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

Abstract

The application belongs to the field of lithium ion battery cathode material preparation, and particularly relates to a high-voltage type single-crystal lithium manganate, a preparation method and application thereof. The scheme mixes a manganese source compound, a lithium source compound and a transition metal oxide according to a molar ratio of 1:0.5-0.6:0.1-0.3, deoxidizes and sinter, to obtain a single-crystal lithium manganate intermediate product; the obtained intermediate product is used as a raw material to prepare a finished product; the deoxidizing and sintering operation is to raise the temperature from room temperature to 800-1000 DEG C at a temperature raising rate of 20-30 DEG C / min, and keep constant temperature for 2-6 h, no temperature keeping operation is performed in the temperature raising process, after the constant temperature stage is finished, the temperature is lowered to 400-500 DEG C at a temperature lowering rate of 50-100 DEG C / h, and keep constant temperature for 2-4 h, to prepare the high-voltage type single-crystal lithium manganate cathode material. The scheme can significantly improve the capacity and high-temperature cycle performance of the lithium manganate material, and inhibit the battery expansion rate, through fast temperature raising, gradient temperature lowering and the cooperation of radius-matched doping elements. Meanwhile, the application also provides application of the high-voltage type single-crystal lithium manganate cathode material in a battery.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of preparation of lithium ion battery cathode materials, and particularly relates to a high-voltage type single-crystal lithium manganate, a preparation method and application thereof. BACKGROUND

[0002] As the core of new energy storage, the safety of lithium ion battery directly affects the reliability of terminal products. The high-voltage type single-crystal lithium manganate (LiMn2O4) has become a key cathode material for power batteries due to its high-voltage platform of 4.7 V or above and low cost advantage. However, the unstable oxygen in the crystal structure of the lithium manganate is prone to be irreversibly precipitated in the process of high-voltage or high-temperature charging and discharging, thereby causing side reactions, leading to battery swelling, deformation, and even thermal runaway. These problems result in certain safety problems of the lithium manganate battery in practical application.

[0003] In the spinel structure, Mn 3+ Redox reactions occur at high voltage or high temperature, generating Mn 4+ and Mn 2+ , and releasing lattice oxygen (O2) at the same time. These oxygen reacts with the electrolyte to generate CO2 and other gases, and the electrolyte decomposition products will further accelerate the dissolution of manganese and the collapse of the structure. In addition, the gas generated by the oxygen evolution reaction accumulates inside the battery, causing the battery shell to swell and deform, increasing the stress on the electrode, promoting the generation of cracks, and exposing more active surfaces, further exacerbating the side reactions.

[0004] In order to improve the safety of lithium manganate batteries, the current mainstream technologies include three types of methods: surface coating modification, high-temperature sintering optimization, and low-temperature resintering. Coating the surface of lithium manganate crystals with metal oxides can only suppress surface side reactions, but cannot prevent the precipitation of bulk phase structure oxygen, and the thickening of the coating layer will hinder the diffusion of lithium ions. High-temperature one-time sintering treatment of lithium manganate under air atmosphere not only aggravates the volatilization of lithium elements, but also reduces Mn 4+ to Mn 3+ / Mn 2+ , destroying the spinel framework. In addition, the residual oxygen vacancies will become the source of secondary oxygen evolution in the cycle. Although the low-temperature resintering process can reduce oxygen defects, the operating temperature is usually above 600℃, which still induces the reduction of part of manganese, and the problem of precise control of directional deoxygenation under inert atmosphere has not been solved.

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

[0006] How to effectively reduce the unstable oxygen of the battery while ensuring that the lithium manganate cathode material has high-voltage stability and safety, avoid the occurrence of side reactions, and at the same time improve the cycle stability and overall performance of the battery. SUMMARY

[0007] To solve the core problem of the above-mentioned high-voltage lithium manganate that the battery produces gas deformation due to the lattice oxygen precipitation, the application provides a high-voltage single-crystal lithium manganate positive material and a preparation method and application thereof. The method combines ultra-fast heating and gradient cooling technology means through the design of the sintering process, realizes the directional removal of the unstable oxygen in the material bulk phase, inhibits the battery gas expansion from the source, and significantly improves the safety and cycle performance of the battery.

[0008] To achieve the above-mentioned purpose, in the first aspect, the application provides a preparation method of a high-voltage single-crystal lithium manganate, comprising the following steps:

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

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

[0011] The specific operation of deoxidizing and sintering in the step S1 is to increase the temperature from room temperature to 800-1000℃ at a heating rate of 20-30℃ / min, and keep the temperature constant for 2-6h, without heat preservation during the heating process. After the constant temperature stage is over, the temperature is decreased to 400-500℃ at a cooling rate of 50-100℃ / h, and kept constant for 2-4h.

