High-activity lithium-rich positive electrode material and secondary battery

Abstract

The invention belongs to the technical field of lithium battery positive electrode materials, and particularly discloses a high-activity lithium-rich positive electrode material and a secondary battery. The chemical formula of the lithium-rich layered lithium manganate positive electrode material disclosed by the invention is Li < 2-x > Na < y > MnO < 3-z > F < z >, wherein 0.02 < = x < = 0.1, 0 < = y < = 0.08, and 0 < = z < = 0.08. Compared with traditional lithium-rich layered lithium manganate, the lithium-rich layered lithium manganate positive electrode material has higher capacity, better structural stability and better electrochemical performance, the activity of the material can be effectively improved and the capacity can be increased by introducing lithium vacancies into the material, sodium ions and fluorine ions can be further doped, and the performance of the material is improved. The rate capability and the cycle performance of the material are improved. The invention also provides a preparation method of the high-activity lithium-rich positive electrode material, and provides a lithium ion secondary battery.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium battery cathode materials, and in particular to a high-activity lithium-rich cathode material and a secondary battery. Background Art

[0002] Lithium-ion batteries have been most widely used in daily life due to their excellent properties such as high energy density and long cycle life. With the rapid development of current portable electronic devices, electric vehicles, and smart grid systems, higher requirements are put forward for lithium-ion battery materials, not only requiring excellent performance but also lower costs. The cathode material accounts for about 50% of the total material cost of lithium-ion batteries. Therefore, it is imperative to develop a cathode material with high reversible capacity, environmental friendliness, and low cost.

[0003] Traditional lithium-ion battery cathode materials, such as LiFePO4, LiMn2O4, LiCoO2, and LiMO2 (M = Ni, Co, etc.), have been widely used on a large scale. However, the low energy density and dependence on limited expensive metal resources cannot simultaneously meet the excellent performance and low-cost requirements of lithium-ion batteries. A new cathode material, lithium-rich layered lithium manganate Li2MnO3 (the chemical formula can be written as Li 1.33 Mn 0.67 O2, where the stoichiometric number of Li is greater than 1) has a high theoretical specific capacity of 459 mAh / g. It is found that its main capacity comes from the contribution of oxygen ions. The raw material cost of lithium-rich layered lithium manganate Li2MnO3 is low, but its electrochemical activity is poor. It is necessary to activate oxygen ions to make oxygen ions also participate in the capacity contribution to show the characteristics of high capacity. The modification of such materials mainly focuses on activating the redox of oxygen ions. Therefore, higher requirements are imposed on the synthesis method and modification treatment of the materials. Currently, the relatively successful synthesis methods include: the three-step method of coprecipitation-hydrothermal-calcination, the sol-gel method, and the low-temperature molten salt method. However, all of these three synthesis methods have certain limitations and the synthesis steps are cumbersome.

[0004] Therefore, it is necessary to further explore the synthesis and modification methods of the lithium-rich layered lithium manganate Li2MnO3 cathode material to improve its electrochemical performance. Summary of the Invention

[0005] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention provides a lithium-rich layered lithium manganese oxide cathode material. The lithium-rich layered lithium manganese oxide cathode material of the present invention has higher capacity, better structural stability and electrochemical performance compared with the traditional lithium-rich layered lithium manganese oxide Li2MnO3. By introducing lithium vacancies into the material, the amount of anions near the vacancies can be regulated in the lithium-rich cathode material, which can effectively improve the activity of the material and increase the capacity. The lithium-rich layered lithium manganese oxide cathode material of the present invention can also be further doped with sodium ions and fluoride ions to improve the rate performance and cycling performance of the material.

[0006] The present invention also provides a method for preparing a lithium-rich layered lithium manganese oxide cathode material.

[0007] The present invention also provides a lithium-ion battery.

[0008] The present invention also proposes the application of the above-mentioned cathode material.

[0009] In a first aspect of the present invention, there is provided a lithium-rich layered lithium manganese oxide cathode material, and the chemical formula of the lithium-rich layered lithium manganese oxide cathode material is Li 2-x Na y MnO 3-z F z ;

[0010] wherein, 0.02 ≤ x ≤ 0.1, 0 ≤ y ≤ 0.08, 0 ≤ z ≤ 0.08.

