Positive electrode material and lithium metal battery

Abstract

The present application belongs to the technical field of energy storage. Provided in the present application are a positive electrode material and a lithium metal pouch battery. The positive electrode material comprises Li, and there are at least three characteristic peaks in an XRD diffraction pattern of the positive electrode material: a first characteristic peak is in the range of 18.24° to 18.35°, the peak intensity being A; a second characteristic peak is in the range of 42.76° to 43.74°, the peak intensity being B; and a third characteristic peak is in the range of 36.19° to 36.34°, the peak intensity being C, wherein 1.30≤A / B≤1.72, and 1.09≤B / C≤1.86. With respect to the positive electrode material of the present application, the kinetics of lithium ion migration can be improved, and the structural phase transition of the positive electrode material can be effectively inhibited, thereby improving the cycle performance of batteries at room temperature and high temperature.

Description

Cathode materials and lithium metal batteries Technical Field

[0001] This application relates to the field of energy storage, and in particular to a cathode material and a lithium metal battery. Background Technology

[0002] Lithium metal batteries, as high-performance energy storage devices, have significant application potential. The negative electrode of a lithium metal battery is typically made of lithium metal, which gives it extremely high energy density, meeting the specific requirements of various application scenarios. With the continuous expansion of application areas, higher demands are being placed on the cycle life and stability of lithium metal batteries.

[0003] Cycle life is a crucial indicator of battery performance, determining its stability and reliability over extended periods. On the other hand, high-temperature performance is another challenge that lithium metal batteries need to overcome. Under high temperatures, battery cells may experience expansion and increased impedance, leading to performance degradation. Therefore, improving the cycle performance of lithium metal batteries at both room temperature and high temperatures has become a pressing technical problem. Summary of the Invention

[0004] This application provides a cathode material and a lithium metal battery. By optimizing the crystal structure of the cathode material, the cycle performance of the battery at room temperature and high temperature can be improved.

[0005] The inventors of this application have discovered that the cathode material contains Li, and its XRD diffraction pattern exhibits at least three characteristic peaks: the first characteristic peak is in the range of 18.24° to 18.35° with an intensity of A; the second characteristic peak is in the range of 42.76° to 43.74° with an intensity of B; and the third characteristic peak is in the range of 36.19° to 36.34° with an intensity of C; 1.30 ≤ A / B ≤ 1.72, and 1.09 ≤ B / C ≤ 1.86. The positions of these characteristic peaks correspond to a well-developed layered structure in the cathode material. The presence of these peaks indicates that the material has high crystallinity and a stable crystal structure, which is beneficial for reducing crystal structure damage and phase transitions during charging and discharging. Furthermore, by adjusting the peak intensity ratios of the characteristic peaks to conform to the aforementioned ranges, the crystal phase composition of the cathode material can be optimized, improving its conductivity and ion diffusion rate, reducing side reactions, and enhancing structural integrity even at high temperatures. Therefore, the cathode material of this application can improve the kinetics of lithium-ion migration and effectively suppress the structural phase transition of the cathode material, thereby improving the cycle performance of the battery at room temperature and high temperature.

[0006] Optionally, the coin cell composed of the positive electrode material and lithium metal, according to the positive electrode material of claim 1, is characterized in that, when the coin cell composed of the positive electrode material and lithium metal is charged and discharged at a current of 0.04C within a voltage range of 2.8V to 4.5V, the discharge curve of the obtained voltage-capacity curve has a plateau between 4.2V and 4.5V, the specific capacity in the 4.2V to 4.5V range of the discharge curve is Q1, and the total specific capacity in the 2.8V to 4.5V range of the discharge curve is Qt, where 0.18 ≤ Q1 / Qt ≤ 0.39. This indicates that the positive electrode material of this application can have a reversible discharge capacity in the high voltage range of 4.2V to 4.5V, and the capacity in this high voltage range is relatively high, enabling the positive electrode material to have a higher energy density.

[0007] Optionally, when a coin cell composed of a cathode material and lithium metal is charged and discharged at a current of 0.04C within a voltage range of 2.8V to 4.5V, the obtained voltage-capacity differential curve shows a first oxidation peak and a first reduction peak in the 3.6V to 4.0V range, and a second oxidation peak and a second reduction peak in the 4.2V to 4.5V range. These oxidation and reduction peaks indicate that the cathode material of this application undergoes significant elemental redox reactions and a significant phase transition in its material structure within the aforementioned voltage range, reflecting the intrinsic structure and compositional characteristics of the cathode material. This phase transition structure is difficult to define using structural formulas and conventional phase transition types, and the redox activity is also difficult to reflect using simple material chemical formulas and material structures. The aforementioned characteristic peaks in the voltage-capacity differential curve of this application indicate that the cathode material of this application possesses unique physicochemical properties. The inventors unexpectedly discovered that these physicochemical properties enable the cathode material to have superior charge-discharge performance and improve the cycle performance of the battery at both room temperature and high temperature.

[0008] Furthermore, the voltage at the peak position of the first oxidation peak is Vo1, and the voltage at the peak position of the second reduction peak is Vr1, with 0.040V ≤ |Vo1 - Vr1| ≤ 0.056V. Meeting this condition can further improve the cycle performance of the battery at both room temperature and high temperature.

[0009] Furthermore, the voltage at the peak position of the second oxidation peak is Vo2, and the voltage at the peak position of the second reduction peak is Vr2, with 0.042V ≤ |Vo2 - Vr2| ≤ 0.058V. Meeting this condition can further improve the cycle performance of the battery at both room temperature and high temperature.

[0010] Furthermore, the peak height of the second oxidation peak ranges from 300 mAh / g / V to 4000 mAh / g / V. Meeting this condition can further improve the cycle performance of the battery at both room temperature and high temperature.

[0011] Optionally, the Li content is 5% to 7.25% by mass, depending on the mass of the cathode material. Meeting this condition can further improve the cycle performance of the battery at room temperature and high temperature.

[0012] Optionally, the cathode material includes Li, M, D, and O elements, wherein the M element is selected from at least one of Na or Ca elements, and the D element includes at least two of Ni, Co, or Mn elements; the cathode material satisfies at least one of the following conditions:

[0013] I. The molar ratio of element M to element D is 0.010 to 0.072;

[0014] II. Cathode materials also include M 1 Element, M 1 The element is selected from at least one of Sr, Al, Mg, or Ti; M 1 The molar ratio of element D to element D is 0.002 to 0.02;

[0015] III. The molar ratio of Li to D is 0.8 to 0.99;

[0016] IV. The molar ratio of Ni to D is 0.45 to 0.6;

[0017] V. The molar ratio of Co to D is 0.001 to 0.1;

[0018] VI. The molar ratio of Mn to D is 0.45 to 0.55.

[0019] When the cathode material meets at least one of the above conditions, the cycle performance of the battery at room temperature and high temperature can be further improved.

[0020] Optionally, the cell parameters of the cathode material satisfy at least one of conditions i to iii;

[0021] i.

[0022] ii.

[0023] iii. 4.5 ≤ c / a ≤ 5.5.

[0024] Meeting at least one of the above conditions can further improve the cycle performance of the battery at room temperature and high temperature.

