High-voltage single-crystal lithium manganate, preparation method and application of high-voltage single-crystal lithium manganate

Abstract

The invention belongs to the field of preparation of a lithium ion battery positive electrode material, and particularly relates to high-voltage type single crystal lithium manganate, a preparation method and application of the high-voltage type single crystal lithium manganate. According to the scheme, a manganese source compound, a lithium source compound and a transition metal oxide are mixed according to the molar ratio of 1: (0.5-0.6): (0.1-0.3), deoxidized and sintered, and a single-crystal lithium manganate intermediate product is obtained; and preparing a finished product by taking the obtained intermediate product as a raw material. The deoxidation sintering operation comprises the steps of heating from room temperature to 800-1000 DEG C at a heating rate of 20-30 DEG C / min, keeping the temperature for 2-6 hours, not carrying out heat preservation operation in the heating process, cooling to 400-500 DEG C at a cooling rate of 50-100 DEG C / h after the constant temperature stage is ended, and keeping the temperature for 2-4 hours, so as to prepare the high-voltage type single crystal lithium manganate positive electrode material. According to the scheme, the capacity and the high-temperature cycle performance of the lithium manganate material can be remarkably improved and the expansion rate of the battery can be inhibited under the cooperation of the doping elements with rapid heating, gradient cooling and radius matching. Meanwhile, the invention also provides an application of the high-voltage single-crystal lithium manganate positive electrode material in a battery.

Description

Technical Field

[0001] The present invention belongs to the field of preparation of positive electrode materials for lithium-ion batteries, and specifically relates to a high-voltage single-crystal lithium manganese oxide, a preparation method and its application. Background Art

[0002] As the core of new energy storage, the safety of lithium-ion batteries directly impacts the reliability of end products. High-voltage single-crystal lithium manganese oxide (LiMn2O4) has become a key cathode material for power batteries due to its high voltage platform above 4.7V and low cost. However, the unstable oxygen in its crystal structure is easily and irreversibly precipitated during high-voltage or high-temperature charging and discharging, triggering side reactions that can lead to battery bloating, deformation, and even thermal runaway. These issues have led to certain safety issues in the practical application of lithium manganese oxide batteries.

[0003] In the spinel structure, Mn 3+ Under high voltage or high temperature, an oxidation-reduction reaction occurs to generate Mn 4+ and Mn 2+ , while releasing lattice oxygen (O2). This oxygen reacts with the electrolyte to produce gases such as CO2. At the same time, the decomposition products of the electrolyte corrode the electrode material, further accelerating the dissolution of manganese and structural collapse. In addition, the gases produced by the oxygen evolution reaction accumulate inside the battery, causing the battery shell to expand and deform, increasing electrode stress, promoting crack formation, and exposing more active surface areas, further exacerbating side reactions.

[0004] In order to improve the safety of lithium manganese oxide batteries, the current mainstream technologies include surface coating modification, high temperature sintering optimization and low temperature burn-back. The use of metal oxides to coat the surface of lithium manganese oxide crystals can only inhibit surface side reactions, but cannot prevent the precipitation of bulk structural oxygen. Moreover, the thickening of the coating layer will hinder the diffusion of lithium ions. The use of high temperature single sintering in air atmosphere to deoxidize lithium manganese oxide will not only aggravate the volatilization of lithium elements, but also increase the Mn 4+ Reduced to Mn 3+ / Mn 2+ This destroys the spinel framework. Furthermore, residual oxygen vacancies can become a source of secondary oxygen evolution during cycling. While low-temperature sintering processes can reduce oxygen defects, the operating temperature typically exceeds 600°C, which can still induce some manganese reduction. Furthermore, the issue of precisely controlling directional deoxidation under an inert atmosphere remains unresolved.

[0005] Based on the above-mentioned defects, the core problem to be solved by the present invention is:

[0006] How to effectively reduce the unstable oxygen in the battery, avoid the occurrence of side reactions, and improve the battery's cycle stability and overall performance while ensuring the high voltage stability and safety of the lithium manganese oxide positive electrode material. Summary of the Invention

[0007] To address the core issue of high-voltage lithium manganese oxide battery gassing and deformation caused by lattice oxygen precipitation, the present invention proposes a high-voltage single-crystal lithium manganese oxide cathode material, its preparation method, and its application. This method, through a designed sintering process that combines ultra-rapid heating with gradient cooling techniques, achieves targeted removal of unstable oxygen from the material's bulk phase, suppressing battery gassing at the source and significantly improving battery safety and cyclability.