[0011] According to a specific embodiment of the present invention, in the lithium-rich layered lithium manganese oxide cathode material provided by the present invention, an appropriate proportion of lithium vacancies is contained, and the magnitude of the x value represents the content of lithium vacancies. These lithium vacancies can activate anion redox, and the amount of charge given by oxygen ions to metal cations decreases (after introducing lithium vacancies, the amount of charge on oxygen ions increases. The specific reason is that in the anion-cation pairing, the anion gives electrons, and after introducing vacancies, the anion does not need to give electrons, and the amount of charge on the anion is more). During the charge-discharge reaction process, the amount of charge that can participate in redox increases, thereby increasing the discharge capacity.

[0012] According to some embodiments of the present invention, in the chemical formula, 0.04 ≤ x ≤ 0.08.

[0013] Through exploration, the present invention can activate more anions to participate in the reaction and contribute to the capacity while avoiding the capacity loss caused by the reduction of active lithium in the material being greater than the capacity contributed by the activated anions by controlling the content of lithium vacancies in the material within a more preferred range, so that the cathode material of the present invention has the best capacity performance.

[0014] According to some embodiments of the present invention, in the chemical formula, 0.03 ≤ y ≤ 0.07.

[0015] The present invention improves the rate performance of the material by doping an appropriate content of Na element into the lithium-rich layered lithium manganese oxide cathode material. Since the radius of the sodium ion is larger than that of the lithium ion, the presence of sodium ions can widen the lithium layer spacing of the lithium-rich layered lithium manganese oxide. When lithium ions migrate inside the material, affected by the steric hindrance effect, the widened layer spacing reduces the resistance encountered by lithium ions during migration, thereby improving the rate performance of the material.

[0016] According to some embodiments of the present invention, in the chemical formula, 0.04 ≤ y ≤ 0.06.

[0017] According to some embodiments of the present invention, in the chemical formula, 0.03 ≤ z ≤ 0.07.

[0018] The present invention also improves the cycle stability of the material by doping an appropriate content of F element into the lithium-rich layered lithium manganese oxide cathode material. Since the electronegativity of the fluoride ion is greater than that of the oxygen ion, the manganese-fluorine bond is more stable than the manganese-oxygen bond and is not easily broken. Therefore, manganese ions do not dissolve in the electrolyte, thereby improving the stability of the material during the charge-discharge cycle.

[0019] According to some embodiments of the present invention, in the chemical formula, 0.04 ≤ z ≤ 0.06.

[0020] The present invention conducts co-doping of Na and F in the lithium-rich layered lithium manganese oxide cathode material. The two act synergistically on the lithium-rich layered lithium manganese oxide, avoiding the decline of the cycle stability and capacity of the cathode material, and improving the comprehensive performance of the cathode material and the lithium battery prepared therefrom.

[0021] In the second aspect of the present invention, there is provided a method for preparing a lithium-rich layered lithium manganese oxide cathode material as described in the first aspect of the present invention, comprising the following steps:

[0022] S1. Weigh the lithium source, manganese source, sodium source, and fluorine source compounds according to the molar ratio of the chemical formula, make them into a slurry and grind it;

[0023] S2. Dry the slurry after ball milling and calcine it to obtain the lithium-rich layered lithium manganese oxide cathode material.

[0024] According to the specific embodiments of the present invention, the preparation method provided by the present invention has at least the following beneficial effects: The preparation method of the lithium-rich layered lithium manganese oxide cathode material provided by the present invention can prepare the lithium-rich layered lithium manganese oxide cathode material product described in the first aspect of the present invention. Therefore, this preparation method also includes the aforementioned advantages of the lithium-rich layered lithium manganese oxide cathode material of the present invention. In addition, in the process of material synthesis of the present invention, only simple methods such as pulping, grinding and calcination are required. Compared with the three common synthesis methods of traditional co-precipitation-hydrothermal-calcination three-step method, sol-gel method and low-temperature molten salt method, this method has lower production costs, higher production efficiency and is easier to realize industrial production.

