O2-phase lithium cobalt oxide as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of lithium ion batteries. The invention provides O2-phase lithium cobalt oxide as well as a preparation method and application thereof.According to the preparation method, Na < + > and Li < + > are subjected to ion exchange in a solution by using a liquid-phase ion exchange reaction so as to ensure that O2-phase lithium cobalt oxide is generated, and O2-phase lithium cobalt oxide can be obtained by controlling the reaction; for example, the interlayer spacing of the (002) crystal face of P2-phase sodium cobaltate is influenced by controlling the Na / Co ratio and the sintering temperature during P2-phase sodium cobaltate synthesis, or the adjustment of the O2-phase lithium cobaltate interplanar spacing is realized by controlling at least one of the temperature and the time of a liquid-phase ion exchange reaction, so that the optimization of the structure is realized. Therefore, high capacity, high magnification and excellent cycle performance are obtained at the same time.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion batteries, and relates to O2 phase lithium cobaltate and a preparation method and application thereof. BACKGROUND

[0002] At present, as a positive active material, lithium cobaltate (LiCoO2) has occupied a dominant position in the application of 3C consumer electronic products, which is mainly due to its high specific capacity, stable high discharge platform and excellent compaction density and other characteristics. With the continuous trend of light and thin, miniaturization of electronic devices, the market puts forward higher requirements for the energy density and cycle stability of the battery.

[0003] The strategy for improving the energy density of lithium ion batteries mainly includes developing active materials with higher specific capacity, improving the compaction density of the material, and improving the working voltage. Among them, improving the working voltage is considered to be the most direct and effective. In theory, when the charge cut-off voltage exceeds 4.4V, the degree of delithiation inside the lithium cobaltate material is enhanced, and more active lithium ions (Li + ) can participate in the deintercalation process of the electrochemical reaction, thereby significantly improving the actual gram capacity of the material.

[0004] However, under high voltage environment, lithium cobaltate material is extremely susceptible to irreversible phase transition of structure, which easily leads to the destruction of its original crystal structure. At the same time, the interface side reaction increases significantly, which not only affects the stability and safety of the material, but also accelerates the capacity decay of the battery, seriously restricting its long-term cycle performance.

[0005] Under this background, researchers turn their attention to lithium cobaltate materials with O2 phase structure. Compared with the traditional O3 phase structure, O2 phase lithium cobaltate has a higher theoretical gram capacity and better rate performance. However, in fact, the O2 phase lithium cobaltate synthesized at present has only made significant progress in initial capacity and charge-discharge rate, and its cycle stability is still poor, which is a problem to be solved by those skilled in the art. SUMMARY

[0006] In view of the problems in the prior art, the purpose of the present application is to provide O2 phase lithium cobaltate and a preparation method and application thereof. The preparation method comprises mixing P2 phase sodium cobaltate with a lithium source, and performing a liquid phase ion exchange reaction to obtain O2 phase lithium cobaltate. Through the liquid phase ion exchange reaction, pure O2 phase lithium cobaltate with high capacity, high rate and excellent cycle performance can be obtained.

[0007] To achieve this purpose, the technical scheme adopted by the present application is as follows:

[0008] In a first aspect, the present application provides a preparation method of O2 phase lithium cobaltate, which comprises mixing P2 phase sodium cobaltate with a lithium source to perform a liquid phase ion exchange reaction to obtain O2 phase lithium cobaltate.

[0009] The preparation method of the present application realizes the ion exchange of Na + and Li + in solution by using a liquid phase ion exchange reaction, so as to ensure the generation of O2 phase lithium cobaltate and enable the O2 phase lithium cobaltate to have high capacity, high rate and excellent cycle performance at the same time by controlling the reaction.

[0010] The following is a preferred technical solution of the present application, but is not a limitation of the technical solution provided by the present application. The technical purpose and beneficial effects of the present application can be better achieved and realized by the following technical solution.

[0011] As a preferred technical solution of the present application, the P2 phase sodium cobaltate comprises Na x CoO2, 0.6≤x≤0.8, for example, 0.6, 0.62, 0.64, 0.66, 0.68, 0.7, 0.72, 0.74, 0.76, 0.78 or 0.8, preferably 0.7≤x≤0.78, and further preferably 0.7≤x≤0.74.

