mesh sieve to obtain a magnesium-lanthanum co-modified high-nickel ternary positive electrode material.

[0010] The morphology of the samples was characterized using a German Zeiss Supra55 field emission scanning electron microscope. Figure 1 This is a scanning electron microscope image of the sample in Example 1. The finished material retains the spherical morphology of the precursor.

[0011] The structure of the prepared samples was characterized by using a Japanese Rigaku UItima III X-ray diffractometer. The X-ray diffraction analysis results of Example 1 of the present invention are as follows: Figure 2 and Figure 3 Analysis of the XRD diffraction peaks of Example 1 revealed a good correspondence with the PDF standard card 89-3601 for the α-LiNiO2 phase. New diffraction peaks appeared near 24.67°, 27.66°, 31.62°, and 33.72°, corresponding to the La4NiLiO8 phase (PDF#52-1671).

[0012] The finished material prepared in the embodiment of the present invention and the comparative example is used as the positive electrode active material, which is mixed with acetylene black conductive agent and polyvinylidene fluoride binder in a mass ratio of 8:1:1 and nitrogen methyl pyrrolidone NMP is added as a solvent to prepare a slurry, which is coated on the surface of the aluminum foil current collector, rolled after drying at 110°C, and vacuum dried in a vacuum oven at 120°C for 12 hours. An electrode sheet with a diameter of 1 cm is made using a punching machine as the positive electrode, a metal lithium sheet as the negative electrode, a polyethylene film as the diaphragm, and 1 mol / L LiPF6+EC+DMC as the electrolyte. The button battery is assembled in a UniLab glove box of M.Braun (H2O<1ppm, O2<1ppm). The electrochemical performance test is carried out using Wuhan Blue Electric CT2001A battery tester, and the voltage range is 2.7~4.3V (vs.Li + / Li), 1C = 200mA·g -1 The test results are as follows. Figure 4 、 Figure 5 As shown in Table 1. The magnesium-lanthanum co-modified high-nickel ternary positive electrode material LiMg prepared by the method of the embodiment of the present invention m Ni x Co y Mn z La nThe first-cycle discharge capacity of the unmodified sample prepared by O2 is lower than that of the comparative method, but the cycle stability of the material is significantly improved.

[0013] Table 1. Electrochemical data of finished materials prepared in Examples and Comparative Examples

[0014]

[0015] Table 2. Li calculated from X-ray diffraction data of electrode sheets made from finished materials of Examples and Comparative Examples + / Ni 2+ Mixed degree data list

[0016]

[0017] In summary, the characteristics and advantages of the method of the present invention are: lanthanum exists in the form of La4NiLiO8 phase, which can inhibit the generation of oxygen vacancies and thus inhibit the lithium-nickel mixing at the beginning of charging or the end of discharging; magnesium occupies the lithium site and uses electrostatic repulsion to prevent Ni 2+ The lanthanum and magnesium doping elements work synergistically to inhibit lithium-nickel intermixing during the entire charge and discharge process of the high-nickel ternary cathode material, significantly improving its electrochemical cycling stability. Furthermore, the preparation method of the present invention is simple, highly controllable, and amenable to large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a scanning electron microscope image of the finished material prepared in Example 1 of the present invention.

[0019] Figure 2 This is the X-ray diffraction spectrum (10-90°) of the finished material prepared in Example 1 of the present invention. The horizontal axis is the diffraction angle 2θ, in degrees (°); the vertical axis is the diffraction peak intensity, in absolute units (au).

[0020] Figure 3 This is the X-ray diffraction spectrum (24-34°) of the finished material prepared in Example 1 of the present invention. The abscissa is the diffraction angle 2θ, in degrees (°); the ordinate is the diffraction peak intensity, in absolute units (au).

[0021] Figure 4 This is the first week charge and discharge curve of the finished material prepared in Example 1 of the present invention at room temperature. The horizontal axis is the discharge capacity in milliampere hours per gram (mAh / g); the vertical axis is the voltage (relative to Li + / Li), unit: volt (V).

[0022] Figure 5This is a room temperature electrochemical cycling performance curve of the finished material prepared in Example 1 of the present invention. The horizontal axis is the number of cycles, in units of weeks; the vertical axis is the discharge capacity, in units of milliampere hours per gram (mAh / g). DETAILED DESCRIPTION

[0023] In order to further illustrate the technical solution of the present invention, the embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the technical solution of the present invention, rather than limiting the claims of the present invention.

[0024] Example 1

[0025] (1) Weigh 20g of nickel cobalt manganese hydroxide precursor Ni 0.91 Co 0.045 Mn 0.045 (OH)2, 3.7366g lithium hydroxide monohydrate, 9.2102g anhydrous lithium nitrate, 0.0218g magnesium oxide, and 0.0880g lanthanum oxide were put into a ball mill and mixed evenly to obtain a mixed material. The ball milling speed was 200 rpm and the ball milling time was 3 h.