[0025] The lithium vacancy in the lithium-rich material prepared by the present invention, that is, the degree of lithium deficiency of the material. The present invention adjusts the dosage of raw materials, starting from the dosage of the lithium source, and obtains a lithium-deficient lithium-rich material by adjusting the degree of lithium deficiency in the lithium-rich material.

[0026] According to some embodiments of the present invention, the lithium source includes at least one of lithium carbonate or lithium hydroxide.

[0027] According to some embodiments of the present invention, the manganese source includes at least one of manganese oxide or manganese carbonate.

[0028] According to some embodiments of the present invention, the sodium source includes at least one of sodium carbonate, sodium fluoride or sodium hydroxide.

[0029] According to some embodiments of the present invention, the fluorine source includes at least one of sodium fluoride or lithium fluoride.

[0030] According to some embodiments of the present invention, the slurry is made of absolute ethanol.

[0031] According to some embodiments of the present invention, the grinding is ball milling in a ball mill for 4 to 8 hours.

[0032] According to some embodiments of the present invention, the temperature of the calcination is 600 to 800 °C and the time is 10 to 15 hours.

[0033] According to some embodiments of the present invention, the temperature of the calcination is raised to 600 to 800 °C at a heating rate of 3 to 7 °C / min.

[0034] According to some embodiments of the present invention, the material obtained after the calcination is also subjected to deionized water washing and separation drying treatment.

[0035] In the third aspect of the present invention, a lithium-ion battery is provided, and the positive electrode of the lithium-ion battery includes the lithium-rich layered lithium manganese oxide cathode material described in the first aspect of the present invention.

[0036] According to some embodiments of the present invention, the positive electrode further includes a conductive agent, a binder, and a positive electrode current collector.

[0037] In a fourth aspect of the present invention, there is provided an application of the lithium-rich layered lithium manganese oxide positive electrode material as described in the first aspect of the present invention in battery preparation.

[0038] Other features and advantages of the present invention will be set forth in the following description, and in part will be obvious from the description, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The present invention will be further described below with reference to the accompanying drawings and examples, where:

[0040] Figure 1 is a schematic structural diagram of the positive electrode material of Example 8 of the present invention;

[0041] Figure 2 is an XDR diffraction pattern of the positive electrode materials of Example 9 and Comparative Example 1 of the present invention;

[0042] Figure 3 is a first charge-discharge curve graph of the secondary battery prepared from the positive electrode material of Example 11 of the present invention;

[0043] Figure 4 is a first charge-discharge curve graph of the secondary battery prepared from the positive electrode material of Comparative Example 1 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0044] The concept of the present invention and the technical effects produced will be clearly and completely described below in conjunction with the embodiments to fully understand the purpose, features, and effects of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0045] For those conditions not specified in the examples, they are carried out according to conventional conditions or conditions recommended by the manufacturer. For reagents or instruments whose manufacturers are not specified, they are all conventional products that can be obtained through commercial purchase.

[0046] Example 1

[0047] This example provides a positive electrode material with the chemical formula Li 1.98 MnO3, where the material can achieve charge balance by losing trace amounts of oxygen anions.

[0048] This example also provides a preparation method for the positive electrode material, and the specific steps are as follows:

[0049] 1) Weigh Li2CO3 and MnO2 according to a molar ratio of 0.99:1. After grinding them evenly, add anhydrous ethanol to make a slurry. Add the slurry to a ball mill tank with a ball-to-material mass ratio of 7:1. The sizes of the zirconia beads used for ball milling are 20 mm, 10 mm, and 6 mm, and the mass ratio of large, medium, and small balls is 2:1:1. The volume of large, medium, and small balls does not exceed 80% of the volume of the ball mill tank. Put it into a ball mill and run the ball milling at a speed of 450 rpm for 6 hours;

[0050] 2) Take out the ball-milled slurry and dry it in a forced-air oven at 80 °C. Transfer the dried material to a corundum crucible and place it in a tube furnace. Set the temperature to rise to 700 °C at a rate of 5 °C / min and keep the temperature for calcination for 12 hours;

[0051] 3) Wash the impurities from the calcined material with deionized water, perform solid-liquid separation by high-speed centrifugation, and dry it to obtain the positive electrode material.

