A lithium-rich manganese-based positive electrode active material and battery

Abstract

The present invention provides a lithium-rich manganese-based positive electrode active material and a battery. In a first aspect, the present invention provides a lithium-rich manganese-based positive electrode active material, comprising a base particle and a coating layer coated on the outer surface of the base particle, wherein the molecular formula of the base particle is Li a‑b1 K c‑ b2 Mn x Co y Ni z M h O 2‑d D d The matrix particles have lithium and potassium vacancies. The lithium-rich manganese-based positive electrode active material provided by the present invention uses potassium to occupy some of the lithium sites, helping to reduce the amount of lithium source used and improving the material's rate performance and structural stability. Furthermore, the formation of potassium vacancies helps accommodate lithium ions embedded back during discharge, thereby improving the battery's discharge specific capacity, initial coulombic efficiency, and cycle life.

Description

Technical Field

[0001] The invention relates to a lithium-rich manganese-based positive electrode active material and a battery, and relates to the technical field of batteries. Background Art

[0002] As new energy vehicles place increasingly higher demands on driving range, improving battery energy density has become a development goal in the battery industry. As a key component of batteries, the specific energy of cathode active materials influences their energy density. Therefore, developing cathode active materials with high specific energy is a top priority.

[0003] Compared with ternary high nickel and lithium iron phosphate, lithium-rich manganese-based positive electrode active materials have higher specific energy (>1000Wh / Kg), but they have problems such as low first coulombic efficiency and rapid capacity and voltage decay during the cycle, which hinder their commercial application. At the same time, compared with conventional ternary positive electrode active materials, lithium-rich manganese-based positive electrode active materials [xLi2MnO3·(1-x)LiMO2, taking x=0.5 as an example] require nearly 50% more lithium source in the synthesis process. As lithium prices continue to rise, the cost advantage of lithium-rich manganese-based positive electrode active materials has gradually declined. Therefore, how to reduce the amount of lithium while improving its low first-week coulombic efficiency and rapid cycle decay is of great significance. Summary of the Invention

[0004] The present invention provides a lithium-rich manganese-based positive electrode active material, which uses potassium to occupy some lithium sites, helping to reduce the amount of lithium source used and improve the material's rate performance and structural stability. At the same time, the formation of potassium vacancies helps to accommodate lithium ions embedded back during the discharge process, thereby improving the battery's discharge specific capacity, first coulombic efficiency and cycle life.

[0005] The present invention also provides a battery comprising the lithium-rich manganese-based positive electrode active material.

[0006] A first aspect of the present invention provides a lithium-rich manganese-based positive electrode active material, comprising a base particle and a coating layer coated on the outer surface of the base particle, wherein:

[0007] The molecular formula of the matrix particles is Li a-b1 K c-b2 Mn x Co y Ni z M h O 2-d D d, the matrix particles have lithium vacancies and potassium vacancies, the molar amount of the lithium vacancies is b1, the molar amount of the potassium vacancies is b2, 1<(a+c)≤1.5, a+c+x+y+z+h=2, 4<a / c<30, 0.05<(b1+b2)≤0.25, 0.15<(c-b2) / (b1+b2)<0.35, x>(y+z+h), 0≤h≤0.1, 0≤d≤0.25;

[0008] M is selected from one or more of Ti, Mo, Te, W, Nb, Ta, V, Sb, Sn, Si, Zr, Cr, Al, La, Y, Sr, Mg, and Zn; D is selected from one or more of F, S, P, N, and B;

[0009] The coating layer includes one or more oxides, fluorides, and polyanion salts of one or more elements selected from the group consisting of Al, Co, P, B, Si, Zr, W, Te, Zn, Mg, Ti, Ta, La, Nb, Sb, V, Y, Ce, and Bi.

