Rare earth doped ternary positive electrode material and preparation method and application thereof

Abstract

The invention provides a rare earth doped ternary positive electrode material and a preparation method and application thereof, the preparation method comprises the following steps: uniformly mixing a ternary precursor, a rare earth dopant, a lithium source and LiCl, and successively carrying out sintering, lithium removal and annealing to obtain the rare earth doped ternary positive electrode material, the lithium source and LiCl are converted into eutectic molten salt under a sintering condition to serve as a reaction raw material and a reaction medium, and a liquid environment is provided. The lithium source and LiCl form eutectic molten salt under the sintering condition, so that the reaction is converted into solid-liquid reaction, ion diffusion is facilitated, the initial temperature of the reaction is reduced, and the reaction time is shortened. Meanwhile, a rare earth doping agent is added, so that a rare earth element replaces part of Ni, the Li / Ni mixed arrangement phenomenon is weakened, and the chemical stability of the layered structure is enhanced; the rare earth elements are doped by adopting a molten salt method, so that the unit cell parameters of the layered material can be reduced, the lithium ion diffusion path is shortened, and the cycle performance and rate capability of the battery are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and relates to a ternary positive electrode material and a preparation method and application thereof, and in particular to a rare earth-doped ternary positive electrode material and a preparation method and application thereof. Background Art

[0002] With the rapid development and innovation of modern industry, the reserves of traditional energy sources such as oil and natural gas that cannot be synthesized are becoming increasingly depleted, and this has brought about increasingly serious environmental problems. Therefore, optimizing the energy structure and developing new energy storage materials and technologies are the only way to achieve sustainable economic development and improve the ecological environment.

[0003] At present, lithium-ion batteries (LIBs) are one of the most viable emerging energy storage technologies and have been widely commercialized in fields such as smart grids and electric vehicles. As the most important part of lithium-ion batteries, high-performance cathode materials are also being continuously innovated. Among the many cathode materials, nickel-based ternary cathode materials, such as ternary nickel-cobalt-manganese LiNi x Co y Mn z O 2 It has a high energy density and a theoretical capacity of 278 mAh / g, which can provide sufficient power and is regarded as one of the most promising positive electrode materials.

[0004] In the prior art, the preparation of ternary materials is mainly carried out by solid phase sintering method, and the reactants are ternary precursors and Li 2 CO 3 , sintering is carried out under high temperature conditions. However, the solid-solid reaction has slow mass transfer, uneven reaction, uneven product morphology and size, and low atomic utilization, which will have a great negative impact on the synthesis and performance of the positive electrode material. In addition, long-term high-temperature heat treatment also makes the solid phase method considered to be a high-energy-consuming technical means. In addition to the above problems, the ternary material itself also has certain defects. For example, during the sintering process of the ternary material, since the ionic radius of Li ions and divalent Ni ions are very similar, if the content of divalent Ni ions in the battery material is too high, the Ni ions discharged from the ternary nickel-cobalt-manganese system will occupy the sites of Li ions, greatly reducing the cycle performance of the ternary material lithium-ion secondary battery, affecting its charge and discharge efficiency and cycle capacity.

[0005] In the prior art, the method of doping rare earth elements is often used to improve the above-mentioned Li / Ni mixing problem: CN111009656A discloses a preparation method of a rare earth metal-doped high-nickel ternary cathode material for a battery. The high-nickel ternary precursor is fully mixed and ground with a lithium source, and then a dopant is added to the mixture, followed by full grinding and low-temperature sintering. Then, the preliminarily sintered material is crushed and sintered at a high temperature. Finally, the finished material is obtained after crushing and grinding. Since solid-phase reaction is not conducive to mass transfer, additional crushing steps and oxidants need to be added, and the preparation process is relatively complex.

[0006] CN102088087A discloses a preparation method of a lithium-ion cathode material doped with rare earth elements. A soluble nickel salt, a soluble manganese salt, a soluble lithium salt, a rare earth oxide, and ammonium citrate are dissolved in deionized water, and a gel is obtained under stirring in a water bath at 90°C to 100°C. Then, the gel is dried in a vacuum drying oven, and finally, the cathode material is prepared by calcining twice in a muffle furnace. However, there are many factors affecting the gel in this method, the morphology and particle size of the product are not easy to control, and the initial charge-discharge capacity of the material is relatively low.

[0007] CN107394175A discloses a method for preparing a rare earth-doped ternary cathode material by a microemulsion method. A lithium source, a nickel source, a cobalt source, a manganese source, and a rare earth source are dissolved in deionized water to form a mixed solution A, and a surfactant, an organic alcohol, and an organic alkane are mixed to form a solution B. Solution B is put into a microemulsion device, and then solution A is slowly added for emulsification. After the emulsified sample is aged and dried in sequence, the obtained substance is crushed and calcined at a high temperature to obtain a rare earth-doped modified ternary cathode material for a lithium-ion battery. However, its preparation process is complex, requires the use of more equipment, thus increasing the preparation cost. At the same time, the preparation process requires the use of more additives, thus increasing the toxicity and pollution of the product.