[0012] In the present application, the O2 phase lithium cobaltate is generated by using a liquid phase ion exchange method to perform ion exchange reaction of Na + and Li + in solution in the P2 phase sodium cobaltate, so that the present application can adjust the interlayer spacing of the P2 phase sodium cobaltate by setting different Na / Co ratios in the P2 phase sodium cobaltate, and then indirectly affect the interlayer spacing of the O2 phase structure of the lithium cobaltate, so as to realize the optimization and modification of the performance of the O2 phase lithium cobaltate.

[0013] The present application finds that when the interlayer spacing of the (002) crystal plane of the P2 phase sodium cobaltate is controlled to be for example,

[0014] or , preferably , and further preferably , the obtained O2 phase lithium cobaltate has excellent modification effect and can have high capacity, high rate and excellent cycle performance at the same time.

[0015] As a preferred technical solution of the present application, the method for preparing the P2 phase sodium cobaltate comprises mixing a cobalt source with a sodium source to perform sintering to obtain the P2 phase sodium cobaltate.

[0016] As a preferred technical solution of the present invention, the amount of sodium source and cobalt source is controlled according to the molar ratio of sodium to cobalt as (0.6-0.8):1, for example, 0.6:1, 0.62:1, 0.64:1, 0.66:1, 0.68:1, 0.7:1, 0.72:1, 0.74:1, 0.76:1, 0.78:1 or 0.8:1, etc., preferably (0.7-0.78):1, and more preferably (0.7-0.74):1.

[0017] In this invention, the molar ratio of sodium to cobalt in the sodium source and the cobalt source represents the value of x in the chemical formula of sodium cobaltate in the P2 phase.

[0018] Preferably, the cobalt source includes cobalt oxide, and more preferably cobalt tetroxide.

[0019] Preferably, the sodium source includes sodium carbonate.

[0020] As a preferred technical solution of the present invention, the method for preparing the P2 phase sodium cobaltate further includes mixing a non-cobalt transition metal source with the cobalt source and the sodium source, and then performing the sintering.

[0021] Preferably, the non-cobalt transition metal source includes at least one of the transition metal elements Al, Mg, Ni, or Mn.

[0022] Preferably, the non-cobalt transition metal source includes oxides of the corresponding elements.

[0023] Preferably, the amount of the non-cobalt transition metal source and the cobalt source is controlled according to the molar ratio of the non-cobalt transition metal element to the cobalt element as (0 to 0.06):1, for example, 0 (i.e., no non-cobalt transition metal source is used), 0.01:1, 0.015:1, 0.02:1, 0.025:1, 0.03:1, 0.035:1, 0.04:1, 0.045:1, 0.05:1, 0.055:1, or 0.06:1, etc.

[0024] As a preferred embodiment of the present invention, the sintering temperature is 600–1000℃, such as 600℃, 630℃, 660℃, 680℃, 700℃, 730℃, 750℃, 780℃, 800℃, 830℃, 850℃, 880℃, 900℃, 930℃, 950℃, 980℃, or 1000℃, preferably 750–950℃, and more preferably 830–870℃, and the time is 6–24h, such as 6h, 8h, 10h, 12h, 14h, 16h, 18h, 20h, 22h, or 24h.

[0025] In this invention, in addition to controlling the Na / Co ratio, the interlayer spacing of the P2 phase sodium cobaltate can also be adjusted by adjusting different sintering temperatures. Within the preferred range, increasing the sintering temperature of the P2 phase sodium cobaltate causes the (002) characteristic peak of the P2 phase sodium cobaltate to shift to a lower angle, which means that the interlayer spacing of the (002) crystal plane becomes larger.

[0026] It should be noted that if the sintering temperature is too low in this invention, the sodium synthesis of the sample will be incomplete. Unreacted sodium source residue on the surface will greatly increase the impedance of the material, leading to poor performance of the synthesized cathode material Na. + The diffusion barrier increases during migration; and excessively high sintering temperature causes severe volatilization of the sodium source during calcination, resulting in insufficient sodium source for the material to be fully sodaified, leading to a decrease in the specific capacity during the first charge and discharge.

