Preparation Method and Application of Lithium-Deficient Layered Spinel Composite Phase Rich-Lithium Manganese-Based Cathode Material

Abstract

The present invention discloses a preparation method and application of a lithium-rich manganese-based cathode material with a "lithium-deficient" layered spinel composite phase synthesized by a rapid thermal shock method. The preparation method includes the following steps: First, a lithium-rich manganese-based precursor is prepared by a coprecipitation method. After mixing the precursor and a lithium salt, the sample is rapidly heated using the Joule heat of the powder sample to obtain a cathode material with a layered spinel composite phase having lithium defects. The ultra-fast heating and cooling rates and short-time heat preservation produce a lithium-rich manganese-based cathode material with a larger lithium deficiency amount, a more excellent performance, and a layered spinel composite structure. The preparation method of the present invention prepares a lithium-rich manganese-based cathode material with a larger lithium deficiency amount and a composite structure through a rapid thermal shock technology, which has high capacity, high initial efficiency, long cycle stability, and the preparation method is simple, greatly reduces the material cost, can be mass-produced, improves production efficiency, and reduces energy consumption.

Description

Technical Field

[0001] The present invention relates to the technical field of preparing cathode materials for lithium-ion batteries, and particularly relates to a preparation method and application of a lithium-deficient layered spinel composite-phase lithium-rich manganese-based cathode material. Background Art

[0002] Developing high-performance lithium battery technology is crucial for the progress of various applications from consumer electronics to electric vehicles. To achieve this goal, cathode materials for lithium-ion batteries must be further improved to achieve longer service life, lower production cost, better safety, and environmental friendliness. Due to low cost, rich resources, and high specific capacity (>250 mAh g −1 ), cobalt-free lithium-rich manganese-based layered transition metal (TM) oxides, as a promising class of cathode materials, are highly competitive among current commercial cathode materials and have attracted extensive attention. In the crystal structure, lithium-rich manganese-based layered oxides can be considered as ordered rock salt derivatives (LiTMO2, R3-m), where octahedrally coordinated TM and Li cations preferably form alternating layers connected by interlayer oxygen, supplemented by a superlattice (Li2MnO3, C2 / m), formed by replacing 1 / 3 TM cations with Li in the TM layer. The unique structure allows anions (O 2− →(O2) n− , 1≤n<3) to undergo redox processes in lithium-rich manganese-based cathodes, which is the reason for the high capacity. However, the anion redox reaction inevitably leads to a certain degree of oxygen release, which is the direct cause of voltage decay in lithium-rich manganese-based cathode materials. At the same time, low initial Coulombic efficiency, severe voltage hysteresis, sluggish kinetics, and irreversible structural phase transformation are the main problems plaguing the current generation of lithium-rich manganese-based cathode materials.

[0003] Modification measures for cobalt-free lithium-rich manganese-based cathode materials with low initial Coulombic efficiency, poor cycling and rate performance include element doping, surface coating, morphology control, and crystal plane regulation, etc. Adjusting the grain boundary structure to optimize the material's properties is a classic approach in materials science. For example, CN 117637994A discloses a lithium-deficient lithium-rich manganese-based cathode material and its preparation method and application. A preparation method of a lithium-deficient lithium-rich manganese-based cathode material in the examples includes the following steps: (1) Mix a lithium-rich manganese-based precursor and lithium hydroxide, and then place the obtained mixture in a muffle furnace and calcine at 900°C for 12 h to obtain a cathode material with lithium deficiency (chemical formula Li 1.12 Ni 0.2 Mn 0.6 O2); the molar ratio of lithium ions in the lithium hydroxide to the total metal ions in the lithium-rich manganese-based precursor is 1.4, and the lithium-rich manganese-based precursor is Ni 0.2 Mn 0.8(OH)2; (2) Place the lithium-deficient cathode material described in step (1) in an ALD reactor. Under a nitrogen atmosphere, with a heating stage temperature of 120 °C, a reactor hot well temperature of 450 °C, and a purge temperature of 100 °C, introduce the coating source gas for 10 s to coat alumina on the lithium-deficient cathode material described in step (1) to obtain the lithium-deficient lithium-rich manganese-based cathode material, where the coating source gas is trimethylaluminum. The lithium-deficient lithium-rich manganese-based cathode material prepared by coupling the lithium defect technology with surface coating and grain boundary coating by this method not only has high rate performance and excellent long-term cycle stability, but also can suppress voltage decay to a certain extent. However, the optimal lithium deficiency amount of the prepared lithium-deficient cathode material is only within 7%, and the calcined cathode material has no special structure. Excessive (>10%) lithium defects usually have the opposite effect (L Huang et al., Advanced Energy Materials, 2023, 13(4): 2202345.). The existence of a large number of lithium vacancies and the slow lithium ion insertion during long-term calcination will lead to phase separation between the Li-rich phase and the Mn-rich phase, thus causing the performance decay of the cathode material. Summary of the Invention