[0010] The lithium-rich manganese-based positive electrode active material provided by the present invention includes a matrix particle, the molecular formula of the matrix particle is Li a-b1 K c-b2 Mn x Co y Ni z M h O 2-d D d , wherein a and c represent the molar amounts of lithium ions and potassium ions in the particle material before the formation of lithium vacancies and potassium vacancies, respectively, and the total molar amount of the two (a+c) is greater than 1 and less than or equal to 1.5. The matrix particles provided by the present invention use potassium to occupy part of the lithium sites, which can produce a lithium layer pillar effect, help increase the interlayer spacing of the lithium layer, promote lithium ion diffusion, inhibit the migration of transition metal ions, and improve the rate performance and structural stability of the material; in addition, the use of cheaper potassium to replace lithium helps to reduce the amount of lithium source used and reduce the preparation cost of the positive electrode active material; at the same time, to ensure the molar amount of lithium ions in the matrix particles, the molar ratio of lithium ions to potassium ions in the present invention, a / c, is greater than 4 and less than 30.

[0011] The matrix particles provided by the present invention also include lithium vacancies and potassium vacancies. The formation of potassium vacancies helps to accommodate lithium ions embedded back during the discharge process, thereby improving the battery's discharge specific capacity, initial coulombic efficiency, and cycle life. The present invention uses b1 and b2 to represent the molar amounts of lithium vacancies and potassium vacancies, respectively. The molar amounts of lithium vacancies and potassium vacancies can be calculated by the molar ratios of Li / TM and K / TM before and after vacancy formation; specifically, the molar amounts of Li, K, and transition metal TM in the particles before vacancy formation are tested, and the molar ratios of Li / TM and K / TM are calculated, recorded as Li / TM.空位前 and K / TM 空位前 Secondly, the molar amounts of Li, K and transition metal TM in the finished positive electrode active material were tested, and the molar ratios of Li / TM and K / TM were calculated, which were recorded as Li / TM 成品 and K / TM 成品 The molar amount of lithium vacancies b1 is calculated by formula 1, and the molar amount of potassium vacancies b2 is calculated by formula 2. The sum of the molar amount of lithium vacancies b1 and the molar amount of potassium vacancies b2 is the molar amount of total vacancies;

[0012] b1=[Li / TM 空位前 -Li / TM 成品 Formula 1

[0013] b2=[K / TM 空位前 -K / TM 成品 ]Formula 2.

[0014] The molar amounts of Li, K, and transition metals in the granular material before vacancy formation and the finished positive electrode active material can be obtained by ICP (Inductively coupled plasma mass spectrometry) testing.

[0015] In order to ensure the amount of lithium ions and the molar ratio of total vacancies, the molar amount b1+b2 of total vacancies in the matrix particles provided by the present invention is greater than 0.05 and less than or equal to 0.25, and the molar ratio of the molar amount of residual potassium ions (c-b2) to the total vacancies (b1+b2) is greater than 0.15 and less than 0.35.

[0016] Furthermore, in the matrix particles provided by the present invention, 0.08≤b1+b2≤0.18, and 0.9≤b2 / (b1+b2)≤1.0, by limiting the molar amount of total vacancies and the proportion of potassium vacancies, the capacity performance can be affected by reducing the amount of lithium source and improving the first coulombic efficiency of the positive electrode active material, thereby avoiding the impact of too low lithium dosage on capacity.

[0017] The cationic doping element M provided by the present invention is selected from one or more of Ti, Mo, Te, W, Nb, Ta, V, Sb, Sn, Si, Zr, Cr, Al, La, Y, Sr, Mg, and Zn. Some of the cationic doping elements can occupy transition metal sites, have higher bond energy with oxygen, and help inhibit oxygen escape to stabilize the structure; some of the cationic doping elements only remain at the grain boundaries, but can also play a role in refining the grains and improving interface stability. Furthermore, the cationic doping element M is selected from one or more of Nb, W, P, Mo, and Ta.

[0018] The anion doping element D provided by the present invention is selected from one or more of F, S, P, N, and B, and has the effect of stabilizing lattice oxygen and improving structural stability. Furthermore, the anion doping element D is selected from one or more of F, P, and S.

[0019] It can be understood that the base particles provided by the present invention do not include cationic doping elements M and anionic doping elements D, or include cationic doping elements M and / or anionic doping elements D, that is, the molar amount h of the cationic doping element M is 0 to 0.1, and the molar amount d of the anionic doping element D is 0 to 0.25, and h and d can be 0 at the same time or at least one of them is greater than 0.