[0008] To achieve the above objectives, in a first aspect, the present invention provides a method for preparing high-voltage single-crystal lithium manganate, comprising the following steps:

[0009] S1: mixing a manganese source compound, a lithium source compound, and a transition metal oxide in a molar ratio of 1:0.5-0.6:0.1-0.3, deoxidizing and sintering to obtain an intermediate product;

[0010] S2: using the obtained intermediate product as a raw material to prepare a finished product;

[0011] The specific operation of the deoxidation sintering in step S1 is to increase the temperature from room temperature to 800-1000°C at a heating rate of 20-30°C / min, and maintain the temperature for 2-6 hours. No insulation operation is performed during the heating process. After the constant temperature stage ends, the temperature is reduced to 400-500°C at a cooling rate of 50-100°C / h and maintained at the temperature for 2-4 hours.

[0012] Preferably, the manganese source compound in step S1 is at least one of manganese oxide, manganese dioxide, dimanganese trioxide, trimanganese tetraoxide, and manganese carbonate.

[0013] Preferably, the lithium source compound in step S1 is at least one of lithium carbonate, lithium hydroxide and lithium acetate.

[0014] Preferably, the transition metal oxide in step S1 is at least one of ferrous oxide, nickelous oxide, cobalt oxide, and titanium oxide.

[0015] Further preferably, the transition metal oxide described in step S1 is at least one of ferrous oxide, nickelous oxide, cobalt oxide, and titanium oxide. Iron ions, nickel ions, cobalt ions, or titanium ions enter the lattice structure of lithium manganese oxide, stabilizing the lattice framework, preventing structural collapse, and effectively increasing the capacity of the battery. The spinel-protective interface layer formed during the co-firing process effectively reduces the direct contact between the electrolyte and the material, inhibiting the Mn 2+ dissolution.

[0016] During the slow heating process, lithium manganese oxide (LMO) materials may form a dense MnO2 or Li2MnO3 intermediate phase in the 300-600°C range, hindering the diffusion of oxygen atoms. A rapid heating schedule of 20-30°C / min allows rapid passage through this temperature range, directly entering the LMO's high-temperature oxygen release zone, reducing the formation of a surface passivation layer and promoting the release of unstable structural oxygen. Rapid heating shortens the low-temperature dwell time, thereby reducing the probability of oxygen atoms being recaptured. Furthermore, rapid heating increases the internal and external temperature gradients of the material, generating non-equilibrium thermal stresses that lead to structural inconsistencies and trigger the Young-Teller effect in the LMO structure, thereby reducing the activation energy for oxygen release and further promoting the release of unstable structural oxygen. Post-sintering, a gradient cooling method provides sufficient time for atoms to rearrange, forming a stable, ordered structure with oxygen vacancies, thus avoiding phase transition back-intercalation at high temperatures. Furthermore, this cooling method allows the material to shrink uniformly, preserving the integrity of the metastable structure after oxygen release. By combining rapid heating and gradient cooling, the structural oxygen in lithium manganese oxide that is prone to side reactions can be removed in advance, while maintaining the structural stability of lithium manganese oxide, thereby improving the cycle stability and safety of the battery.

[0017] Preferably, the specific operations of step S2 are:

[0018] The obtained intermediate product and the reducing agent are mixed in a mass ratio of 1:0.01-0.03, placed in an inert gas atmosphere, heated to 200-500° C., and kept at the constant temperature for 3-6 hours to obtain a finished product.

[0019] Preferably, the reducing agent is one or more combinations of glucose, sucrose, and coke.

[0020] Preferably, the inert gas is at least one of argon and nitrogen.

[0021] The low-temperature deoxidation sintering in step S2 can effectively remove the oxygen atoms that are embedded back during the cooling in step S1, thereby solving the problem of incomplete external deoxidation of lithium manganese oxide.

[0022] In addition, a high-voltage single-crystal lithium manganate positive electrode material is also disclosed, which is prepared by any of the above-mentioned preparation methods.

[0023] In addition, the present application also discloses the application of the above-mentioned high-voltage single-crystal lithium manganese oxide positive electrode material in lithium batteries.

[0024] The beneficial effects of the present invention are:

[0025] 1. Under the coordination of rapid heating and gradient cooling, the structural oxygen in lithium manganese oxide that is prone to side reactions is removed while maintaining the structural stability of lithium manganese oxide.

[0026] 2. Doping introduces iron, cobalt, nickel, titanium and other ions into the lattice structure of lithium manganese oxide, stabilizing the lattice framework and preventing the structure from collapsing due to excessive deoxidation of lithium manganese oxide or reduction of manganese ions. The spinel-protective interface layer formed during the co-firing process effectively reduces the direct contact between the electrolyte and the material, inhibiting the Mn 2+ dissolution.