[0012] Preferably, the manganese source compound in the 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 the step S1 is at least one of lithium carbonate, lithium hydroxide and lithium acetate.

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

[0015] Further preferably, the transition metal oxide in the 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 crystal lattice structure of lithium manganate, stabilize the lattice framework, prevent the structure from collapsing, and can effectively improve the capacity of the battery. The spinel-protective interface layer formed during the co-sintering process effectively reduces the direct contact of the electrolyte with the material, and inhibits the dissolution of Mn 2+ .

[0016] During the slow heating process, the lithium manganate material may form a dense MnO2 or Li2MnO3 intermediate phase in the range of 300-600 DEG C, which hinders the diffusion of oxygen atoms. Through a rapid heating scheme of 20-30 DEG C / min, this temperature range can be quickly crossed, directly entering the high-temperature oxygen release zone of lithium manganate, reducing the formation of a surface passivation layer, and promoting the release of unstable structural oxygen. Rapid heating shortens the low-temperature residence time, thereby reducing the probability of oxygen atoms being recaptured. In addition, rapid heating increases the internal and external temperature gradient of the material, generates non-equilibrium thermal stress, causes the internal and external structures to be different, triggers the Yang-Taylor effect of the lithium manganate structure, thereby reducing the activation energy of oxygen release, and further promoting the release of unstable structural oxygen. The gradient cooling method after sintering provides sufficient time for atomic rearrangement to form a stable oxygen vacancy ordered structure, avoiding phase change back to intercalation at high temperature. At the same time, this cooling method makes the material shrink uniformly, maintaining the integrity of the metastable structure after oxygen release. By combining rapid heating and gradient cooling, the structural oxygen prone to side reactions in lithium manganate can be released in advance, while the structural stability of lithium manganate is maintained, thereby improving the cycle stability and safety of the battery.

[0017] Preferably, the specific operation of the step S2 is:

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

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

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

[0021] The low-temperature deoxygenation sintering of step S2 can effectively release the oxygen atoms intercalated during the cooling of step S1, solving the problem of incomplete deoxygenation of lithium manganate.

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

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

[0024] The beneficial effects of the application are:

[0025] 1. Under the cooperation of rapid heating and gradient cooling, the structural oxygen prone to side reactions in lithium manganate is released, while the structural stability of lithium manganate is maintained.

[0026] 2. Doping iron, cobalt, nickel, titanium ions into the crystal lattice structure of lithium manganate, stabilizing the crystal lattice framework, preventing excessive deoxidation of lithium manganate or reduction of manganese ions to cause structure collapse. The spinel-protective interface layer formed during co-firing effectively reduces the direct contact of electrolyte with the material and inhibits the dissolution of Mn 2+ .

[0027] The lithium manganate positive electrode material provided by the application has outstanding stability under high voltage and high temperature conditions, significantly avoids the phenomenon of oxygen release and gas production of lithium manganate under high voltage, and has a relatively high specific capacity. DETAILED DESCRIPTION

[0028] To better illustrate the purpose, technical scheme and advantages of the application, the application will be further described below in combination with specific experiments.

[0029] Example 1: A high-voltage single-crystal lithium manganate positive electrode material and a preparation method thereof

[0030] S1: uniformly mix trimanganese tetraoxide, lithium carbonate and ferrous oxide according to a molar ratio of 1:0.5:0.3, place in an air atmosphere, and raise the temperature from room temperature to 1000℃ at a temperature raising rate of 20℃ / min, and keep the temperature constant for 2h, without temperature keeping operation during the temperature raising process, after the constant temperature stage ends, reduce the temperature to 500℃ at a temperature reducing rate of 75℃ / h, keep the temperature constant for 4h, and then naturally cool to room temperature to obtain a single-crystal lithium manganate intermediate product;

[0031] S2: mix the single-crystal lithium manganate intermediate product prepared in step S1 with glucose according to a mass ratio of 1:0.01, place in an argon gas atmosphere, raise the temperature to 500℃, and keep the temperature constant for 3h to obtain a finished product.

[0032] Example 2: A high-voltage single-crystal lithium manganate positive electrode material and a preparation method thereof

[0033] S1: uniformly mix trimanganese tetraoxide, lithium carbonate and ferrous oxide according to a molar ratio of 1:0.6:0.2, place in an air atmosphere, and raise the temperature from room temperature to 800℃ at a temperature raising rate of 25℃ / min, and keep the temperature constant for 6h, without temperature keeping operation during the temperature raising process, after the constant temperature stage ends, reduce the temperature to 450℃ at a temperature reducing rate of 100℃ / h, keep the temperature constant for 2h, and then naturally cool to room temperature to obtain a single-crystal lithium manganate intermediate product;

[0034] S2: mix the single-crystal lithium manganate intermediate product prepared in step S1 with glucose according to a mass ratio of 1:0.02, place in an argon gas atmosphere, raise the temperature to 200℃, and keep the temperature constant for 6h to obtain a finished product.

