A positive electrode active material and use thereof

Abstract

The application provides a positive electrode active material and application thereof. The positive electrode active material comprises a metal oxide, the lithium metal oxide has a molecular formula shown in formula 1; in an X-ray diffraction pattern, the lithium metal oxide is a cubic crystal system Cmca space group, and has a 002 peak with 2θ of 17.9°-18.1° and a 131 peak with 2θ of 67.0°-67.5°; the molar content ratio m1 of Li elements and Na elements satisfies 12≤m1≤80; wherein M is a doping element. The special composition and crystal phase structure of the positive electrode active material help to improve the specific capacity and cycle performance of the battery, and especially under high pressure conditions, the battery can still perform excellently. n‑y Na y Co 1‑a M a O2, formula 1, in formula 1, 0.6≤n≤0.8, 0

Description

Technical Field

[0001] This invention relates to an electrode material, and more particularly to a positive electrode active material and its application, belonging to the field of secondary battery technology. Background Technology

[0002] With the development and advancement of lithium-ion battery technology, increasingly higher demands are being placed on its capacity. In the composition of a lithium-ion battery, the capacity of the positive electrode active material plays a crucial role in the battery's overall capacity.

[0003] To increase the capacity of lithium-ion batteries, the most common method is to increase their charge and discharge voltage. However, as the voltage increases, the crystal structure of the positive electrode active material collapses, leading to a series of problems such as rapid capacity decay and a significant reduction in cycle performance.

[0004] Therefore, developing a positive electrode active material for lithium-ion batteries with high specific capacity and good cycle performance is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] This invention provides a positive electrode active material whose special composition and crystal phase structure help improve the specific capacity and cycle performance of the battery, especially under high voltage conditions, it can still enable the battery to perform well.

[0006] The present invention provides a positive electrode sheet comprising the above-mentioned positive electrode active material, which helps to improve the relevant electrical performance of the battery.

[0007] The present invention also provides a lithium-ion battery comprising the above-mentioned positive electrode, thereby exhibiting excellent performance in terms of specific capacity and cycle performance.

[0008] The present invention provides a positive electrode active material, wherein the positive electrode active material comprises a lithium metal oxide, and the lithium metal oxide has the molecular formula shown in Formula 1;

[0009] In the X-ray diffraction pattern, the lithium metal oxide is a cubic crystal system in space group Cmca, and has a 002 peak with a 2θ of 17.9° to 18.1° and a 131 peak with a 2θ of 67.0° to 67.5°.

[0010] Li n-y Na y Co 1-a M a O2 Formula 1

[0011] In Equation 1, 0.6≤n≤0.8, 0<y≤0.05, 0≤a≤0.2;

[0012] The molar ratio of Li to Na, m1, satisfies: 12 ≤ m1 ≤ 80;

[0013] Where M is a dopant element.

[0014] The positive electrode active material as described above, wherein the lithium metal oxide has the molecular formula shown in Formula 2;

[0015] Li n-y Na y Co 1-a1-a2 M1 a1 M2 a2 O2 Formula 2

[0016] In Equation 2, 0 < a1 ≤ 0.1, 0 ≤ a2 ≤ 0.1, and a1 + a2 = a;

[0017] M1 is selected from at least one of Te, W, Al, B, P and K; M2 is a doping element different from M1.

[0018] The positive electrode active material as described above, wherein the positive electrode active material is composed of matrix particles including the lithium metal oxide and a coating layer covering at least a portion of the surface of the matrix particles.

[0019] The positive electrode active material as described above, wherein when the cutoff voltage is 3.0 to 3.6V and the SOC is zero, 0.7 ≤ n ≤ 1.0, and the molar ratio m2 of Li element to Na element satisfies: 16 ≤ m2 ≤ 93.

[0020] The positive electrode active material as described above, wherein m2-m1>3.

[0021] The positive electrode active material as described above, wherein the median particle size of the positive electrode active material is 12 μm to 20 μm.

[0022] The present invention provides a positive electrode sheet, wherein the positive electrode sheet comprises the positive electrode active material as described above.

[0023] The positive electrode as described above includes a current collector, a safety layer, and a positive electrode active layer.

[0024] The safety layer is sandwiched between the current collector and the positive electrode active layer, and the positive electrode active layer includes the positive electrode active material.

[0025] In the positive electrode sheet described above, the compaction density of the positive electrode active layer is greater than or equal to 3.5 g / cm³. 3 .

[0026] The present invention provides a lithium-ion battery, wherein the lithium-ion battery includes a positive electrode as described above.