[0025] In another aspect of this application, this application provides a lithium metal pouch battery, including a positive electrode, an electrolyte, and a negative electrode, wherein the positive electrode includes the positive electrode material described above.

[0026] The lithium metal pouch battery based on this application, including the cathode material mentioned above, can improve the reversibility of lithium-ion migration and effectively suppress the structural phase transition of the cathode material, thereby improving the cycle performance and high-temperature cycle performance of the lithium metal pouch battery.

[0027] Optionally, the electrolyte includes a lithium salt and an organic solvent; the electrolyte includes a first substance, which includes at least one of lithium nitrate, lithium difluorophosphate, lithium bis(oxalato)borate, 1,3-propenesulfonate lactone, or vinyl sulfate. Based on the mass of the electrolyte, the mass content of the first substance is 0.1% to 1%. Adding the first substance to the electrolyte, in conjunction with the positive electrode material of this application, helps to further improve the cycle performance of the battery at room temperature and high temperature.

[0028] Additional aspects and advantages of the embodiments of this application will be described, shown, or illustrated in part by way of implementation of the embodiments of this application in the following description. Attached Figure Description

[0029] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 shows the XRD patterns of the cathode materials in Examples 1-6 of this application;

[0031] Figure 2 shows the voltage-capacity differential curves of the coin cells using the cathode materials of Examples 1-6 of this application during the second week;

[0032] Figure 3 shows the charge-discharge curves of the coin cells using the cathode materials of Examples 1-6 of this application during the second week. Detailed Implementation

[0033] The embodiments of this application will be described in detail below. These embodiments should not be construed as limiting the scope of this application.

[0034] Unless otherwise expressly stated, the terms used in this application shall have the meanings indicated below.

[0035] Due to their high energy density and low cost, ternary lithium-ion batteries have been widely used in power tools, electric vehicles, bicycles, electric motorcycles, electric cars, and special equipment. However, the cycle performance of ternary cathode materials at both room temperature and high temperature still has room for improvement in practical applications. The inventors have discovered that during charge-discharge cycles, transition metal ions in the transition metal layer of the cathode material undergo irreversible migration to the lithium layer, causing irreversible phase transitions in the structure. For example, phase transitions from layered structures to spinel structures and from layered structures to rock salt phase structures lead to severe voltage decay and capacity loss, adversely affecting the improvement of lithium-ion battery cycle performance. Based on this, this application provides a cathode material and a lithium metal pouch battery that can solve the problem of irreversible phase transitions caused by the irreversible migration of transition metal ions in the transition metal layer to the lithium layer.

[0036] In one embodiment, this application provides a lithium metal pouch battery, which includes at least a positive electrode, a negative electrode, and an electrolyte as described below.

[0037] I. Positive electrode

[0038] The positive electrode in the embodiments of this application includes a positive electrode material. The positive electrode material is a substance that can insert and extract ions during battery discharge, and it directly determines the performance of the battery. Therefore, selecting a suitable positive electrode material is crucial for improving the overall performance of lithium metal pouch batteries.

[0039] The cathode material contains Li, and its XRD diffraction pattern exhibits at least three characteristic peaks: the first characteristic peak is in the range of 18.24° to 18.35° with an intensity of A; the second characteristic peak is in the range of 42.76° to 43.74° with an intensity of B; and the third characteristic peak is in the range of 36.19° to 36.34° with an intensity of C; 1.30 ≤ A / B ≤ 1.72, and 1.09 ≤ B / C ≤ 1.86. The inventors discovered that cathode materials satisfying these characteristics possess a good layered structure. The presence of these peaks indicates that the material has high crystallinity and a stable crystal structure, which can improve the kinetics of lithium-ion migration and effectively suppress structural phase transitions in the cathode material, thereby improving the cycle performance of the battery under both room temperature and high temperature conditions.

[0040] In addition, the positive electrode material layer formed using the positive electrode material in the embodiments of this application can be one or more layers when assembling the battery.

[0041] In some embodiments, from the viewpoint of improving the cycle performance of the battery, the mass content of Li element in the cathode material may be a value within the range of 5%, 5.25%, 5.5%, 5.75%, 6.0%, 6.25%, 6.5%, 6.75%, 7.0%, 7.25%, or any two thereof, based on the mass of the cathode material.

[0042] In some embodiments, from the viewpoint of improving battery cycle performance, the cathode material includes Li, M, D, and O elements, wherein the D element includes at least two of Ni, Co, or Mn elements, and the molar ratio of M to D elements is a value within the range of 0.010, 0.020, 0.050, 0.060, 0.070, 0.071, 0.072, or any two of these. By introducing the M element into the cathode material, the internal electronic structure of the cathode material can be changed to improve the overall performance of the battery. The M element is selected from at least one of Na and Ca elements.

[0043] In some embodiments, from the viewpoint of improving the cycle performance of the battery, the cathode material further includes M 1 Element, M 1 The molar ratio of element M to element D is a value within the range of 0.002, 0.004, 0.008, 0.010, 0.015, 0.018, 0.020, or any two of these ranges. This is achieved by introducing M into the cathode material. 1 Elements that can alter the internal electronic structure of cathode materials can improve the overall performance of the battery. M 1 The element is selected from at least one of Sr, Al, Mg, and Ti.

[0044] In some embodiments, from the viewpoint of improving the cycle performance of the battery, the molar ratio of Li to D is a value within the range of 0.80, 0.82, 0.84, 0.86, 0.88, 0.9, 0.92, 0.94, 0.96, 0.98, 0.99, or any two of these.

[0045] In some embodiments, from the viewpoint of improving the cycle performance of the battery, the molar ratio of Ni to D is a value within the range of 0.45, 0.48, 0.51, 0.54, 0.57, 0.60, or any two of these.

[0046] In some embodiments, from the viewpoint of improving the cycle performance of the battery, the molar ratio of Co to D is a value within the range of 0.01, 0.020, 0.040, 0.080, 0.10, or any two of these.

[0047] In some embodiments, from the viewpoint of improving the cycle performance of the battery, the molar ratio of Mn to D is a value within the range of 0.40, 0.42, 0.45, 0.47, 0.049, 0.051, 0.053, 0.55, or any two of these.

[0048] In some embodiments, when a coin cell composed of a cathode material having the characteristic peaks and peak intensity ratios described above and lithium metal is charged and discharged at a current of 0.04C within a voltage range of 2.8V to 4.5V, the voltage-capacity differential curve of the second charge-discharge cycle shows a first oxidation peak and a first reduction peak in the 3.6V to 4.0V range, and a second oxidation peak and a second reduction peak in the 4.2V to 4.5V range. The first oxidation peak and the first reduction peak can be values ​​within the range of 3.6V, 3.7V, 3.8V, 3.9V, 4.0V, or any two of these ranges. The second oxidation peak and the second reduction peak can be values ​​within the range of 4.2V, 4.3V, 4.4V, 4.5V, or any two of these ranges. Since each redox reaction contributes a portion of the capacity, the two pairs of redox peaks present in this application can provide a higher specific capacity, thus the cathode material having the above characteristics is beneficial for further improving the cycle performance of the battery.