[0052] Example 2

[0053] This example provides a positive electrode material with the chemical formula Li 1.96 MnO3.

[0054] This example also provides a preparation method for this positive electrode material. The difference from Example 1 is that in step 1) of this example, Li2CO3 and MnO2 are weighed according to a molar ratio of 0.98:1, and the remaining steps are the same as those in Example 1.

[0055] Example 3

[0056] This example provides a positive electrode material with the chemical formula Li 1.94 MnO3.

[0057] This example also provides a preparation method for this positive electrode material. The difference from Example 1 is that in step 1) of this example, Li2CO3 and MnO2 are weighed according to a molar ratio of 0.97:1, and the remaining steps are the same as those in Example 1.

[0058] Example 4

[0059] This example provides a positive electrode material with the chemical formula Li 1.92 MnO3.

[0060] This example also provides a preparation method for this positive electrode material. The difference from Example 1 is that in step 1) of this example, Li2CO3 and MnO2 are weighed according to a molar ratio of 0.96:1, and the remaining steps are the same as those in Example 1.

[0061] Example 5

[0062] This example provides a positive electrode material with the chemical formula Li 1.98 Na0.03 MnO3。

[0063] This embodiment also provides a preparation method of the positive electrode material, and the specific steps are as follows:

[0064] 1) Weigh Li2CO3, MnO2 and Na2CO3 according to the molar ratio of 0.99:1:0.015. After grinding evenly, add anhydrous ethanol to make a slurry. Add the slurry to a ball milling tank and put it into a ball mill, and run the ball mill at a speed of 450 rpm for 6 hours;

[0065] 2) Take out the ball-milled slurry, dry it in a blast drying oven at 80 °C. Transfer the dried material to a corundum crucible, place it in a tube furnace, set the temperature to rise to 700 °C at a rate of 5 °C / min, and keep the temperature for calcination for 12 hours;

[0066] 3) Wash the impurities of the calcined material with deionized water, separate the solid and liquid by high-speed centrifugation, and dry to obtain the positive electrode material.

[0067] Example 6

[0068] This embodiment provides a positive electrode material with the chemical formula Li 1.98 Na 0.05 MnO3。

[0069] This embodiment also provides a preparation method of the positive electrode material. The difference from Example 5 is that in step 1) of this embodiment, Li2CO3, MnO2 and Na2CO3 are weighed according to the molar ratio of 0.99:1:0.025, and the other steps are the same as those in Example 5.

[0070] Example 7

[0071] This embodiment provides a positive electrode material with the chemical formula Li 1.98 Na 0.07 MnO3。

[0072] This embodiment also provides a preparation method of the positive electrode material. The difference from Example 5 is that in step 1) of this embodiment, Li2CO3, MnO2 and Na2CO3 are weighed according to the molar ratio of 0.99:1:0.035, and the other steps are the same as those in Example 5.

[0073] Example 8

[0074] This embodiment provides a positive electrode material with the chemical formula Li 1.98 Na 0.05 MnO 2.97 F 0.03 。The structural schematic diagram of this material is as Figure 1As shown, among them, the yellow atoms are F atoms substituting for the red O atoms, the white atoms are Li vacancies, the purple atoms are Na atoms substituting for the green Li atoms, and the blue atoms are Mn atoms.

[0075] This embodiment also provides a preparation method for this cathode material, and the specific steps are as follows:

[0076] 1) Weigh Li2CO3, MnO2, Na2CO3, and LiF according to a molar ratio of 0.975:1:0.025:0.03. After grinding evenly, add anhydrous ethanol to make a slurry. Add the slurry to a ball milling tank and put it into a ball mill, and run the ball mill at a speed of 450 rpm for 6 hours;

[0077] 2) Take out the ball-milled slurry, dry it in a blast drying oven at 80 °C. Transfer the dried material to a corundum crucible, place it in a tube furnace, set the temperature to rise to 700 °C at a rate of 5 °C / min, and keep the temperature for calcination for 12 hours;

[0078] 3) Wash the impurities from the calcined material with deionized water, separate the solid and liquid by centrifugation in a high-speed centrifuge, and dry it to obtain the cathode material.