[0004] In order to overcome the drawback that traditional methods cannot prepare more lithium-deficient cathode materials, the present invention provides a preparation method and application of a lithium-deficient layered spinel composite-phase lithium-rich manganese-based cathode material.

[0005] The preparation method of the present invention uses Ni x Mn 1-x CO3 and lithium salts as raw materials, and utilizes the characteristics of rapid heating and cooling and short-time heat preservation in the high-temperature thermal shock technology to achieve the preparation of a large amount of lithium-deficient (lithium deficiency amount up to 20%) lithium-rich manganese-based cathode materials. At the same time, the existence of a large number of lithium vacancies in-situ induces the formation of a layered spinel composite structure, making the cathode material have a high initial efficiency and excellent long-cycle stability. This method has simple process steps, greatly reduces the lithium dosage, saves the lithium source cost, and is conducive to large-scale popularization and production.

[0006] Specifically, the object of the present invention is achieved through the following technical solutions: A preparation method for synthesizing a "lithium-deficient" layered spinel composite-phase lithium-rich manganese-based cathode material by a rapid thermal shock method, the preparation method comprising the following steps:

[0007] (1) Mix Ni x Mn 1-x CO3 and lithium salts; the molar ratio of lithium ions in the lithium salt to the total metal ions in the precursor is less than 1.5; 0.2 ≤ x < 1; the lithium salt includes but is not limited to lithium carbonate and / or lithium hydroxide.

[0008] (2) The powder after uniform mixing in step (1) is spread flat on a heating substrate, and the heating substrate is electrified in an air atmosphere to perform thermal shock treatment on the powder. The temperature is 800 - 1000 °C, and the heat preservation time is 20 - 60 s to obtain the lithium-deficient lithium-rich manganese-based cathode material. The thermal shock temperature is preferably 900 °C, and the duration is preferably 20 s. In the heating and cooling program, the heating and cooling rate is 100 °C / s - 500 °C / s.

[0009] By reducing the lithium dosage in the present invention, lithium vacancies can be generated during the sintering process, inducing the formation of a spinel structure. The three-dimensional lithium-ion diffusion channels of the spinel phase are conducive to accelerating the lithium-ion transmission speed and improving the rate performance. At the same time, it can alleviate the irreversible phase transformation during the cycling process of the lithium-rich manganese-based cathode material and reduce the capacity and voltage decay. The lithium deficiency of the lithium-deficient lithium-rich manganese-based cathode material formed by traditional tube furnace calcination is 7%, not exceeding 10%. However, mixtures with less lithium dosage (lithium deficiency greater than 10%) will cause phase separation between the Li-rich phase and the Mn-rich phase due to slow lithium-ion insertion and lithium evaporation phenomena during long-term calcination in a tube furnace, resulting in the attenuation of the performance of the cathode material.

[0010] For the lithium-deficient lithium-rich manganese-based cathode material in the present invention, rapid heating in the high-temperature thermal shock method is used to rapidly insert lithium ions into the precursor lattice. The short heat preservation time inhibits the volatilization of lithium elements and the phase separation phenomenon between the Li-rich phase and the Mn-rich phase. After rapid cooling, a layered spinel lithium-rich manganese-based cathode material with uniform composition and a larger lithium deficiency is formed, improving the first-cycle Coulombic efficiency and long-cycle performance of the lithium-rich manganese-based cathode material.