[0027] As a preferred technical solution of the present invention, the amount of sodium cobaltate and lithium source in the P2 phase is controlled according to a molar ratio of sodium to lithium of 1:(10-30), such as 1:10, 1:12, 1:14, 1:16, 1:18, 1:20, 1:22, 1:24, 1:26, 1:28 or 1:30, etc., but not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0028] Preferably, the lithium source includes at least one of lithium hydroxide, lithium carbonate, or lithium chloride. A mixture of lithium hydroxide and lithium chloride is preferred.

[0029] Preferably, the P2 phase sodium cobaltate is mixed with a lithium source in water to prepare a solution, and then the liquid-phase ion exchange reaction is carried out.

[0030] Preferably, the total concentration of the P2 phase sodium cobaltate and lithium source in the solution is 4 to 6 mol / L, such as 4 mol / L, 4.2 mol / L, 4.4 mol / L, 4.6 mol / L, 4.8 mol / L, 5 mol / L, 5.2 mol / L, 5.4 mol / L, 5.6 mol / L, 5.8 mol / L, or 6 mol / L.

[0031] As a preferred embodiment of the present invention, the temperature of the liquid-phase ion exchange reaction is ≥80℃, for example, 70℃, 73℃, 75℃, 78℃, 80℃, 83℃, 85℃, 88℃, 90℃, 93℃, 95℃ or 98℃, preferably 80~98℃, more preferably 88~95℃; the time is ≥4h, for example, 4h, 6h, 8h, 10h, 12h, 16h, 18h, 20h, 22h, 24h, 26h, 28h, 30h, 32h, 34h, 36h, 38h, 40h, 42h, 44h, 46h, 48h, 50h, 52h, 54h, 56h, 58h, 60h, 62h, 64h, 66h, 68h, 70h or 72h, preferably 12~36h, more preferably 20~28h.

[0032] This invention can directly adjust the interlayer spacing of the obtained O2 phase lithium cobalt oxide by controlling the temperature and reaction time of the liquid phase ion exchange reaction, thereby directly optimizing the structure of the O2 phase lithium cobalt oxide, so that the modified lithium cobalt oxide material has high capacity, high rate and excellent cycle performance.

[0033] In this invention, the interlayer spacing of the (002) characteristic peak of the P2 phase sodium cobalt oxide can be controlled by adjusting the temperature or reaction time of the liquid phase ion exchange reaction. It is preferable to control the interlayer spacing of the (002) crystal plane of the O2 phase lithium cobalt oxide to be 0.47-0.5 nm, such as 0.471 nm, 0.472 nm, 0.473 nm, 0.474 nm, 0.475 nm, 0.476 nm, 0.477 nm, 0.478 nm, 0.479 nm or 0.48 nm, etc., preferably 0.472-0.482 nm, and more preferably 0.472-0.480 nm.

[0034] It should also be noted that, compared to solid-phase ion exchange reactions, which readily yield mixed-phase lithium cobalt oxide (such as a mixture of at least two of the T2, O2, or O3 phases), the liquid-phase ion exchange reaction used in this invention at low temperatures ensures that the product obtained is a pure O2 phase, rather than a mixed O2 / O3 phase. This is because the conversion temperature (the temperature of the liquid-phase ion exchange reaction) is lower than the conversion conditions for O2 to O3. Typically, solid-phase ion exchange reactions require reaction temperatures above 280°C. While high-temperature reactions can increase the Li / Co ratio to some extent, thus increasing its capacity, excessively high temperatures can cause lithium cobalt oxide converted to the O2 phase to revert to the O3 phase. For example, the characteristic peaks of the O3 phase are often easily observed in the XRD patterns of products from solid-phase ion exchange reactions at 300°C. Therefore, solid-phase ion exchange reactions more readily yield mixed-phase lithium cobalt oxide rather than the pure O2 phase of this invention.

[0035] Preferably, after the liquid-phase ion exchange reaction is completed, the product is washed and dried to obtain the O2 phase lithium cobalt oxide.

