Negative-electrode-free secondary lithium battery and charging and discharging method thereof
By performing room temperature static and low current charging and discharge cycles in a negative electrode-free lithium battery, the SEI layer is reconstructed, and the problems of uneven lithium deposition and lithium dendrites are solved, and the cycle stability and life of the battery are improved.
Patent Information
- Application Number
- CN202510625137.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-05-15
- Publication Date
- 2025-08-08
AI Technical Summary
During the cycle process, there are problems of uneven lithium deposition, lithium dendrites growth and SEI structure damage, resulting in poor cycle stability and limited life.
After standing at room temperature, the SEI layer was transformed at a rate of 0.1C, and the first constant current charge and discharge cycle was carried out, and then the second constant current charge and discharge cycle was carried out at a low current density of 0.05mA/cm² to 0.1mA/cm², the SEI layer was reconstructed and the lithium deposition was uniform.
It effectively inhibits the growth of lithium dendrites, improves the cycle stability and life of the battery, reduces side reactions, and improves the efficiency of Coulomb.
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Figure CN120453534A_ABST
Abstract
Description
Technical Field
[0001] The present application relates to the field of electrochemistry, and in particular to a negative electrode-free secondary lithium battery and a charging and discharging method thereof. Background Art
[0002] In recent years, anode-free lithium metal batteries have become a practical path to achieving the next generation of high-energy-density batteries by storing the lithium source completely in the positive electrode without the need for additional lithium metal. This design eliminates the need for a graphite negative electrode and has the advantages of high energy density, simplified process, reduced cost, and improved safety due to the absence of excess active lithium. However, the reversibility of lithium metal deposition / stripping on the negative electrode current collector is poor, resulting in low Coulombic efficiency and limited cycle life. In addition, the growth of lithium dendrites exacerbates side reactions, the formation of dead lithium, and even battery short circuits. Therefore, how to improve the cycle stability of anode-free lithium metal batteries and extend their cycle life has become an urgent problem to be solved by researchers in this field. Summary of the Invention
[0003] To improve the cycle stability and stabilize lithium deposition of anode-free lithium metal batteries, related technologies usually improve this problem by designing cyclic charge and discharge conditions (such as voltage, cutoff voltage, capacity, etc.). For example, Jiaqi Huang et al. (Adv. Energy Mater. 2023, 13, 2300959) adopted a partial stripping strategy during the cycle of anode-free batteries, that is, changing the discharge cutoff voltage of the cycle. The retained active lithium can serve as a nucleation site, reducing the nucleation overpotential and promoting the reuse of the solid electrolyte interface (SEI), thereby reducing the generation of dead lithium and inactive SEI and improving the cycle stability of the battery. Yi Cui et al. (Nature. 2024, 626, 306–312) allowed the battery to stand in the discharge state. Compared with standing in the charge state, standing in the discharge state effectively reduced the side reaction between active lithium and electrolyte, allowing some of the originally isolated inactive lithium to re-enter the electrochemical cycle, thereby improving the long-term cycle performance of anode-free lithium metal batteries. JRDahn et al. (AJLouli et al., 2021, J.Electrochem.Soc., 168, 020515) proposed an asymmetric cycling strategy in which the charge rate is lower than the discharge rate. This strategy helps to reduce the loss of lithium during the electroplating and stripping processes, and emphasizes the importance of the relative size of the charge and discharge rates to battery performance. In addition, Zhang et al. (patent application number: CN104600803A) control the reduction in the capacity of the battery relative to the capacity of the lithium-sulfur battery at the beginning of each charge and discharge cycle of the lithium-sulfur battery to a fixed value (within 40%), and also always control the voltage of the lithium-sulfur battery between a charging upper limit threshold and a discharging lower limit threshold. By adopting the combination of capacity and voltage thresholds, the charge and discharge stability of the battery can be effectively improved and its service life can be extended. Xu et al. (patent application number: CN112684356A) continuously increase the charging cutoff voltage during the battery cycle to maintain a set constant capacity during the cycle, which can ensure that the amount of lithium removed from the material is consistent each time, and the retention rate of discharge capacity and energy is improved compared to the constant voltage charging cycle mode, thereby overcoming the defect that the battery reaches the cutoff voltage too early and the charging capacity decreases accordingly. In addition, the internal polarization of the battery is evaluated by calculating the increase in the cutoff voltage each time. Ding Hao (patent application number: CN112684356A) adopts a staged charging method during the battery charging process, that is, different currents are used for charging in different SOC ranges of the battery, and a method is proposed to determine the maximum continuous rate allowed for battery charging and the corresponding cutoff SOC state, so as to determine a reasonable battery charging strategy.