[0049] In some embodiments, for a coin cell composed of a cathode material and lithium metal, the peak intensities of the second oxidation peak and the second reduction peak in the voltage-capacity differential curve (dQ / dV-V curve) in the 2.5V to 4.5V range can be within the range of 300mAh / g / V, 400mAh / g / V, 600mAh / g / V, 800mAh / g / V, 1000mAh / g / V, 1200mAh / g / V, 1400mAh / g / V, 1600mAh / g / V, 1800mAh / g / V, 2000mAh / g / V, 2200mAh / g / V, 2400mAh / g / V, 2800mAh / g / V, 3200mAh / g / V, 3600mAh / g / V, 4000mAh / g / V, or any combination thereof. Cathode materials within this peak intensity range are beneficial for further improving the cycle performance of the battery under both room temperature and high temperature conditions.

[0050] In some embodiments, when a coin cell composed of a positive electrode material and lithium metal is charged and discharged at a current of 0.04C within a voltage range of 2.8V to 4.5V, the voltage-capacity curve of the second charge-discharge cycle satisfies the following: the discharge curve has a plateau between 4.2V and 4.5V; the specific capacity of the discharge curve in the 4.2V to 4.5V range is Q1; the total specific capacity of the discharge curve in the 2.8V to 4.5V range is Qt; and Q1 / Qt can be a value within the range of 0.18, 0.19, 0.20, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29, 0.30, 0.31, 0.32, 0.33, 0.34, 0.35, 0.36, 0.37, 0.38, 0.39, or any two of these values. This cathode material exhibits good electrochemical activity at high voltages, enabling it to continuously provide electrical energy at higher voltages, while also contributing to capacity in the lower voltage range, thus demonstrating good energy density. Furthermore, based on the crystal structure characterized by the above features, assembling the cathode material of this application into electrochemical devices such as lithium-ion pouch batteries can improve their cycle performance and safety performance.

[0051] In some embodiments, when a coin cell composed of a cathode material and lithium metal is charged and discharged at a current of 0.04C within a voltage range of 2.8V to 4.5V, the voltage-capacity differential curve of the charge and discharge cycle in the second week satisfies the following: the voltage at the peak position of the first oxidation peak is Vo1, the voltage at the peak position of the first reduction peak is Vr1, and |Vo1-Vr1| can be a value within the range of 0.040, 0.042, 0.044, 0.046, 0.048, 0.050, 0.052, 0.054, 0.056, or any two of them.

[0052] Therefore, cathode materials with at least three characteristic peaks in the above XRD patterns exhibit relatively mild structural changes in the 3.6V to 4.0V range, without drastic phase transitions or lattice recombination. Their redox reactions have high reversibility, enabling the cathode material to effectively recover to its initial state during charge-discharge cycles. This reduces irreversible capacity loss of the cathode and further improves the cycle performance of the battery.

[0053] In some embodiments, when a coin cell composed of a cathode material and lithium metal is charged and discharged at a current of 0.04C within a voltage range of 2.8V to 4.5V, the voltage-capacity differential curve of the second charge-discharge cycle satisfies the following: the voltage at the peak position of the second oxidation peak is Vo2, the voltage at the peak position of the second reduction peak is Vr2, and |Vo2-Vr2| can be a value within the range of 0.042, 0.044, 0.046, 0.048, 0.050, 0.052, 0.054, 0.056, 0.058, or any two of these values. Therefore, cathode materials with at least three characteristic peaks in the above XRD pattern exhibit relatively mild structural changes in the 4.1V to 4.5V range, without drastic phase transitions or lattice recombination. Their redox reactions have high reversibility, enabling the cathode material to effectively recover to its initial state during charge-discharge cycles, thereby reducing irreversible capacity loss of the cathode and further improving the cycle performance of the battery.

[0054] In some embodiments, the cell parameter a can be: Or a value within the range of any two of them. The cell parameter c can be... The ratio of cell parameter a to cell parameter c can be 4.5, 5, 5.5, or any value within the range of any two of these. Satisfying any of these conditions can enhance the crystal structure stability, electrochemical stability, lithium-ion diffusion rate, and overall energy density of the cathode material, thereby contributing to further improvements in battery cycle performance and high-temperature storage performance.

[0055] In some embodiments, the above-mentioned cathode material can be obtained by the following preparation method:

[0056] Step 1: Prepare a Ni-containing mixture according to the element molar ratio. 2+ Mn 2+ A mixed solution of Ni was reacted with a precipitant and a complexing agent. By controlling the reaction time to be 10–72 h and the pH to be 11–12.5, the precursor Ni was obtained. a Mn c (OH)2. The average particle size Dv50 of the precursor is 2–18 μm. The precipitant can be selected from at least one of sodium hydroxide, ammonia, sodium sulfate, sodium nitrate, ammonium sulfate, ammonium oxalate, ammonium nitrate, sodium bicarbonate, sodium phosphate, potassium hydroxide, ammonium carbonate, and sodium carbonate. The complexing agent can be selected from at least one of ammonia, ethylenediaminetetraacetic acid, citric acid, tartaric acid, oxalic acid, urea, adipic acid, malonic acid, lactic acid, and potassium tartrate carbonate.

[0057] Step 2: Grind and mix the precursor and sodium source from the above steps in a uniform ratio, calcine them at 750-950℃ in air for 16-24 hours, then cool them to room temperature in a mixed atmosphere of nitrogen and argon, and finally crush and sieve them to obtain the intermediate product.

[0058] Step 3: Mix the intermediate product from the above steps with the lithium source in a certain proportion, heat the mixture to 360-440°C at a heating rate of 16-34°C / min, and hold the temperature for 10-72 hours to obtain the cathode material.

[0059] In some embodiments, after obtaining the cathode material in step 3), the product can be cooled to room temperature in an argon-air mixture (volume ratio of 1:1) at a cooling rate of 50°C / min. The product is then fully soaked and stirred in deionized water, and after filtration, vacuum drying, crushing, and sieving, the cathode material is obtained.

[0060] In the lithium metal pouch battery of this application, the positive electrode material layer is located on at least one surface of the positive electrode current collector. The positive electrode can be prepared by coating a positive electrode slurry containing a positive electrode material, a binder, a solvent, etc., onto the positive electrode current collector, drying it, and then calendering it to form a positive electrode material layer on the surface of the positive electrode current collector, thereby obtaining the positive electrode.

[0061] The positive electrode material layer may also include a positive electrode conductive material. In this embodiment, there is no limitation on the type of positive electrode conductive material; any known conductive material can be used. Examples of positive electrode conductive materials may include, but are not limited to, carbon black such as acetylene black; carbon materials such as amorphous carbon such as needle coke; carbon nanotubes; graphene, etc. The above-mentioned positive electrode conductive materials can be used alone or in any combination.

[0062] There are no restrictions on the type of solvent used to form the positive electrode slurry, as long as it is a solvent that can dissolve or disperse the positive electrode material, conductive material, and positive electrode binder.