[0008] The preparation methods of the existing rare earth-doped cathode materials have complex preparation processes, many influencing factors in the preparation process, and require additional additives, resulting in relatively high costs. Therefore, how to simply and efficiently prepare high-performance rare earth-doped cathode materials is crucial for solving the problems existing in the existing processes. Summary of the Invention

[0009] Aiming at the problems of slow mass transfer in the solid-phase reaction of the prior art methods, uneven reaction, non-uniform product morphology and size, and low atomic utilization rate, the present invention provides a rare-earth doped ternary cathode material, a preparation method thereof and an application. By converting a lithium source and LiCl into a eutectic molten salt as a reaction raw material and a reaction medium under sintering conditions and providing a liquid environment, the reaction is converted into a solid-liquid reaction, which facilitates ion diffusion, thereby reducing the starting temperature of the reaction and shortening the reaction time. At the same time, by adding a rare-earth dopant, rare-earth elements replace part of Ni in the ternary material, thereby weakening the Li / Ni mixing phenomenon and enhancing the chemical stability of the layered structure; doping rare-earth elements by the molten salt method can reduce the unit cell parameters of the layered material, shorten the diffusion path of lithium ions, and improve the cycle performance and rate performance of the battery.

[0010] To achieve this purpose, the present invention adopts the following technical solutions:

[0011] In a first aspect, the present invention provides a preparation method for preparing a rare-earth doped ternary cathode material by a molten salt method. The method includes: uniformly mixing a ternary precursor, a rare-earth dopant, a lithium source and LiCl, and sequentially performing sintering, lithium removal and annealing to obtain the rare-earth doped ternary cathode material; the lithium source and LiCl are converted into a eutectic molten salt as a reaction raw material and a reaction medium under sintering conditions and provide a liquid environment.

[0012] In the present invention, by converting a lithium source and LiCl into a eutectic molten salt as a reaction raw material and a reaction medium under sintering conditions and providing a liquid environment, the reaction is converted into a solid-liquid reaction, which facilitates ion diffusion, thereby reducing the starting temperature of the reaction and shortening the reaction time. At the same time, by adding a rare-earth dopant, rare-earth elements replace part of Ni in the ternary material, thereby weakening the Li / Ni mixing phenomenon and enhancing the chemical stability of the layered structure; doping rare-earth elements by the molten salt method can reduce the unit cell parameters of the layered material, shorten the diffusion path of lithium ions, and improve the cycle performance and rate performance of the battery.

[0013] Preferably, the ternary precursor includes any one or at least two combinations of hydroxides, nitrates or oxides containing nickel, cobalt and manganese. Typical but non-limiting combinations include a combination of hydroxides containing nickel, cobalt and manganese and nitrates containing nickel, cobalt and manganese, or a combination of hydroxides containing nickel, cobalt and manganese, nitrates containing nickel, cobalt and manganese and oxides containing nickel, cobalt and manganese.

[0014] Preferably, the doping elements of the rare-earth dopant include any one or at least two combinations of La, Ce, Y, Eu, Nd or Gd. Typical but non-limiting combinations include a combination of La and Ce, a combination of Y and Eu, or a combination of Eu, Nd and Gd.

[0015] Preferably, the rare earth dopant includes rare earth oxides and / or rare earth chlorides containing the doping elements.

[0016] Preferably, the lithium source includes LiOH, Li 2 CO 3 , LiNO 3 , Li 2 SO 4 or CH 3 COOLi, or any combination of at least two of them. Typical but non-limiting combinations include the combination of LiOH and Li 2 CO 3 , the combination of LiNO 3 and Li 2 SO 4 , or the combination of LiNO 3 , Li 2 SO 4 and CH 3 COOLi.

[0017] Preferably, the lithium source and the LiCl are both in powder form for the mixing.

[0018] Preferably, the mixing method includes grinding.

[0019] The present invention uses a molten salt system formed by a lithium source and LiCl. Among them, LiCl can be melted into a molten salt liquid at the sintering temperature. For the lithium source that cannot form a molten salt at the sintering temperature originally, in the presence of the LiCl molten salt, a part of it will form a uniform eutectic molten salt compound with the LiCl molten salt, thereby providing a liquid mass transfer environment. On the other hand, at the sintering temperature, a part of the lithium source will decompose to form lithium oxide. Lithium oxide is used as the lithium raw material for reacting with the ternary precursor to synthesize the ternary material. And the LiCl molten salt is the only salt that has solubility for lithium oxide, which can further promote the synthesis reaction to proceed faster. Therefore, the solid-liquid reaction achieved by the method of the present invention can greatly improve the reaction efficiency and product quality.