[0027] The positive electrode active material of the present invention has a special crystal phase structure and chemical composition. When applied to batteries, the cycle performance and specific capacity of the batteries are significantly improved. Even under high voltage conditions of 4.5V and above, batteries using this positive electrode active material can still maintain excellent electrical performance and will not experience structural collapse due to poor voltage resistance of the positive electrode active material. Attached Figure Description

[0028] Figure 1 This is a partial structural schematic diagram of an embodiment of the negative electrode sheet in the lithium-ion battery of the present invention;

[0029] Figure 2 This is a SEM image of the positive electrode active material in Example 1 of the present invention;

[0030] Figure 3 This is a SEM image of the positive electrode active material in Comparative Example 1 of the present invention;

[0031] Figure 4 This is the XRD pattern of the positive electrode active material in Example 1 of the present invention.

[0032] Explanation of reference numerals in the attached figures:

[0033] 20: Negative electrode active layer;

[0034] 30: Lithium material layer;

[0035] 101: Negative electrode current collector. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0037] The first aspect of the present invention provides a positive electrode active material, the positive electrode active material comprising lithium metal oxide, wherein the lithium metal oxide has the molecular formula shown in Formula 1;

[0038] In the X-ray diffraction pattern, the lithium metal oxide is a cubic crystal system in space group Cmca, and has a 002 peak with a 2θ of 17.9° to 18.1° and a 131 peak with a 2θ of 67.0° to 67.5°.

[0039] Li n-y Na y Co 1-a Ma O2 Formula 1

[0040] In Equation 1, 0.6≤n≤0.8, 0<y≤0.05, 0≤a≤0.2;

[0041] The molar ratio of Li to Na, m1, satisfies: 12 ≤ m1 ≤ 80;

[0042] Where M is a dopant element.

[0043] The lithium metal oxide described above in this invention specifically includes oxides of at least cobalt, lithium, and sodium. Furthermore, it may be doped with M. This invention does not limit the specific selection of M and it can be any doping element commonly found in the art. For example, it can be at least one of the elements W, Mg, Ti, Mn, Al, Te, Ni, Nb, Zr, La, F, Ce, Sr, Y, K, B, and P.

[0044] This invention does not impose excessive restrictions on y, m1, and a within the above-mentioned limits.

[0045] For example, in Equation 1, y is 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.010, 0.012, 0.015, 0.018, 0.020, 0.022, 0.024, 0.025, 0.026, 0.028, 0.03, 0.04, or 0.05; m1 is 12, 13, 15, 20, 40, 50, 65, 78, or 80; and a is 0.001, 0.002, 0.003, or 0.004. 0.004, 0.005, 0.006, 0.007, 0.008, 0.010, 0.012, 0.015, 0.018, 0.020, 0.022, 0.024, 0.025, 0.026, 0.028, 0.030, 0.032, 0.034, 0.035, 0.04, 0.045, 0.05, 0.055, 0.06, 0.065, 0.07, 0.075, 0.08, 0.085, 0.09, or 0.095.

[0046] It should be emphasized that the above limitation on n refers to the molar amount of lithium in a unit mole of lithium metal oxide in the positive electrode active material that has not undergone any charge-discharge treatment. The above limitation on m1 refers to the ratio of the molar content of Li to the molar content of Na in a unit mole of lithium metal oxide in the positive electrode active material that has not undergone any charge-discharge treatment; furthermore, m1 is 22-73.

[0047] It is understandable that when this positive electrode active material is applied to a lithium-ion battery for any charge-discharge treatment, the molar amount of lithium in a unit mole of lithium metal oxide will vary under different charge-discharge mechanisms and charge-discharge nodes, and the ratio of the molar content of Li to the molar content of Na in a unit mole of lithium metal oxide will also vary.

[0048] According to the above-described solution provided by the present invention, compared with other positive electrode active materials, the application of the positive electrode active material including this lithium metal oxide to lithium-ion batteries significantly improves the specific capacity and cycle performance of lithium-ion batteries. Even under high-voltage operating conditions, the electrical performance of lithium-ion batteries does not deteriorate. Based on this phenomenon, the inventors analyzed it and believe that it may be because when the molar ratio of Li to Na is within a certain range, the lithium metal oxide has a more complete T2 structure. The partial supporting role of sodium in the structure allows the lithium metal in the Cmca space group of the cubic crystal system to improve the lithium-ion insertion / extraction efficiency, thereby promoting the improvement of the cycle performance and specific capacity of lithium-ion batteries.

[0049] Furthermore, the inventors discovered that by classifying the doping elements in lithium metal oxides, the performance of the cathode active material can be further improved. In some embodiments of the present invention, the lithium metal oxide has the molecular formula shown in Formula 2;

[0050] Li n-y Na y Co 1-a1-a2 M1 a1 M2 a2 O2 Formula 2

[0051] In Equation 2, 0 < a1 ≤ 0.1, 0 ≤ a2 ≤ 0.1, and a1 + a2 = a;

[0052] M1 is selected from at least one of Te, W, Al, B, P and K; M2 is a doping element different from M1.