[0011] In certain embodiments of the present invention, the molar ratio of lithium ions in the lithium salt to the total metal ions in the lithium-rich manganese-based precursor is 1.1 - 1.4. Further preferably 1.2;

[0012] The heating substrate used in the present invention generates heat when electrified and can be carbon cloth, graphite paper, or metal foil.

[0013] The Ni x Mn 1-x CO3 can be obtained by a conventional co-precipitation method.

[0014] The present invention also relates to the application of the lithium-deficient layered spinel composite-phase lithium-rich manganese-based cathode material prepared by the above method as a cathode material for lithium batteries.

[0015] Compared with the prior art, the beneficial effects brought by the present invention are as follows:

[0016] The beneficial effects of the present invention lie in providing a lithium-deficient lithium-rich manganese-based cathode material with a larger lithium deficiency prepared by a high-temperature thermal shock method. Its unique layered spinel composite structure has a high initial efficiency and excellent long-cycle performance. The ultra-fast heating and cooling rates enable lithium ions to quickly embed into the material matrix during the calcination process. The short holding time inhibits the volatilization of lithium sources and the separation of Li-rich and Mn-rich phases, preparing a lithium-rich manganese-based cathode material with uniform composition, solving the phase separation phenomenon caused by excessive lithium deficiency during the slow and long-time synthesis process in a traditional tube furnace, and realizing the preparation of a high-performance layered spinel composite structure lithium-rich manganese-based cathode material in such a high-lithium-deficient environment. The first discharge specific capacity of the lithium-deficient lithium-rich manganese-based cathode material prepared by this method reaches 282 mAh / g at 0.1C, the initial efficiency is 94%, and the capacity retention rate is 91% after 100 cycles and 80% after 200 cycles in a half-cell at 1C within the voltage range of 2.0 - 4.8V. This shows that the material of the present invention has excellent electrochemical performance as a cathode material for lithium-ion batteries.

[0017] The present invention provides a method for preparing a lithium-deficient layered spinel composite structure lithium-rich manganese-based cathode material. This method greatly reduces the lithium dosage, saves the cost of lithium sources, and has simple process steps, which is expected to achieve large-scale popularization and production. Brief Description of the Drawings

[0018] Figure 1 is the temperature-time change curve of high-temperature thermal shock during the calcination process in the present invention;

[0019] Figure 2 is the XRD pattern of the lithium-deficient layered spinel composite structure lithium-rich manganese-based cathode material Li 0.96 Ni 0.2 Mn 0.6 O2 prepared by the high-temperature thermal shock method;

[0020] Figure 3 is the high-resolution transmission electron microscope image HRTEM of the lithium-deficient layered spinel composite structure lithium-rich manganese-based cathode material Li 0.96 Ni 0.2 Mn 0.6 O2 prepared by the high-temperature thermal shock method.

[0021] Figure 4 is the first charge-discharge curve of the layered spinel composite structure lithium-rich manganese-based cathode material Li x Ni 0.2 Mn 0.6 O2 with different lithium deficiencies prepared by the high-temperature thermal shock method as an electrode material at a current density of 0.1C;

[0022] Figure 5The cyclic performance curves of the layered spinel composite structured lithium-rich manganese-based cathode material Li x Ni 0.2 Mn 0.6 O2 samples prepared by the high-temperature thermal shock method as electrode materials at a current density of 1C;

[0023] Figure 6 The first charge-discharge curves of the lithium-rich manganese-based cathode material Li x Ni 0.2 Mn 0.6 O2 samples prepared by the traditional tube furnace with different lithium deficiencies as electrode materials at a current density of 0.1C;

[0024] Figure 7 The XRD pattern of the lithium-deficient layered spinel composite structured lithium-rich manganese-based cathode material Li 0.96 Ni 0.2 Mn 0.6 O2 prepared by the sol-gel method combined with the high-temperature thermal shock method;

[0025] Figure 8 The first charge-discharge curves of the lithium-deficient layered spinel composite structured lithium-rich manganese-based cathode material Li 0.96 Ni 0.2 Mn 0.6 O2 samples prepared by the sol-gel method combined with the high-temperature thermal shock method as electrode materials at a current density of 0.1C. Specific embodiments

[0026] The technical solutions of the present invention will be further described below through specific examples.