[0020] Preferably, the molar ratio of the lithium element in the lithium source to the sum of the transition metal elements in the ternary precursor is (1-5):1. For example, it can be 1:1, 1.3:1, 1.5:1, 1.8:1, 2:1, 2.3:1, 2.5:1, 2.8:1, 3:1, 3.3:1, 3.5:1, 3.8:1, 4:1, 4.3:1, 4.5:1, 4.8:1 or 5:1, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0021] Preferably, the sum of the molar amounts of the lithium source and the ternary precursor is M, and the molar ratio of LiCl to M is (0.1-5):1. For example, it can be 0.1:1, 0.5:1, 0.8:1, 1:1, 1.3:1, 1.5:1, 1.8:1, 2:1, 2.3:1, 2.5:1, 2.8:1, 3:1, 3.3:1, 3.5:1, 3.8:1, 4:1, 4.3:1, 4.5:1, 4.8:1 or 5:1. However, it is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0022] Preferably, the molar ratio of the lithium element in the lithium source to the rare earth element in the rare earth dopant is 1:(0.01-0.1). For example, it can be 1:0.01, 1:0.02, 1:0.03, 1:0.04, 1:0.05, 1:0.06, 1:0.07, 1:0.08, 1:0.09 or 1:0.1. However, it is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0023] In the method of the present invention, rare earth element doping is carried out in the eutectic molten salt system formed by the lithium salt and LiCl, which is not only beneficial to the uniform distribution of elements, but also beneficial to the uniform dispersion of rare earth elements themselves in the ternary material. The combination of the molten salt method and rare earth doping helps to improve the uniformity of the material. At the same time, the doping ratio of rare earth elements will affect the effect of rare earth doping. Within the preferred doping ratio range, the prepared ternary cathode material has excellent electrical properties.

[0024] Preferably, the preparation method further includes adding an auxiliary molten salt raw material for the mixing simultaneously.

[0025] Preferably, the auxiliary molten salt raw material includes NaCl, NaNO 3 , KCl or K 2 CO 3 or any combination of at least two of them. Typical but non-limiting combinations include the combination of NaCl and NaNO 3 , the combination of KCl and K 2 CO 3 , or the combination of NaNO 3 , KCl and K 2 CO 3 of them.

[0026] Preferably, the holding temperature for sintering is 500°C - 750°C. For example, it can be 500°C, 550°C, 600°C, 650°C, 700°C or 750°C. However, it is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0027] In the method of the present invention, the sintering temperature not only affects the uniformity of the eutectic molten salt, but also affects the doping effect of rare earth elements. When the sintering temperature is too high, the degree of Li / Ni mixing will increase; when the sintering temperature is too low, the crystal growth is incomplete and the layered structure is incomplete.

[0028] Preferably, the heat preservation time of the sintering is 0.5h to 6h, for example, it can be 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h or 6h, but not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0029] In the method of the present invention, the sintering time not only affects the uniformity of the eutectic molten salt, but also affects the doping effect of rare earth elements. When the sintering time is too long, the primary particles are not tightly combined; when the sintering time is too short, the crystal growth is insufficient.

[0030] Preferably, the atmosphere of the sintering is air atmosphere.

[0031] Preferably, the heating rate of the sintering is 3℃ / min - 5℃ / min, for example, it can be 3℃ / min, 3.5℃ / min, 4℃ / min, 4.5℃ / min or 5℃ / min, but not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0032] Preferably, the lithium removal includes washing with a detergent.

[0033] Preferably, the detergent includes deionized water.

[0034] The present invention removes excess lithium salts by lithium removal, especially removing LiCl. Insufficient removal of chloride ions will have an adverse effect on the charge and discharge process of the battery.

[0035] Preferably, the number of washing times for the cleaning is 3 to 5 times, for example, it can be 3 times, 4 times or 5 times.

[0036] Preferably, drying is carried out after the cleaning.

[0037] Preferably, the drying includes drying by baking.

[0038] Preferably, the heat preservation temperature for the drying is 80℃ to 120℃, for example, it can be 80℃, 85℃, 90℃, 95℃, 100℃, 105℃, 110℃, 115℃ or 120℃, but not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0039] Preferably, the heat preservation time for drying is 12 h to 36 h. For example, it can be 12 h, 15 h, 18 h, 22 h, 24 h, 27 h, 30 h, 33 h, or 36 h. However, it is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0040] Preferably, sieving treatment is performed after drying.