[0053] It is understood that the lithium metal oxide of the present invention has the molecular formula shown in Formula 2, specifically an oxide comprising at least cobalt, lithium, sodium, and M1. Furthermore, it may be doped with M2, which is different from M1. The present invention does not limit the specific selection of M2, and it can be a doping element commonly used in the art. For example, it can be at least one of the elements Mg, Ti, Mn, Al, Te, Ni, Nb, Zr, La, F, Ce, Sr, Y, K, B, and P.

[0054] This invention does not impose excessive restrictions on y, a1, and a2 within the above-mentioned limits.

[0055] For example, in Equation 2, y is 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.010, 0.012, 0.015, 0.018, 0.020, 0.022, 0.024, 0.025, 0.026, 0.028, 0.03, 0.04, or 0.05; a 1 represents 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.010, 0.012, 0.015, 0.018, 0.020, 0.022, 0.024, 0.025, 0.026, 0.028, 0.030, 0.032, 0.034, 0.035, 0.04, 0.045, 0.05, 0.055, 0.06, 0.065, 0.07, 0.075, 0.08, 0.085, 0.09, or 0.095; a2 is 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.010, 0.012, or 0.01 5, 0.018, 0.020, 0.022, 0.024, 0.025, 0.026, 0.028, 0.030, 0.032, 0.034, 0.035, 0.04, 0.045, 0.05, 0.055, 0.06, 0.065, 0.07, 0.075, 0.08, 0.085, 0.09, or 0.095.

[0056] In this invention, the application of the lithium metal oxide positive electrode active material, including Formula 2, to lithium-ion batteries can further improve the specific capacity and cycle performance of lithium-ion batteries, enabling them to operate at high voltage for longer periods without degradation. Based on this phenomenon, the inventors believe the following possibilities exist: Firstly, the doping of M1 helps support the structure of the lithium metal oxide, improving its structural stability to a certain extent. Therefore, regardless of whether the operating environment is at normal or high voltage, a structurally stable lithium metal oxide is more conducive to improving the efficiency of lithium-ion insertion / extraction, thus promoting the improvement of the cycle performance and specific capacity of the lithium-ion battery. Secondly, the lithium metal oxide with the aforementioned crystal characteristics has a more complete layered crystal phase structure, reducing or suppressing the occurrence of internal mixing phenomena within the crystal phase, thereby enabling smooth lithium-ion insertion / extraction, especially exhibiting multiple small charge / discharge plateaus during high-voltage charging and discharging processes.

[0057] In addition to the positive effects of lithium metal oxide on battery-related electrical performance, the battery performance is further improved when a coating layer is applied to at least a portion of the surface of the lithium metal oxide. By incorporating the coating layer, the positive electrode active material has a core-shell structure comprising a lithium metal oxide core and a coating layer covering the core. This coating layer helps reduce or suppress side reactions between the lithium metal oxide and the electrolyte. Even when the battery operates under high voltage, a stable interface can still be formed between the positive electrode active material and the electrolyte, improving the battery's cycle performance by preventing excessive dissolution of metal ions from the positive electrode active material and avoiding electrolyte shortage. Simultaneously, the suppression or reduction of side reactions also reduces gas production within the battery, thereby ensuring battery safety.

[0058] This invention does not limit the choice of coating material, as long as it can suppress side reactions and ensure the normal migration of lithium ions. To further improve lithium-ion conductivity, the coating material can be made of carbon-containing compounds, fast ion conductors, or other similar materials.

[0059] As mentioned earlier, in lithium metal oxides without any charge / discharge treatment, n is between 0.6 and 0.8, and the molar ratio of Li to Na, m1, is between 12 and 80. When a positive electrode sheet including the positive electrode active material and a lithium metal negative electrode sheet are assembled into a battery and charged and discharged, with <10 charge / discharge cycles, and the battery's remaining SOC is 0 (i.e., in a fully discharged state) and the discharge cutoff voltage is 3.0 to 3.6V, the n of the lithium metal oxide is between 0.7 and 1.0, and the molar ratio of Li to Na, m2, is between 16 and 93. Specifically, after charging and discharging, the composition of the lithium metal oxide changes, especially the molar amount of lithium ions increases significantly. This is because lithium metal oxides with the aforementioned crystal structure have some vacancies. Therefore, when charged and discharged, these vacancies can accept lithium atoms from the lithium negative electrode, thereby increasing the molar amount of lithium ions compared to before charging and discharging. This feature helps to further improve the battery's cycle performance and specific capacity.

[0060] Furthermore, when the difference between m2 and m1 is greater than 3, the battery has a more superior specific capacity.

[0061] In particular, when the battery's remaining charge SOC is 0 (i.e., when it is fully discharged to 3.0V) and the discharge cutoff voltage is 3.0 to 3.6V, the n of lithium metal oxide is between 0.7 and 1.0, the molar ratio of Li to Na elements m2 is between 26 and 93, and the difference between m2 and m1 is greater than 3, the battery has superior cycle performance and specific capacity.