[0027] The technical solutions and advantages in the present invention will be clearly and completely described below in combination with the embodiments in the present invention.

[0028] The raw materials used in the present invention are all conventional commercially available products without special instructions; the methods used in the present invention are all conventional methods in the art without special instructions.

[0029] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. The singular forms of "a", "the" and "said" used in the embodiments of the present application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0030] In the following embodiments, Ni 1 / 4 Mn 3 / 4CO3 is used as a sample to illustrate the present invention so that those skilled in the art can fully understand the embodiments and technical effects of the present invention. Those skilled in the art should understand that other Ni x Mn 1-x CO3 obtained by the co-precipitation method are also equally applicable to the present invention. Ni 1 / 4 Mn 3 / 4 CO3 is only for the purpose of describing specific embodiments and is not intended to limit this application.

[0031] Example 1

[0032] This example provides a preparation method for a lithium-rich manganese-based cathode material with a "lithium defect" type layered spinel composite phase synthesized by a rapid thermal shock method. The preparation method includes the following steps:

[0033] (1) Synthesize Ni 1 / 4 Mn 3 / 4 CO3 by the co-precipitation method. The specific method is as follows: Mix nickel sulfate and manganese sulfate according to n(Ni):n(Mn) = 1:3, and prepare an aqueous solution with a total metal ion concentration of 1.8 mol·L -1 in a volume of 5.0 L. Prepare an aqueous solution of sodium carbonate with a total concentration of 2 mol·L -1 , and prepare an aqueous solution of ammonia with a molar concentration of 1.5 mol·L -1 in a volume of 7.0 L. Then, add the mixed salt solution, sodium carbonate solution, and ammonia water solution to the co-precipitation reactor in a co-current manner and continuously stir. The dropping rate is 1 mL·min -1 . Control the temperature of the reactor at 55 °C, the stirring speed at 1100 rpm, pH = 10.9, and the complexing agent concentration at 0.55 mol·L -1 . After carrying out the co-precipitation reaction for 48 h, obtain a lithium-rich manganese-based carbonate precursor Ni 1 / 4 Mn 3 / 4 CO3;

[0034] (2) Uniformly mix the lithium-rich manganese-based cathode precursor Ni 1 / 4 Mn 3 / 4 CO3 synthesized by co-precipitation and lithium carbonate. The molar ratio of lithium ions in the lithium carbonate to the total metal ions in the precursor is 1.2;

[0035] (3) Spread the powder uniformly mixed in step (2) on the carbon cloth and calcine it in the air. The energized current is 45 A, the target temperature is 900 °C, and keep it for 20 s after reaching the target temperature; in the air environment, the heating and cooling rates are both about 400 °C / s. Finally, calcine to form a lithium-rich manganese-based cathode material Li 0.96 Ni 0.2 Mn 0.6 O2.

[0036] Figure 1 is the temperature-time change curve of the material during the high-temperature thermal shock process; Figure 2 is the XRD pattern of the lithium-deficient layered spinel composite-structured lithium-rich manganese-based cathode material Li 0.96 Ni 0.2 Mn 0.6 O2. Its diffraction peaks can match the R-3m phase, and the diffraction peaks at 22-25° are attributed to the superlattice structure of the C2 / m phase. The diffraction peaks of all materials are relatively sharp, and the split peaks of (006) / (102) and (018) / (110) are also very obvious, showing good layer structure and crystallinity. Due to the low spinel content inside, it cannot be detected by XRD, but from Figure 3 the high-resolution transmission electron microscope, it can be found that its diffraction spots can be matched to the ( 0)( 11), (001) planes of the layered structure and the (220) plane of the spinel phase, which also proves the synthesis of the layered spinel composite structure through a large number of lithium defects.