[0020] The surface of the base particles provided by the present invention includes a coating layer, which helps to reduce interface side reactions, improve interface stability, inhibit oxygen release, and improve the stability of the positive electrode active material during charge and discharge at high voltage; the coating layer includes one or more oxides, fluorides, and polyanion salts of one or more elements selected from the group consisting of Al, Co, P, B, Si, Zr, W, Te, Zn, Mg, Ti, Ta, La, Nb, Sb, V, Y, Ce, and Bi.

[0021] Furthermore, the coating layer includes one or more of LiAlO2, Al2O3, AlF3, and AlPO4.

[0022] In a specific embodiment, the D50 of the lithium-rich manganese-based positive electrode active material is 3 to 14 μm, where D50 refers to the particle size corresponding to when the cumulative particle size distribution percentage of the positive electrode active material reaches 50%, specifically selected from a range of 3 μm, 4 μm, 5 μm, 8 μm, 10 μm, 12 μm, 14 μm or any two thereof, and can be obtained by testing with a particle size analyzer.

[0023] In a specific embodiment, the compaction density of the lithium-rich manganese-based positive electrode active material at 3.5T is 2.3-3.3 g / m 3 , specifically selected from 2.3g / m 3 , 2.5g / m 3 , 2.8g / m 3 3.0g / m 3 , 3.1g / m 3 3.2g / m 3 3.3g / m 3 Or a range consisting of any two of them; the compaction density can be obtained by a compaction density meter test. During the test, a certain weight of positive electrode active material powder is added to a hard mold with a fixed diameter and height, and the powder is moved and deformed under a pressure of 3.5T to form a compact with a certain density and strength. The result is calculated based on the net weight of the powder and the compressed volume.

[0024] In a specific embodiment, the specific surface area of ​​the lithium-rich manganese-based positive electrode active material is 0.2 to 5 m 2 / g, specifically selected from 0.2m 2 / g, 0.5m 2 / g, 0.8m 2 / g, 1.0m 2 / g, 1.5m 2 / g, 2.0m 2 / g, 2.5m 2 / g, 3.0m 2 / g, 3.5m 2 / g, 4.0m 2 / g, 4.5m 2 / g, 5.0m 2 / g or the range of any two of them can be obtained by using the BET test method.

[0025] In a specific embodiment, the base particles provided by the present invention are obtained by washing the base particle precursor with water, and the molecular formula of the base particle precursor is Li a K c Mn x Co y Ni z M h O 2-d D d , the water washing process uses an aqueous solution containing potassium ions.

[0026] Among them, the matrix particle precursor refers to the granular material before the formation of lithium vacancies and potassium vacancies, which is specifically obtained by performing a first sintering treatment on the first mixed material. The first mixed material includes a lithium source, a potassium source, a nickel-cobalt-manganese precursor, a doping source containing a cationic doping element M, and a doping source containing an anionic doping element D.

[0027] Furthermore, the lithium source is selected from one or more of LiCO3, LiOH, CH3COOLi, and LiNO3; the potassium source is selected from one or more of K2CO3, KOH, KNO3, and CH3COOK; the nickel-cobalt-manganese precursor is selected from one or more of carbonates, hydroxides, and oxalates containing nickel, cobalt, and manganese elements; further, the nickel-cobalt-manganese precursor is selected from one or more of carbonates Ni containing nickel, cobalt, and manganese elements. x Co y Mn z CO3, hydroxide containing nickel, cobalt and manganese elements Ni x Co y Mn z (OH)2, (x+y+z=1).

[0028] The cationic doping source containing the doping element M is selected from oxides, hydroxides, oxyhydroxyls, fluorides or polyanionic salts containing cations, such as one or more of TiO2, MoO3, WO3, TeO2, Nb2O5, Ta2O5, V2O5, Sb2O5, SnO2, SiO2, ZrO2, CrO2, Al2O3, Al(OH)3, Co4O3, CoOOH, AlPO4, AlF3, La2O3, Y2O3, SrO, MgO, and ZnO.