[0079] Example 9

[0080] This embodiment provides a cathode material with the chemical formula Li 1.98 Na 0.05 MnO 2.95 F 0.05 .

[0081] This embodiment also provides a preparation method for this cathode material. The difference from Example 8 is that in step 1) of this embodiment, Li2CO3, MnO2, Na2CO3, and LiF are weighed according to a molar ratio of 0.965:1:0.025:0.05, and the remaining steps are the same as those in Example 8.

[0082] Example 10

[0083] This embodiment provides a cathode material with the chemical formula Li 1.98 Na 0.05 MnO 2.93 F 0.07 .

[0084] This embodiment also provides a preparation method for this cathode material. The difference from Example 8 is that in step 1) of this embodiment, Li2CO3, MnO2, Na2CO3, and LiF are weighed according to a molar ratio of 0.955:1:0.025:0.07, and the remaining steps are the same as those in Example 8.

[0085] Example 11

[0086] This embodiment provides a cathode material with the chemical formula Li 1.94 Na 0.05 MnO 2.95 F 0.05 .

[0087] This embodiment also provides a method for preparing the cathode material. The difference from Example 8 is that in step 1) of this embodiment, Li2CO3, MnO2, Na2CO3, and LiF are weighed according to a molar ratio of 0.945:1:0.025:0.05, and the remaining steps are the same as those in Example 8.

[0088] Comparative Example 1

[0089] This comparative example provides a cathode material with the chemical formula Li2MnO3.

[0090] This comparative example also provides a method for preparing the cathode material. The specific steps are as follows:

[0091] 1) Weigh Li2CO3 and MnO2 according to a molar ratio of 1:1. After grinding evenly, add anhydrous ethanol to make a slurry. Add the slurry to a ball mill tank and put it into a ball mill, and run the ball mill at a speed of 450 rpm for 6 h;

[0092] 2) Take out the ball-milled slurry, dry it in a blast drying oven at 80 °C. Transfer the dried material to a corundum crucible, place it in a tubular furnace, set the temperature to rise to 700 °C at a rate of 5 °C / min, and keep the temperature for calcination for 12 h;

[0093] 3) Wash the calcined material with deionized water to remove impurities, separate the solid and liquid by high-speed centrifugation, and dry it to obtain the cathode material.

[0094] Comparative Example 2

[0095] This comparative example provides a cathode material with the chemical formula Li2Na 0.05 MnO3, and each 1 mol of the material contains 0.05 mol of sodium ions.

[0096] This comparative example also provides a method for preparing the cathode material. The difference from Comparative Example 1 is that in step 1) of this comparative example, Li2CO3, MnO2, and Na2CO3 are weighed according to a molar ratio of 1:1:0.025, and the remaining steps are the same as those in Comparative Example 1.

[0097] Comparative Example 3

[0098] This comparative example provides a cathode material with the chemical formula Li2MnO 2.95 F 0.05 , and each 1 mol of the material contains 0.05 mol of fluoride ions.

[0099] This comparative example also provides a method for preparing the positive electrode material. The difference from Comparative Example 1 is that in step 1) of this comparative example, Li2CO3, MnO2, and LiF are weighed according to a molar ratio of 0.975:1:0.05, and the remaining steps are the same as those in Comparative Example 1.

[0100] Application Example 1

[0101] This application example provides a lithium-ion secondary battery prepared using the positive electrode material of Example 1. The specific steps are as follows:

[0102] 1) The positive electrode material of Example 1, the conductive agent acetylene black (SP), and the binder polyvinylidene fluoride (PVDF) are fully stirred and mixed evenly in an N-methylpyrrolidone solvent system according to a mass ratio of 90:5:5, and then coated on the positive electrode current collector aluminum foil. After drying and cold pressing, a positive electrode plate is obtained.

