Method for improving high-temperature electrochemical performance of LiNi0. 5Mn1. 5O4 positive electrode material

Abstract

The invention discloses a method for improving the high-temperature electrochemical performance of a lithium ion battery positive electrode material LiNi0. 5Mn1. 5O4, and belongs to the technical field of lithium ion battery materials. According to the method, a LiNi0. 5Mn1. 5O4 single-crystal positive electrode material with good dispersity is prepared by adopting a high-temperature solid-phase reaction method, and then a lithium fluosilicate coating layer is prepared on the surface of the LiNi0. 5Mn1. 5O4 single-crystal positive electrode material by adopting an ethanol solution method. The preparation method comprises the following specific steps: weighing Li2SiF6 according to the mass ratio of 0.5 wt%-5wt% of LiNi0. 5Mn1. 5O4, dissolving the Li2SiF6 in absolute ethyl alcohol, then adding the LiNi0. 5Mn1. 5O4 single-crystal positive electrode material with good dispersity into the Li2SiF6 absolute ethyl alcohol solution, heating at low temperature, stirring, carrying out rotary drying, grinding into powder, transferring into a tubular furnace, and calcining in an argon atmosphere to obtain the LiNi0. 5Mn1. 5O4 single-crystal positive electrode material coated with Li2SiF6. The modification method is simple in process, low in raw material cost and high in adaptability, the prepared surface coating layer has the characteristics of compactness, uniform thickness, good stability, remarkable surface modification effect and the like, and the method for improving the high-temperature electrochemical performance through surface modification of the positive electrode material has practical value.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium ion battery materials, and particularly relates to a lithium ion battery positive electrode material LiNi 0.5 Mn 1.5 Methods for improving the high-temperature electrochemical performance of O4. Background Art

[0002] LiNi spinel-structured high-voltage lithium-ion battery cathode material 0.5 Mn 1.5 O₄ (LNMO) has broad application prospects in new energy vehicles, energy storage systems, and consumer electronics due to its high theoretical specific capacity (147 mAh / g), high operating voltage of 4.7 V (relative to metallic lithium), low cost, cobalt-free nature, and environmental friendliness. LNMO is considered one of the next-generation high-energy-density cathode materials with great industrial potential, particularly in the context of pursuing high energy density and low cost.

[0003] However, LiNi 0.5 Mn 1.5 O4 materials still face many challenges in practical applications, especially in high temperature environments, where their structural stability, interface compatibility, and electrochemical performance are all significantly insufficient. 0.5 Mn 1.5 O4 is prone to violent side reactions with traditional carbonate electrolytes under high temperature and high voltage conditions, leading to oxidative decomposition of the electrolyte, unstable interface film, and Mn 3+ Dissolution and active material structure collapse and other problems, which accelerate the battery capacity decay, seriously affecting the battery cycle life and safety. 0.5 Mn 1.5 O4 materials due to the synthesis conditions, Ni / Mn order and Mn 3+ Factors such as residual further aggravate its interfacial side reactions, electrochemical instability and polarization phenomena under high temperature conditions.

[0004] Academia and industry focus on LiNi 0.5 Mn 1.5 A variety of modification strategies have been studied for O4 cathode materials, including surface coating, element doping, electrolyte optimization, and composite construction. Among them, surface coating is an effective technical means to significantly improve interface stability, inhibit metal ion dissolution, reduce interface side reactions, and enhance thermal stability. 0.5 Mn 1.5 A dense, stable, and well-conducting coating layer is introduced onto the surface of the O4 particles, which can effectively isolate the active material from direct erosion by the electrolyte, delay structural degradation, inhibit surface side reactions, and improve its high-temperature charge and discharge cycle performance.