[0062] The positive electrode active material of the present invention can be single-crystal or polycrystalline, and the specific morphology is related to the selection and proportion of its doping elements. Specifically, when it is polycrystalline, it is spherical or near-spherical particles; when it is single-crystal, it can be whisker-like, plate-like, or other arbitrary irregular shapes.

[0063] Furthermore, the median particle size of the positive electrode active material of the present invention is 12–20 μm, for example, 3 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, or 20 μm. The inventors have discovered that when the median particle size of the positive electrode active material meets the above requirements, on the one hand, its corresponding specific surface area can accommodate more lithium ion insertion / extraction; on the other hand, the agglomeration phenomenon between positive electrode active materials is effectively controlled, thereby enabling stable dispersion in the slurry during the slurry preparation process.

[0064] The inventors discovered that by further limiting the content and type of doping elements in lithium metal oxides, multiple discharge plateaus during the charging and discharging process exhibited superior discharge capacity.

[0065] Clearly, in the discharge process under high-voltage conditions, both the first-stage discharge capacity ratio and the second-stage discharge capacity ratio exhibit excellent performance. Therefore, the positive electrode active material, including the lithium metal oxide of this invention, has strong voltage resistance, thereby enabling the specific capacity of the battery to be increased by performing a voltage boosting process.

[0066] The present invention does not limit the preparation method of the above-mentioned lithium metal oxide. In one specific embodiment, the lithium metal oxide of the present invention can be prepared by mixing the sodium metal oxide shown in Formula 1a with a lithium compound and performing ion treatment.

[0067] Na x Co 1-a M a O2 Formula 1a

[0068] In Equation 1a, 0.68 < x < 0.74, 0 <a≤0.2。

[0069] The aforementioned ion exchange treatment is a thermal treatment process, specifically referring to the heat treatment of a mixture of sodium metal oxide and lithium compound at 80℃ to 300℃ for no more than 10 hours. After the ion exchange treatment, the system is washed and dried to finally obtain lithium metal oxide. The drying temperature is 80℃ to 180℃, and the time is at least 10 hours. There are no limitations on the equipment used for ion exchange treatment and drying. For example, the ion exchange treatment equipment can be a closed container with sealing and stirring capabilities, such as a wet coating reaction device or a co-precipitation reaction device; the drying equipment can be a forced-air drying oven, a vacuum drying oven, a rotary kiln, a disc dryer, or an oven.

[0070] The lithium compound mentioned above can be a commonly used lithium source compound in the art, such as at least one of lithium carbonate, lithium chloride, lithium bromide, lithium iodide, lithium nitrate, lithium hydroxide, and lithium fluoride. In the ion exchange process, the mass ratio of the lithium compound to the sodium metal oxide is not less than 1:1, preferably (1-3):1.

[0071] Furthermore, when it is necessary to prepare a positive electrode active material with a coating layer on the outside of lithium metal oxide, in addition to the raw materials including sodium metal oxide and lithium compound, a coating layer raw material also needs to be added during the ion exchange process.

[0072] For the sodium metal compound shown in Formula 1a, by way of example, it can be prepared by a method including the following process:

[0073] The cobalt source and the sodium source are mixed in at least the target ratio and then calcined to obtain the sodium metal compound shown in Formula 1a.

[0074] Specifically, the calcination temperature is 700–900℃, and the time is 8–50 hours. The calcination can be carried out in an oxygen or air atmosphere. The equipment used for calcination can be high-temperature sintering equipment such as muffle furnaces, tunnel furnaces, roller kilns, and tube furnaces.

[0075] Preferably, the lithium metal oxide of the present invention can also be prepared by mixing the sodium metal oxide shown in Formula 1a with a lithium compound and then subjecting it to ion treatment.

[0076] Na x Co 1-a1-a2 M1 a1 M2 a2 O2 Formula 2a

[0077] In Equation 2, 0 < a1 ≤ 0.1, 0 ≤ a2 ≤ 0.1, and a1 + a2 = a.

[0078] For example, the M1 source, M2 source, cobalt source, and sodium source can be mixed in a target ratio and then calcined to obtain the sodium metal compound shown in Formula 2a.

[0079] The mixing of the various sources mentioned above can be performed using high-speed mixing equipment, sand milling equipment, ball milling equipment, plow milling equipment, inclined milling equipment, etc. It should be noted that if sand milling or ball milling equipment is used and a solvent (water, ethanol, or other solvent media) is added during the ball milling or sand milling process, the mixed system needs to be dried after the mixing process is completed. Generally, the mixing time should not exceed 4 hours.