[0103] 2) A circular positive electrode plate with a diameter of 15.8 mm is punched out from the positive electrode plate. A lithium sheet is selected as the negative electrode plate, a polyethylene (PE) porous polymer film is used as the separator, and the electrolyte is 1.0 mol / L LiPF6 / ethylene carbonate (EC) / dimethyl carbonate (DMC)+ethyl methyl carbonate (EMC), and the volume ratio of EC:DMC:EMC is 1:1:1. A CR2032 button secondary battery is assembled.

[0104] Application Examples 2 - 11

[0105] The positive electrode materials of Examples 2 - 11 are respectively used, and lithium-ion secondary batteries of Application Examples 2 - 11 are prepared according to the method of Application Example 1.

[0106] Application Comparative Examples 1 - 3

[0107] The positive electrode materials of Comparative Examples 1 - 3 are respectively used, and lithium-ion secondary batteries of Application Comparative Examples 1 - 3 are prepared according to the method of Application Example 1.

[0108] Performance Test:

[0109] 1. XRD Test:

[0110] The positive electrode materials obtained in Example 9 and Comparative Example 1 are subjected to X-ray diffraction (XRD) test. The equipment used for the XRD test of the present invention is D8 ADVANCE of BRUKER Corporation. Test conditions: Cu target (2.2 kw) is used as the anode target material; the scanning speed for qualitative analysis is 5.0° / min.

[0111] The XRD test results are as Figure 2As shown in the figure, by comparing the XRD diffraction patterns of the cathode materials of Example 9 and Comparative Example 1, it can be seen that the main peak of the Na-doped lithium-rich layered manganese oxide shifts to the left. One peak in the figure represents one crystal plane. The (003) peak is the characteristic peak of the lithium layer in the layered material, representing that the lithium layer crystal plane is the main peak in the test. Shifting to the left means that the lithium layer spacing becomes larger. After the lithium layer lacks lithium ions, its layer spacing will expand (lacking some cations to bind anions), thus verifying the existence of lithium vacancies in the lithium-rich cathode material prepared by the method of the present invention.

[0112] 2. Inductively coupled plasma atomic emission spectrometry (ICP-OES) test:

[0113] The cathode materials obtained in Example 1, Examples 5-7 and Comparative Example 1 were subjected to ICP-OES test to characterize the sodium element content in the materials. ICP-OES can perform qualitative and quantitative test analysis on the main, secondary, and trace element components in solids, liquids, and gases. The instrument used in the present invention is Optima8300 type / PerkinElmer.

[0114] Taking deionized water as a comparison sample to exclude the influence of Na ion concentration in life. Taking Comparative Example 1 as an example, the specific normalization calculation method is as follows: Taking Mn as 1, the stoichiometric number of Li element in the chemical formula = (4.1219 / 6.961 (molar mass of lithium atom)) × (1 / (16.1181 / 54.938 (molar mass of manganese atom))) ≈ 2.01. Then, according to the ICP-OES results, the actual chemical formula of the cathode material in Comparative Example 1 is Li 2.01 MnO3. It can be determined by ICP-OES test that the synthesized material conforms to the theoretical design chemical formula. The complete test and calculation results are shown in Table 1.

[0115] Table 1 ICP-OES test results

[0116]

[0117] 3. Capacity test:

[0118] Test temperature: room temperature 25°C, voltage window: 2 - 4.8V (lithium-rich cathode material), theoretical capacity current density: 1C = 300mA (that is, the current value that completely discharges the theoretical capacity within 1 hour). The secondary batteries applying Examples 1-4 and Comparative Example 1 were charged at a constant current of 0.1C to 4.8V and discharged at a constant current of 0.1C to 2V. The obtained discharge capacity is the actual capacity. The test results are shown in Table 2.