[0029] The anion doping source containing the doping element D is selected from a compound containing anions, for example, one or more of LiF, KF, NH4F, Li2S, K2S, BN, AlN, Si3N4, NH4H2PO4, (NH4)2HPO4, Li3PO4, and K3PO4.

[0030] According to the chemical formula Li a K c Mn x Co y Ni z M h O 2-d D d The above compounds are weighed and mixed to obtain a first mixed material, and the first mixed material is subjected to a first sintering treatment. It should be noted that during the weighing process, an excess of 0 to 6% of the lithium source should be weighed to reduce lithium amount errors caused by lithium volatilization and the generation of residual lithium during the first sintering treatment.

[0031] The first sintering treatment can be carried out in a high-temperature heating device such as a tubular furnace, a muffle furnace, a box furnace, a roller kiln, a pusher kiln, or a rotary kiln, while introducing air or oxygen. The treatment process includes a first stage and a second stage; the heating rate of the first stage is 1°C to 5°C / min, the temperature is 400°C to 800°C, and the time is 0 to 8 hours; the heating rate of the second stage is 1°C to 5°C / min, the temperature is 800°C to 950°C, and the time is 10 to 20 hours.

[0032] After the first sintering treatment is completed, a matrix particle precursor is obtained, which is cooled to room temperature and placed in an aqueous solution containing potassium ions. Since potassium ions are more active than lithium ions, potassium ions will preferentially undergo proton exchange reaction with hydrogen in the aqueous solution, causing potassium ions to escape and form potassium vacancies.

[0033] The potassium vacancy content is regulated by controlling the concentration of potassium ions in the aqueous solution and the washing time. Specifically, the concentration of potassium ions in the aqueous solution containing potassium ions is 0.005-0.05 mol / L, the temperature of the aqueous solution is 0-25°C, the mass ratio of the aqueous solution to the matrix particle precursor is 1:0.5-2, and the mixing time is 1-30 min. At the same time, under the above-mentioned washing conditions, it is also helpful to reduce the escape of lithium ions and reduce the formation of lithium vacancies.

[0034] After the treatment is completed, solid particles are collected by solid-liquid separation and dried to obtain matrix particles containing potassium vacancies and lithium vacancies.

[0035] Furthermore, solid-liquid separation can be performed by any one of centrifugation, suction filtration, and filter pressing, and the drying temperature is 90-130°C.

[0036] After the base particles are obtained, they can be mixed with the coating material to obtain a second mixed material, and then subjected to a second sintering treatment to obtain a finished product of the lithium-rich manganese-based positive electrode active material.

[0037] Specifically, the coating material is an oxide, hydroxide, oxyhydroxyl, fluoride or polyanion salt containing one or more elements of Al, Co, P, B, Si, Zr, W, Te, Zn, Mg, Ti, Ta, La, Nb, Sb, V, Y, Ce, Bi, such as Al2O3, Al(OH)3, Co4O3, CoOOH, AlPO4, AlF3, etc.

[0038] Furthermore, the mass of the coating material is 0.01 to 1 wt% of the total mass of the base particles and the coating material.

[0039] The second sintering treatment can also be carried out in a high-temperature heating device such as a tubular furnace, a muffle furnace, a box furnace, a roller kiln, a pusher kiln, or a rotary kiln. The second sintering treatment is carried out in an air atmosphere with a heating rate of 1 to 5°C / min, a temperature of 200 to 500°C, and a time of 3 to 12 hours.

[0040] Furthermore, the temperature of the second sintering treatment is 300-400°C. As the second sintering temperature increases, the vacancy area will gradually transition from a layered phase to a spinel phase, and eventually form a structural transformation trend of an inert rock salt phase, affecting the overall performance of the battery.

[0041] It should be noted that the nickel-cobalt-manganese precursor is generally prepared by a co-precipitation process. However, since the co-precipitation process generally uses Na2CO3 or NaOH as a precipitant, Na impurities are inevitably introduced. During the sintering process, excessive Na content will produce impurities, affecting the structure and performance of the matrix particles. Therefore, the Na content in the finished lithium-rich manganese-based positive electrode active material needs to be controlled to 50-5000ppm.