[0080] This invention does not limit the specific selection of the cobalt source, sodium source, M1 source, and M2 source. Exemplarily, the cobalt source is selected from one or more of cobalt hydroxide, cobalt tetroxide, doped cobalt tetroxide, cobalt suboxide, cobalt hydroxyl oxide, cobalt nitrate, and cobalt sulfate; the sodium source is selected from one or more of sodium carbonate, sodium nitrate, sodium hydroxide, sodium bicarbonate, and sodium sulfate; the M1 source can be an oxide of M1. When M1 is W, the M1 source is, for example, tungstic acid and / or sodium tungstate; when M1 is Te, the M1 source is, for example, telluric acid and / or sodium tellurate; when M1 is Al, the M1 source is, for example, aluminum sulfate. One or more of aluminum nitrate, aluminum hydroxide, etc.; when M1 is B, the source of M1 is, for example, boric acid and / or sodium borate, etc.; when M1 is P, the source of M1 is, for example, phosphoric acid and / or sodium phosphate, etc.; when M1 is K, the source of M1 is, for example, potassium carbonate, potassium nitrate, potassium hydroxide, potassium bicarbonate, potassium sulfate, etc., one or more of them; the source of M2 can be an oxide of M2, for example, one or more of basic magnesium carbonate, magnesium hydroxide, zirconium oxide, yttrium oxide, lanthanum oxide, lanthanum fluoride, nickel oxide, niobium oxide, etc.

[0081] A second aspect of the present invention provides a positive electrode sheet comprising the positive electrode active material described in the first aspect above.

[0082] Based on the characteristics of the positive electrode active material in the first aspect, the positive electrode sheet of the present invention helps to improve the cycle performance and specific capacity of lithium-ion batteries.

[0083] In one specific embodiment, the positive electrode sheet of the present invention includes a positive current collector and a positive active layer disposed on at least one surface of the positive current collector, the positive active layer including the aforementioned positive active material.

[0084] It is understood that, in addition to the positive electrode active material, the positive electrode active layer also includes a conductive agent and a binder. For example, the positive electrode active layer comprises, by weight percentage, 70-99 wt% positive electrode active material, 0.5-15 wt% conductive agent, and 0.5-15 wt% binder; more specifically, it comprises 80-98 wt% positive electrode active material, 1-10 wt% conductive agent, and 1-10 wt% binder.

[0085] The selection of conductive agent and binder is not special and can be conventional in the field. For example, the conductive agent is selected from at least one of conductive carbon black, acetylene black, Ketjen black, conductive graphite, conductive carbon fiber, carbon nanotube, single-walled carbon nanotube, multi-arm carbon nanotube, and carbon fiber, and the binder is selected from at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and lithium polyacrylate (PAALi).

[0086] Furthermore, to enhance safety performance, a safety layer can be placed between the positive electrode active layer and the current collector. The safety layer is typically made of non-conductive safety materials, such as iron-containing compounds (e.g., lithium iron phosphate, lithium phosphate) or aluminum-containing compounds (e.g., ceramic alumina). Of course, the safety layer also includes a binder, and the ratio of binder to safety material can be further determined according to specific requirements.

[0087] In some embodiments of the present invention, the compaction density of the positive electrode active layer is greater than or equal to 3.5 g / cm³. 3 This can further improve the battery's cycle performance and specific capacity.

[0088] A third aspect of the present invention also provides a lithium-ion battery comprising the above-described positive electrode, thereby exhibiting outstanding performance in terms of cycle performance and specific capacity.

[0089] According to the present invention, the lithium-ion battery further includes a negative electrode, a separator, and an electrolyte.

[0090] Exemplarily, the electrolyte is a conventional electrolyte known in the art, comprising a lithium salt and a solvent, wherein the solvent contains ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), or fluoroethylene carbonate (FEC). Further, it also includes an additive represented by Formula T, wherein the mass percentage of the additive in the electrolyte is 0.1% to 10%, etc.

[0091]

[0092] For example, the negative electrode can be a lithium metal-rich negative electrode, such as a lithium foil or... Figure 1 The negative electrode shown. Specifically, Figure 1 The negative electrode sheet includes a negative electrode current collector 101, a negative electrode active layer 20, and a lithium material layer 30 stacked together. Figure 1 The negative electrode sheet is double-sided, but it can also be a negative electrode sheet with a negative electrode active layer 20 and a lithium material layer 30 only on one side of the negative electrode current collector. The lithium material layer is, for example, a lithium foil, and further, the areal density of metallic lithium in the lithium material layer is 0.09 mg / cm2 to 3.5 mg / cm2; the negative electrode active layer includes a negative electrode active material, a conductive agent, and a binder.

[0093] In one specific embodiment, the negative electrode active layer comprises, by weight percentage, 70-99 wt% of negative electrode active material, 0.5-15 wt% of conductive agent, and 0.5-15 wt% of binder; more specifically, it comprises 80-98 wt% of negative electrode active material, 1-10 wt% of conductive agent, and 1-10 wt% of binder. The negative electrode active material is selected from one or more of artificial graphite, natural graphite, hard carbon, mesophase carbon microspheres, lithium titanate, silicon carbide, and silicon suboxide.

[0094] For example, the diaphragm is a polypropylene-based material, or a coated diaphragm with ceramic coating on one or both sides.