[0041] Preferably, the mesh number for the sieving treatment is 200 mesh - 300 mesh. For example, it can be 200 mesh, 220 mesh, 240 mesh, 260 mesh, 280 mesh, or 300 mesh. However, it is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0042] Preferably, the heat preservation temperature for annealing is 600 °C to 950 °C. For example, it can be 600 °C, 630 °C, 650 °C, 680 °C, 700 °C, 720 °C, 750 °C, 780 °C, 800 °C, 830 °C, 850 °C, 880 °C, 900 °C, 930 °C, or 950 °C. However, it is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0043] Preferably, the heat preservation time for annealing is 2 h to 8 h. For example, it can be 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 5 h, 5.5 h, 6 h, 6.5 h, 7 h, 7.5 h, or 8 h. However, it is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0044] Preferably, the atmosphere for annealing is an air atmosphere.

[0045] In the method of the present invention, the role of annealing is to provide a high - temperature environment to promote further crystal growth. Therefore, if the annealing temperature is too low or the annealing time is too short, the crystal growth will be incomplete. If the annealing temperature is too high or the annealing time is too long, the single - crystal grains that make up the polycrystalline grains will grow too thick, and the degree of Li / Ni mixing will increase, which is not conducive to the infiltration of the electrolyte and is also not conducive to the transport of lithium ions.

[0046] As a preferred technical solution of the present invention, the preparation method includes the following steps:

[0047] Mix a ternary precursor, a rare earth dopant, a lithium source, and LiCl according to a ratio where the molar ratio of lithium element in the lithium source to the sum of transition metal elements in the ternary precursor is (1 - 5):1, the molar ratio of LiCl to the total molar amount of the lithium source and the ternary precursor is (0.1 - 5):1, and the molar ratio of lithium element in the lithium source to rare earth element in the rare earth dopant is 1:(0.01 - 0.1), and grind them to obtain a mixture; sinter the mixture in an air atmosphere by heating it to 500°C - 750°C for 0.5 - 6 h, and obtain a sintered material after cooling; sinter the mixture in an air atmosphere by heating it to 500°C - 750°C for 0.5 h - 6 h, and obtain a sintered material after cooling; wash the sintered material 3 - 5 times to obtain a washed material; dry and screen the washed material to obtain a screened material; anneal the screened material in an air atmosphere at 600°C - 950°C for 2 h - 8 h to obtain the rare earth doped ternary cathode material.

[0048] In a second aspect, the present invention provides a rare earth doped ternary cathode material, which is prepared by using the preparation method described in the first aspect.

[0049] Preferably, in the rare earth doped ternary cathode material, the ternary cathode material includes LiNi x Co y Mn z O 2 , where x + y + z = 1.

[0050] Preferably, in the rare earth doped ternary cathode material, the doping amount of the rare earth element is ≤ 4500 ppm, and for example, it can be 50 ppm, 100 ppm, 300 ppm, 500 ppm, 800 ppm, 1000 ppm, 1300 ppm, 1500 ppm, 1800 ppm, 2000 ppm, 2300 ppm, 2500 ppm, 2800 ppm, 3000 ppm, 3300 ppm, 3600 ppm, 3800 ppm, 4000 ppm, 4200 ppm, or 4500 ppm, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0051] In a third aspect, the present invention provides a lithium ion battery, which includes the rare earth doped ternary cathode material described in the second aspect.

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

[0053] The present invention adopts the molten salt method, using the eutectic molten salt formed by a lithium source and LiCl as the reaction raw material and reaction medium. It has solubility for lithium oxide, and the liquid phase environment provided in the molten state is conducive to ion diffusion, helps the contact and reaction of raw materials, enables the reactants to reach a molecular level of mixing, thereby reducing the starting temperature of the reaction and shortening the reaction time, accelerating the mass transfer process of the synthesis reaction, and increasing the uniformity of the reaction. At the same time, the present invention reduces the cation mixing degree in the ternary material through rare earth doping, enhances the binding strength of transition metal-oxygen, effectively improves the stability of the crystal structure, reduces the charge transfer resistance, and thus prepares a nickel-cobalt-manganese ternary cathode material with high chemical stability and low lithium-nickel mixing degree. The preparation method described in the present invention is simple, low-cost, and compatible with current ternary material synthesis equipment and preparation conditions. Description of the Drawings

[0054] Figure 1 SEM image of the ternary cathode material prepared in Example 1;

[0055] Figure 2 SEM image of the ternary cathode material prepared in Comparative Example 1;

[0056] Figure 3 Comparison chart of the first charge-discharge performance of the batteries prepared from the ternary cathode materials prepared in Example 3, Comparative Examples 1-2, and Comparative Example 5;

[0057] Figure 4 Comparison chart of the cycle test at 30 °C of the batteries prepared from the ternary cathode materials prepared in Example 3, Comparative Examples 1-2, and Comparative Example 5. Detailed Description of the Embodiments

[0058] The technical solutions of the present invention will be further described below in conjunction with the drawings and through specific embodiments. However, the following examples are only simple examples of the present invention and do not represent or limit the scope of the protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0059] Example 1