[0042] In summary, the lithium-rich manganese-based positive electrode active material provided by the present invention uses the doping element potassium to occupy the lithium site, which can play a lithium layer pillar effect, help increase the lithium layer interlayer spacing, promote lithium ion diffusion, inhibit transition metal ion migration, and improve rate performance and structural stability; in addition, the use of cheaper potassium to replace lithium helps to reduce the amount of lithium source used and reduce the preparation cost of the positive electrode active material; at the same time, the lithium-rich manganese-based positive electrode active material provided by the present invention also has potassium vacancies. The formation of potassium vacancies helps to accommodate the lithium ions embedded back during the discharge process, improve the first coulomb efficiency, and improve the cycle life.

[0043] A second aspect of the present invention provides a battery comprising any of the above-mentioned lithium-rich manganese-based positive electrode active materials.

[0044] Based on the characteristics of the lithium-rich manganese-based positive electrode active material provided in the first aspect of the present invention, the battery provided by the present invention has good rate performance and cycle life.

[0045] In a specific embodiment, the battery includes a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the positive electrode sheet includes a positive electrode collector and a positive electrode active material layer arranged on the surface of the positive electrode collector, and the positive electrode collector can be selected from the positive electrode collectors conventionally used in the art, such as aluminum foil, etc.; the positive electrode active material layer includes the lithium-rich manganese-based positive electrode active material provided by the first aspect of the present invention, as well as a conductive agent, a binder, etc. The selection of the conductive agent and the binder is not special and can be conventionally selected in the art. For example, the conductive agent is selected from one or more of conductive carbon black, acetylene black, Ketjen black, conductive graphite, conductive carbon fiber, carbon nanotubes, single-walled carbon nanotubes, multi-arm carbon nanotubes, and carbon fibers, and the binder is selected from one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and lithium polyacrylate (PAALi).

[0046] The negative electrode plate includes a negative electrode current collector and a negative electrode active material layer arranged on the surface of the negative electrode current collector, wherein the negative electrode current collector can be selected from negative electrode current collectors conventionally used in the art, such as copper foil, etc.; the negative electrode active material layer includes a negative electrode active material, a conductive agent and a binder; the negative electrode active material can be selected from one or more of silicon, silicon carbon, SiOx (0<X<2), lithium silicon alloy, silicon alloy, artificial graphite, natural graphite, hard carbon, soft carbon, and mesophase carbon microspheres.

[0047] The electrolyte and the diaphragm are both conventional materials in this field and can be selected according to actual needs.

[0048] The lithium-rich manganese-based positive electrode active material provided by the present invention uses K element to occupy lithium sites, which can play a lithium layer pillar effect, help increase the interlayer spacing of the lithium layer, promote lithium ion diffusion, inhibit transition metal ion migration, and improve rate performance and structural stability; in addition, the use of cheaper potassium to replace lithium helps to reduce the amount of lithium source used and reduce the preparation cost of the positive electrode active material; at the same time, the lithium-rich manganese-based positive electrode active material provided by the present invention also has potassium vacancies. The formation of potassium vacancies helps to accommodate lithium ions embedded back during the discharge process, improve the first coulombic efficiency, and improve the cycle life. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0050] Figure 1 XRD test results of the positive electrode active materials provided in Example 3 and Comparative Example 1 of the present invention;

[0051] Figure 2 This is a scanning electron microscope image of the positive electrode active material provided in Example 3 of the present invention;

[0052] Figure 3 This is a scanning electron microscope image of the positive electrode active material provided in Comparative Example 1 of the present invention;

[0053] Figure 4 The cycle performance test results of the batteries including the positive electrode active materials provided by Example 3 of the present invention and Comparative Example 1 are shown. DETAILED DESCRIPTION

[0054] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0055] Example 1

[0056] The preparation method of the lithium-rich manganese-based positive electrode active material provided in this embodiment includes the following steps:

[0057] A lithium source, a potassium source, Nb2O5 and a nickel-cobalt-manganese precursor (Ni:Co:Mn=33:1:66 in the nickel-cobalt-manganese precursor) are uniformly mixed to obtain a first mixed material, the first mixed material is placed in a box furnace, and the temperature is increased to 500°C at a heating rate of 2°C / min under an air atmosphere and kept warm for 5 hours, and then the temperature is increased to 850°C at a heating rate of 2°C / min and kept warm for 12 hours, and then cooled to obtain a matrix particle precursor;

[0058] The matrix particle precursor was mixed with a potassium carbonate aqueous solution (potassium ion concentration of 0.02 mol / L) to form a suspension. The aqueous solution temperature was 0°C. After stirring for 10 minutes, the suspension was filtered and the filter cake was dried in a forced air oven at 110°C to obtain matrix particles.