[0037] Example 2

[0038] This example provides a preparation method for synthesizing a lithium-rich manganese-based cathode material with a "lithium-deficient" layered spinel composite phase by a rapid thermal shock method. The preparation method includes the following steps:

[0039] (1) Uniformly mix the co-precipitated synthesized lithium-rich manganese-based cathode precursor Ni 1 / 4 Mn 3 / 4 CO3 and lithium carbonate lithium salt; the molar ratio of lithium ions in the lithium carbonate lithium salt to the total metal ions in the precursor is 1.1;

[0040] (2) Spread the uniformly mixed powder in step (1) on carbon cloth and calcine it in air. The electric current is 45 A, the target temperature is 900 °C, and it is maintained for 20 s after reaching the target temperature; in the air environment, the heating and cooling rates are both about 400 °C / s, and finally the lithium-rich manganese-based cathode material Li 0.88 Ni 0.2 Mn 0.6 O2 is formed.

[0041] Example 3

[0042] This example provides a preparation method for synthesizing a lithium-rich manganese-based cathode material with a "lithium-deficient" layered spinel composite phase by a rapid thermal shock method. The preparation method includes the following steps:

[0043] (1) Uniformly mix the co-precipitated synthesized lithium-rich manganese-based cathode precursor Ni 1 / 4 Mn 3 / 4Mix CO3 and lithium carbonate lithium salt evenly; the molar ratio of lithium ions in the lithium carbonate lithium salt to the total metal ions in the precursor is 1.2;

[0044] (2) Spread the evenly mixed powder in step (1) on carbon cloth and calcine it in air. The energized current is 40 A, the target temperature is 850 °C, and keep it for 20 s after reaching the target temperature; in the air environment, the heating and cooling rates are both about 400 °C / s, and finally calcine to form the lithium-rich manganese-based cathode material Li 0.96 Ni 0.2 Mn 0.6 O2.

[0045] Example 4

[0046] This example provides a preparation method of a lithium-rich manganese-based cathode material with a "lithium defect" type layered spinel composite phase synthesized by a rapid thermal shock method. The preparation method includes the following steps:

[0047] (1) Mix the co-precipitated synthesized lithium-rich manganese-based cathode precursor Ni 1 / 4 Mn 3 / 4 CO3 and lithium carbonate lithium salt evenly; the molar ratio of lithium ions in the lithium carbonate lithium salt to the total metal ions in the precursor is 1.2;

[0048] (2) Spread the evenly mixed powder in step (1) on carbon cloth and calcine it in air. The energized current is 50 A, the target temperature is 950 °C, and keep it for 20 s after reaching the target temperature; in the air environment, the heating and cooling rates are both about 400 °C / s, and finally calcine to form the lithium-rich manganese-based cathode material Li 0.96 Ni 0.2 Mn 0.6 O2.

[0049] Example 5

[0050] This example provides a preparation method of a lithium-rich manganese-based cathode material with a "lithium defect" type layered spinel composite phase synthesized by a rapid thermal shock method. Except that the molar ratio of lithium ions in the lithium carbonate lithium salt in step (1) to the total metal ions in the precursor is 1.3, the rest are the same as in Example 1, and finally calcine to form the lithium-rich manganese-based cathode material Li 1.04 Ni 0.2 Mn 0.6 O2.

[0051] Example 6

[0052] This embodiment provides a preparation method of a lithium-rich manganese-based cathode material with a "lithium-deficient" layered spinel composite phase synthesized by a rapid thermal shock method. Except that the molar ratio of lithium ions in the lithium carbonate lithium salt to the total metal ions in the precursor in step (1) is 1.4, the rest are the same as in Example 1, and finally a lithium-rich manganese-based cathode material Li 1.12 Ni 0.2 Mn 0.6 O2 is formed by calcination.