[0005] The present invention provides a method for effectively improving LiNi by surface coating measures. 0.5 Mn 1.5 The method uses a coating with good interface stability to achieve the electrochemical performance of LiNiO4 cathode materials at high temperature without changing the main structure of the material. 0.5 Mn 1.5 The effective regulation of O4 surface reaction behavior provides a basis for the development of LiNi 0.5 Mn 1.5 The safe and reliable operation of O4-based lithium-ion batteries provides a feasible solution. Summary of the Invention

[0006] The purpose of the present invention is to provide a LiNi 0.5 Mn 1.5 The method for improving the high-temperature electrochemical performance of O4 positive electrode materials, that is, improving the high-temperature electrochemical performance of this type of positive electrode materials through surface chemical modification, has achieved remarkable results and has good application value.

[0007] The specific contents are:

[0008] (1) According to the stoichiometric ratio of Li:Ni:Mn:O = (1.01 ~ 1.05):0.5:1.5, commercially available analytical pure Li2CO3, MnO2, and NiO were weighed and mixed thoroughly. The mixed powder was placed in a muffle furnace, calcined at an appropriate temperature for a certain time, cooled naturally to room temperature, and ground to obtain LiNi with good dispersion. 0.5 Mn 1.5 O4 single crystal positive electrode material.

[0009] (2) According to 0.5 wt% ~ 5 wt% LiNi 0.5 Mn 1.5 Weigh Li2SiF6 with a mass ratio of O4 and dissolve it in a certain amount of anhydrous ethanol. Then, add LiNi 0.5 Mn 1.5 The O4 single crystal cathode material was added to the Li2SiF6 anhydrous ethanol solution, heated at low temperature and stirred, rotary dried, ground into powder, transferred to a tube furnace, introduced into an argon atmosphere, and calcined at 150 ~ 800 ° C for 2 ~ 24 hours to obtain Li2SiF6 coated LiNi 0.5 Mn 1.5 O4 single crystal positive electrode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 This is a scanning electron microscope (SEM) photograph of the sample prepared in the present invention.

[0011] Figure 2 This is a transmission electron microscope (TEM) photograph of the sample prepared in the present invention.

[0012] Figure 3 The sample prepared in this invention is combined with a metal lithium sheet to assemble a button battery, and the specific capacity is compared with that of uncoated LiNi0.5Mn1.5O4 after 200 charge and discharge cycles at 1 C current rate at 55°C. DETAILED DESCRIPTION

[0013] Example 1:

[0014] (1) All chemical reagents were of analytical grade and purchased from Xilong Chemical Co., Ltd. According to the stoichiometric ratio, 1.8852 g of nickelous oxide (NiO, purity ≥ 99%), 7.6712 g of manganese dioxide (MnO2, purity ≥ 85%), and 1.9975 g of lithium carbonate (Li2CO3, purity ≥ 97%) were weighed and ground and mixed. The mixed powder was placed in a high-temperature reactor and heated to 600 °C at a heating rate of 10 °C / min. The mixture was calcined for 5 hours, then continued to be heated to 800 °C and calcined for 24 hours. The mixture was cooled naturally to room temperature in the furnace and ground to obtain the target product. The SEM and TEM photos of the mixture are respectively shown in the attached manual. Figure 1 (a) Attachment Figure 2 (a) It can be seen that the sample particles have an octahedral single crystal morphology, their surface is flat, clean, without a foreign layer, and the particles have good dispersion.

[0015] (2) Weigh 0.0309 g of lithium hexafluorosilicate (Li2SiF6, purity ≥ 97%) and dissolve it in 15 mL of anhydrous ethanol. Add the LiNi prepared in step (1) under magnetic stirring. 0.5 Mn 1.5 2.0000g of O4 single crystal positive electrode material was stirred continuously and kept in a constant temperature oil bath at 80℃ for 6 hours. The mixture was then rotary dried, collected, and manually ground with an agate mortar. The mixture was then transferred to a tube furnace, purged with argon and heated to 400℃. The mixture was calcined for 5 hours and then cooled naturally to room temperature. The target product 1% Li2SiF6@LiNi was obtained by grinding. 0.5 Mn 1.5 O4 sample. Its SEM and TEM photos are respectively in the appendix of the manual. Figure 1 (b) Attachment Figure 2 (b) It can be seen that the sample particles still have an octahedral morphology, and a uniform and dense coating layer with a thickness of about 2 to 3 nm is obtained on the surface.