[0095] The lithium-ion battery of the present invention is suitable for high-voltage systems. Specifically, under the condition of ≥4.55V (relative to lithium) for the lithium-ion coin cell including the aforementioned positive electrode, the specific capacity of the positive electrode is ≥225mAh / g, and it also has excellent cycle performance at ≥4.50V (corresponding to the aforementioned negative electrode).

[0096] Therefore, the lithium-ion battery of the present invention has good cycle stability and high specific capacity at higher voltages such as 4.50V, which can meet the usage requirements of high-end digital products for thinner and lighter designs.

[0097] The technical solution of the present invention will be further explained and described below with reference to specific embodiments.

[0098] Example 1

[0099] The positive electrode active material in this embodiment is prepared according to the following method:

[0100] (1) Weigh 36.56g of sodium carbonate powder and 291.05g of cobalt nitrate hexahydrate powder, put them into a high-speed mixing device, set the mixing program, mix at 300rpm for 3 minutes, mix at 500rpm for 5 minutes, and then mix at 1000rpm for 10 minutes. Take out the mixture and confirm that there are no white sodium carbonate spots in the mixture. It is considered that the mixture is uniform.

[0101] (2) Take about 30g of the well-mixed material and evenly pack it into a ceramic crucible. Use a VBF-1200X well-type muffle furnace for high-temperature sintering. The sintering temperature rise rate is 5℃ / min. When the temperature reaches 750℃, sinter at a constant temperature for 10h. After sintering, allow it to cool naturally to room temperature and then remove the sample. The sodium metal oxide Na was detected by inductively coupled plasma atomic emission spectrometry (ICP). 0.69 CoO2;

[0102] (3) Weigh 10.49g of lithium hydroxide monohydrate and 17.24g of lithium nitrate granules into a reaction vessel. Add the two lithium compounds separately into the reaction vessel. Weigh 10g of the Na synthesized in step (2). 0.69 CoO2 was poured into a reaction vessel and mixed initially, then subjected to ion exchange at 280℃ for 0.5 h to obtain the crude product;

[0103] (4) After the crude product was washed by deionized water filtration three times, it was dried at 90℃ for 8 hours to obtain sample 1A#.

[0104] ICP was used to detect and analyze #1, and the specific results are shown in Table 1.

[0105] Example 2

[0106] The preparation method of the positive electrode active material in this embodiment is basically the same as that in Example 1, except that:

[0107] In step (3), ion exchange was performed at 260℃ for 1.2 h to obtain the crude product; after treatment in step (4), sample 2A#Li was obtained. 0.70 Na 0.025 CoO2.

[0108] Example 3

[0109] The preparation method of the positive electrode active material in this embodiment is basically the same as that in Example 1, except that:

[0110] In step (3), ion exchange was performed at 95℃ for 3.4 h to obtain the crude product; after treatment in step (4), sample 3A#Li was obtained. 0.72 Na 0.023 CoO2.

[0111] Example 4

[0112] The preparation method of the positive electrode active material in this embodiment is basically the same as that in Example 1, except that:

[0113] In step (3), ion exchange was performed at 105℃ for 3.0 h to obtain the crude product; after treatment in step (4), sample 4A#Li was obtained. 0.73 Na 0.017 CoO2.

[0114] Example 5

[0115] The preparation method of the positive electrode active material in this embodiment is basically the same as that in Example 1, except that:

[0116] Step (1) is as follows: Take 36.56g of sodium carbonate powder, 0.21g of potassium carbonate powder, 282.31g of cobalt nitrate hexahydrate powder and 1.21g of nano magnesium oxide powder, put them into a high-speed mixing device, set the mixing program, mix at 300rpm for 3 minutes, mix at 500rpm for 5 minutes, and then mix at 1000rpm for 10 minutes. Take out the mixture and confirm that there are no white sodium carbonate spots in the mixture. It is considered that the mixture is uniform.

[0117] The sodium metal oxide obtained in step (2) is Na 0.69 K 0.003 Co 0.97 Mg 0.03 O2;

[0118] After processing in step (4), sample 5A#Li was obtained. 0.71 Na 0.02 K 0.003 Co 0.97 Mg 0.03 O2.

[0119] Example 6

[0120] The preparation method of the positive electrode active material in this embodiment is basically the same as that in Example 5, except that:

[0121] In step (3), ion exchange was performed at 100℃ for 2.8 h to obtain the crude product; after treatment in step (4), sample 6A#Li was obtained. 0.72 Na 0.021 K 0.003 Co 0.97 Mg 0.03 O2.

[0122] Example 7

[0123] The preparation method of the positive electrode active material in this embodiment is basically the same as that in Example 5, except that:

[0124] In step (3), ion exchange was performed at 260℃ for 1.5 h to obtain the crude product; after treatment in step (4), sample 7A#Li was obtained. 0.73 Na 0.017 K 0.003 Co 0.97 Mg 0.03 O2.