[0063] Examples of solvents used to form the positive electrode slurry may include any of aqueous solvents and organic solvents. Examples of aqueous media may include, but are not limited to, water and mixed media composed of alcohol and water. Examples of organic media may include, but are not limited to, aliphatic hydrocarbons such as hexane; aromatic hydrocarbons such as benzene, toluene, xylene, and methylnaphthalene; heterocyclic compounds such as quinoline and pyridine; ketones such as acetone, methyl ethyl ketone, and cyclohexanone; esters such as methyl acetate and methyl acrylate; amines such as diethylenetriamine and N,N-dimethylaminopropylamine; ethers such as diethyl ether, propylene oxide, and tetrahydrofuran; amides such as N-methylpyrrolidone, dimethylformamide, and dimethylacetamide; and aprotic polar solvents such as hexamethylphosphoramide and dimethyl sulfoxide. In some embodiments, the viscosity of the positive electrode slurry is a value within the range of about 3000 mPas, 3500 mPas, 4000 mPas, 4500 mPas, 5000 mPas, 5500 mPas, 6000 mPas, or any two thereof, to facilitate coating.

[0064] There are no particular limitations on the type of positive electrode current collector; it can be any material known to be suitable for use as a positive electrode current collector. Examples of positive electrode current collectors may include, but are not limited to, metallic materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum; and carbon materials such as carbon cloth and carbon paper. In some embodiments, the positive electrode current collector is a metallic material. In some embodiments, the positive electrode current collector is aluminum.

[0065] To reduce the electronic contact resistance between the positive current collector and the positive electrode material layer, the surface of the positive current collector may include a conductive additive or a conductive coating. Examples of conductive additives include, but are not limited to, carbon and precious metals such as gold, platinum, and silver. Examples of conductive coatings may include a mixture layer containing inorganic oxides, conductive agents, and binders.

[0066] II. Electrolyte

[0067] Electrolytes play a crucial role in lithium-ion batteries, serving not only as the medium for lithium-ion transport but also influencing battery safety and cycle stability. Lithium salts and organic solvents are the main components of electrolytes, and the choice of lithium salt significantly impacts the electrolyte's thermal stability.

[0068] The electrolyte includes an organic solvent, a lithium salt, and additives. The organic solvent in the electrolyte according to this application can be any organic solvent known in the prior art that can be used as an electrolyte solvent. There are no limitations on the electrolyte used in the electrolyte according to this application; it can be any electrolyte known in the prior art. Furthermore, the electrolyte according to this application may include additives, and the additives can be any additive known in the prior art that can be used as an electrolyte additive.

[0069] In some embodiments, the first substance includes at least one selected from lithium nitrate, lithium difluorophosphate, lithium bis(oxalato)borate, 1,3-propenesulfonate lactone, and vinyl sulfate. The mass content of the first substance may be 0.1%, 0.2%, 0.5%, 0.7%, 0.9%, 1%, or a value within any two of these ranges.

[0070] In some embodiments, the electrolyte also includes other lithium salts, including at least one of lithium perchlorate, lithium tetrafluoroborate, lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalate)borate, lithium difluorooxalateborate, lithium tri(oxalate)phosphate, lithium difluorobis(oxalate)phosphate, and lithium tetrafluoro(oxalate)phosphate.

[0071] In some embodiments, the molar content of lithium salt can be 1 mol·L⁻¹ based on the total mass of the electrolyte. -1 2 mol·L -1 3 mol·L -1 4 mol·L -1 5 mol·L -1 Or values ​​within a range of any two of these. By setting the content to the above range, a higher ionic conductivity can be maintained, a more stable SEI film can be formed on the positive and negative electrode surfaces, thereby improving their cycle performance.

[0072] In some embodiments, by further selecting the specific type of organic solvent, it is made to have good compatibility with the negative electrode and to have synergistic effects with the aforementioned lithium salt, thereby improving the cycle performance of the electrochemical device. Organic solvents include ether compounds and alkane compounds.

[0073] In some embodiments, the electrolyte further includes ether compounds, including at least one selected from dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, ethyl propyl ether, methoxyethoxy, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol methyl ethyl ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, triethylene glycol, tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether, tetraethylene glycol methyl ethyl ether, polyethylene glycol dimethyl ether, polyethylene glycol diethyl ether, polyethylene glycol methyl ethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, ethylene glycol dibutyl ether, and ethylene glycol diethyl ether. Alkane compounds include dimethoxyethane, diethoxyethane, and fluorinated 1,4-dimethoxybutane.

[0074] In some embodiments, the preparation of an electrolyte is also involved, wherein an organic solvent and a lithium salt are mixed in a dry argon atmosphere to obtain an electrolyte.

[0075] III. Negative electrode

[0076] The negative electrode includes the negative electrode active material, which is a key component of lithium-ion batteries and is crucial for improving the overall performance of the battery. This application does not have any particular limitations, as long as the purpose of this application can be achieved.

[0077] In some embodiments, the negative electrode active material includes metallic lithium or a lithium alloy, which can improve the specific capacity of the battery. The lithium alloy includes any one or a combination of two or more of Li-Sn alloy, Li-Mg alloy, Li-B alloy, and Li-Al alloy. Working synergistically with the positive electrode and electrolyte described above, they not only overcome the problems of pure lithium metal negative electrodes, such as dead lithium or lithium dendrite formation, but also improve the overall performance and safety of the battery to a certain extent. Furthermore, the Li-Sn alloy can be rolled into a thin sheet of a certain thickness and uniform thickness, and then punched to a size of 38mm × 58mm.

[0078] It is important to know that the negative electrode material layer may also include a negative electrode binder, which is a key component ensuring good adhesion between the electrode material and the current collector. A suitable binder can improve the cycle stability of the electrode. There are no particular limitations on the type of negative electrode binder, as long as it is a material stable to the electrolyte or the solvent used in electrode manufacturing. In some embodiments, the negative electrode binder includes a resin binder. Examples of resin binders include, but are not limited to, fluoropolymers, polyacrylonitrile (PAN), polyimide resins, acrylic resins, polyolefin resins, etc. When a negative electrode slurry is prepared using an aqueous solvent, the negative electrode binder includes, but is not limited to, carboxymethyl cellulose (CMC) or its salts, styrene-butadiene rubber (SBR), polyacrylic acid (PAA) or its salts, polyvinyl alcohol, polyacrylic acid, polyimide, etc.

[0079] As the current collector for retaining the negative electrode material, any known current collector can be used. Examples of negative electrode current collectors include, but are not limited to, metallic materials such as copper, nickel, stainless steel, and nickel-plated steel. In some embodiments, the negative electrode current collector is copper.

[0080] The negative electrode can be prepared by coating a negative electrode slurry containing negative electrode material, resin binder, etc. onto a negative electrode current collector, drying it, and then calendering it to form a negative electrode material layer on both sides of the negative electrode current collector, thereby obtaining the negative electrode.

[0081] IV. Separating membrane

[0082] To prevent short circuits, a separator is typically placed between the positive and negative electrodes. In this case, the electrolyte of this application is typically used after penetrating into the separator.