[0004] Although the above reports can effectively inhibit lithium dendrites and improve lithium cycle efficiency and stability, most of these current cyclic charge and discharge strategies are based on the cycle life test method of the GB / T31484-2015 standard, that is, using a certain rate constant current and constant voltage charging, and then discharging at a certain rate constant current after standing, and the charge and discharge rate of each cycle remains unchanged. However, due to the uneven distribution of lithium ion concentration and electric field on the surface of the current collector of the anode-free battery, as the number of battery cycles increases, localized unevenness of lithium deposition morphology will still occur during the cycling process. On the other hand, the volume expansion of lithium metal destroys the initially formed solid electrolyte interface (SEI) structure, resulting in the continuous reaction of newly deposited lithium with the electrolyte, further consuming active lithium.
[0005] In view of this, the present application provides a negative electrode-free secondary lithium battery and a charging and discharging method thereof to solve the above technical problems.
[0006] The first aspect of the present application provides a charge and discharge method for a negative electrode-free secondary lithium battery, comprising the following steps: assembling a negative electrode-free secondary lithium battery, and allowing the negative electrode-free secondary lithium battery to stand at a constant temperature at room temperature; forming the negative electrode-free secondary lithium battery after standing at a rate of 0.1C, and subjecting the formed negative electrode-free secondary lithium battery to a first round of constant current charge and discharge cycle; subjecting the negative electrode-free secondary lithium battery after the first round of constant current charge and discharge cycle to a second round of constant current charge and discharge cycle at a first current density, wherein the number of cycles of the two rounds of constant current charge and discharge cycles is 1 to 3, wherein the first current density is 0.05 mA / cm 2 Up to 0.1 mA / cm 2 .
[0007] Based on the first aspect, in some possible implementations, the standing time is 10 hours to 24 hours.
[0008] Based on the first aspect, in some possible implementations, the number of cycles of the first round of constant current charge and discharge cycles is 10 to 50, and the charge and discharge voltage is 2.7V to 3.8V.
[0009] Based on the first aspect, in some possible implementations, the method for assembling the negative electrode-free secondary lithium battery includes:
[0010] The negative electrode current collector, the separator, and the positive electrode sheet coated with the positive electrode material are assembled into an electrode assembly; the electrode assembly is placed in a packaging material and a liquid electrolyte is added to obtain the negative electrode-free secondary lithium battery.
[0011] Based on the first aspect, in some possible embodiments, the positive electrode material includes lithium iron phosphate, the liquid electrolyte includes an organic solvent, a lithium salt and an additive, wherein the lithium salt includes lithium bis(trifluoromethanesulfonyl)imide, the organic solvent includes 1,3-dioxolane and ethylene glycol dimethyl ether, and the additive includes lithium nitrate.
[0012] Based on the first aspect, in some possible embodiments, the molar concentration of the lithium bis(trifluoromethanesulfonyl)imide is 0.5 mol / L to 3 mol / L; based on the mass of the liquid electrolyte, the mass proportion of the lithium nitrate is 1% to 3%; and the volume ratio of the 1,3-dioxolane to the ethylene glycol dimethyl ether is 1:1.
[0013] Based on the first aspect, in some possible embodiments, the positive electrode material includes a high-nickel ternary material, and the liquid electrolyte includes an organic solvent, a lithium salt, and an additive, wherein the lithium salt includes lithium difluorooxalatoborate and lithium tetrafluoroborate, and the organic solvent includes fluoroethylene carbonate and diethyl carbonate.
[0014] Based on the first aspect, in some possible implementations, the molar content of the lithium salt is 0.6 mol / L to 2 mol / L; and the volume ratio of the fluoroethylene carbonate to the diethyl carbonate is 2:1.
[0015] Based on the first aspect, in some possible implementations, the negative electrode current collector includes at least one of copper foil, copper mesh, foam copper, nickel foil, iron foil, carbon paper, or carbon cloth.
[0016] In a second aspect, the present application provides a negative electrode-free secondary lithium battery, which is prepared by the above-mentioned negative electrode-free secondary lithium battery charging and discharging method.