[0036] In a second aspect, the present invention provides an O2 phase lithium cobalt oxide, obtained according to the preparation method described in the first aspect.

[0037] Thirdly, the present invention provides a lithium-ion battery containing the O2-phase lithium cobalt oxide described in the second aspect.

[0038] Compared with existing technical solutions, the present invention has at least the following beneficial effects:

[0039] The preparation method of the present invention achieves Na+ preparation in solution through liquid-phase ion exchange reaction. + and Li + Ion exchange is performed to ensure the formation of O2 phase lithium cobalt oxide, and the reaction can be controlled to give it high capacity, high rate and excellent cycle performance.

[0040] The preparation method of the present invention affects the interlayer spacing of the (002) crystal plane of the P2 phase sodium cobalt oxide by controlling the Na / Co ratio and sintering temperature during the synthesis of P2 phase sodium cobalt oxide. The interlayer spacing of the (002) crystal plane of the P2 phase sodium cobalt oxide and at least one of the temperature or time of the liquid phase ion exchange reaction are adjusted to achieve the adjustment of the interlayer spacing of the O2 phase lithium cobalt oxide, thereby optimizing its structure and ensuring that it has high capacity, high rate and excellent cycle performance at the same time. Attached Figure Description

[0041] Figure 1 and Figure 2 These are XRD patterns of sodium cobaltate in the P2 phase obtained in Examples 1, 4-6 and 9. Detailed Implementation

[0042] The technical solution of the present invention will be further illustrated below through specific embodiments.

[0043] Those skilled in the art will understand that the embodiments described are merely illustrative of the invention and should not be construed as limiting the invention.

[0044] Example 1

[0045] This embodiment provides a method for preparing O2 phase lithium cobalt oxide, the method comprising:

[0046] (1) Cobalt tetroxide, sodium carbonate, and Al2O3 were weighed and mixed in a molar ratio of n(Na):n(Co):n(Al) = 0.6:1:0.02, and sintered in a muffle furnace under air atmosphere. The sintering temperature was controlled at 850℃ and the sintering time was 12h to obtain P2 phase Na. x CoO2;

[0047] (2) The obtained P2 phase Na x CoO2 and a lithium source (lithium hydroxide and lithium chloride in a 1:1 ratio) were mixed at a sodium to lithium molar ratio of 1:30. The mixture was then added to deionized water to prepare a 5M solution. A liquid-phase ion exchange reaction was carried out in a reactor at a controlled temperature of 95°C for 24 hours. After the exchange was completed, the reaction product was washed multiple times with deionized water and ethanol to remove residual lithium source. The product was then dried in a vacuum oven at 180°C to obtain O2-phase lithium cobalt oxide.

[0048] Example 2

[0049] This embodiment provides a method for preparing O2 phase lithium cobalt oxide. In step (1) of the preparation method, the ratio of n(Na):n(Co) is adjusted from 0.6:1 to 0.58:1. Except for the above, the other conditions are exactly the same as in Example 1.

[0050] Example 3

[0051] This embodiment provides a method for preparing O2 phase lithium cobalt oxide. In step (1) of the preparation method, the ratio of n(Na):n(Co) is adjusted from 0.6:1 to 0.64:1. Except for the above, the other conditions are exactly the same as in Example 1.

[0052] Example 4

[0053] This embodiment provides a method for preparing O2 phase lithium cobalt oxide. In step (1) of the preparation method, the ratio of n(Na):n(Co) is adjusted from 0.6:1 to 0.7:1. Except for the above, the other conditions are exactly the same as in Example 1.

[0054] Example 5

[0055] This embodiment provides a method for preparing O2 phase lithium cobalt oxide. In step (1) of the preparation method, the ratio of n(Na):n(Co) is adjusted from 0.6:1 to 0.72:1. Except for the above, the other conditions are exactly the same as in Example 1.

[0056] Example 6

[0057] This embodiment provides a method for preparing O2 phase lithium cobalt oxide. In step (1) of the preparation method, the ratio of n(Na):n(Co) is adjusted from 0.6:1 to 0.73:1. Except for the above, the other conditions are exactly the same as in Example 1.