[0060] This example provides a preparation method for a rare earth-doped ternary cathode material, and the preparation method includes:

[0061] Step 1: Mix Ni 0.5 Co 0.2 Mn 0.3 (OH) 2 precursor, Y 2 O 3 and LiCl·H 2 O with Li 2 CO 3Manually grind it into a uniform mixture in an agate mortar in the form of powder; control Li 2 CO 3 The molar amount of lithium in and the total molar amount of nickel, cobalt and manganese in Ni 0.5 Co 0.2 Mn 0.3 (OH) 2 The molar ratio is 1.1:1. Control the molar ratio of LiCl·H 2 O to the sum of the molar amounts of Ni 0.5 Co 0.2 Mn 0.3 (OH) 2 and Li 2 CO 3 is 0.2:1. Control the molar ratio of the lithium element in Li 2 CO 3 to the Y element in Y 2 O 3 is 1:0.05 to obtain a mixed material;

[0062] Step 2: Place the obtained mixed material in a corundum crucible, put it into a muffle furnace, and heat it to 735 °C at a heating rate of 5 °C / min. Carry out low-temperature sintering for 4 h in an air atmosphere, then cool it to 300 °C at a cooling rate of 2 °C / min, and then cool it to room temperature to obtain a sintered material;

[0063] Step 3: Wash the obtained mixture with deionized water and grind it with an agate mortar, and wash it repeatedly 4 times to obtain a washed material;

[0064] Step 4: Dry the obtained washed material in an oven at 100 °C for 24 h and pass it through a 200-mesh sieve to obtain a sieved material;

[0065] Step 5: Anneal the obtained sieved material at 900 °C for 8 h to obtain a rare-earth-doped ternary cathode material.

[0066] Figure 1 This is the scanning electron microscope image of the rare-earth-doped ternary cathode material prepared in this example. It can be seen from the figure that LiCl used in this example can form a eutectic molten salt with Li 2 CO 3 The obtained product forms complete polycrystalline grains, and the primary grains are tightly bonded.

[0067] Example 2

[0068] The difference between this example and Example 1 is only that, except for controlling the molar amount of LiCl·H 2 O and Ni 0.5 Co 0.2 Mn 0.3 (OH) 2and Li 2 CO 3 Except that the molar ratio of the sum of the molar amounts of LiCl·H₂O and Li₂CO₃ is adjusted from 0.2:1 to 0.5:1, the rest are the same as in Example 1.

[0069] Example 3

[0070] The difference between this example and Example 1 is only that, except that in Step 1, the molar ratio of the molar amount of LiCl·H₂O to the sum of the molar amounts of Ni(OH)₂, Co(OH)₂, Mn(OH)₂ and Li₂CO₃ is adjusted from 0.2:1 to 1:1, the rest are the same as in Example 1. 2 O to Ni 0.5 Co 0.2 Mn 0.3 (OH)₂ 2 and Li 2 CO 3 Except that the molar ratio of the sum of the molar amounts of LiCl·H₂O and Li₂CO₃ is adjusted from 0.2:1 to 1:1, the rest are the same as in Example 1.

[0071] Example 4

[0072] The difference between this example and Example 1 is only that, except that in Step 1, the molar ratio of the molar amount of LiCl·H₂O to the sum of the molar amounts of Ni(OH)₂, Co(OH)₂, Mn(OH)₂ and Li₂CO₃ is adjusted from 0.2:1 to 1.5:1, the rest are the same as in Example 1. 2 O to Ni 0.5 Co 0.2 Mn 0.3 (OH)₂ 2 and Li 2 CO 3 Except that the molar ratio of the sum of the molar amounts of LiCl·H₂O and Li₂CO₃ is adjusted from 0.2:1 to 1.5:1, the rest are the same as in Example 1.

[0073] Example 5

[0074] The difference between this example and Example 1 is only that, except that in Step 1, the molar ratio of the molar amount of LiCl·H₂O to the sum of the molar amounts of Ni(OH)₂, Co(OH)₂, Mn(OH)₂ and Li₂CO₃ is adjusted from 0.2:1 to 2:1, the rest are the same as in Example 1. 2 O to Ni 0.5 Co 0.2 Mn 0.3 (OH)₂ 2 and Li 2 CO 3 Except that the molar ratio of the sum of the molar amounts of LiCl·H₂O and Li₂CO₃ is adjusted from 0.2:1 to 2:1, the rest are the same as in Example 1.

[0075] Example 6

[0076] The difference between this example and Example 1 is only that, except that the sintering temperature in Step 2 is adjusted from 735 °C to 450 °C, the rest are the same as in Example 1.

[0077] Example 7

[0078] The difference between this example and Example 1 is only that, except that the sintering temperature in Step 2 is adjusted from 735 °C to 500 °C, the rest are the same as in Example 1.