[0083] There are no particular limitations on the material and shape of the separator, as long as it does not significantly impair the effectiveness of this application. The separator may be a resin, glass fiber, inorganic material, or other material formed from a material stable to the electrolyte of this application. In some embodiments, the separator includes a porous sheet or non-woven fabric-like material with excellent liquid retention properties. Examples of materials for resin or glass fiber separators may include, but are not limited to, polyolefins, aromatic polyamides, polytetrafluoroethylene, polyethersulfone, etc. In some embodiments, the polyolefin is polyethylene or polypropylene. In some embodiments, the polyolefin is polypropylene. The above-mentioned separator materials can be used alone or in any combination.

[0084] The separator can also be a material formed by laminating the above-mentioned materials, examples of which include, but are not limited to, a three-layer separator formed by laminating polypropylene, polyethylene, and polypropylene in that order.

[0085] Examples of inorganic materials may include, but are not limited to, oxides such as alumina and silicon dioxide, nitrides such as aluminum nitride and silicon nitride, and sulfates (e.g., barium sulfate, calcium sulfate, etc.). Inorganic materials may be in, but are not limited to, particulate or fibrous forms.

[0086] The separator can be in the form of a thin film, examples of which include, but are not limited to, nonwoven fabrics, woven fabrics, microporous membranes, etc. In the form of a thin film, the pore size of the separator is 0.01 μm to 1 μm, and the thickness is 5 μm to 50 μm. In addition to the above-mentioned independent thin film separators, the following separators can also be used: separators formed by using a resin-based adhesive to form a composite porous layer containing the above-mentioned inorganic particles on the surface of the positive and / or negative electrodes, for example, a separator formed by using fluororesin as an adhesive to form a porous layer of alumina particles with a particle size of less than 1 μm on both sides of the positive electrode.

[0087] The thickness of the separator is arbitrary. In some embodiments, the thickness of the separator is greater than 1 μm, greater than 5 μm, or greater than 8 μm. In some embodiments, the thickness of the separator is less than 50 μm, less than 40 μm, or less than 30 μm. When the thickness of the separator is within the above ranges, insulation and mechanical strength can be ensured, as well as the DC resistance characteristics and energy density of the secondary battery.

[0088] This application also provides a lithium metal pouch battery, the use of which is not particularly limited, and it can be used in any electronic device known in the prior art. In some embodiments, the secondary battery of this application can be used in, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, household large-capacity batteries, and lithium-ion capacitors, etc.

[0089] Example

[0090] The following uses a lithium metal pouch cell as an example to illustrate the implementation of the electrochemical device of this application in more detail through embodiments and comparative examples. Those skilled in the art will understand that the preparation methods described in this application are merely examples, and any other suitable preparation methods are within the scope of this application.

[0091] Comparative Example 1

[0092] Cathode materials and their preparation methods

[0093] 1) Prepare a mixed solution containing NiSO4 and MnSO4 according to the elemental molar ratio Ni:Mn = 5:5. Mix this solution with a precipitant (NaOH solution) and a complexing agent (ammonia water) and react them. By controlling the reaction time, ammonia water concentration, and pH value, the precursor Ni is obtained. 0.5 Mn 0.5 (OH)2.

[0094] 2) Grind and mix the precursor and lithium carbonate in a certain proportion, calcine at 850°C in air for 20 hours, cool to room temperature at a certain rate, and finally obtain the cathode material by crushing and sieving.

[0095] Lithium metal pouch cells and their preparation methods

[0096] <Preparation of the positive electrode>

[0097] A positive electrode slurry was prepared by mixing polyvinylidene fluoride (PVDF) as a binder, conductive carbon black (Super P) as a conductive agent, and positive electrode material in a weight ratio of 1.5:1.5:97. The viscosity of the positive electrode slurry was adjusted to 6000 mPas. The mixed slurry was then uniformly coated onto aluminum foil with a single-layer thickness of 200 μm, applied to one side only. After drying, the slurry was rolled to form the desired electrode. The electrode processing and transport environment was kept at a humidity of 45%. The areal density of the coated electrode was 14 mg / cm³. 2The positive electrode sheet is obtained after drying and then punched into a size of 38mm×58mm for later use.

[0098] <Alloy Anode Preparation>

[0099] The Li-Sn alloy was rolled into thin sheets of a certain thickness and uniform thickness, and then cut into 40mm×60mm sizes for later use.

[0100] <Preparation of Electrolyte>

[0101] Preparation of ether electrolyte for lithium metal pouch batteries: In an argon atmosphere glove box with a water content of <10ppm, first mix dioxane (DOL) and dimethyl ether (DME) in a 1:1 volume ratio, then add lithium bis(fluorosulfonyl)imide (LiFSI) to an organic solvent to dissolve and mix evenly to obtain an electrolyte with a lithium salt molar concentration of 3mol / L.

[0102] <Lithium Metal Pouch Battery Assembly>

[0103] A 15μm thick polyethylene (PE) separator was selected, with the alloy negative electrode placed in the middle. The upper and lower layers were single-sided coated positive electrodes, with the separator between the positive and negative electrodes. After stacking, the four corners of the entire stacked structure were fixed with tape, and then placed in an aluminum-plastic film. After top and side sealing, electrolyte injection, and encapsulation, a lithium metal pouch battery was finally obtained.

[0104] Comparative Example 2

[0105] Cathode materials and their preparation methods

[0106] The preparation method is the same as that of the cathode material in Comparative Example 1, except that the ratio of nickel and manganese in the precursor is changed. The specific results are shown in Table 1.

[0107] Lithium metal pouch cells and their preparation methods

[0108] The difference between this and the lithium metal pouch battery and its preparation method in Comparative Example 1 is that the cathode material used in the preparation of the cathode is the same as that in this Comparative Example.

[0109] Example 1-1

[0110] Cathode materials and their preparation methods

[0111] 1) A mixed solution containing NiSO4 and MnSO4 was prepared according to the elemental molar ratio Ni:Mn = 45:55. This solution was then reacted with a precipitant (NaOH solution) and a complexing agent (ammonia). By controlling the reaction time, ammonia concentration, and pH value, a precursor Ni with an average particle size Dv50 of 10 μm was obtained. 0.45 Mn 0.55 (OH)2.

[0112] 2) Grind and mix the precursor and sodium carbonate in a certain proportion, calcine at 850°C in air for 24 hours, cool to room temperature in a mixed atmosphere of nitrogen and argon, and finally crush and sieve to obtain the intermediate product.

[0113] 3) The intermediate product from the above steps is mixed with a lithium source (a mixture of lithium hydroxide and lithium nitrate in a molar ratio of 1:1) at a mass ratio of 1:10. The mixture is heated to 450°C at a heating rate of 30°C / min and held at that temperature for 10 hours. Then, it is cooled to room temperature in an argon and air mixture (volume ratio of 1:1) at a cooling rate of 50°C / min. The product is thoroughly soaked in deionized water and stirred. After filtration, vacuum drying, crushing, and sieving, the cathode material is obtained.

[0114] Lithium metal pouch cells and their preparation methods

[0115] The difference between this and the lithium metal pouch battery and its preparation method in Comparative Example 1 is that the positive electrode material used in this embodiment is the same as that used in the preparation of the positive electrode.

[0116] Examples 1-2 to Examples 1-5

[0117] Cathode materials and their preparation methods

[0118] Similar to the preparation method of Comparative Example 1, the difference lies in that the types and relative contents of element D in the precursors are changed in Examples 1-2 to 1-5, as detailed in Table 1.