[0125] Comparative Example 1

[0126] The preparation method of the positive electrode active material in this comparative example is basically the same as that in Example 1, except that:

[0127] In step (3), ion exchange was performed at 75℃ for 24 hours to obtain the crude product; after treatment in step (4), sample 1a#Li was obtained. 0.50 Na 0.48 CoO2.

[0128] Comparative Example 2

[0129] The preparation method of the positive electrode active material in this comparative example is basically the same as that in Example 1, except that:

[0130] In step (3), ion exchange was performed at 90℃ for 24 hours to obtain the crude product; after treatment in step (4), sample 2a#Li was obtained. 0.89 Na 0.005 CoO2.

[0131] Comparative Example 3

[0132] The preparation method of the positive electrode active material in this comparative example is basically the same as that in Example 5, except that:

[0133] In step (3), ion exchange was performed at 280℃ for 0.1 h to obtain the crude product; after treatment in step (4), sample 3a#Li was obtained. 0.3 9Na 0.60 K 0.003 Co 0.97 Mg 0.03 O2.

[0134] Comparative Example 4

[0135] The preparation method of the positive electrode active material in this comparative example is basically the same as that in Example 5, except that:

[0136] In step (3), ion exchange at 85℃ for 30 h yields crude product; after treatment in step (4), sample 4a#Li is obtained. 0.86 Na 0.006 K 0.003 Co 0.97 Mg 0.03 O2.

[0137] Comparative Example 5

[0138] The preparation method of the positive electrode active material in this comparative example is basically the same as that in Example 5, except that:

[0139] In step (3), ion exchange at 280℃ for 0.35 h yields crude product; after treatment in step (4), sample 5a#Li is obtained. 0.69 Na 0.06 K 0.003 Co 0.97 Mg 0.03 O2.

[0140] Comparative Example 6

[0141] The preparation method of the positive electrode active material in this comparative example is basically the same as that in Example 1, except that:

[0142] In step (3), ion exchange at 280℃ for 15 h yields crude product; after treatment in step (4), sample 6a#Li is obtained. 0.93 Na 0.03 CoO2.

[0143] Experimental Example 1

[0144] 1) The morphology of the positive electrode active materials of Example 1 and Comparative Example 1 were tested using SEM, respectively. Figure 2 and Figure 3 As shown, the positive electrode active material in Example 1 has a large particle size distribution, which enables more complete lithium ion insertion and extraction, thus helping to improve the battery's specific capacity and cycle performance.

[0145] 2) XRD diffraction was performed on the products of all examples and comparative examples, and the results are shown in Table 2.

[0146] Figure 4 This is the XRD pattern of the positive electrode active material in Example 1 of the present invention. Figure 4 It can be seen that the positive electrode active material in Example 1 of the present invention has a characteristic peak at 18.06° and a characteristic peak at 67.43562°.

[0147] Experimental Example 2

[0148] After fabricating the products from all the embodiments and comparative examples into positive electrode sheets, they were assembled with negative electrode sheets, electrolytes, and separators according to the following method to obtain a lithium-ion battery. The method includes:

[0149] 1) The positive electrode active materials in the examples and comparative examples were mixed with conductive carbon black and PVDF at a weight ratio of 96%:2%:2% respectively, and dispersed to obtain a positive electrode slurry. The slurry was coated onto an aluminum foil current collector and rolled to prepare a positive electrode sheet;

[0150] 2) Artificial graphite, styrene-diene rubber (SBR), sodium carboxymethyl cellulose, and conductive carbon black were mixed in a weight ratio of 94%:3%:2%:1%. The mixture was dispersed in water and then mixed using a double planetary mixer to obtain a negative electrode slurry. This slurry was coated onto a copper current collector, followed by rolling and drying.

[0151] Subsequently, a lithium material layer, which is a lithium foil, is deposited on the surface of the negative electrode active layer by rolling. The areal density of metallic lithium is 1.0 mg / cm³. 2 Ultimately, a negative electrode containing lithium metal is obtained.

[0152] 3) Then, the positive electrode, negative electrode and separator are assembled into a lithium-ion battery and injected with a non-aqueous electrolyte.

[0153] The electrolyte is a conventional electrolyte known in the art, which is mixed with ethylene carbonate (EC): diethyl carbonate (DEC): propylene carbonate (PC) in a mass ratio of 2:5:3. Then, 5% of fluoroethylene carbonate (FEC) and 13% of lithium hexafluorophosphate (LiPF6) are added, along with the additive shown in Formula T, with the additive content accounting for 2% of the total electrolyte content. The capacity retention rate of each lithium-ion battery was tested. The specific test method was as follows: at 25°C, the battery was charged at a constant current rate of 1C to 4.50V, then charged at a constant voltage rate of 0.05C to 4.50V, and then discharged at a discharge rate of 1C to 3.0V. This charge-discharge cycle was repeated 500 times. The discharge capacity at the first cycle and the discharge capacity at the 500th cycle were measured. The capacity retention rate after 500 cycles was calculated according to the following formula. The results are shown in Table 2.