[0027] The lithium manganate positive electrode material provided by the present invention has outstanding stability under high voltage and high temperature conditions, significantly avoids the phenomenon of lithium manganate releasing oxygen and producing gas under high voltage, and at the same time has a higher gram capacity. DETAILED DESCRIPTION

[0028] In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific experiments.

[0029] Example 1: A high-voltage single-crystal lithium manganate cathode material and its preparation method

[0030] S1: Manganese manganate, lithium carbonate and ferrous oxide are uniformly mixed in a molar ratio of 1:0.5:0.3, placed in an air atmosphere, and heated from room temperature to 1000°C at a rate of 20°C / min, and kept at this temperature for 2 hours. No heat preservation operation is performed during the heating process. After the constant temperature stage, the temperature is lowered to 500°C at a rate of 75°C / h, kept at this temperature for 4 hours, and then naturally cooled to room temperature to obtain a single crystal lithium manganate intermediate product;

[0031] S2: The single crystal lithium manganate intermediate product obtained in step S1 is mixed with glucose in a mass ratio of 1:0.01, placed in an argon gas atmosphere, heated to 500° C., and kept at this temperature for 3 hours to obtain a finished product.

[0032] Example 2: A high-voltage single-crystal lithium manganate cathode material and its preparation method

[0033] S1: Manganese manganate, lithium carbonate and ferrous oxide are uniformly mixed in a molar ratio of 1:0.6:0.2, placed in an air atmosphere, and heated from room temperature to 800°C at a rate of 25°C / min, and kept at this temperature for 6 hours without holding the temperature during the heating process. After the constant temperature stage, the temperature is lowered to 450°C at a rate of 100°C / h, kept at this temperature for 2 hours, and then naturally cooled to room temperature to obtain a single crystal lithium manganate intermediate product;

[0034] S2: The single crystal lithium manganate intermediate product obtained in step S1 is mixed with glucose in a mass ratio of 1:0.02, placed in an argon gas atmosphere, heated to 200° C., and kept at this temperature for 6 hours to obtain a finished product.

[0035] Example 3: A high-voltage single-crystal lithium manganate cathode material and its preparation method

[0036] S1: Manganese manganate, lithium carbonate and ferrous oxide are uniformly mixed in a molar ratio of 1:0.575:0.1, placed in an air atmosphere, and heated from room temperature to 900°C at a rate of 30°C / min, and kept at this temperature for 3 hours without holding the temperature during the heating process. After the constant temperature stage, the temperature is lowered to 400°C at a rate of 50°C / h, kept at this temperature for 3 hours, and then naturally cooled to room temperature to obtain a single crystal lithium manganate intermediate product;

[0037] S2: The single crystal lithium manganate intermediate product obtained in step S1 is mixed with glucose in a mass ratio of 1:0.01, placed in an argon gas atmosphere, heated to 350° C., and kept at this temperature for 4 hours to obtain a finished product.

[0038] Example 4: A high-voltage single-crystal lithium manganate cathode material and its preparation method

[0039] Except that cobalt oxide is used instead of ferrous oxide in step S1, other conditions are the same as those in Example 3.

[0040] Example 5: A high-voltage single-crystal lithium manganate cathode material and its preparation method

[0041] Except that nickel oxide is used instead of ferrous oxide in step S1, other conditions are the same as those in Example 3.

[0042] Example 6: A high-voltage single-crystal lithium manganate cathode material and its preparation method

[0043] Except that titanium oxide is used instead of ferrous oxide in step S1, other conditions are the same as those in Example 3.

[0044] Comparative Example 1

[0045] S1: Mix manganese dioxide and lithium carbonate in a molar ratio of 1:0.575, place the mixture in an air atmosphere, and heat it from room temperature to 900°C at a rate of 30°C / min, hold it at that temperature for 3 hours, without holding the temperature during the heating process. After the hold temperature stage, cool it down to 400°C at a rate of 50°C / h, hold it at that temperature for 3 hours, and then naturally cool it to room temperature to obtain a single crystal lithium manganate intermediate product;

[0046] S2: The single crystal lithium manganate intermediate product obtained in step S1 is mixed with glucose in a mass ratio of 1:0.01, placed in an argon gas atmosphere, heated to 350° C., and kept at this temperature for 4 hours to obtain a finished product.