[0058] Example 7

[0059] This embodiment provides a method for preparing O2 phase lithium cobalt oxide. In step (1) of the preparation method, the ratio of n(Na):n(Co) is adjusted from 0.6:1 to 0.74:1. Except for the above, the other conditions are exactly the same as in Example 1.

[0060] Example 8

[0061] This embodiment provides a method for preparing O2 phase lithium cobalt oxide. In step (1) of the preparation method, the ratio of n(Na):n(Co) is adjusted from 0.6:1 to 0.78:1. Except for the above, the other conditions are exactly the same as in Example 1.

[0062] Example 9

[0063] This embodiment provides a method for preparing O2 phase lithium cobalt oxide. In step (1) of the preparation method, the ratio of n(Na):n(Co) is adjusted from 0.6:1 to 0.8:1. Except for the above, the other conditions are exactly the same as in Example 1.

[0064] Example 10

[0065] This embodiment provides a method for preparing O2 phase lithium cobalt oxide. In step (1) of the preparation method, the ratio of n(Na):n(Co) is adjusted from 0.6:1 to 0.82:1. Except for the above, the other conditions are exactly the same as in Example 1.

[0066] Example 11

[0067] This embodiment provides a method for preparing O2 phase lithium cobalt oxide. In step (1) of the preparation method, the sintering temperature is adjusted from 850℃ to 600℃. Except for the above, the other conditions are exactly the same as in Example 1.

[0068] Example 12

[0069] This embodiment provides a method for preparing O2 phase lithium cobalt oxide. In step (1) of the preparation method, the sintering temperature is adjusted from 850℃ to 1000℃. Except for the above, the other conditions are exactly the same as in Example 1.

[0070] Example 13

[0071] This embodiment provides a method for preparing O2 phase lithium cobalt oxide. In step (2) of the preparation method, the temperature of the liquid phase ion exchange reaction is adjusted from 95°C to 65°C. Except for the above, the other conditions are exactly the same as those in Example 6.

[0072] Example 14

[0073] This embodiment provides a method for preparing O2 phase lithium cobalt oxide. In step (2) of the preparation method, the temperature of the liquid phase ion exchange reaction is adjusted from 95°C to 70°C. Except for the above, the other conditions are exactly the same as those in Example 6.

[0074] Example 15

[0075] This embodiment provides a method for preparing O2 phase lithium cobalt oxide. In step (2) of the preparation method, the temperature of the liquid phase ion exchange reaction is adjusted from 95°C to 80°C. Except for the above, the other conditions are exactly the same as those in Example 6.

[0076] Example 16

[0077] This embodiment provides a method for preparing O2 phase lithium cobalt oxide. In step (2) of the preparation method, the temperature of the liquid phase ion exchange reaction is adjusted from 95°C to 98°C. Except for the above, the other conditions are exactly the same as those in Example 6.

[0078] Example 17

[0079] This embodiment provides a method for preparing O2 phase lithium cobalt oxide. In step (2) of the preparation method, the time of the liquid phase ion exchange reaction is adjusted from 24h to 3h. Except for the above, the other conditions are exactly the same as those in Example 6.

[0080] Example 18

[0081] This embodiment provides a method for preparing O2 phase lithium cobalt oxide. In step (2) of the preparation method, the time of the liquid phase ion exchange reaction is adjusted from 24h to 6h. Except for the above, the other conditions are exactly the same as those in Example 6.

[0082] Example 19

[0083] This embodiment provides a method for preparing O2 phase lithium cobalt oxide. In step (2) of the preparation method, the time of the liquid phase ion exchange reaction is adjusted from 24h to 12h. Except for the above, the other conditions are exactly the same as those in Example 6.

[0084] Example 20

[0085] This embodiment provides a method for preparing O2 phase lithium cobalt oxide. In step (2) of the preparation method, the time of the liquid phase ion exchange reaction is adjusted from 24h to 18h. Except for the above, the other conditions are exactly the same as those in Example 6.

[0086] Example 21

[0087] This embodiment provides a method for preparing O2 phase lithium cobalt oxide. In step (2) of the preparation method, the time of the liquid phase ion exchange reaction is adjusted from 24h to 30h. Except for the above, the other conditions are exactly the same as those in Example 6.