[0119] Lithium metal pouch cells and their preparation methods

[0120] The difference between this and the lithium metal pouch battery and its preparation method in Comparative Example 1 is that the positive electrode material used in the preparation of the positive electrode is the same as that in the corresponding example.

[0121] Examples 1-6 to Examples 1-9

[0122] Cathode materials and their preparation methods

[0123] Similar to the preparation method of Comparative Example 1, the difference is that in Example 1-6 to Example 1-9, in step 2), a certain amount of M needs to be added while mixing the precursor with sodium carbonate. 1 The doping elements are derived from strontium hydroxide octahydrate (Sr), nano-alumina (Al), nano-magnesium oxide (Mg), and nano-titanium dioxide (Ti). Please refer to Table 1 for details.

[0124] Lithium metal pouch cells and their preparation methods

[0125] The difference between this and the lithium metal pouch battery and its preparation method in Comparative Example 1 is that the positive electrode material used in the preparation of the positive electrode is the same as that in the corresponding example.

[0126] Examples 1-10 to Examples 1-13

[0127] Cathode materials and their preparation methods

[0128] Similar to the preparation method in Examples 1-1, the difference is that in Step 2) of Examples 1-10 to 1-13, a certain amount of M1 dopant and calcium hydroxide need to be added while the precursor is mixed with sodium carbonate. Sr is strontium hydroxide octahydrate, Al is nano aluminum oxide, Mg is nano magnesium oxide, and Ti is nano titanium dioxide. For details, please refer to Table 1.

[0129] Lithium metal pouch cells and their preparation methods

[0130] The difference between this and the lithium metal pouch battery and its preparation method in Comparative Example 1 is that the positive electrode material used in the preparation of the positive electrode is the same as that in the corresponding example.

[0131] Examples 2-1 to 2-3

[0132] Lithium metal pouch cells and their preparation methods

[0133] The difference between the lithium metal pouch batteries in Examples 2-1 to 2-3 and those in Examples 1-9 and their preparation methods is that some lithium nitrate is added to the electrolyte. The amount of lithium nitrate added is shown in Table 4.

[0134] Examples 2-4

[0135] Lithium metal pouch cells and their preparation methods

[0136] The difference between the lithium metal pouch batteries in Examples 2-4 and Examples 1-9 and their preparation methods is that some lithium difluorophosphate is added to the electrolyte. The amount of lithium difluorophosphate added is shown in Table 4.

[0137] Examples 2-5

[0138] Lithium metal pouch cells and their preparation methods

[0139] The difference between the lithium metal pouch batteries in Examples 2-5 and Examples 1-9 and their preparation methods is that some lithium bis(oxalate-borate) is added to the electrolyte. The amount of lithium bis(oxalate-borate) added is shown in Table 4.

[0140] Examples 2-6

[0141] Lithium metal pouch cells and their preparation methods

[0142] The difference between the lithium metal pouch batteries in Examples 2-6 and Examples 1-9 and their preparation methods is that some 1,3-propenesulfonate lactone is added to the electrolyte. The amount of 1,3-propenesulfonate lactone added is shown in Table 4.

[0143] Examples 2-7 to 2-9

[0144] Lithium metal pouch cells and their preparation methods

[0145] The difference between the lithium metal pouch batteries in Examples 2-7 to 2-12 and those in Examples 1-9 and their preparation methods is that some vinyl sulfate is added to the electrolyte. The amount of vinyl sulfate added is shown in Table 4.

[0146] Cathode material performance testing

[0147] XRD test:

[0148] The cathode materials in Examples 1-1 to 1-13, as well as Comparative Examples 1 and 2, were ground into powder. Using a Cu Kα radiation source, the voltage and current were set to 40 kV / 40 mA, and the scanning angle range was set to 10° to 70°. XRD patterns were recorded using a Bruker D8 Advance instrument. The patterns were processed using software, and the ratio of the c-axis to the a-axis of the unit cell parameter c / a was calculated using the software built into the X-ray diffractometer. The test results are shown in Table 2.

[0149] Elemental content testing of cathode materials:

[0150] Elemental content testing of cathode material: The cathode material was dissolved in aqua regia (e.g., 0.4g of cathode material was dissolved in 10ml of aqua regia solution (the volume ratio of aqua regia to deionized water was 1:1, and the volume ratio of concentrated hydrochloric acid to concentrated nitric acid was 3:1). The cathode material was then fully digested in a CEM-Mars5 / Mars6 microwave digester, and the volume was adjusted to 100mL. The mass percentage content of elements such as Li, M, Mg, Ni, Co, and Mn in the solution was tested using an inductively coupled plasma optical emission spectrometer (ICP-OES) system, and converted into the corresponding amounts of substance. Taking Li as an example, the formula for calculating the amount of substance of Li is: Amount of Li = Mass of cathode material digested by ICP × Mass percentage content of Li ÷ Molar mass of Li. Similarly, the amounts of Li can be calculated separately. The amounts of substance of elements M, M1, Ni, Co, and Mn were determined. The molar ratios of these elements to element D were then calculated. Taking the molar ratio of Li to D as an example, the formula is: Molar ratio of Li to D = Amount of Li ÷ (Amount of Co + Amount of Ni + Amount of Mn). Where the amount of D is defined as 1, i.e.: D = Amount of Ni ÷ (Amount of Co + Amount of Ni + Amount of Mn) + Amount of Co ÷ (Amount of Co + Amount of Ni + Amount of Mn) + Amount of Mn ÷ (Amount of Co + Amount of Ni + Amount of Mn). Specific test results are shown in Table 1.

[0151] Q1 / Qt, dQ / dV tests:

[0152] Fabrication of lithium-ion coin cells:

[0153] A positive electrode slurry was prepared by mixing polyvinylidene fluoride (PVDF) as a binder, conductive carbon black (Super P) as a conductive agent, and the positive electrode materials from Examples 1-1 to 1-13, as well as Comparative Examples 1 and 2, in a weight ratio of 1.5:1.5:97. The viscosity of the positive electrode slurry was adjusted to 6000 mPas. The mixed slurry was then uniformly coated onto aluminum foil with a single-layer thickness of 200 μm, applied to one side only. After drying, the electrode was rolled to form the desired electrode. The humidity during electrode processing and transport was 45%. The areal density of the coated electrode was 14 mg / cm³. 2 The positive electrode sheet is obtained after drying and then punched into a size of 38mm×58mm for later use.

[0154] The separator is cut into 2018mm discs; the negative electrode is a lithium metal sheet with a diameter of 18mm; LiPF6 is added to a solvent containing a uniform mixture of propylene carbonate (PC), ethylene carbonate (EC), and diethyl carbonate (DEC) (weight ratio 1:1:1) to obtain an electrolyte with a LiPF6 mass concentration of 12.5%; the positive electrode, separator paper, negative electrode (lithium sheet), electrolyte, battery casing, and other accessories are moved into a glove box (water content must be less than 11ppm), and the battery is assembled and injected with electrolyte in the following stacking order from bottom to top: negative electrode casing > flat pad + appropriate amount of electrolyte > lithium metal sheet + appropriate amount of electrolyte > one layer of separator paper + appropriate amount of electrolyte > positive electrode + appropriate amount of electrolyte > flat pad + appropriate amount of electrolyte > spring sheet > positive electrode casing; the battery is then packaged on a packaging machine to obtain a button cell.