[0026] (2) The mixed materials are pre-fired and sintered in an oxygen atmosphere. The first pre-fire temperature is 250°C and the pre-fire time is 5 hours. The second pre-fire temperature is 500°C and the pre-fire time is 5 hours. The sintering temperature is 720°C and the sintering time is 15 hours.

[0027] (3) The product calcined in step (2) was crushed and then passed through a 400-mesh sieve to obtain the sample of Example 1 of the present invention.

[0028] The scanning electron microscope image is as follows Figure 1 The X-ray diffraction spectrum is shown as Figure 2 and Figure 3 As shown, the charge and discharge curves for the first week are as follows Figure 4 As shown, the discharge capacity of the material is 226.93 mAh / g, and the charge-discharge cycle performance curve is shown in Figure 5 As shown, the capacity retention rate after 100 cycles is 79.20%.

[0029] Example 2

[0030] (1) Weigh 20g of nickel cobalt manganese hydroxide precursor Ni 0.91 Co 0.045 Mn 0.045 (OH)2, 4.5801 g of lithium hydroxide monohydrate, 7.5262 g of anhydrous lithium nitrate, 0.0158 g of magnesium hydroxide, and 0.0513 g of lanthanum hydroxide were put into a ball mill and mixed evenly to obtain a mixed material. The ball milling speed was 100 rpm and the ball milling time was 5 h.

[0031] (2) The mixed materials are pre-fired and sintered in an oxygen atmosphere. The first pre-fire temperature is 300°C and the pre-fire time is 3 hours. The second pre-fire temperature is 550°C and the pre-fire time is 3 hours. The sintering temperature is 690°C and the sintering time is 20 hours.

[0032] (3) The product calcined in step (2) was crushed and then passed through a 400-mesh sieve to obtain the sample of Example 2 of the present invention. The discharge specific capacity of the material was 228.16 mAh / g, and the capacity retention rate after 100 cycles was 72.63%.

[0033] Example 3

[0034] (1) Weigh 20g of nickel cobalt manganese hydroxide precursor Ni 0.91 Co 0.045 Mn 0.045 (OH)2, 4.0813g lithium hydroxide monohydrate, 8.9420g anhydrous lithium nitrate, 0.1028g anhydrous magnesium chloride, and 0.2651g anhydrous lanthanum chloride were put into a ball mill and mixed evenly to obtain a mixed material. The ball milling speed was 300rpm and the ball milling time was 1h.

[0035] (2) The mixed materials are pre-fired and sintered in an oxygen atmosphere. The first pre-fire temperature is 200°C and the pre-fire time is 8 hours. The second pre-fire temperature is 450°C and the pre-fire time is 8 hours. The sintering temperature is 750°C and the sintering time is 10 hours.

[0036] (3) The product calcined in step (2) was crushed and then passed through a 400-mesh sieve to obtain the sample of Example 3 of the present invention. The discharge specific capacity of the material was 224.09 mAh / g, and the capacity retention rate after 100 cycles was 75.80%.

[0037] Example 4

[0038] (1) Weigh 20g of nickel cobalt manganese hydroxide precursor Ni 0.8 Co 0.1 Mn 0.1 (OH)2, 3.7444g lithium hydroxide monohydrate, 9.2293g anhydrous lithium nitrate, 0.0218g magnesium oxide, and 0.0882g lanthanum oxide were put into a ball mill and mixed evenly to obtain a mixed material. The ball milling speed was 200 rpm and the ball milling time was 3 h.

[0039] (2) The mixed materials are pre-fired and sintered in an oxygen atmosphere. The first pre-fire temperature is 250°C and the pre-fire time is 5 hours. The second pre-fire temperature is 500°C and the pre-fire time is 5 hours. The sintering temperature is 750°C and the sintering time is 15 hours.

[0040] (3) The product calcined in step (2) was crushed and then passed through a 400-mesh sieve to obtain the sample of Example 4 of the present invention. The discharge specific capacity of the material was 199.98 mAh / g, and the capacity retention rate after 100 cycles was 90.91%.

[0041] Comparative Example 1

[0042] (1) Weigh 20g of nickel cobalt manganese hydroxide precursor Ni 0.91 Co 0.045 Mn 0.045 (OH)2, 3.7366g of lithium hydroxide monohydrate, and 9.2102g of anhydrous lithium nitrate were put into a ball mill and mixed evenly to obtain a mixed material. The ball milling speed was 200 rpm and the ball milling time was 3 h.

[0043] (2) The mixed materials are pre-fired and sintered in an oxygen atmosphere. The first pre-fire temperature is 250°C and the pre-fire time is 5 hours. The second pre-fire temperature is 500°C and the pre-fire time is 5 hours. The sintering temperature is 720°C and the sintering time is 15 hours.

