Lithium-rich manganese-based lithium ion battery
The lithium-rich manganese-based positive electrode material was synthesized by the high-temperature solid phase method and lithium bisoxalate borate was added as an additive to the electrolyte solution to construct a CEI passivation layer, which solved the problem of irreversible oxygen loss in the high-charge state of lithium-rich cathode and improved the cycle stability of the battery.
Patent Information
- Application Number
- CN202510254771.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-05
- Publication Date
- 2025-06-10
AI Technical Summary
The irreversible oxygen loss of lithium-rich positive electrode materials in a high charge state leads to structural distortion, affecting the stability of the cycle process.
The lithium-rich manganese-based positive electrode material was synthesized by high-temperature solid phase method, and lithium bisoxalate borate was added as an additive to the electrolyte solution to build a high-quality positive electrode-electrolyte solid phase interface (CEI) passivation layer to inhibit irreversible oxygen release.
It effectively solves the structural distortion problem caused by irreversible oxygen loss in the high charge state of lithium-rich positive electrode, and improves the cycle stability of the battery.
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Abstract
Description
Technical Field
[0001] The present invention relates to a lithium-rich manganese-based lithium-ion battery, belonging to the field of lithium-ion batteries. Background Art
[0002] In recent years, with the further in-depth research on lithium-rich cathode materials, the multiphase composite material LRLO oxide has attracted wide attention because of its high specific capacity (generally greater than 250 mAh / g), which can greatly meet the requirements of LIB batteries for high energy density, low cost and green non-toxicity (expected to replace Co-containing cathodes), and is regarded as one of the candidate cathode materials for future energy storage applications.
[0003] At present, the main modification strategies include two aspects: modification of cathode materials and modification of electrolytes. Modification of electrolytes is considered to be an effective means to improve the electrochemical performance of lithium-rich cathode materials. The use of electrolyte additives has the remarkable advantages of trace amount and high efficiency. Borate additives are commonly used film-forming additives for lithium-ion batteries, which can preferentially oxidize and decompose on the cathode surface before the electrolyte and participate in the construction of the cathode-electrolyte solid-phase interface (CEI) to inhibit the decomposition of the electrolyte, while protecting the structure of the cathode material, thereby improving the electrochemical performance of the material.
[0004] Through existing research, it is found that lithium-rich manganese-based cathode materials have high specific energy and high energy density, but there are problems of capacity decay and voltage decline during the cycling process due to irreversible oxygen release, while electrolyte modification can effectively improve the instability of the lithium-rich manganese-based cathode during the cycling process. Summary of the Invention
[0005] The purpose of the present invention is to provide a lithium-ion battery to solve the problem that the irreversible oxygen loss under the existing high state of charge (SOC) of the lithium-rich cathode leads to structural distortion and affects the stability of the cycling process.
[0006] The lithium-ion battery provided by the present invention includes a positive electrode, a negative electrode, an electrolyte and a separator; The electrolyte includes a lithium salt, a solvent and an additive; The additive is lithium difluorooxalate borate and / or lithium bis(oxalate)borate, preferably lithium bis(oxalate)borate.
[0007] Among them, in the electrolyte, the concentration of the lithium salt can be 0.5 M to 3 M, preferably 0.8 M to 1.6 M, and more preferably 1.2 M; The lithium salt can be LiPF 6 , LiBF 4 , LiClO 4 , LiCF 3 SO 3 , LiN(SO 2 CF 3 )2 and one or more of LiN(SO 2 F) 2 among others, preferably LiPF 6 .
[0008] Preferably, the amount of the additive is 1-5% of the mass of the lithium salt, preferably 2%.
[0009] Preferably, the solvent is one or more of dimethyl carbonate, vinylene carbonate, propylene carbonate, ethylene carbonate, diethyl carbonate and ethyl methyl carbonate, and more preferably a mixed solution of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) with a mass ratio of 3:7.
[0010] Preferably, the cathode material used for the cathode is Li 1.2 Ni 0.2 Mn 0.6 O 2 ; The cathode material is synthesized by the high-temperature solid-phase method.
[0011] The steps of the high-temperature solid-phase method are as follows: Mix the nickel-manganese precursor Ni 0.25 Mn0 .75 CO 3 with a lithium source, place it in a crucible, and calcine it in a muffle furnace in an air atmosphere; after preheating at 500-550°C for 4-5 h, calcine it at 800-900°C for 8-9 h, and the calcined product is naturally cooled to obtain; The lithium source is lithium carbonate or lithium hydroxide.
[0012] In the present invention, the separator is one or more of polyolefin separators, polyamide separators, polysulfone separators, and polyphosphazene separators; preferably, a polypropylene separator (PP) is used.