[0155] The coin cells composed of the cathode materials and lithium metal from Examples 1-1 to 1-13, Comparative Example 1, and Comparative Example 2 were charged and discharged at a current of 0.04C within a voltage range of 2.8V to 4.5V. The charge and discharge conditions in the second week were recorded. The test method is as follows:

[0156] 1. Using an electrochemical workstation, the charge-discharge curves of lithium-ion coin cells in the voltage range of 2.8V to 4.5V were obtained at 25℃.

[0157] 2. First, charge at a constant current of 0.04C to 4.5V, then charge at a constant voltage of 4.5V until the current is 0.02C;

[0158] 3. After standing for 5 minutes, discharge at a constant current of 0.04C to 2.8V, and then stand for 5 minutes.

[0159] 4. The discharge capacity in the voltage range of 4.2 to 4.5V is calculated to be Q1, and the discharge capacity in the voltage range of 2.8V to 4.5V is calculated to be Qt.

[0160] 5. Simultaneously, based on the dQ / dV curve, obtain the peak position Vo1 (V) of the first oxidation peak, the peak position Vr1 (V) of the first reduction peak, the peak position Vo2 of the second oxidation peak, and the peak height, and the peak position Vr2 (V) of the second reduction peak in the voltage-capacity differential curve (dQ / dV) in the range of 4.2V to 4.5V. Record the results as shown in Table 1.

[0161] The cathode materials in Examples 1-1 to 1-13 and Comparative Example 2 in Table 1 differ from those in Comparative Example 1 only in that the cathode material composition is adjusted according to Table 1. The distribution of the three characteristic peaks of the XRD diffraction pattern of the cathode material is shown in Table 1.

[0162] Figure 1 shows the XRD patterns of the cathode materials of Examples 1-6 of this application. It can be seen that the XRD diffraction patterns of the cathode materials of Examples 1-6 of this application have at least three characteristic peaks: the first characteristic peak is in the range of 18.24° to 18.35°, the second characteristic peak is in the range of 42.76° to 43.74°, and the third characteristic peak is in the range of 36.19° to 36.34°.

[0163] Figure 2 shows the voltage-capacity differential curves of the coin cells of the cathode materials in Examples 1-6 of this application during the second week; it can be seen that the voltage-capacity differential curves contain a first oxidation peak and a first reduction peak in the range of 3.6V to 4.0V, and a second oxidation peak and a second reduction peak in the range of 4.2V to 4.5V.

[0164] Figure 3 shows the charge-discharge curves of the coin cell battery charge-discharge test of the cathode materials of Examples 1-6 of this application in the second week. It can be seen that the discharge curve has a plateau between 4.2V and 4.5V.

[0165] Lithium metal pouch battery performance testing

[0166] Lithium metal pouch cell capacity retention test at 25°C:

[0167] The performance of lithium metal pouch batteries was tested using Examples 1-1 to 1-13, Comparative Example 1, and Comparative Example 2 as the first group of experiments, and Examples 1-9 and Examples 2-1 to 2-12 as the second group of experiments. The test results of the first group of experiments are shown in Table 3, and the test results of the second group of experiments are shown in Table 4. The test methods are as follows:

[0168] 1. Place the lithium metal pouch battery in a 25°C constant temperature chamber and let it stand for 30 minutes to allow the lithium metal pouch battery to reach a constant temperature.

[0169] 2. Charge the lithium metal pouch battery, which has reached a constant temperature, at 45°C with a constant current of 1.5C to 4.3V, and then charge it at 4.3V with a constant voltage to 0.02C.

[0170] 3. Let it stand for 5 minutes, then discharge it to 2.8V with a constant current of 4C, let it stand for 5 minutes, and record the discharge capacity of this test as the first cycle discharge capacity.

[0171] 4. Repeat this charge-discharge cycle 300 times. The discharge capacity of the battery on the 300th cycle is recorded as the discharge capacity on the 300th cycle.

[0172] 5. Capacity retention rate (%) of lithium metal pouch battery after 300 cycles at 25℃ = Discharge capacity of the 300th cycle / Discharge capacity of the first cycle × 100%.

[0173] Lithium-ion pouch battery 45℃ cycle capacity retention test

[0174] Battery performance tests were conducted on the lithium metal pouch batteries used in Examples 1-1 to 1-13, as well as Comparative Examples 1 and 2. The test results are shown in Table 3. The test methods are as follows:

[0175] 1. Place the lithium metal pouch battery in a 45℃ constant temperature chamber and let it stand for 30 minutes to allow the lithium-ion battery to reach a constant temperature.

[0176] 2. Charge the lithium metal pouch battery, which has reached a constant temperature, at 45°C with a constant current of 1.5C to 4.3V, and then charge it at 4.3V with a constant voltage to 0.02C.

[0177] 3. Let it stand for 5 minutes, then discharge it to 2.8V with a constant current of 4C, let it stand for 5 minutes, and record the discharge capacity of this test as the first cycle discharge capacity.

[0178] 4. Repeat this charge-discharge cycle 300 times. The discharge capacity of the battery on the 300th cycle is recorded as the discharge capacity on the 300th cycle.

[0179] 5. Capacity retention rate (%) of lithium-ion battery after 300 cycles at 45℃ = Discharge capacity of the 300th cycle / Discharge capacity of the first cycle × 100%.

[0180] Table 1 Note: In Table 1, " / " indicates that the element is not present.

[0181] Table 2 shows the battery performance of lithium-ion coin cells assembled from the cathode materials of Examples 1-1 to 1-13 and Comparative Example 1. The cycle performance is shown in Table 2.

[0182] Table 2 Note: In Table 2, " / " indicates that the data was not tested.

[0183] In Table 2, compared with the cathode materials in Comparative Examples 1 and 2, Examples 1-1 to 1-13 show that the first characteristic peak A is at 18.24°-18.35°, the second characteristic peak B is at 42.76°-43.74°, and the third characteristic peak C is at 36.19°-36.34°, all shifting to the left. The peak intensity ratios 1.30≤A / B≤1.72 and 1.09≤B / C≤1.86 are also reduced.

[0184] To further understand the impact of this change in the cathode material on its electrochemical performance, lithium-ion coin cells were assembled using the cathode materials from Examples 1-1 to 1-13, and performance tests were conducted. The test results are shown in Table 2. The coin cell had a specific capacity of Q1 at the 4.2V to 4.5V plateau and a total specific capacity of Qt at 2.8V to 4.5V. The ratio of the plateau capacity Q1 to the total capacity Qt satisfied the condition: 0.26 ≤ Q1 / Qt ≤ 0.39, indicating an increase in capacity. Furthermore, the oxidation peak voltage of the coin cell in the 3.6V to 4.0V range was Vo1, and the reduction peak voltage was Vr1, both at 0.040V. V≤|Vo1-Vr1|≤0.056V, the peak voltage of the oxidation peak in the 3.6V to 4.0V range is Vo1, and the peak voltage of the reduction peak is Vr1. 0.040V≤|Vo1-Vr1|≤0.056V, the peak height of the voltage-capacity differential curve (dQ / dV) in the 4.2V to 4.5V range is 300mAh / g / V to 4000mAh / g / V. These characteristics in the XRD diffraction pattern of the cathode material can improve the electrochemical performance of the cathode material, thereby improving the room temperature cycle performance and high temperature cycle performance of the battery.