[0044] (3) The product calcined in step (2) was crushed and then passed through a 400-mesh sieve to obtain the sample of comparative example 1 of the present invention. The discharge specific capacity of the material was 230.31 mAh / g, and the capacity retention rate after 100 cycles was 62.08%.

[0045] Comparative Example 2

[0046] (1) Weigh 20g of nickel cobalt manganese hydroxide precursor Ni 0.91 Co 0.045 Mn 0.045 (OH)2, 3.7366g of lithium hydroxide monohydrate, 9.2102g of anhydrous lithium nitrate, and 0.0218g of magnesium oxide were put into a ball mill and mixed evenly to obtain a mixed material. The ball milling speed was 200 rpm and the ball milling time was 3 h.

[0047] (2) The mixed materials are pre-fired and sintered in an oxygen atmosphere. The first pre-fire temperature is 250°C and the pre-fire time is 5 hours. The second pre-fire temperature is 500°C and the pre-fire time is 5 hours. The sintering temperature is 720°C and the sintering time is 15 hours.

[0048] (3) The product calcined in step (2) was crushed and then passed through a 400-mesh sieve to obtain the sample of comparative example 2 of the present invention. The discharge specific capacity of the material was 226.23 mAh / g, and the capacity retention rate after 100 cycles was 63.26%.

[0049] Comparative Example 3

[0050] (1) Weigh 20g of nickel cobalt manganese hydroxide precursor Ni 0.91 Co0.045 Mn 0.045 (OH)2, 3.7366g of lithium hydroxide monohydrate, 9.2102g of anhydrous lithium nitrate, and 0.0880g of lanthanum oxide were put into a ball mill and mixed evenly to obtain a mixed material. The ball milling speed was 200 rpm and the ball milling time was 3 h.

[0051] (2) The mixed materials are pre-fired and sintered in an oxygen atmosphere. The first pre-fire temperature is 250°C and the pre-fire time is 5 hours. The second pre-fire temperature is 500°C and the pre-fire time is 5 hours. The sintering temperature is 720°C and the sintering time is 15 hours.

[0052] (3) The product calcined in step (2) was crushed and then passed through a 400-mesh sieve to obtain the sample of comparative example 3 of the present invention. The discharge specific capacity of the material was 227.10 mAh / g, and the capacity retention rate after 100 cycles was 65.39%.

Claims

1. A magnesium-lanthanum co-modified high-nickel ternary positive electrode material, characterized in that: The chemical composition of the material is LiMg m Ni x Co y Mn z La n O2, wherein 0.8≤x≤0.92, 0≤y≤0.1, 0≤z≤0.1, 0.00125≤m≤0.005, 0.00125≤n≤0.005, wherein magnesium occupies the lithium site, and La exists in the form of La4NiLiO8 phase after calcination.

2. A method for preparing the magnesium-lanthanum co-modified high-nickel ternary positive electrode material according to claim 1, characterized in that: The steps include: (1) weighing the corresponding amounts of magnesium compound, lanthanum compound, nickel cobalt manganese hydroxide precursor and lithium compound according to the molar ratio of n(Li):n(Ni+Co+Mn)=1.01:1~1.05:1, n(Mg):n(Ni+Co+Mn)=0.00125:1~0.005:1, and n(La):n(Ni+Co+Mn)=0.00125:1~0.005:1 and mixing them uniformly using a ball mill at a ball milling speed of 100~300 rpm and a ball milling time of 1~3 h; (2) pre-sintering and sintering the mixed materials in an oxygen atmosphere, wherein the first pre-sintering temperature is 200-300° C., the pre-sintering time is 5-8 hours, the second pre-sintering temperature is 450-550° C., the pre-sintering time is 5-8 hours, and the sintering temperature is 690-750° C., and the sintering time is 15-20 hours; (3) Grinding and crushing the product after calcination in step (2), and then passing it through a 400-mesh sieve to obtain a magnesium-lanthanum co-modified high-nickel ternary positive electrode material.

3. The preparation method according to claim 2, characterized in that The magnesium compound in step (1) is one or more of magnesium oxide, magnesium hydroxide and magnesium chloride.

4. The preparation method according to claim 2, characterized in that The lanthanum compound in step (1) is one or more of lanthanum oxide, lanthanum hydroxide and lanthanum chloride.

5. The preparation method according to claim 2, characterized in that The chemical composition of the nickel cobalt manganese hydroxide precursor in step (1) is Ni x Co y Mn z (OH)2, where 0.8≤x≤0.92, 0≤y≤0.1, 0≤z≤0.

1.

6. The preparation method according to claim 2, characterized in that The lithium compound described in step (1) is a mixture of lithium hydroxide and lithium nitrate, with n (lithium hydroxide): n (lithium nitrate) = 1:1 to 2:3.

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