[0013] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention provides a lithium-rich manganese-based cathode material Li 1.2 Ni 0.2 Mn 0.6 O 2 .
[0014] (2) The present invention provides a borate compound as an additive. By using a trace amount of lithium salt additive, a high-quality CEI passivation layer is constructed to inhibit the irreversible oxygen release problem, protect the cathode structure of the lithium-rich material during the cycle, and effectively solve the problem of structural distortion caused by irreversible oxygen loss of the lithium-rich cathode at a high state of charge, thereby improving the cycle stability of the battery. Description of the Drawings
[0015] Figure 1 The curve showing the relationship between the number of cycles and the capacity of the lithium-rich manganese-based lithium-ion battery obtained in Example 1 and Example 3.
[0016] Figure 2 To record the curve showing the relationship between the number of cycles, capacity and Coulomb efficiency of the lithium-rich manganese-based lithium-ion battery obtained in Example 1 and Example 2.
[0017] Figure 3 For the lithium-rich manganese-based lithium-ion batteries of Example 1 and Example 3, the changing trend of the lithium-ion diffusion rate during the charge and discharge process at the 15th cycle.
[0018] Figure 4 TEM images of the surface of the lithium-rich cathode material of the lithium-rich manganese-based lithium-ion batteries of Example 1 and Example 3 before and after cycling. Detailed implementation manners
[0019] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods.
[0020] Unless otherwise specified, the materials, reagents, etc. used in the following examples can all be obtained from commercial sources.
[0021] The lithium-rich manganese-based cathode material used in the following examples was synthesized according to the following method: Mix the nickel-manganese precursor Ni 0.25 Mn 0.75 CO 3 with the lithium source in a ratio of 1:1.05; place the mixed powder in a crucible and calcine it in a muffle furnace under an air atmosphere; after preheating at 500 °C for 5 h, calcine it at 900 °C for 20 h; let the calcined product cool naturally to obtain the lithium-rich manganese-based cathode material, where the lithium source is lithium carbonate (Li 2 CO 3 ).
[0022] Example 1. Preparation of the lithium-rich manganese-based lithium-ion battery 1. Preparation of the electrolyte Mix ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a mass ratio of EC:EMC = 3:7. Add lithium hexafluorophosphate (LiPF 6 ), and taking the total weight of the lithium salt as 100%, add 2 wt% of the bis(oxalato)borate compound as a lithium salt additive, and keep the lithium salt concentration at 1.2 M.
[0023] 2. Preparation of the positive electrode sheet Mix the positive electrode active material (Li 1.2 Ni 0.2 Mn 0.6 O 2),(super-P) and binder (PVDF) are dispersed in an organic solvent (NMP), and stirred thoroughly to obtain the positive electrode paste. The positive electrode paste is evenly coated on both sides of the aluminum foil, and after drying, rolling and vacuum drying, the positive electrode sheet is obtained.
[0024] 3. Button cell assembly: Using the lithium-rich positive electrode sheet as the working electrode, fresh metallic lithium as the counter electrode, and Celgard 2325 as the separator, in a glove box filled with an Ar gas atmosphere, stack lithium sheets (thickness, 0.5 mm) and 75 μL of the basic electrolyte in sequence to assemble the lithium-metal half cell.
[0025] Most of the steps in the following examples and comparative examples are basically the same as those in Example 1, except that: Example 2, Lithium difluorooxalate borate (LiDFOB) shown in Table 1 is added to the electrolyte as a lithium salt additive.
[0026] Example 3, 1.2 M lithium hexafluorophosphate (LiPF6) is added to the electrolyte, without other lithium salt components.
[0027] Comparative Examples 1-4, LiPF with concentrations of 0.8 M, 1.0 M, 1.4 M, and 1.6 M shown in Table 1 are added respectively. 6 .
[0028] The present invention is further illustrated by the following examples.
[0029] Table 1 Raw materials used in each of Example 1 and Comparative Examples
[0030] The formation and cycling test parameters shown in Example 1 to Comparative Example 4 in Table 1 are adopted.
[0031] Using the lithium-rich lithium-metal button cell shown in Table 1, formation is carried out at a current density of 10 mA / g (vs Li / Li + ) within the voltage range of 2 V - 4.8 V, and then cycling test is carried out at a current density of 40 mA / g. For the electrochemical measurement of the button cell, it is mainly carried out using a Neware battery tester at a constant temperature of about 25 °C.
[0032] Using the lithium-rich lithium-metal button cell shown in Example 1, a synchronous constant current intermittent titration technique (GITT) test is carried out on the charge and discharge process, and the corresponding lithium ion diffusion coefficient logDLi in this process is calculated. + .
[0033] For the electrochemical measurement of coin cells, it was mainly carried out using a Neware battery tester at a constant temperature of about 25 °C.