[0047] Comparative Example 2

[0048] S1: Mix manganese dioxide and lithium carbonate in a molar ratio of 1:0.575, place the mixture in an air atmosphere, and heat it from room temperature to 600°C at a rate of 5°C / min, hold the temperature for 3 hours, then heat it from 600°C to 900°C at a rate of 5°C / min, hold the temperature for 3 hours, and then cool it naturally to room temperature to obtain a single crystal lithium manganate intermediate product;

[0049] S2: The single crystal lithium manganate intermediate product obtained in step S1 is mixed with glucose in a mass ratio of 1:0.01, placed in an argon gas atmosphere, heated to 350° C., and kept at this temperature for 4 hours to obtain a finished product.

[0050] Comparative Example 3

[0051] S1: Manganese manganate, lithium carbonate and ferrous oxide are mixed uniformly in a molar ratio of 1:0.575:0.1, placed in an air atmosphere, and heated from room temperature to 600°C at a rate of 5°C / min, maintained at this temperature for 3 hours, then heated from 600°C to 900°C at a rate of 5°C / min, maintained at this temperature for 3 hours. After the constant temperature stage, the mixture is naturally cooled to room temperature to obtain a single crystal lithium manganate intermediate product;

[0052] S2: The single crystal lithium manganate intermediate product obtained in step S1 is mixed with glucose in a mass ratio of 1:0.01, placed in an argon gas atmosphere, heated to 350° C., and kept at this temperature for 4 hours to obtain a finished product.

[0053] Comparative Example 4

[0054] Except that cobalt oxide is used instead of ferrous oxide in step S1, other conditions are the same as those in comparative example 3.

[0055] Comparative Example 5

[0056] Except that nickelous oxide is used instead of ferrous oxide in step S1, other conditions are the same as those in comparative example 3.

[0057] Comparative Example 6

[0058] Except that titanium oxide is used instead of ferrous oxide in step S1, other conditions are the same as those in comparative example 3.

[0059] Comparative Example 7

[0060] Except that strontium oxide is used instead of ferrous oxide in step S1, other conditions are the same as those in comparative example 3.

[0061] Comparative Example 8

[0062] Except that barium oxide is used instead of ferrous oxide in step S1, other conditions are the same as those in comparative example 3.

[0063] Comparative Example 9

[0064] Except that strontium oxide is used instead of ferrous oxide in step S1, other conditions are the same as those in Example 3.

[0065] Comparative Example 10

[0066] Except that barium oxide is used instead of ferrous oxide in step S1, other conditions are the same as those in Example 3.

[0067] Performance Testing

[0068] The finished products obtained in the above examples and comparative examples were prepared into 1000mAh soft-pack batteries according to the following method for performance testing:

[0069] The obtained lithium manganate, carbon nanotubes, and PVDF were mixed evenly in a mass ratio of 97%:1.5%:1.5% to prepare a coating slurry. The steps are as follows:

[0070] Dissolve PVDF in NMP to prepare a paste with an 8% solids content. Add the carbon nanotube slurry and mix at high speed for 1.5 hours. Then add this product and knead and stir for 6 hours. Add an appropriate amount of NMP to adjust the slurry viscosity to 7500 mPa.s. This creates a positive electrode slurry for lithium batteries.

[0071] The negative electrode slurry is prepared by the same method and formula to obtain the negative electrode slurry for lithium battery.

[0072] The positive electrode slurry is coated on aluminum foil, and the negative electrode slurry is coated on copper foil. After drying, rolling, powdering, welding the tabs, winding, liquid injection, and sealing, the soft pack battery is prepared.

[0073] After assembly, the battery is subjected to electrical performance tests, including: 3.0~4.6V 1C discharge capacity, 45℃ high temperature 1C cycle retention for 500 weeks, and 60℃ high temperature storage for 15 days battery expansion rate test.

[0074] The test method for 3.0~4.6V 1C discharge capacity is: electrochemical test cabinet, constant current and constant voltage charging at 1C rate and then discharging at 1C constant current, the nominal specific capacity is 125mAh / g;

[0075] The test method for the retention rate of 500 cycles at 1C at 45°C is as follows: the prepared soft-pack battery is activated by 1C charge and discharge, then transferred to a 45°C constant temperature box, and cycled according to the 1C charge and discharge process step to calculate the capacity retention rate after 500 cycles;

[0076] The battery expansion rate test method for 15 days of 60°C high temperature storage is as follows: the battery cell is heated in a natural convection or flowing air oven with the oven temperature set to 60°C for 15 days, and the battery thickness is measured after cooling. The battery expansion rate is calculated based on the battery thickness before and after high temperature storage.

[0077] The specific performance results are shown in Table 1.

[0078] Table 1

[0079]

[0080]

[0081] Battery testing results from Examples 1-6 show that, in addition to high discharge capacity, this solution maintains excellent cycling performance and expansion rate even in high-temperature environments. This demonstrates that combining rapid heating and cooling with a radius-matched doping element significantly improves the capacity and high-temperature cycling performance of lithium manganese oxide materials while suppressing battery expansion rate.