[0088] Example 22

[0089] This embodiment provides a method for preparing O2 phase lithium cobalt oxide. In step (2) of the preparation method, the time of the liquid phase ion exchange reaction is adjusted from 24h to 60h. Except for the above, the other conditions are exactly the same as those in Example 6.

[0090] Example 23

[0091] This embodiment provides a method for preparing O2 phase lithium cobalt oxide. In step (1) of the preparation method, no other transition metal source such as Al2O3 is used. Except for the above, the other conditions are exactly the same as those in Example 6.

[0092] Comparative Example 1

[0093] This comparative example provides a method for preparing lithium cobalt oxide. In step (2) of the preparation method, a solid-phase ion exchange method is used, specifically as follows:

[0094] Cobalt tetroxide, sodium carbonate, and Al₂O₃ were weighed and mixed in a molar ratio of n(Na):n(Co):n(Al) = 0.73:1:0.02, and sintered in a muffle furnace under air atmosphere. The sintering temperature was controlled at 850℃ and the sintering time was 12 h to obtain P₂ phase Na. x CoO2; the resulting P2 phase Na x CoO2 and lithium nitrate were mixed at a molar ratio of 1:10 and reacted in a muffle furnace under air atmosphere. The conversion temperature was controlled at 300℃ and the conversion time was 6h. After the conversion was completed, the reaction product was washed multiple times with deionized water and ethanol to remove the residual lithium source. Then it was dried in a vacuum oven at 180℃ to obtain mixed-phase lithium cobalt oxide.

[0095] The (002) interlayer spacing of the P2 phase sodium cobalt oxide and the O2 phase lithium cobalt oxide obtained in the examples, as well as the (002) interlayer spacing of the lithium cobalt oxide obtained in the comparative example, were tested:

[0096] Figure 1 and Figure 2 These are XRD patterns of sodium cobaltate in the P2 phase obtained in Examples 1, 4-6, and 9. The patterns show that as the Na / Co ratio changes, the Na in the P2 phase... x The peak position of the (002) characteristic peak of CoO2 is shifted. By importing the X-ray diffraction test data into Jade software for fitting, the interlayer spacing corresponding to the (002) characteristic diffraction peak can be obtained.

[0097] Other results are recorded in Table 1.

[0098] Table 1

[0099]

[0100] As can be seen from Table 1:

[0101] Comparing Example 1 with Examples 2-10, it was found that by adjusting the Na phase of P2... x By adjusting the interlayer spacing of the (002) characteristic peak in CoO2 using different Na / Co ratios, the interlayer spacing of O2-phase lithium cobalt oxide can be regulated. At the same sintering temperature, when the Na / Co ratio is too high or too low, a P2 phase impurity is formed, leading to significant variations in the interlayer spacing. Specifically, when the Na / Co ratio is below 0.7, increasing the Na / Co ratio reduces the interlayer spacing, indicating it is not pure P2-phase sodium cobalt oxide; however, when the Na / Co ratio is greater than or equal to 0.7 but less than 0.8, the interlayer spacing further decreases with increasing Na / Co ratio, but the interlayer spacing remains relatively constant. Within a certain range, the synthesized phase is a relatively pure P2 phase with small interlayer spacing. When the Na / Co ratio is greater than 0.8, the interlayer spacing changes again, and the phase exists as a miscible sodium cobaltate. In the subsequent P2 to O2 conversion process, the miscible sodium cobaltate leads to the formation of Li... + with Na + There is strong diffusion resistance between them. Therefore, the preferred molar ratio of Na / Co in this invention is between 0.7 and 0.78, and more preferably between 0.7 and 0.74.

[0102] Comparing Example 1 with Examples 11-12, it was found that increasing the reaction temperature increased the interlayer spacing of the P2 phase, and as Na was continuously removed, O... 2- -O 2- Increased repulsive forces lead to an increase in the C-axis, i.e., a larger interlayer spacing. However, excessively high sintering temperatures result in increased Na volatilization, leading to the formation of different phases and causing the interlayer spacing to deviate from the pure P2 phase, thus affecting the Li... + with Na + The conversion efficiency between transformations is low.