[0035] Example 3: A high-voltage single-crystal lithium manganate positive electrode material and a preparation method thereof

[0036] S1: uniformly mix manganese sesquioxide, lithium carbonate and ferrous oxide according to a molar ratio of 1:0.575:0.1, place in an air atmosphere, raise the temperature from room temperature to 900℃ at a temperature raising rate of 30℃ / min, do not perform a temperature holding operation during the temperature raising process, after the temperature holding stage ends, lower the temperature to 400℃ at a temperature lowering rate of 50℃ / h, after temperature holding for 3h, naturally cool to room temperature, to obtain a single-crystal lithium manganate intermediate product;

[0037] S2: mix the single-crystal lithium manganate intermediate product obtained in step S1 with glucose according to a mass ratio of 1:0.01, place in an argon gas atmosphere, raise the temperature to 350℃, temperature hold for 4h, to obtain a finished product.

[0038] Example 4, a high-voltage single-crystal lithium manganate positive electrode material and a preparation method thereof

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

[0040] Example 5, a high-voltage single-crystal lithium manganate positive electrode material and a preparation method thereof

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

[0042] Example 6, a high-voltage single-crystal lithium manganate positive electrode material and a preparation method thereof

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

[0044] Comparative Example 1

[0045] S1: uniformly mix manganese sesquioxide and lithium carbonate according to a molar ratio of 1:0.575, place in an air atmosphere, raise the temperature from room temperature to 900℃ at a temperature raising rate of 30℃ / min, do not perform a temperature holding operation during the temperature raising process, after the temperature holding stage ends, lower the temperature to 400℃ at a temperature lowering rate of 50℃ / h, after temperature holding for 3h, naturally cool to room temperature, to obtain a single-crystal lithium manganate intermediate product;

[0046] S2: mix the single-crystal lithium manganate intermediate product obtained in step S1 with glucose according to a mass ratio of 1:0.01, place in an argon gas atmosphere, raise the temperature to 350℃, temperature hold for 4h, to obtain a finished product.

[0047] Comparative Example 2

[0048] S1: uniformly mix the trimanganese tetraoxide and lithium carbonate according to a molar ratio of 1:0.575, place in an air atmosphere, and raise the temperature from room temperature to 600 DEG C at a temperature raising rate of 5 DEG C / min, keep the temperature constant for 3 h, then raise the temperature from 600 DEG C to 900 DEG C at a temperature raising rate of 5 DEG C / min, keep the temperature constant for 3 h, after the constant temperature stage, naturally cool to room temperature, and obtain a single-crystal lithium manganate intermediate product;

[0049] S2: mix the single-crystal lithium manganate intermediate product obtained in step S1 with glucose according to a mass ratio of 1:0.01, place in an argon gas atmosphere, raise the temperature to 350 DEG C, and keep the temperature constant for 4 h to obtain a finished product.

[0050] Comparative Example 3

[0051] S1: uniformly mix the trimanganese tetraoxide, lithium carbonate and ferrous oxide according to a molar ratio of 1:0.575:0.1, place in an air atmosphere, and raise the temperature from room temperature to 600 DEG C at a temperature raising rate of 5 DEG C / min, keep the temperature constant for 3 h, then raise the temperature from 600 DEG C to 900 DEG C at a temperature raising rate of 5 DEG C / min, keep the temperature constant for 3 h, after the constant temperature stage, naturally cool to room temperature, and obtain a single-crystal lithium manganate intermediate product;

[0052] S2: mix the single-crystal lithium manganate intermediate product obtained in step S1 with glucose according to a mass ratio of 1:0.01, place in an argon gas atmosphere, raise the temperature to 350 DEG C, and keep the temperature constant for 4 h 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 nickel 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] The other conditions are the same as those in Example 3 except that barium oxide is used instead of ferrous oxide in step S1.

[0065] Comparative Example 10

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

[0067] Performance test

[0068] The finished products prepared in the above examples and comparative examples are prepared into 1000 mAh soft package batteries according to the following method for performance test:

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

[0070] The PVDF is dissolved in NMP to prepare a glue solution with a solid content of 8%, and then the carbon nanotube slurry is added and mixed and dispersed at high speed for 1.5 h, followed by adding the product and kneading and stirring for 6 h, and adding an appropriate amount of NMP to adjust the slurry viscosity to 7500 mPa.s. A positive electrode slurry for lithium batteries is obtained.

[0071] The negative electrode slurry is prepared by the same method and formula, and a negative electrode slurry for lithium batteries is obtained.