[0034] Examples 1 to Comparative Example 4 were formed according to the formation method in Table 1 to obtain the first-cycle electrochemical data of the lithium-ion batteries and filled into Table 2.
[0035] Table 2 Performance of lithium-ion batteries prepared in each example and comparative example
[0036] Comparing the results of Examples 1 to 3 in Table 2, it can be seen that the use of lithium salt additives will lead to a decrease in the first-cycle Coulombic efficiency, which is because the additives need to consume some active lithium to form a film by oxidation on the surface of the positive electrode.
[0037] Comparing the results of Example 3 and Comparative Examples 1 to 4 in Table 2, it can be seen that the concentration of lithium salt has a certain influence on the initial Coulombic efficiency. And 1.2 M LiPF 6 is most conducive to the transport of lithium ions in this electrolyte system, enabling Example 3 to maintain a high first-cycle initial Coulombic efficiency. And Example 1 has a higher first-cycle Coulombic efficiency and discharge capacity, that is, bis(oxalato)borate as an additive is more suitable for this lithium-rich system.
[0038] Record the relationship curve between the number of cycles and the capacity trend of the lithium-rich manganese-based lithium-ion batteries obtained in Example 1 and Example 3, as recorded Figure 1 shown.
[0039] Record the relationship curve between the number of cycles, the capacity and the Coulombic efficiency trend of the lithium-rich manganese-based lithium-ion batteries obtained in Example 1 and Example 2, as recorded Figure 2 shown.
[0040] Record the change trend of the lithium-ion diffusion rate during the charge-discharge process when the lithium-rich manganese-based lithium-ion batteries in Example 1 and Example 3 reach the 15th cycle, as recorded Figure 3 shown.
[0041] Record the transmission electron microscope images of the lithium-rich positive electrode surface materials of the lithium-rich manganese-based lithium-ion batteries in Example 1 and Example 3 before and after cycling, as recorded Figure 4 shown.
[0042] From Figure 1 the test results, it can be seen that using bis(oxalato)borate as an additive in the electrolyte can effectively inhibit the capacity decay during cycling.
[0043] From Figure 2It can be seen from the test results that when lithium difluorooxalate borate is used as an additive to the electrolyte, initially, due to the lower Coulombic efficiency at the initial stage of electrolyte decomposition, which is caused by the continuous oxidation and decomposition of lithium bis(oxalate)borate, it further leads to the problem of capacity fade in the later stage. While when lithium bis(oxalate)borate is used as an additive, the formation of the CEI film can inhibit the continuous decomposition of the electrolyte, thus suppressing the problem of capacity fade during cycling.
[0044] From Figure 3 It can be seen from the test results that using lithium bis(oxalate)borate as an additive to the electrolyte can form a CEI film that is conducive to lithium-ion transfer, and the lithium-ion diffusion rate during cycling is higher than that in Example 3.
[0045] From Figure 4 It can be seen from the test results that using lithium bis(oxalate)borate as an additive to the electrolyte can form a CEI film that is conducive to lithium-ion transfer, inhibit the phenomenon of structural distortion during cycling, protect the cathode structure, and thus maintain the stability during cycling.
Claims
1. A lithium-ion battery comprising a positive electrode, a negative electrode, an electrolyte and a separator; The electrolyte comprises a lithium salt, a solvent and an additive; The additive is lithium difluorooxalatoborate and / or lithium bisoxalatoborate; The amount of the additive is 1-5% of the mass of the lithium salt.
2. The lithium-ion battery according to claim 1, characterized in that: In the electrolyte, the concentration of the lithium salt is 0.5M to 3M; The lithium salt is one or more of LiPF6, LiBF4, LiClO4, LiCF3SO3, LiN(SO2CF3)2 and LiN(SO2F)2.
3. The lithium ion battery according to claim 1 or 2, characterized in that: The solvent is one or more of dimethyl carbonate, vinylene carbonate, propylene carbonate, ethylene carbonate, diethyl carbonate and ethyl methyl carbonate.
4. The lithium ion battery according to claim 1 or 2, characterized in that: The positive electrode material used in the positive electrode is Li 1.2 Ni 0.2 Mn 0.6 O2; The positive electrode material is synthesized by a high-temperature solid phase method.
5. The lithium-ion battery according to claim 4, characterized in that: The steps of the high temperature solid phase method are as follows: The nickel-manganese precursor Ni 0.25 Mn 0.75 CO3 is mixed with a lithium source and placed in a crucible, and calcined in an air atmosphere through a muffle furnace; after preheating at 500-550°C for 4-5 hours, calcined at 800-900°C for 8-9 hours, and the calcined product is naturally cooled.
6. The lithium-ion battery according to claim 5, characterized in that: The lithium source is lithium carbonate or lithium hydroxide.