[0079] Example 8

[0080] The difference between this example and Example 1 is only that, except that the sintering temperature in Step 2 is adjusted from 735 °C to 800 °C, the rest are the same as in Example 1.

[0081] Example 9

[0082] The difference between this example and Example 1 is only that, except that the annealing temperature in Step 5 is adjusted from 900 °C to 550 °C, the rest are the same as in Example 1.

[0083] Example 10

[0084] The difference between this example and Example 1 is only that, except that the annealing temperature in Step 5 is adjusted from 900 °C to 600 °C, the rest are the same as in Example 1.

[0085] Example 11

[0086] The difference between this example and Example 1 is only that, except that the annealing temperature in Step 5 is adjusted from 900 °C to 1000 °C, the rest are the same as in Example 1.

[0087] Example 12

[0088] This example provides a method for preparing a rare earth doped ternary cathode material, and the preparation method includes:

[0089] Step 1: Manually grind Ni 0.5 Co 0.2 Mn 0.3 (OH) 2 precursor, Y 2 O 3 and LiCl·H 2 O, Li 2 CO 3 and NaCl in powder form through an agate mortar until evenly mixed; control the molar ratio of lithium in Li 2 CO 3 to the total molar amount of nickel, cobalt and manganese in Ni 0.5 Co 0.2 Mn 0.3 (OH) 2 to be 1:1, control the molar ratio of the molar amount of LiCl·H 2 O to the sum of the molar amounts of Ni 0.5 Co 0.2 Mn 0.3 (OH) 2 and Li 2 CO 3 to be 0.1:1, and control the lithium element in Li 2 CO 3 to Y2 O 3 The molar ratio of Y element in it is 1:0.01 to obtain a mixed material; the molar ratio of LiCl·H 2 O and NaCl is 1:1;

[0090] Step 2: Place the obtained mixed material in a corundum crucible, put it into a muffle furnace, heat it at a heating rate of 4 °C / min to 500 °C, carry out low-temperature sintering for 6 h in an air atmosphere, then cool it at a cooling rate of 1 °C / min to 300 °C, and then cool it to room temperature to obtain a sintered material;

[0091] Step 3: Wash the obtained mixture with deionized water and grind it with an agate mortar, wash it repeatedly 3 times to obtain a washed material;

[0092] Step 4: Dry the obtained washed material in an oven at 120 °C for 12 h and sieve it through a 200-mesh sieve to obtain a sieved material;

[0093] Step 5: Anneal the obtained sieved material at 950 °C for 2 h to obtain the rare-earth doped ternary cathode material.

[0094] Example 13

[0095] This example provides a preparation method of a rare-earth doped ternary cathode material, and the preparation method includes:

[0096] Step 1: Manually grind Ni 0.5 Co 0.2 Mn 0.3 (OH) 2 precursor, Y 2 O 3 and LiCl·H 2 O and Li 2 CO 3 in powder form through an agate mortar until evenly mixed; control the molar ratio of lithium in Li 2 CO 3 to the total molar amount of nickel, cobalt and manganese in Ni 0.5 Co 0.2 Mn 0.3 (OH) 2 is 5:1, control the molar ratio of the molar amount of LiCl·H 2 O to Ni 0.5 Co 0.2 Mn 0.3 (OH) 2 and the sum of the molar amounts of Li 2 CO 3 is 5:1, control the lithium element in Li 2 CO 3 to Y 2 O3 The molar ratio of Y element in it is 1:0.1 to obtain a mixed material;

[0097] Step 2: Place the obtained mixed material in a corundum crucible, put it into a muffle furnace, heat it at a heating rate of 3 °C / min to 750 °C, carry out low-temperature sintering for 0.5 h in an air atmosphere, then cool it at a cooling rate of 3 °C / min to 200 °C, and then cool it to room temperature to obtain a sintered material;

[0098] Step 3: Wash the obtained mixture with deionized water and grind it with an agate mortar, wash it repeatedly 5 times to obtain a washed material;

[0099] Step 4: Dry the obtained washed material in an oven at 80 °C for 36 h and sieve it through a 300-mesh sieve to obtain a sieved material;

[0100] Step 5: Anneal the obtained sieved material at 650 °C for 8 h to obtain the rare-earth doped ternary cathode material.

[0101] Comparative Example 1

[0102] The difference between this comparative example and Example 1 is only that, except that in Step 1, Li 2 CO 3 is used to replace LiCl·H 2 O in an equimolar amount, the rest are the same as in Example 1.

[0103] Figure 2 This is the scanning electron microscope image of the rare-earth doped ternary cathode material prepared in this comparative example. It can be seen from the figure that LiCl is not used in this comparative example, and Li 2 CO 3 cannot form a molten salt in the sintering stage, the reaction is a solid-solid reaction, and the morphology of the obtained product is non-uniform.