[0059] The base particles were evenly mixed with 0.3 wt% of the coating material Al2O3, placed in a box furnace, heated to 300°C at a heating rate of 2°C / min under air atmosphere and kept warm for 8 hours, and then cooled and sieved to obtain a lithium-rich manganese-based positive electrode active material.

[0060] The preparation methods of the lithium-rich manganese-based positive electrode active materials provided in Examples 2 to 11 and Comparative Examples 1 to 6 are basically the same as those in Example 1, except that: the molar ratios of lithium ions and potassium ions added in Examples 2 to 8 and Comparative Examples 1 to 3 are different, and the molar ratios of lithium ions, potassium ions and transition metals in the matrix particle precursor are adjusted differently; the temperature of the second sintering treatment is adjusted differently in Examples 9 to 10 and Comparative Examples 4 to 5; and the concentration of potassium ions in the potassium carbonate aqueous solution is adjusted differently in Example 11 and Comparative Example 6. The specific differences are listed in Table 1.

[0061] The molar amounts of Li, K, and transition metal TM in the matrix particle precursor and the finished cathode active material were measured by ICP (Inductively coupled plasma mass spectrometry). The molar ratios of Li / TM and K / TM were calculated based on the molar amounts of Li, K, and TM in the matrix particle precursor, and were recorded as Li / TM. 空位前 and K / TM 空位前 According to the molar amount of Li, K and transition metal TM in the finished positive electrode active material, the molar ratio of Li / TM and K / TM is calculated and recorded as Li / TM 成品 and K / TM 成品 The calculation results are shown in Table 1, and the molar ratio of total vacancies to transition metal elements is calculated according to Formulas 1 to 2. The calculation results are shown in Table 1.

[0062] Table 1

[0063]

[0064]

[0065] The lithium-rich manganese-based positive electrode active material, conductive agent Super-P, and adhesive PVDF provided in Examples 1 to 11 and Comparative Examples 1 to 6 were added to NMP solvent in a ratio of 90:5:5 and mixed evenly to obtain a positive electrode active material layer slurry. The positive electrode active material layer slurry was then coated on the surface of the positive electrode current collector aluminum foil, and the positive electrode sheet was obtained by drying, punching, and rolling. The button battery stainless steel shell, positive electrode sheet, PP separator, and lithium sheet were stacked in sequence, and a certain amount of electrolyte was added dropwise and then packaged and kept stationary to obtain a half-cell. The discharge capacity, first coulomb efficiency, rate performance, capacity retention rate, and voltage decay of the half-cell were tested. The test method is as follows, and the test results are shown in Table 2.

[0066] (1) 0.2C discharge capacity

[0067] After the assembled half-cell rested for 5 hours, it was charged to 4.55V at a constant current of 0.2C, then charged at a constant voltage of 4.55V until the cutoff current was equal to 0.05C. After resting for 5 minutes, it was discharged to 2.5V at a constant current of 0.2C. The resulting discharge capacity is the 0.2C discharge capacity.

[0068] (2) First Coulomb efficiency

[0069] After the assembled half-cell was left to rest for 5 h, it was charged to 4.55 V at a constant current of 0.2 C, then charged to a cutoff current of 0.05 C at a constant voltage of 4.55 V. After resting for 5 min, it was discharged to 2.5 V at a constant current of 0.2 C. The first coulombic efficiency was calculated using the obtained discharge capacity / charge capacity.

[0070] (III) 1C / 0.2C rate performance

[0071] The assembled half-cell was charged and discharged for one cycle at a rate of 0.2C, and then charged and discharged for one cycle at a rate of 1C. The resulting 1C discharge capacity / 0.2C discharge capacity is the 1C / 0.2C rate performance.