[0119] Table 2 Capacity test results of the cathode materials of Examples 1-4 and Comparative Example 1

[0120] Secondary battery Chemical formula of the positive electrode material Actual capacity of the material at 0.1C (mAh / g) Application Example 1 <![CDATA[Li 1.98 MnO3]]> 232 Application Example 2 <![CDATA[Li 1.96 MnO3]]> 241 Application Example 3 <![CDATA[Li 1.94 MnO3]]> 251 Application Example 4 <![CDATA[Li 1.92 MnO3]]> 249 Application Comparative Example 1 <![CDATA[Li 2.0 MnO3]]> 195

[0121] From the above test results, it can be seen that the lithium-rich layered lithium manganate containing lithium vacancies has a higher capacity. It is speculated that this is because more anions are activated to participate in the reaction and contribute to the capacity. However, the capacity of Example 4 is slightly lower than that of Example 3. It is speculated that this is because the capacity loss caused by the reduction of active lithium in the material is greater than the capacity contributed by the anions participating in the reaction. Based on this test result, the lithium-rich cathode material prepared by the solution of the present invention preferably contains 0.04 to 0.08 mol of lithium vacancies per 1 mol of the material.

[0122] 4. Rate performance test:

[0123] The secondary batteries of Application Examples 1, 5 to 7 and Application Comparative Example 1 were charged at a constant current of 0.2C and then discharged at 0.2C, 0.5C, 1C and 2C respectively, and the discharge capacities at different rates were collected. (The discharge capacities here are all discharge specific capacities, and the specific capacity = actual discharge capacity / weight of the active material on the positive electrode sheet). The test results are shown in Table 3.

[0124] Table 3 Rate performance test results of the positive electrode materials of Examples 1, 5 to 7 and Comparative Example 1

[0125]

[0126] From the above test results, it can be seen that the battery polarization increases under high current, and the polarization can be reduced and the capacity can be increased by improving the ion migration ability. By comparing Examples 1, 5 to 7 with Comparative Example 1, it can be known that the lithium-rich layered lithium manganate with Na ions in the lithium layer has a larger capacity at high discharge rates, indicating that its lithium ion migration ability is stronger. It is speculated that this is because the Na ions widen the lithium layer spacing. However, as the content of Na ions increases, the rate performance decreases. This is because the ability of Na ions to widen the layer spacing is limited, and too many Na ions will instead have a certain blocking effect on the lithium ion migration path.

[0127] 5. Cycle performance test

[0128] The secondary batteries obtained from Application Example 6, 8 to 10 and Application Comparative Example 1 were charged to 4.8V at a current of 0.2C at 25°C, and the discharge capacity obtained by discharging at a current of 0.2C to 2V was the first discharge capacity, and then 100 charge-discharge cycles were carried out, and the discharge capacity of the 100th time was recorded. The test results are shown in Table 4.

[0129] Table 4 Cycle performance test results of the positive electrode materials of Examples 6, 8 to 10 and Comparative Example 1

[0130]

[0131] From the above test results, it can be seen that the material with lithium vacancies in lithium-rich layered lithium manganate has relatively high activity, but its cycling stability decreases slightly. After F substitutes O to form Mn-F bonds with manganese, the cycling stability of the material increases, which benefits from the more stable Mn-F bonds that can inhibit Mn dissolution. In Application Example 10, the stability of the battery made of the material with a high F content also decreases. It is speculated that as the F content increases, the Mn valence state will decrease, which will produce the Jahn-Teller effect, and the Jahn-Teller effect will cause crystal structure distortion, which is not conducive to structural stability.

[0132] The secondary batteries obtained from Test Example 11 and Comparative Examples 1 to 3 were tested, and their comprehensive performances were compared, as shown in Table 5.

[0133] Table 5 Comprehensive performances of the cathode materials of Example 11 and Comparative Examples 1 to 3

[0134]

[0135]

[0136] From the above test results, it can be seen that after lithium-rich layered lithium manganate is only doped with Na ions, the rate performance of the material is improved, but its cycling stability is reduced. After only doping with F ions, the cycling performance of the material is improved, but the discharge capacity is reduced. By using the solution of the present invention, after introducing lithium vacancies and doping with Na and F in lithium-rich layered lithium manganate, both the capacity and stability of the material are significantly improved, achieving the optimal comprehensive performance.