[0082] According to the battery test results of Examples 3 to 6 and Comparative Examples 1 to 10, it was found that the rapid heating scheme can quickly pass through the low-temperature side reaction zone of lithium manganate and directly enter the high-temperature oxygen release zone, while making the internal and external structures inconsistent, thereby reducing the activation energy of oxygen separation, and effectively removing the structural oxygen in lithium manganate that is prone to side reactions. The gradient cooling method after sintering can provide enough time for atoms to rearrange, forming a stable oxygen vacancy ordered structure, and maintaining the integrity of the metastable structure after oxygen separation. By combining rapid heating and gradient cooling, the structural oxygen in lithium manganate that is prone to side reactions can be removed in advance, while maintaining the structural stability of lithium manganate, thereby significantly improving the cycle stability and safety of the battery.

[0083] In addition, according to the battery test results of Examples 1 to 6 and Comparative Examples 7 to 10, it was found that the type of doping element significantly affects the implementation effect of the rapid temperature rise sintering scheme. Through Comparative Examples 7 to 10, it can be found that rapid temperature rise sintering helps to regulate the oxygen vacancy concentration in lithium manganese oxide, thereby reducing the structural oxygen that is prone to side reactions and inhibiting the decline in battery cycle stability and the increase in expansion rate at high temperatures. However, when the doping element is Ba or Sr, the improvement effect of rapid temperature rise sintering is significantly weaker than when doped with elements such as Fe, Co, Ni or Ti. This may be because Mn 3+ The ionic radius of Fe is 66 pm. 3+ The ionic radius of Co is 64 pm. 3+ The ionic radius of Ni is 63 pm. 3+ The ionic radius of Ti is 62 pm. 4+ The ionic radius of Ba is 68 pm, while 2+ The ionic radius of Sr is 135 pm. 2+ The ionic radius of Mn is 113 pm. 3+ Fe with similar ionic radius 3+ 、Co 3+ 、Ni 3+ 、Ti 4+Entering the lattice structure of lithium manganate, it stabilizes the lattice framework and prevents the structure from collapsing due to excessive deoxidation of lithium manganate or reduction of manganese ions. 2+ 、Sr 2+ The entry of plasma into the lattice will cause lattice distortion and increased porosity, exacerbating the risk of collapse, resulting in high-temperature cyclability of the battery and high battery expansion rate.

[0084] In summary, through the combination of radius-matched doping elements, rapid heating and gradient cooling, the lithium manganese oxide battery has high capacity while having good high-temperature cycle performance and battery expansion inhibition effect.

[0085] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing high-voltage single-crystal lithium manganate, characterized in that: The steps include: S1: mixing a manganese source compound, a lithium source compound, and a transition metal oxide in a molar ratio of 1:0.5-0.6:0.1-0.3, deoxidizing and sintering to obtain a single crystal lithium manganate intermediate product; S2: using the obtained intermediate product as a raw material to prepare a finished product; The specific operation of the deoxidation sintering in step S1 is to increase the temperature from room temperature to 800-1000°C at a heating rate of 20-30°C / min, and maintain the temperature for 2-6 hours. No insulation operation is performed during the heating process. After the constant temperature stage, the temperature is reduced to 400-500°C at a cooling rate of 50-100°C / h and maintained at the temperature for 2-4 hours.

2. The method according to claim 1, characterized in that The specific operations of step S2 are: The obtained intermediate product and the reducing agent are mixed in a mass ratio of 1:0.01-0.03, placed in an inert gas atmosphere, heated to 200-500° C., and kept at the constant temperature for 3-6 hours to obtain a finished product.

3. The method according to claim 1 or 2, characterized in that The manganese source compound is at least one of manganese oxide, manganese dioxide, dimanganese trioxide, trimanganese tetraoxide, and manganese carbonate; The lithium source compound is at least one of lithium carbonate, lithium hydroxide, and lithium acetate; The transition metal oxide is at least one of ferrous oxide, nickelous oxide, cobalt oxide, and titanium oxide.

4. The method according to claim 2, characterized in that The reducing agent is one or more combinations of glucose, sucrose and coke.

5. The method according to claim 2, characterized in that The inert gas is at least one of argon and nitrogen.

6. A high voltage single crystal lithium manganese oxide positive electrode material, characterized in that: The method is prepared by any one of claims 1 to 5.

7. Use of the high-voltage single-crystal lithium manganate positive electrode material as claimed in claim 6 in a lithium battery.

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