[0154] Capacity retention rate Q = (Discharge capacity at the 500th cycle) / (Discharge capacity at the first cycle) * 100%

[0155] Experimental Example 3

[0156] After fabricating the products from all embodiments and comparative examples into positive electrode sheets, they were assembled with negative electrode sheets, electrolytes, and separators according to the following method to obtain a coin cell. The method includes:

[0157] The positive electrode active materials from the examples and comparative examples were mixed with conductive carbon black (SP) and PVDF in a weight ratio of 80%:10%:10% to obtain a positive electrode slurry through dispersion. This slurry was coated onto an aluminum foil current collector and rolled to prepare a positive electrode sheet. The positive electrode sheet was then punched into small discs with a diameter of 12 mm using a die-cutting tool. After drying and weighing, the discs were assembled into a coin cell using a 2025 coin cell casing, a Li metal disc as the negative electrode, and conventional high-voltage lithium cobalt oxide electrolyte in a glove box under an Ar protective atmosphere.

[0158] After each coin cell was left to stand for 4 hours under normal conditions, its initial charge-discharge capacity was tested. The test conditions were: charging at 0.1C to 4.55V, constant voltage charging to 0.025C cutoff, standing for 3 minutes, and then discharging at 0.1C to 3.0V. During the discharge process, the initial discharge capacity C0 and the initial charge capacity were recorded, and the initial efficiency was calculated. The results are shown in Table 2.

[0159] Experimental Example 4:

[0160] The lithium-ion battery in Experiment Example 2 was discharged to 3.0V at 1 / 10 of its rated capacity. Its voltage was tested and found to be 3.0-3.6V. The lithium-ion battery was then disassembled, the positive electrode was removed, and it was soaked in dimethyl carbonate (DMC) for 3 hours. After being naturally dried in a drying room, it was calcined in a muffle furnace at 300℃ for 3 hours. After being sieved through a 200-mesh sieve, the sample powder was obtained. The content of each element in the sample powder was tested by ICP. The test results are shown in Table 2.

[0161] Table 1

[0162]

[0163] Table 2

[0164]

[0165]

[0166] According to Tables 1 and 2:

[0167] 1. According to the examples and comparative examples, different preparation parameters, such as reaction temperature, reaction time, and raw material selection, have a certain impact on the composition and crystal structure of lithium metal oxides, and ultimately affect the relevant performance of lithium-ion batteries. In particular, strict control of synthesis conditions is required to obtain pure-phase positive electrode active materials.

[0168] 2. As can be seen from Table 2, the positive electrode active material prepared in the embodiments of the present invention has superior specific capacity and cycle performance when applied to lithium-ion batteries.

[0169] 3. As can be seen from Examples 1-4 and Examples 5-7, compared with the undoped positive electrode active material, the specific capacity of the positive electrode active material with doped elements remains basically unchanged when applied to lithium-ion batteries, while the cycle performance is significantly enhanced.

[0170] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A positive electrode plate, characterized in that, The positive electrode sheet includes the following positive electrode active materials; The positive electrode active material includes lithium metal oxide. In the X-ray diffraction pattern, the lithium metal oxide is a cubic crystal system in space group Cmca, and has a 002 peak with a 2θ of 17.9°~18.1° and a 131 peak with a 2θ of 67.0°~67.5°. The lithium metal oxide has the molecular formula shown in Formula 2; Li n-y Na y Co 1-a1-a2 M1 a1 M2 a2 O2 type 2 In Equation 2, 0.6≤n≤0.8, 0<y≤0.05, 0<a1≤0.1, 0≤a2≤0.1; Wherein, M1 is selected from at least one of Te, W, Al, B, P and K; M2 is a doping element different from M1; the molar ratio of Li to Na m1 satisfies: 12≤m1≤80; the positive electrode active material is composed of matrix particles including the lithium metal oxide and a coating layer covering at least part of the surface of the matrix particles; The coating layer is selected from carbon-containing compounds or fast ion conductors; The positive electrode includes a current collector, a safety layer, and a positive electrode active layer; The safety layer is sandwiched between the current collector and the positive electrode active layer, and the positive electrode active layer includes the positive electrode active material.

2. The positive electrode sheet according to claim 1, characterized in that, When the cutoff voltage is 3.0~3.6V and the SOC is zero, the positive electrode active material has 0.7≤n≤1.0, and the molar ratio of Li to Na elements m2 satisfies: 16≤m2≤93.

3. The positive electrode sheet according to claim 2, characterized in that, m2-m1>3.

4. The positive electrode sheet according to claim 1, characterized in that, The median particle size of the positive electrode active material is 12 μm to 20 μm.

5. The positive electrode sheet according to claim 1, characterized in that, The compaction density of the positive electrode active layer is greater than or equal to 3.5 g / cm³. 3 .

6. A lithium-ion battery, characterized in that, The lithium-ion battery includes the positive electrode sheet as described in any one of claims 1-5.

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