[0103] A comparison of Example 6 with Examples 13-16 revealed that increasing the transition temperature between the P2 and O2 phases is beneficial for improving the Li... + with Na + The conversion rate between transformations promotes the conversion of more P2 phases into O2 phases, which in turn increases the Li / Co ratio.

[0104] Comparing Example 6 with Examples 17-22, it was found that increasing the conversion time between the P2 and O2 phases initially increases the interlayer spacing, indicating the transformation of the P2 phase into P2*. Further extending the conversion time then promotes the transformation of more P2* into the O2 phase, at which point the interlayer spacing decreases, and the Li / Co ratio increases. However, excessively long conversion times no longer change the interlayer spacing, and the conversion rate between the P2 and O2 phases remains constant. Nevertheless, excessively long conversion times can damage the bulk structure of the O2 phase, leading to a deterioration in electrical performance.

[0105] Comparing Example 6 with Example 23, it was found that the addition of the transition metal source increased the interlayer spacing of the P2 phase, which was beneficial to Li + with Na + Transformation between transformations. Furthermore, the O2 phase layers fall within the optimal range.

[0106] Comparing Comparative Example 1 with Example 6, it was found that the interlayer spacing of O2 obtained by different conversion methods is very different. The main reason is that the solid-phase conversion method obtains mixed-phase lithium cobalt oxide, so the interlayer spacing is larger, while the liquid-phase conversion method obtains relatively pure O2 phase lithium cobalt oxide.

[0107] The lithium cobalt oxide obtained in the examples and comparative examples was used as the positive electrode material. It was dispersed in N-methylpyrrolidone (NMP) solvent with conductive agent SuperP and binder polyvinylidene fluoride (PVDF) at a mass ratio of 97.18:1.56:1.26. The mixture was stirred evenly in a degassing machine to obtain a positive electrode slurry. This slurry was then uniformly coated onto the surface of aluminum foil and baked in a vacuum oven at 100°C for 12 hours. Afterward, it was rolled and cut to obtain the positive electrode sheet. In a glove box, the positive electrode sheet, lithium negative electrode, and a PP / PE / PP three-layer separator were assembled into a button cell using a 1 mol / L LiPF6 / (EC+DEC) electrolyte (solvent volume ratio 1:1) for electrochemical testing.

[0108] For the obtained button batteries, the test temperature was controlled at 25℃, and the capacity performance was first tested under the condition of a voltage range of 3.0 to 4.5V, with discharge rates of 0.1C, 0.5C, and 1C respectively. The electrical performance test results are shown in Table 2. Then, a high-temperature 45℃ cycle performance test was conducted under the condition of a charge-discharge rate of 1C and a voltage range of 3.0 to 4.6V. The test results are shown in Table 2.

[0109] Table 2

[0110]

[0111]

[0112] As can be seen from Table 2:

[0113] A comparison between Examples 1 and Examples 2-10 reveals that the electrical performance of O2-phase lithium cobalt oxide varies depending on the Na / Co ratio. A low Na / Co ratio results in more cobalt sources remaining unreacted, leading to a risk of low capacity in the cathode material; a high Na / Co ratio results in more Na sources remaining on the surface, increasing the diffusion barrier during Na+ migration in the synthesized cathode material, thus affecting Li... + with Na + Low conversion rates between conversions lead to reduced capacity and poorer cycle life.

[0114] A comparison of Examples 1 and 11-12 reveals that with a constant Na / Co ratio, the sintering temperature of the P2 phase is too low, resulting in incomplete sodium formation of the synthesized sample. Unreacted sodium sources remaining on the surface significantly increase the material's impedance, leading to poor Na content in the synthesized cathode material. + The diffusion barrier increases during migration; and excessively high sintering temperature causes severe volatilization of the sodium source during calcination, resulting in insufficient sodium source for the material to be fully sodaified, leading to a decrease in the specific capacity during the first charge and discharge.

[0115] A comparison of Examples 6 and Examples 13-16 reveals that increasing the conversion temperature of P2 to O2 phase can improve conversion efficiency and enhance electrical performance.