[0072] (IV) 1C cycle 100T capacity retention rate

[0073] The assembled half-cell was charged and discharged for 100 cycles at a rate of 1C. The discharge capacity of the 100th cycle divided by the discharge capacity of the 1st cycle was the 1C cycle 100T capacity retention rate.

[0074] (V) 1C cycle 100T voltage decay

[0075] The assembled half-cell was charged and discharged for 100 cycles at a 1C rate. The average discharge voltage of the 100th cycle minus the average discharge voltage of the 1st cycle was the 1C cycle 100T voltage decay (average discharge voltage = discharge energy / discharge capacity).

[0076] (6) Material cost saving

[0077] The raw material cost A1 used in Comparative Example 1 was calculated, and the raw material cost used in Examples 1 to 11 and Comparative Examples 2 to 3 was A2. The cost saving percentage was calculated as (A1-A2) / A1*100%, wherein the cost of water washing materials was negligible.

[0078] Table 2

[0079]

[0080]

[0081] According to the data provided in Examples 1 to 8 and Comparative Examples 1 to 3, when the total molar amount of lithium ions and potassium ions remains unchanged, as the potassium ion content continues to increase, the content of lithium ions continues to decrease, and the cost saving of materials continues to increase. The content of lithium ions in the finished lithium-rich manganese-based positive active material is no different from that of the raw material, but the residual potassium ions and vacancy content gradually increase. According to Table 2, the comprehensive performance of the battery provided by Examples 1 to 8 is improved compared with Comparative Examples 1 to 3, indicating that the lithium-rich manganese-based positive active material provided by the present invention can improve the first coulomb efficiency, discharge specific capacity, rate performance and cycle stability of the battery while reducing material cost. In Comparative Example 2, the molar amount of potassium ions is too low, resulting in higher material cost and poor battery performance, while in Comparative Example 3, the molar amount of potassium ions is too high, active lithium is reduced, and a low discharge specific capacity is exhibited, and the first coulomb efficiency exceeds 100%.

[0082] According to literature reports, for layered positive electrode active materials with vacancies, as the sintering temperature increases, the vacancy region will gradually transition from a layered phase to a spinel phase, and eventually form a structural transformation trend of an inert rock salt phase. The present invention also uses Examples 3, 9-10 and Comparative Examples 4-5 to verify the secondary sintering temperature, indicating that as the secondary sintering temperature increases, the overall performance of the battery continues to decline. In Comparative Examples 4-5, due to the high secondary sintering temperature, the layered structure with vacancies will undergo transition metal ion migration, that is, the transition metal ions will migrate to the lithium layer and transform into a spinel or rock salt structure, resulting in the lithium vacancy calculation method no longer being applicable.

[0083] In Examples 3, 11 and Comparative Example 6, the concentration of potassium ions in the aqueous solution containing potassium ions was verified by gradient. By estimating the vacancy content Va value, it can be found that for the calcined samples with the same potassium compounding amount, the residual K content and vacancy content after washing are related to the concentration of potassium ions in the washing solution. This is because the release of potassium ions is affected by the concentration difference.

[0084] In addition, the present invention carries out XRD and SEM characterization of the lithium-rich manganese-based positive electrode active materials provided in Example 3 and Comparative Example 1. The characterization results are as follows: Figures 1 to 3 As shown, according to Figure 1 It can be seen that there is no significant difference in the XRD patterns of the positive electrode active materials provided by Example 3 and Comparative Example 1, indicating that a good layered structure can still be formed after K is used to replace Li for composite. Figures 2-3 It can be seen that the positive electrode active material provided in Example 3 has good sphericity and a clean surface, which is consistent with the morphology of the lithium-rich manganese-based positive electrode active material provided in the prior art.

[0085] In addition, the assembled half-cell was subjected to a 0.2C charge-discharge test, and the charge-discharge capacity mAh / g and voltage V were recorded. The results are as follows: Figure 4 As shown, it can be seen that compared with Comparative 1, although the charging capacity of Example 3 is reduced, the discharge specific capacity is significantly improved. This is attributed to the fact that the vacancies formed after the potassium ions are released can serve as acceptance points for lithium ion embedding, accepting more lithium ions, which helps to improve the discharge specific capacity, first coulombic efficiency and cycle life of the battery.