[0104] Comparative Example 2

[0105] The difference between this comparative example and Example 1 is only that, except that in Step 1, LiCl·H 2 O is used to replace Li 2 CO 3 in an equimolar amount, the rest are the same as in Example 1.

[0106] Comparative Example 3

[0107] The difference between this comparative example and Example 1 is only that, except that in Step 1, the rare-earth dopant Y 2 O 3 is not used, the rest are the same as in Example 1.

[0108] Comparative Example 4

[0109] The difference between this comparative example and Example 1 is only that, except for not performing Step 5, the rest are the same as in Example 1.

[0110] Comparative Example 5

[0111] The difference between this comparative example and Example 1 is only that, except that LiCl·H is replaced with an equimolar amount of KCl in Step 1 2 O, the rest are the same as in Example 1.

[0112] Figure 3 Figure 5 is a comparison chart of the first charge-discharge performance of the batteries prepared from the rare-earth doped ternary cathode materials prepared in Example 3, Comparative Examples 1-2, and Comparative Example 5. It can be seen from the figure that the ternary cathode material obtained in Example 3 has the highest capacity;

[0113] Figure 4 Figure 6 is a comparison chart of the cycle test at 30 °C of the batteries prepared from the rare-earth doped ternary cathode materials prepared in Example 3, Comparative Examples 1-2, and Comparative Example 5. It can be seen from the figure that the ternary cathode material obtained in Example 3 has the best cycle performance.

[0114] Test Method

[0115] The rare-earth doped ternary cathode materials obtained in Examples 1-13 and Comparative Examples 1-5 were prepared into 2025-type coin cells and subjected to electrochemical performance tests. The preparation and test methods are as follows: The positive electrode was made according to ternary cathode material: Super P: PVDF = 80:10:10, the negative electrode was metallic lithium, and the electrolyte was a silicon-carbon electrolyte. The battery was assembled; the charge-discharge voltage range was 2.8 V to 4.3 V, and the capacity at 1C and the cycle performance were tested at room temperature. The results are shown in Table 1.

[0116] Table 1

[0117]

[0118]

[0119] It can be seen from the test results that:

[0120] (1) The data results of Examples 1-13 and Comparative Examples 1-5 show that in the present invention, by converting the lithium source and LiCl into eutectic molten salt as reaction raw materials and reaction media under sintering conditions, a liquid environment is provided, enabling the reaction to turn into a solid-liquid reaction, facilitating ion diffusion, thereby reducing the starting temperature of the reaction and shortening the reaction time. At the same time, by adding rare earth dopants, the rare earth elements replace part of Ni in the ternary material, thus weakening the Li / Ni mixing phenomenon and enhancing the chemical stability of the layered structure; doping rare earth elements by the molten salt method can reduce the unit cell parameters of the layered material, shorten the diffusion path of lithium ions, and improve the cycle performance and rate performance of the battery.

[0121] (2) It can be seen from Example 1 and Examples 2-5 that reasonably controlling the total molar ratio of the LiCl to the lithium source and the ternary precursor helps to improve the cycle performance and rate performance of the battery. Within the range of the preferred molar ratio, the prepared ternary cathode material has excellent electrical properties.

[0122] (3) It can be seen from Example 1 and Examples 6-8 that when the sintering temperature is too low, the synthetic chemical reaction cannot proceed smoothly and the synthesis is incomplete; when the sintering temperature is too high, serious loss of lithium salt will occur, and a high-performance rare earth-doped ternary cathode material cannot be synthesized either.

[0123] (4) It can be seen from Example 1 and Examples 9-11 that when the annealing temperature is too low, the single crystal particles forming the polycrystalline spheres grow incompletely, thus affecting the performance of the cathode material; when the annealing temperature is too high, the single crystal particles grow too large, which is not conducive to the infiltration of the electrolyte, thus affecting the transport of lithium ions.

[0124] (5) It can be seen from Example 1 and Comparative Examples 1, 3-5 that if Li 2 CO 3 is used to replace LiCl or KCl is used to replace LiCl, during the reaction process, eutectic molten salt cannot be formed during the preparation process, and both the first discharge capacity and the cycle retention rate of the battery decrease; if no rare earth doping is carried out, the element distribution of the prepared ternary cathode material is uneven, resulting in a decrease in both the first discharge capacity and the cycle retention rate of the battery; if no annealing treatment is carried out during the preparation process, the crystals of the rare earth-doped ternary cathode material cannot grow further and there are many lattice defects, resulting in a decrease in both the first discharge capacity and the cycle retention rate of the battery.

[0125] (6) It can be seen from Example 1 and Comparative Example 2 that an appropriate amount of LiCl is beneficial to the formation of eutectic molten salt and provides a liquid environment, facilitating ion diffusion, thereby being beneficial to further improving the cycle performance and rate performance of the battery.