[0053] Example 7

[0054] This embodiment provides a preparation method of a lithium-rich manganese-based cathode material with a "lithium-deficient" layered spinel composite phase synthesized by a rapid thermal shock method. Except that the energization time in step (2) is 10 s, the rest are the same as in Example 1, and finally a lithium-rich manganese-based cathode material Li 0.96 Ni 0.2 Mn 0.6 O2 is formed by calcination.

[0055] Example 8

[0056] This embodiment provides a preparation method of a lithium-rich manganese-based cathode material with a "lithium-deficient" layered spinel composite phase synthesized by a rapid thermal shock method. Except that the energization time in step (2) is 40 s, the rest are the same as in Example 1, and finally a lithium-rich manganese-based cathode material Li 0.96 Ni 0.2 Mn 0.6 O2 is formed by calcination.

[0057] Through Figure 4 The layered spinel composite structure lithium-rich manganese-based cathode materials Li x Ni 0.2 Mn 0.6 O2 samples with different lithium deficiency amounts prepared by the high-temperature thermal shock method are used as electrode materials. From the first-cycle charge-discharge curve at a current density of 0.1 C, it can be seen that Li 1.12 Ni 0.2 Mn 0.6 O2, Li 1.04 Ni 0.2 Mn 0.6 O2, Li 0.96 Ni 0.2 Mn 0.6 O2, Li 0.88 Ni 0.2 Mn 0.6 The first-cycle discharge specific capacities of the O2 materials at 0.1 C are 266, 266, 282, and 277 mAh g −1, the Coulombic efficiencies are 75.6%, 75.6%, 94%, and 90.9% respectively. When the molar ratio of lithium ions in lithium carbonate to the total metal ions in the precursor is 1.1 (Li 0.88 Ni 0.2 Mn 0.6 O2 material), although the lithium deficiency has reached 26%, due to the rapid heating and cooling and extremely short holding time of high-temperature thermal shock, the lithium ions in the lithium-deficient lithium-rich manganese-based cathode material are rapidly embedded to form a cathode material with uniform element distribution, inhibiting the phase separation of lithium-rich and manganese-rich phases under extreme lithium deficiency, so that the first-cycle discharge capacity and the first Coulombic efficiency can also be maintained at a very high performance level. The empty 16c sites in the spinel phase with a large amount of lithium vacancies generated by lithium deficiency can store more lithium ions, reducing the irreversible loss capacity in the first cycle, thereby improving the discharge specific capacity and Coulombic efficiency. However, compared with the case where the molar ratio is 1.2 (Li 0.96 Ni 0.2 Mn 0.6 O2 material), the Li 0.88 Ni 0.2 Mn 0.6 O2 material contains the most spinel phase, and as shown in the Figure 5 cycle curve, its cycling performance is inferior to that of the Li 0.96 Ni 0.2 Mn 0.6 O2 material.

[0058] Figure 5 The cycling performance of lithium-rich materials with different lithium contents in 1.12 Ni 0.2 Mn 0.6 O2, Li 1.04 Ni 0.2 Mn 0.6 O2, Li 0.96 Ni 0.2 Mn 0.6 O2, Li 0.88 Ni 0.2 Mn 0.6 O2 materials shows that the reversible capacities retained after 200 cycles at 1C are 143, 134, 176, and 155 mAh g −1 respectively, and the capacity retention rates are 68.9%, 66.3%, 80%, and 75% respectively. Among the layered spinel composite materials, the Li 0.96 Ni 0.2 Mn 0.6 O2 material has the highest capacity retention rate (80%). This is related to the good crystal structure, appropriate grain size, and appropriate spinel phase content of this material.

[0059] Comparative Example 1

[0060] This comparative example provides a preparation method for a lithium-rich manganese-based cathode material synthesized by a rapid thermal shock method to form a "lithium-deficient" layered spinel composite phase. Except that the molar ratio of lithium ions in the lithium carbonate lithium salt to the total metal ions in the precursor in step (1) is 1.5, the rest are the same as in Example 1. Finally, the lithium-rich manganese-based cathode material Li 1.2 Ni 0.2 Mn 0.6 O2 is formed.