[0086] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements 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 lithium-rich manganese-based positive electrode active material, characterized in that: The lithium-rich manganese-based positive electrode active material includes a base particle and a coating layer coated on the outer surface of the base particle, wherein: The molecular formula of the matrix particles is Li a-b1 K c-b2 Mn x Co y Ni z M h O 2-d D d , the matrix particles have lithium vacancies and potassium vacancies, the molar amount of the lithium vacancies is b1, the molar amount of the potassium vacancies is b2, 1<(a+c)≤1.5, a+c+x+y+z+h=2, 4<a / c<30, 0.05<(b1+b2)≤0.25, 0.15<(c-b2) / (b1+b2)<0.35, x>(y+z+h), 0≤h≤0.1, 0≤d≤0.25; M is selected from one or more of Ti, Mo, Te, W, Nb, Ta, V, Sb, Sn, Si, Zr, Cr, Al, La, Y, Sr, Mg, and Zn; D is selected from one or more of F, S, P, N, and B; The coating layer includes one or more oxides, fluorides, and polyanion salts of one or more elements selected from the group consisting of Al, Co, P, B, Si, Zr, W, Te, Zn, Mg, Ti, Ta, La, Nb, Sb, V, Y, Ce, and Bi.

2. The lithium-rich manganese-based positive electrode active material according to claim 1, characterized in that 0.08≤b1+b2≤0.18, 0.9≤b2 / (b1+b2)≤1.

0.

3. The lithium-rich manganese-based positive electrode active material according to claim 1, characterized in that The D50 of the lithium-rich manganese-based positive electrode active material is 3 to 14 μm.

4. The lithium-rich manganese-based positive electrode active material according to claim 1, characterized in that The compaction density of the lithium-rich manganese-based positive electrode active material at 3.5T is 2.3-3.3 g / m 3 , with a specific surface area of ​​0.2 to 5 m 2 / g.

5. The lithium-rich manganese-based positive electrode active material according to any one of claims 1 to 4, characterized in that: The matrix particles are obtained by washing the matrix particle precursor with water. The molecular formula of the matrix particle precursor is Li a K c Mn x Co y Ni z M h O 2-d D d , the water washing process uses an aqueous solution containing potassium ions.

6. The lithium-rich manganese-based positive electrode active material according to claim 5, characterized in that The concentration of potassium ions in the aqueous solution containing potassium ions is 0.005-0.05 mol / L, the mass ratio of the aqueous solution to the matrix particle precursor is 1:0.5-2, the water washing temperature is 0-25° C., and the washing time is 1-30 min.

7. The lithium-rich manganese-based positive electrode active material according to claim 5, characterized in that The matrix particle precursor is obtained by performing a first sintering process on a first mixed material, wherein the first mixed material includes a lithium source, a potassium source, a nickel-cobalt-manganese precursor, a doping source containing a cationic doping element M, and a doping source containing an anionic doping element D; The first sintering treatment is carried out in air or oxygen atmosphere, and includes a first stage and a second stage; the heating rate of the first stage is 1°C to 5°C / min, the temperature is 400°C to 800°C, and the time is 0 to 8h; the heating rate of the second stage is 1°C to 5°C / min, the temperature is 800°C to 950°C, and the time is 10 to 20h.

8. The lithium-rich manganese-based positive electrode active material according to claim 5, characterized in that The lithium-rich manganese-based positive electrode active material is obtained by performing a second sintering process on a second mixed material, wherein the second mixed material includes the base particles and the coating material; The second sintering treatment is carried out in an air atmosphere, with a heating rate of 1 to 5° C. / min, a temperature of 200 to 500° C., and a time of 3 to 12 hours.

9. The lithium-rich manganese-based positive electrode active material according to claim 8, characterized in that The mass of the coating material is 0.01 to 1 wt % of the total mass of the base particles and the coating material.

10. A battery, characterized in that: The invention comprises the lithium-rich manganese-based positive electrode active material according to any one of claims 1 to 9.

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