[0017] The above-mentioned charging and discharging method of the negative electrode-free secondary lithium battery is simple to operate. After a certain number of cycles, the negative electrode-free secondary lithium battery is charged at a low current density (0.05 mA / cm 2 Up to 0.1 mA / cm 2 ) repair cycle, which can reconstruct the degraded solid electrolyte interface (SEI) during the cycle, forming a dense SEI layer rich in inorganic components such as LiF, effectively inhibiting electrolyte decomposition and side reactions, and reducing interface impedance. In addition, at low current density (0.05mA / cm 2 Up to 0.1 mA / cm 2 ), the lithium ion concentration gradient and electric field distribution are more uniform, thereby driving the deposition of lithium metal in the form of a network rather than local lithium dendrite deposition. Moreover, after low-current repair, the SEI recovers to a smooth and uniform morphology, which can induce a uniform lithium deposition process and reduce the risk of short circuit caused by dendrites, thereby improving the cycle performance and cycle life of the negative electrode-free secondary lithium battery.
[0018] Furthermore, the above-mentioned charging and discharging method of the negative electrode-free secondary lithium battery is highly versatile, suitable for lithium iron phosphate and high-nickel ternary positive electrode materials, and can match different electrolyte systems (such as DOL-DME or FEC-DEC solvent combinations). It is also simple to operate, and the strategy only requires adjusting the charging and discharging parameters. No additional equipment or complex processes are required, and it is easy to achieve large-scale industrial application. BRIEF DESCRIPTION OF THE DRAWINGS
[0019] Figure 1 Graph showing changes in discharge specific capacity during cycling of negative electrode-free secondary lithium batteries at a 0.5C charge rate and a 1C discharge rate in Examples 1 to 5 and Comparative Examples 1 to 4 of the present application.
[0020] Figure 2 This is a graph showing the change in coulombic efficiency during the cycling of the negative electrode-free secondary lithium battery in Examples 1 to 5 and Comparative Examples 1 to 4 of the present application at a charge rate of 0.5C and a discharge rate of 1C.
[0021] Figure 3 This is a graph showing the changes in current and voltage over time for the negative electrode-free secondary lithium battery in Comparative Example 1 of the present application after 100 cycles.
[0022] Figure 4 This is a graph showing the change in current and voltage over time for the negative electrode-free secondary lithium battery in Example 2 of the present application after 100 cycles. DETAILED DESCRIPTION
[0023] The embodiments of the present application are described in detail below. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present application and are not to be construed as limiting the present application. The reagents and materials described in the following embodiments can all be obtained from commercial sources.
[0024] One embodiment of the present application provides a method for charging and discharging a negative electrode-free secondary lithium battery, comprising the following steps:
[0025] Step 1: assembling a negative electrode-free secondary lithium battery, and placing the negative electrode-free secondary lithium battery at a constant temperature at room temperature.
[0026] In some embodiments, the standing time is 10 h to 24 h.
[0027] In some embodiments, the assembly method of a negative electrode-free secondary lithium battery includes: assembling a negative electrode current collector, a separator, and a positive electrode sheet coated with a positive electrode material into an electrode assembly; placing the electrode assembly in a packaging material and adding a liquid electrolyte to obtain a negative electrode-free secondary lithium battery.
[0028] Among them, the positive electrode plate is made by uniformly mixing the positive electrode material, the conductive agent and the adhesive and then coating them on the aluminum current collector. This application does not limit the types of the conductive agent and the adhesive, as long as they can meet the requirements of this application.
[0029] In some embodiments, the positive electrode material includes lithium iron phosphate, and the liquid electrolyte includes an organic solvent, a lithium salt, and an additive. The lithium salt includes lithium bis(trifluoromethanesulfonyl)imide, the organic solvent includes 1,3-dioxolane and ethylene glycol dimethyl ether, and the additive includes lithium nitrate. The molar concentration of the lithium bis(trifluoromethanesulfonyl)imide is 0.5 mol / L to 3 mol / L; the weight percentage of lithium nitrate is 1% to 3% based on the weight of the liquid electrolyte; and the volume ratio of 1,3-dioxolane to ethylene glycol dimethyl ether is 1:1.
[0030] In some embodiments, the positive electrode material includes a high-nickel ternary material, and the liquid electrolyte includes an organic solvent, a lithium salt, and an additive. The lithium salt includes lithium difluorooxalatoborate and lithium tetrafluoroborate, and the organic solvent includes fluoroethylene carbonate and diethyl carbonate. The molar content of the lithium salt is 0.6 mol / L to 2 mol / L, and the volume ratio of fluoroethylene carbonate to diethyl carbonate is 2:1.
[0031] In some embodiments, the negative electrode current collector includes at least one of copper foil, copper mesh, copper foam, nickel foil, iron foil, carbon paper, or carbon cloth.