[0061] Comparative Example 2

[0062] This example provides a preparation method for a lithium-rich manganese-based cathode material synthesized by a rapid thermal shock method to form a "lithium-deficient" layered spinel composite phase. The preparation method is as follows:

[0063] (1) Synthesize a lithium-rich manganese-based lithium-containing precursor by the sol-gel method. The specific method is as follows: Dissolve lithium acetate, nickel acetate, and manganese acetate in absolute ethanol according to the stoichiometric ratio to form solution A. Dissolve citric acid in absolute ethanol to form solution B. Add absolute ethanol to a three-necked flask, place the three-necked flask in an oil bath and heat it. Solution A and B are simultaneously added dropwise to the three-necked flask at a certain rate, and stirred evenly during the titration process. The heating temperature is 80 °C. After the titration is completed, raise the heating temperature of the oil bath to 100 °C until all the sol is converted into a gel. After gelation, place the three-necked flask in a vacuum drying oven and dry it for a period of time. The heating temperature is 100 °C and the heating time is 12 h to obtain a dried lithium-rich manganese-based precursor containing lithium; the molar ratio of lithium ions in the lithium acetate lithium salt to the total metal ions in the precursor is 1.2.

[0064] (2) Spread the lithium-rich manganese-based lithium-containing precursor powder synthesized by the sol-gel method on carbon cloth and calcine it in air. The energized current is 45 A, the target temperature is 900 °C, and it is maintained for 20 s after reaching the target temperature; in an air environment, the heating and cooling rates are both about 400 °C / s. Finally, the lithium-rich manganese-based cathode material Li 0.96 Ni 0.2 Mn 0.6 O2 is formed.

[0065] Figure 4 Shows the comparative material Li 1.2 Ni 0.2 Mn 0.6 O2 has an initial discharge specific capacity of 250 mAh g −1 , and the Coulombic efficiency is 61% respectively. When the lithium doping amount is the normal theoretical value, its first Coulombic efficiency is only 61%, with a large irreversible capacity. The capacity retention rate after 200 cycles at 1C is 80.6% ( Figure 5 ).

[0066] Figure 6 shows the first charge-discharge curves of Li-rich manganese-based cathode materials with different lithium deficiencies synthesized by slow heating using a traditional tube furnace as electrode materials at a current density of 0.1C. The data shows that Li x Ni 0.2 Mn 0.6 O2 samples, Li 1.12 Ni 0.2 Mn 0.6 O2, Li 1.04 Ni 0.2 Mn 0.6 O2, Li 0.96 Ni 0.2 Mn 0.6 O2, Li 0.88 Ni 0.2 Mn 0.6 O2 materials have first-cycle discharge specific capacities of 266, 252, 183, and 159 mAh g −1 , and Coulombic efficiencies of 76%, 81%, 88%, and 104.8% respectively. It can be seen that as the lithium content decreases, both the charge specific capacity and the discharge specific capacity decrease, and the Coulombic efficiency gradually increases. Li 1.2 Ni 0.2 Mn 0.6 O2 and Li 1.12 Ni 0.2 Mn 0.6 O2 materials retain the highest reversible capacity during cycling. Li 1.12 Ni 0.2 Mn 0.6 O2 material has a higher first-cycle Coulombic efficiency than Li 1.2 Ni 0.2 Mn 0.6 O2. It can be seen that during the calcination process in the tube furnace, the maximum lithium deficiency cannot exceed 7%. If the lithium content continues to decrease, the lithium ions are embedded slowly during the high-temperature long-time calcination process. The insufficient lithium amount and the slow embedding of lithium ions will lead to phase separation between the lithium-rich and manganese-rich phases inside the material, thus affecting the performance of the first-cycle reversible capacity. When the lithium deficiency reaches 14% (Li 1.04 Ni 0.2 Mn 0.6 O2 material), the first-cycle discharge capacity is only 183 mAh g −1 . Therefore, when using a tube furnace for long-time high-temperature calcination to prepare "lithium-deficient" layered spinel composite-phase Li-rich manganese-based cathode materials, an appropriate lithium content is required. Too little lithium content will cause structural collapse, thus affecting the performance of the capacity. At the same time, Figure 7 shows the XRD patterns of the Li-rich manganese-based lithium-containing precursor prepared by the sol-gel method after thermal shock heating, showing poor crystallinity and small particles. The synthesized Li-rich manganese-based cathode material Li 0.96 Ni0.2 Mn 0.6 A weak NiO diffraction peak appeared on the left side of the (104) peak of 0.6 , indicating the formation of impurities. Figure 8 The 0.1C charge-discharge curves of the cathode materials are shown, with low capacity. Therefore, the lithium-rich manganese-based precursor prepared by the coprecipitation method has uniform particle size, and the prepared cathode material has excellent performance and strong comparability.