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

[0073] After assembly, the battery is tested for electrical performance, and the test items include 3.0-4.6V 1C discharge capacity, 45°C high temperature 1C cycle 500 times retention rate, and 60°C high temperature storage for 15 days battery expansion rate test.

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

[0075] The test method for 45°C high temperature 1C cycle 500 times retention rate is: after activation by 1C charge and discharge of the soft package battery prepared above, it is transferred to a 45°C constant temperature oven, and the 1C charge and discharge steps are repeated for cycle test, and the capacity retention rate after 500 cycles is calculated;

[0076] The test method for 60°C high temperature storage for 15 days battery expansion rate is: the battery is heated in a natural convection or flowing air oven, the oven temperature is set to 60°C, the setting time is 15 days, the battery thickness is measured after cooling, and the battery expansion rate is calculated by 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] According to the battery test results of Examples 1-6, it is found that the present scheme not only has a higher discharge capacity, but also can maintain excellent cycle performance and expansion rate in a high temperature environment. This indicates that by combining fast heating, gradient cooling and radius matching of the doped elements, the capacity and high temperature cycle performance of the lithium manganate material can be significantly improved, and the battery expansion rate can be inhibited.

[0082] According to the battery test results of Examples 3-6 and Comparative Examples 1-10, it is found that the use of the fast 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 causing the internal and external structures to be inconsistent, thereby reducing the activation energy of oxygen detachment and enabling the effective removal of structural oxygen in lithium manganate that is prone to cause side reactions. The gradient cooling method after sintering can provide sufficient time for atoms to rearrange and form a stable ordered structure of oxygen vacancies, maintaining the integrity of the metastable structure after oxygen detachment. By combining fast heating and gradient cooling, structural oxygen in lithium manganate that is prone to cause 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 1-6 and Comparative Examples 7-10, it is found that the type of doped elements significantly affects the implementation effect of the fast heating sintering scheme. It can be found from Comparative Examples 7-10 that fast heating sintering helps to regulate the oxygen vacancy concentration in lithium manganate, thereby reducing structural oxygen prone to cause side reactions and inhibiting the decrease in cycle stability and the increase in expansion rate of the battery at high temperature. However, when the doped element is Ba or Sr, the improvement effect of fast heating sintering is significantly weaker than when the element is Fe, Co, Ni or Ti. This may be because the ionic radius of Mn 3+ is 66 pm, the ionic radius of Fe 3+ is 64 pm, the ionic radius of Co 3+ is 63 pm, the ionic radius of Ni 3+ is 62 pm, the ionic radius of Ti 4+ is 68 pm, and the ionic radius of Ba 2+ is 135 pm, and the ionic radius of Sr 2+ is 113 pm. Fe 3+ , Co 3+ , Ni 3+ , Ti 3+ , and Mn 4+Into the crystal structure of lithium manganate, the lattice framework is stabilized, preventing lithium manganate from excessive deoxidation or reduction of manganese ions leading to structure collapse; and Ba 2+ , Sr 2+ and other ions with large ionic radius entering the lattice will cause lattice distortion and increase in porosity, aggravating the risk of collapse, thus making the high-temperature cycle performance of the battery and the battery expansion rate high.

[0084] In summary, by combining the radius-matched doping elements, rapid heating and gradient cooling, the lithium manganate battery has high capacity, good high-temperature cycle performance and battery expansion inhibition effect.

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

Claims

1. A method for preparing high-voltage single-crystal lithium manganese oxide, characterized in that, Comprising the following steps: S1: mixing a manganese source compound, a lithium source compound and a transition metal oxide according to a molar ratio of 1:0.5-0.6:0.1-0.3, deoxygenating and sintering to obtain a single-crystal lithium manganate intermediate product; S2: mixing the obtained intermediate product with a reducing agent according to a mass ratio of 1:0.01-0.03, placing in an inert gas atmosphere, heating to 200-500℃, and keeping constant temperature for 3-6h to obtain a finished product; The specific operation of deoxygenating and sintering in the step S1 is to increase the temperature from room temperature to 800-1000℃ at a heating rate of 20-30℃ / min, keeping constant temperature for 2-6h, without holding operation during the heating process, after the end of the constant temperature stage, decreasing the temperature to 400-500℃ at a cooling rate of 50-100℃ / h, keeping constant temperature for 2-4h, and then naturally cooling to room temperature; 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.

2. The method of claim 1, wherein, The reducing agent is one or a combination of more than one of glucose, sucrose, and coke.

3. The method of claim 1, wherein, The inert gas is at least one of argon and nitrogen.

4. A high-voltage type single-crystal lithium manganate cathode material, characterized in that, Prepared by the method of any one of claims 1-3.

5. Application of the high-voltage single-crystal lithium manganate cathode material of claim 4 in a lithium battery.

Images