[0032] Step 2: forming the negative electrode-free secondary lithium battery at a rate of 0.1C after standing still.
[0033] Step 3: subjecting the formed negative electrode-free secondary lithium battery to a first round of constant current charge and discharge cycles.
[0034] In some embodiments, the number of cycles of the first constant current charge and discharge cycle is 10 to 50, and the charge and discharge voltage is 2.7V to 3.8V.
[0035] Step 4: After the first round of constant current charge and discharge cycle, the negative electrode-free secondary lithium battery is subjected to a second round of constant current charge and discharge cycle at the first current density. The number of cycles of the second round of constant current charge and discharge cycle is 1 to 3, wherein the first current density is 0.05 mA / cm 2 Up to 0.1 mA / cm 2 .
[0036] The present invention controls the current density of the first current to be 0.05 mA / cm 2 Up to 0.1 mA / cm 2 The lithium ion concentration gradient and electric field distribution are more uniform, driving the deposition of lithium metal in a network rather than localized lithium dendrites. After low-current repair, the SEI returns to a smooth and uniform morphology, inducing a uniform lithium deposition process and significantly reducing the risk of short circuits caused by dendrites.
[0037] One embodiment of the present application further provides a negative electrode-free secondary lithium battery, which is prepared using the above-mentioned charge and discharge method for a negative electrode-free secondary lithium battery. The negative electrode-free secondary lithium battery of the present application has good cycle stability and a long cycle life.
[0038] The following describes the charge and discharge method of the negative electrode-free secondary lithium battery of the present application through specific examples and comparative examples. Those skilled in the art should understand that the preparation method described in this application is only an example, and any other suitable preparation method is within the scope of this application.
[0039] Example 1
[0040] A method for charging and discharging a negative electrode-free secondary lithium battery comprises the following steps:
[0041] S1: Assembly of negative electrode-free secondary lithium battery;
[0042] The negative electrode current collector, the separator, and the positive electrode sheet coated with the positive electrode material are assembled into an electrode assembly; the electrode assembly is placed in a packaging material and a liquid electrolyte is added to obtain a negative electrode-free secondary lithium battery.
[0043] Among them, lithium iron phosphate is used as the positive electrode material, and the composition of the liquid electrolyte is: lithium bis(trifluoromethanesulfonyl)imide as the lithium salt, a mixture of 1,3-dioxolane and ethylene glycol dimethyl ether as the organic solvent system, and lithium nitrate as the additive; the molar concentration of the lithium salt is 1 mol / L, based on the mass of the liquid electrolyte, the mass proportion of the additive is 2%, and the volume ratio of 1,3-dioxolane and ethylene glycol dimethyl ether is 1:1.
[0044] S2: After the negative electrode-free secondary lithium battery is assembled, it is placed in a constant temperature room at 25°C for 10 hours.
[0045] S3: The non-negative-electrode secondary lithium battery after standing is subjected to formation at a rate of 0.1C.
[0046] S4: The formed negative electrode-free secondary lithium battery is charged at a current density of 0.5C and discharged at a current density of 1C (1C = 170mAh / g) for a cycle, and the charge and discharge voltage range of the battery is controlled to be 2.7V to 3.8V. After the negative electrode-free secondary lithium battery has been charged and discharged for 10 cycles, the current density is 0.1mA / cm 2 The current density was cycled for 1 cycle.
[0047] The above-assembled negative electrode-free secondary lithium battery was subjected to electrochemical testing. The results showed that after 100 cycles of testing, the discharge specific capacity was 66.5 mAh / g, the capacity retention rate was 50.6%, and the average coulombic efficiency was 98.5%, showing better cycle stability than Comparative Examples 1 to 4.
[0048] Example 2
[0049] A method for charging and discharging a negative electrode-free secondary lithium battery comprises the following steps:
[0050] S1: Assembly of negative electrode-free secondary lithium battery;
[0051] The negative electrode current collector, the separator, and the positive electrode sheet coated with the positive electrode material are assembled into an electrode assembly; the electrode assembly is placed in a packaging material and a liquid electrolyte is added to obtain a negative electrode-free secondary lithium battery.
[0052] Among them, lithium iron phosphate is used as the positive electrode material, and the composition of the liquid electrolyte is: lithium bis(trifluoromethanesulfonyl)imide as the lithium salt, a mixture of 1,3-dioxolane and ethylene glycol dimethyl ether as the organic solvent system, and lithium nitrate as the additive; the molar concentration of the lithium salt is 1 mol / L, based on the mass of the liquid electrolyte, the mass proportion of the additive is 2%, and the volume ratio of 1,3-dioxolane and ethylene glycol dimethyl ether is 1:1.