[0137] 6. Calculation of the theoretical charge amount of anions:

[0138] An atomic structure containing lithium vacancies was constructed, and Bader charge calculations were performed using the VASP software to quantify the influence of lithium vacancies on the charge amount of nearby anions. The results are shown in Table 6.

[0139] Table 6

[0140] Average charge amount of oxygen ions without lithium vacancies Average charge amount of oxygen ions with lithium vacancies 6.9878 7.1258

[0141] From the above calculation results, it can be seen that after introducing lithium vacancies, the charge amount on oxygen ions increases, and the charge amount that can participate in redox reactions during the charge-discharge reaction increases, which can contribute more discharge capacity.

[0142] 7. First charge-discharge performance test:

[0143] The secondary batteries obtained from Example 11 and Comparative Example 1 were subjected to the first charge-discharge test, and their first charge-discharge curves are respectively as Figure 3 and Figure 4As shown. Among them, the first charge efficiency of the secondary battery prepared from the positive electrode material of Example 11 reaches 95%, while that of Comparative Example 1 is 85%. The secondary battery prepared using the positive electrode material of the solution of the present invention has significantly better first charge and discharge performance.

[0144] In summary, the positive electrode material provided by the invention has higher capacity, better structural stability and electrochemical performance. Among them, lithium vacancies can effectively improve the activity of the material and increase the capacity; sodium ions can broaden the ion migration channels, promote the migration of lithium ions inside the material, and improve the rate performance; the introduction of fluoride ions inhibits the dissolution of manganese ions and improves the structural stability of the material. The present invention combines the introduction of lithium vacancies and the doping of Na and F ions, which can further improve the comprehensive performance of the positive electrode material and the prepared secondary battery, further improve the performance of the lithium-rich layered lithium manganate material, and meet the current requirements for higher-performance lithium-ion batteries.

[0145] The above has described the embodiments of the present invention in detail, but the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those of ordinary skill in the art, various changes can be made without departing from the spirit of the present invention. In addition, the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

Claims

1. A lithium-rich layered lithium manganese oxide cathode material, characterized in that, The chemical formula of the lithium-rich layered lithium manganese oxide cathode material is Li 2-x Na y MnO 3-z F z ; Among them, 0.02 ≤ x ≤ 0.1, 0 ≤ y ≤ 0.08, 0 ≤ z ≤ 0.

08.

2. The lithium-rich layered lithium manganese oxide cathode material according to claim 1, characterized in that, In the chemical formula, 0.04 ≤ x ≤ 0.

08.

3. The lithium-rich layered lithium manganese oxide cathode material according to claim 1, wherein In the chemical formula, 0.03 ≤ y ≤ 0.

07.

4. The lithium-rich layered lithium manganese oxide cathode material according to claim 1, characterized in that, In the chemical formula, 0.03 ≤ z ≤ 0.

07.

5. A method for preparing a lithium-rich layered lithium manganese oxide cathode material according to any one of claims 1 to 4, characterized in that, It includes the following steps: S1. Weigh lithium source, manganese source, sodium source and fluorine source compounds according to the molar ratio of the chemical formula, make them into a slurry and grind it. S2. Dry the slurry after ball milling and calcine it to obtain the lithium-rich layered lithium manganese oxide cathode material.

6. The preparation method according to claim 5, wherein, The lithium source includes at least one of lithium carbonate or lithium hydroxide; and / or, the manganese source includes at least one of manganese oxide or manganese carbonate; and / or, the sodium source includes at least one of sodium carbonate, sodium fluoride or sodium hydroxide; and / or, the fluorine source includes at least one of sodium fluoride or lithium fluoride.

7. The preparation method according to claim 5, characterized in that, The grinding is ball milling in a ball mill for 4 - 8 h.

8. The preparation method according to claim 5, characterized in that, The temperature of the calcination is 600 - 800 °C and the time is 10 - 15 h.

9. A lithium-ion battery, characterized in that, The cathode of the lithium ion battery includes the lithium-rich layered lithium manganese oxide cathode material according to any one of claims 1 - 4.

10. Use of the lithium-rich layered lithium manganese oxide cathode material according to any one of claims 1 - 4 in battery preparation.

Images