[0116] A comparison of Examples 6 and Examples 17-22 reveals that if the conversion time is too short, the conversion from P2 phase to O2 phase is insufficient, resulting in poor electrical performance. On the other hand, if the conversion time is too long, it will damage the bulk structure of the O2 phase, leading to a deterioration in electrical performance.

[0117] Comparing Example 6 with Example 23, it was found that the addition of a transition metal source improved the cycle stability of the O2 phase lithium cobalt oxide.

[0118] Comparing Comparative Example 1 with Example 6, it was found that the electrical performance of the O2 phase lithium cobalt oxide obtained by the liquid phase conversion method was better than that obtained by the solid phase conversion method. The main reason is that the solid phase conversion method is carried out at high temperature, which will cause the generated O2 phase lithium cobalt oxide to become O3 lithium cobalt oxide and generate Co3O4 at the same time, which will lead to the deterioration of the electrical performance of the cathode material.

[0119] This invention illustrates the detailed process equipment and process flow through the above embodiments. However, this invention is not limited to the detailed process equipment and process flow described above, meaning that this invention does not necessarily depend on the detailed process equipment and process flow to be implemented. Those skilled in the art should understand that any improvements to this invention, equivalent substitutions of raw materials for the product of this invention, addition of auxiliary components, and selection of specific methods, all fall within the protection scope and disclosure scope of this invention.

[0120] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0121] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0122] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A method for preparing O2-phase lithium cobalt oxide, characterized in that, The preparation method includes mixing P2 phase sodium cobalt oxide with a lithium source and carrying out a liquid-phase ion exchange reaction to obtain O2 phase lithium cobalt oxide.

2. The preparation method according to claim 1, characterized in that, The P2 phase sodium cobaltate includes Na x CoO2, 0.6≤x≤0.

8.

3. The preparation method according to claim 1 or 2, characterized in that, The method for preparing the P2 phase sodium cobaltate includes mixing a cobalt source and a sodium source, and then sintering them to obtain the P2 phase sodium cobaltate.

4. The preparation method according to claim 3, characterized in that, The amounts of sodium and cobalt sources are controlled according to a molar ratio of sodium to cobalt of (0.6–0.8):

1. Preferably, the cobalt source includes cobalt oxide, and more preferably cobalt tetroxide; Preferably, the sodium source includes sodium carbonate.

5. The preparation method according to claim 3 or 4, characterized in that, The method for preparing the P2 phase sodium cobaltate further includes mixing a non-cobalt transition metal source with the cobalt source and the sodium source, and then performing the sintering. Preferably, the non-cobalt transition metal source includes at least one of the transition metal elements Al, Mg, Ni, or Mn; Preferably, the non-cobalt transition metal source comprises an oxide of the corresponding element; Preferably, the amount of the non-cobalt transition metal source and the cobalt source is controlled according to a molar ratio of non-cobalt transition metal element to cobalt element of (0 to 0.06):

1.

6. The preparation method according to any one of claims 3-5, characterized in that, The sintering temperature is 600–1000℃, and the time is 6–24 hours.

7. The preparation method according to any one of claims 1-6, characterized in that, The amount of sodium cobalt oxide and lithium source in the P2 phase is controlled according to a molar ratio of sodium to lithium of 1:(10-30); Preferably, the lithium source includes at least one of lithium hydroxide, lithium carbonate, or lithium chloride; Preferably, the P2 phase sodium cobaltate is mixed with a lithium source in water to prepare a solution, and then the liquid-phase ion exchange reaction is carried out. Preferably, the total concentration of the P2 phase sodium cobaltate and lithium source in the solution is 4–6 mol / L.

8. The preparation method according to any one of claims 1-7, characterized in that, The temperature of the liquid-phase ion exchange reaction is ≥80℃, and the time is ≥4h. Preferably, after the liquid-phase ion exchange reaction is completed, the product is washed and dried to obtain the O2 phase lithium cobalt oxide.

9. An O2-phase lithium cobalt oxide, characterized in that, The preparation method according to any one of claims 1-8 is obtained.

10. A lithium-ion battery, characterized in that, It contains the O2 phase lithium cobalt oxide as described in claim 9.

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