[0126] In summary, in the present invention, the lithium source and LiCl are converted into a eutectic molten salt as reaction raw materials and reaction media under sintering conditions, providing a liquid environment to transform the reaction into a solid-liquid reaction, facilitating ion diffusion, thereby reducing the starting temperature of the reaction and shortening the reaction time. At the same time, by adding rare earth dopants, rare earth elements replace part of Ni in the ternary material, thereby weakening the Li / Ni mixing phenomenon and enhancing the chemical stability of the layered structure; doping rare earth elements by the molten salt method can reduce the lattice parameters of the layered material, shorten the diffusion path of lithium ions, and improve the cycle performance and rate performance of the battery.

[0127] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by any person skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A method for preparing a rare earth doped ternary cathode material by a molten salt method, characterized in that: The method comprises: The ternary precursor, the rare earth dopant, the lithium source and LiCl are uniformly mixed, and sintered, de-lithiumed and annealed in sequence to obtain the rare earth doped ternary positive electrode material; The lithium source and LiCl are transformed into eutectic molten salt under sintering conditions as reaction raw materials and reaction medium and provide a liquid environment.

2. The preparation method according to claim 1, characterized in that: The ternary precursor includes any one or a combination of at least two of the hydroxides, nitrates or oxides containing nickel, cobalt and manganese; Preferably, the doping element of the rare earth dopant includes any one or a combination of at least two of La, Ce, Y, Eu, Nd or Gd; Preferably, the rare earth dopant comprises a rare earth oxide and / or a rare earth chloride containing the doping element; Preferably, the lithium source comprises any one or a combination of at least two of LiOH, Li2CO3, LiNO3, Li2SO4 or CH3COOLi; Preferably, the lithium source and the LiCl are mixed in powder form; Preferably, the mixing method comprises grinding.

3. The preparation method according to claim 1 or 2, characterized in that: The molar ratio of the lithium element in the lithium source to the sum of the transition metal elements in the ternary precursor is (1-5):1; Preferably, the sum of the molar amounts of the lithium source and the ternary precursor is M, and the molar ratio of LiCl to M is (0.1-5):1; Preferably, the molar ratio of the lithium element in the lithium source to the rare earth element in the rare earth dopant is 1:(0.01-0.1).

4. The preparation method according to any one of claims 1 to 3, characterized in that The preparation method further comprises simultaneously adding an auxiliary molten salt raw material to carry out the mixing; Preferably, the auxiliary molten salt raw material includes any one of NaCl, NaNO3, KCl or K2CO3, or a combination of at least two of them.

5. The preparation method according to any one of claims 1 to 4, characterized in that: The sintering holding temperature is 500°C to 750°C; Preferably, the sintering holding time is 0.5h to 6h; Preferably, the sintering atmosphere is an air atmosphere.

6. The preparation method according to any one of claims 1 to 5, characterized in that: The lithium removal includes washing with a detergent; Preferably, the detergent comprises deionized water; Preferably, the cleaning is followed by drying; Preferably, the drying comprises oven drying; Preferably, the drying is followed by screening.

7. The preparation method according to any one of claims 1 to 6, characterized in that: The annealing holding temperature is 600°C to 950°C; Preferably, the annealing holding time is 2h to 8h; Preferably, the annealing atmosphere is an air atmosphere.

8. The preparation method according to any one of claims 1 to 7, characterized in that: The preparation method comprises: The ternary precursor, the rare earth dopant, the lithium source and LiCl are mixed and ground in a ratio of (1-5) molar ratio of the lithium element in the lithium source to the sum of the transition metal elements in the ternary precursor: 1: (0.1-5) molar ratio of LiCl to the total molar amount of the lithium source and the ternary precursor: 1: (0.01-0.1) molar ratio of the lithium element in the lithium source to the rare earth element in the rare earth dopant to obtain a mixture; The mixed material is heated to 500° C. to 750° C. in an air atmosphere and sintered for 0.5 h to 6 h, and then cooled to obtain a sintered material; Washing the sintered material 3 to 5 times to obtain a washed material; The washed material is sequentially dried and sieved to obtain sieved material; The sieved material is annealed at 600° C. to 950° C. for 2 h to 8 h in an air atmosphere to obtain the rare earth-doped ternary positive electrode material.

9. A rare earth doped ternary positive electrode material, characterized in that: The rare earth doped ternary positive electrode material is prepared by the preparation method according to any one of claims 1 to 8; Preferably, in the rare earth doped ternary positive electrode material, the ternary positive electrode material comprises LiNi x Co y Mn z O2, x+y+z=1; Preferably, in the rare earth-doped ternary positive electrode material, the doping amount of the rare earth element is ≤4500ppm.

10. A lithium ion battery, characterized in that: The lithium-ion battery comprises the rare earth-doped ternary positive electrode material according to claim 9.

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