[0067] Table 1 shows the electrochemical performance of the lithium-rich manganese-based cathode materials with different lithium deficiencies obtained in the examples and comparative examples, and the test results are as follows:

[0068] Table 1

[0069] <![CDATA[Initial discharge specific capacity / mAh g −1 > Initial Coulomb efficiency / % Retention rate after 200 cycles Example 1 282 94 80 Example 2 277 90.9 75 Example 3 272 93 77 Example 4 262 83 75 Example 5 266 75.6 66.3 Example 6 266 76 68.9 Example 7 272 90.7 80 Example 8 267 96 77.2 Comparative example 1 250 75 80.6 Comparative example 2 184 87 75

[0070] It can be seen from the above table that the lithium deficiency of the lithium-rich manganese-based cathode material with a "lithium defect" type layered spinel composite phase prepared by high-temperature thermal shock can reach 20%, and its electrochemical performance is the best. The present invention uses the rapid heating and cooling and extremely short holding time of high-temperature thermal shock to promote the rapid insertion of lithium ions in the lithium-deficient lithium-rich manganese-based cathode material to form a cathode material with uniform element distribution, inhibits the phase separation of the lithium-rich and manganese-rich phases at extremely low lithium deficiencies, and enables the first-cycle discharge capacity and the first Coulomb efficiency to also be maintained at a very high performance level, which cannot be achieved by traditional tube furnaces. This method can greatly reduce the lithium dosage, save the cost of lithium sources, has simple process steps, is expected to be widely produced on a large scale, and at the same time provides a design idea for the lithium-deficient layered spinel composite structure lithium-rich manganese-based cathode material.

[0071] The above is only a preferred embodiment of the present invention, and does not impose any form of limitation on the present invention. Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to the above-disclosed technical content to obtain equivalent embodiments with equivalent changes, but as long as the technical content of the present invention is not departed from, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. Preparation method of lithium-deficient layered spinel composite phase lithium-rich manganese-based cathode material, characterized in that, It includes the following steps: (1) Mix Ni x Mn 1-x CO3 with a lithium salt; the molar ratio of lithium ions in the lithium salt to the total metal ions in the lithium-rich manganese-based precursor is 1.1 to 1.4; 0.2 ≤ x < 1; (2) The powder after being uniformly mixed in step (1) is spread on a heating substrate, and the heating substrate is electrified in an air atmosphere to perform thermal shock treatment on the powder. The temperature is 800-1000 °C, the heat preservation time is 20-60 s, and the heating and cooling rate of the thermal shock is 100 °C / s-500 °C / s, so as to obtain the lithium-deficient layered spinel composite phase lithium-rich manganese-based cathode material.

2. The preparation method according to claim 1, characterized in that, The molar ratio of lithium ions in the lithium salt to the total metal ions in the lithium-rich manganese-based precursor is 1.

2.

3. The preparation method according to claim 1, characterized in that, In step (2), the temperature of the thermal shock is 900 °C and the duration is 20 s.

4. The preparation method according to claim 1, characterized in that The lithium salt in step (1) includes lithium carbonate and / or lithium hydroxide.

5. The preparation method according to claim 1, characterized in that, The heating substrate used in step (2) is carbon cloth, graphite paper, or metal foil.

6. Application of the lithium-deficient layered spinel composite phase lithium-rich manganese-based cathode material prepared by the preparation method according to any one of claims 1-5 as a cathode material for lithium batteries.

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