[0016] (3) The active material samples prepared in steps (1) and (2) are used to make an electrochemical performance test cell according to conventional experimental methods. The specific steps are as follows: 0.2000 g of the above-prepared active material, 0.0250 g of the conductive agent acetylene black, and 0.0250 g of the binder polyvinylidene fluoride were weighed in a mass ratio of 8:1:1, and the mixture was manually ground with an agate mortar until uniformly mixed. The mixture was transferred to a slurry bottle and an appropriate amount of N-methyl-2-pyrrolidone was added dropwise. The mixture was stirred on a magnetic stirrer until the slurry had no stratification or granularity. The slurry was then evenly coated on the surface of aluminum foil and transferred to a vacuum drying oven and dried at 100 °C for 12 h. The electrode discs with a radius of 6 mm were cut with a cutting machine and weighed. The prepared disc electrode was used as the positive electrode, the metal lithium sheet was used as the negative electrode, a 1.0 M LiPF6-ethylene carbonate-dimethyl carbonate (EC / DMC = 3 / 7 volume ratio) solution was used as the electrolyte, and a ceramic coating film was used as the separator. The mixture was heated to 37 ℃ in an argon atmosphere (H2O < 0.01 ppm, O2 < 0.01 ppm) glove box to assemble CR2032 button batteries, and then perform electrochemical performance tests after standing for a period of time.

[0017] (4) Place the battery to be tested in a 55°C constant temperature test chamber and use the LAND battery test system (CT-2001A) to perform constant current charge and discharge tests in the voltage range of 3.5~4.95 V. Figure 3 It can be seen that the constant current charge and discharge performance test was carried out at a current density of 1 C (1 C = 147 mA / g), where 1% Li2SiF6 @ LiNi 0.5 Mn 1.5 The initial discharge capacity of the O4 sample is 131.27 mAh / g. After 200 continuous charge and discharge cycles, the remaining capacity is 100.81 mAh / g, and the capacity retention rate is 75.34%. 0.5 Mn 1.5 Under the same charge and discharge conditions, the initial discharge capacity of O4 is 132.30 mAh / g. After more than 80 cycles, the capacity has decayed to about 40.70 mAh / g. After 200 cycles, the capacity remains 11.84 mAh / g, and the capacity retention rate is only 8.95%. 0.5 Mn 1.5 Compared with the matrix material, the high-temperature electrochemical performance of the O4 sample has been significantly improved.

Claims

1. A LiNi 0.5 Mn 1.5 The method for improving the high temperature electrochemical performance of O4 cathode materials has the following characteristics and specific preparation steps: according to 0.5 wt% ~ 5 wt% LiNi 0.5 Mn 1.5 Weigh Li2SiF6 with a mass ratio of O4 and dissolve it in anhydrous ethanol. Then, add LiNi 0.5 Mn 1.5 The O4 single crystal cathode material was added to the Li2SiF6 anhydrous ethanol solution, heated at low temperature and stirred, rotary dried, ground into powder, transferred to a tube furnace, introduced into an argon atmosphere, and calcined at 150 ~ 800 ℃ for 2 ~ 24 hours to obtain Li2SiF6 coated LiNi 0.5 Mn 1.5 O4 single crystal positive electrode material.

2. The method according to claim 1, characterized in that The coating compound raw material is not limited to Li2SiF6. Other inorganic fluorine-silicon-lithium compounds, organic fluorine-silicon-lithium compounds, and other substances containing fluorine, silicon, and lithium elements that can chemically react with the surface of the positive electrode material to form the coating are all applicable to this method.

3. The method according to claim 1-2 is also applicable to the modification of cathode materials of sodium ion batteries, magnesium ion batteries, potassium ion batteries and zinc ion batteries.

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