[0185] Comparing Examples 1-1, 1-2, and 1-3, changing the Ni and Mn content alters the cycle stability. Satisfying the molar ratio of Ni to D of 0.45 to 0.6 is beneficial for improving the battery's room temperature and high temperature cycle performance. In particular, the cycle performance is extremely excellent when the Ni / D molar ratio is 0.5.

[0186] Comparing Examples 1-2, 1-4, and 1-5, cobalt doping is beneficial to improving structural stability. Controlling the molar ratio of Co to D to be 0.001 to 0.1 can improve the cycle performance of the battery.

[0187] Comparing Examples 1-1 and 1-6 to 1-13, doping the material with other elements can effectively suppress irreversible phase transitions and improve cycle stability. For example, when the following conditions are met: the molar ratio of Mn to D is 0.45 to 0.55; the cathode material also includes M... 1 Element, M 1 The element is selected from at least one of Sr, Al, Mg, or Ti, and M 1 The molar ratio of element M to element D is 0.002 to 0.02; the molar ratio of element M to element D is 0.010 to 0.072; which can further improve the cycle performance of the battery under normal temperature and high temperature conditions.

[0188] Compared with the cathode materials in Examples 1-1 to 1-13, the cathode materials in Examples 1-5 have extremely excellent electrochemical properties.

[0189] The lithium metal pouch batteries in Examples 1-1 to 1-13 and Comparative Examples 1 and 2 in Table 3 differ from Comparative Example 1 only in that the cathode material composition is adjusted according to Table 3, and the relevant performance test results are shown in Table 3.

[0190] Table 3

[0191] In Table 3, compared with the lithium metal pouch batteries in Comparative Examples 1 and 2, the lithium metal pouch batteries in Examples 1-1 to 1-13 have better cycle performance, regardless of whether the temperature is 25°C or 45°C. Furthermore, Examples 1-5 are the optimal experimental scheme, which further illustrates that the cathode material in the examples of this application has good cycle performance under the conditions of 25°C and 45°C.

[0192] In Table 4, the lithium metal pouch batteries of Examples 2-1 to 2-9 differ from those of Examples 1-9 only in that the electrolyte also includes the first substance component with the mass content shown in Table 4. The relevant performance test results are shown in Table 4.

[0193] Table 4 Note: In Table 4, " / " indicates that the substance is not present.

[0194] In Table 4, the lithium metal pouch batteries of Examples 1-9 exhibit better cycle performance than those of Examples 2-1 to 2-9. In particular, comparing Examples 2-1 to 2-9 with Examples 1-9 reveals that when the cathode material according to this application and an electrolyte containing the aforementioned first substance (especially vinyl sulfate) are used in combination in an electrochemical device, the cycle performance of the electrochemical device can be significantly improved.

[0195] It should be noted that, in this document, the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, or article that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, or article.

[0196] The various embodiments in this specification are described in a related manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0197] The above are merely preferred embodiments of this application and are not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A positive electrode material, characterized in that, The cathode material contains Li, and the XRD diffraction pattern of the cathode material has at least three characteristic peaks: the first characteristic peak is in the range of 18.24° to 18.35°, and the peak intensity is A; The second characteristic peak is in the range of 42.76° to 43.74°, with a peak intensity of B; the third characteristic peak is in the range of 36.19° to 36.34°, with a peak intensity of C. 1.30≤A / B≤1.72, and 1.09≤B / C≤1.

86.

2. The cathode material according to claim 1, characterized in that, When the coin cell composed of the positive electrode material and lithium metal is charged and discharged at a current of 0.04C within a voltage range of 2.8V to 4.5V, the discharge curve of the obtained voltage-capacity curve has a plateau between 4.2V and 4.5V. The specific capacity in the 4.2V to 4.5V range of the discharge curve is Q1, and the total specific capacity in the 2.8V to 4.5V range of the discharge curve is Qt, where 0.18≤Q1 / Qt≤0.

39.

3. The positive electrode material according to claim 1, characterized in that, When the coin cell composed of the cathode material and lithium metal is charged and discharged at a current of 0.04C in the voltage range of 2.8V to 4.5V, the obtained voltage-capacity differential curve has a first oxidation peak and a first reduction peak in the range of 3.6V to 4.0V, and a second oxidation peak and a second reduction peak in the range of 4.2V to 4.5V.

4. The cathode material according to claim 3, characterized in that, The voltage at the peak position of the first oxidation peak is Vo1, and the voltage at the peak position of the second reduction peak is Vr1, where 0.040V≤|Vo1-Vr1|≤0.056V.

5. The cathode material according to claim 3, characterized in that, The voltage at the peak position of the second oxidation peak is Vo2, and the voltage at the peak position of the second reduction peak is Vr2, where 0.042V≤|Vo2-Vr2|≤0.058V.

6. The cathode material according to claim 3, characterized in that, The peak height of the second oxidation peak ranges from 300 mAh / g / V to 4000 mAh / g / V.

7. The cathode material according to any one of claims 1 to 6, characterized in that, Based on the mass of the cathode material, the mass content of the Li element is 5% to 7.25%.

8. The cathode material according to any one of claims 1 to 6, characterized in that, The cathode material includes Li, M, D, and O elements, wherein the M element is selected from at least one of Na or Ca, and the D element includes at least two of Ni, Co, and Mn elements. The cathode material satisfies at least one of the following conditions: I. The molar ratio of element M to element D is 0.010 to 0.072; II. The positive electrode material also includes M 1 Element, M 1 The element is selected from at least one of Sr, Al, Mg, or Ti; the M 1 The molar ratio of element D to element D is 0.002 to 0.02; III. The molar ratio of Li to D is 0.8 to 0.99; IV. The molar ratio of Ni to D is 0.45 to 0.6; V. The molar ratio of Co to D is 0.001 to 0.1; VI. The molar ratio of the Mn element to the D element is 0.45 to 0.

55.

9. The cathode material according to any one of claims 1 to 6, characterized in that, The cell parameters of the cathode material satisfy at least one of conditions i to iii; ⅰ、 ⅱ、 iii. 4.5 ≤ c / a ≤ 5.

5.

10. A lithium metal pouch battery, comprising a positive electrode, an electrolyte, and a negative electrode, characterized in that, The positive electrode comprises the positive electrode material according to any one of claims 1 to 9.

11. The lithium metal pouch battery according to claim 10, characterized in that, The electrolyte comprises a first substance, which includes at least one of lithium nitrate, lithium difluorophosphate, lithium bis(oxalato)borate, 1,3-propenesulfonate lactone, or vinyl sulfate; the mass content of the first substance is 0.1% to 1% based on the mass of the electrolyte.

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