[0053] S2: After the negative electrode-free secondary lithium battery is assembled, it is placed in a constant temperature room at 25°C for 10 hours.
[0054] S3: The non-negative-electrode secondary lithium battery after standing is subjected to formation at a rate of 0.1C.
[0055] S4: The formed negative electrode-free secondary lithium battery is charged at a current density of 0.5C and discharged at a current density of 1C (1C = 170mAh / g) for a cycle, and the charge and discharge voltage range of the battery is controlled to be 2.7V to 3.8V. After the negative electrode-free secondary lithium battery has been charged and discharged for 25 cycles, the current density is 0.1mA / cm 2 The current density was cycled for 1 cycle.
[0056] The above-assembled negative electrode-free secondary lithium battery was subjected to electrochemical testing. The results showed that after 100 cycles of testing, the discharge specific capacity was 71.5 mAh / g, the capacity retention rate was 51.7%, and the average coulombic efficiency was 98.7%, showing better cycle stability than Comparative Examples 1 to 4.
[0057] Example 3
[0058] A method for charging and discharging a negative electrode-free secondary lithium battery comprises the following steps:
[0059] S1: Assembly of negative electrode-free secondary lithium battery;
[0060] The negative electrode current collector, the separator, and the positive electrode sheet coated with the positive electrode material are assembled into an electrode assembly; the electrode assembly is placed in a packaging material and a liquid electrolyte is added to obtain a negative electrode-free secondary lithium battery.
[0061] Among them, lithium iron phosphate is used as the positive electrode material, and the composition of the liquid electrolyte is: lithium bis(trifluoromethanesulfonyl)imide as the lithium salt, a mixture of 1,3-dioxolane and ethylene glycol dimethyl ether as the organic solvent system, and lithium nitrate as the additive; the molar concentration of the lithium salt is 1 mol / L, based on the mass of the liquid electrolyte, the mass proportion of the additive is 2%, and the volume ratio of 1,3-dioxolane and ethylene glycol dimethyl ether is 1:1.
[0062] S2: After the negative electrode-free secondary lithium battery is assembled, it is placed in a constant temperature room at 25°C for 10 hours.
[0063] S3: The non-negative-electrode secondary lithium battery after standing is subjected to formation at a rate of 0.1C.
[0064] S4: The formed negative electrode-free secondary lithium battery is cycled at a current density of 0.5C and a current density of 1C (1C = 170mAh / g), and the charge and discharge voltage range of the battery is controlled to be 2.7V to 3.8V. After every 50 charge and discharge cycles of the negative electrode-free secondary lithium battery, it is cycled at a current density of 0.1mA / cm2 for one cycle.
[0065] The above-assembled negative electrode-free secondary lithium battery was subjected to electrochemical testing. The results showed that after 100 cycles of testing, the discharge specific capacity was 58.4 mAh / g, the capacity retention rate was 43.8%, and the average coulombic efficiency was 98.4%, showing better cycle stability than Comparative Examples 1 and 3.
[0066] Example 4
[0067] A method for charging and discharging a negative electrode-free secondary lithium battery comprises the following steps:
[0068] S1: Assembly of negative electrode-free secondary lithium battery:
[0069] The negative electrode current collector, the separator, and the positive electrode sheet coated with the positive electrode material are assembled into an electrode assembly; the electrode assembly is placed in a packaging material and a liquid electrolyte is added to obtain a negative electrode-free secondary lithium battery.
[0070] Among them, lithium iron phosphate is used as the positive electrode material, and the composition of the liquid electrolyte is: lithium bis(trifluoromethanesulfonyl)imide as the lithium salt, a mixture of 1,3-dioxolane and ethylene glycol dimethyl ether as the organic solvent system, and lithium nitrate as the additive; the molar concentration of the lithium salt is 1 mol / L, based on the mass of the liquid electrolyte, the mass proportion of the additive is 2%, and the volume ratio of 1,3-dioxolane and ethylene glycol dimethyl ether is 1:1.
[0071] S2: After the negative electrode-free secondary lithium battery is assembled, it is placed in a constant temperature room at 25°C for 10 hours.
[0072] S3: The non-negative-electrode secondary lithium battery after standing is subjected to formation at a rate of 0.1C.
[0073] S4: The formed negative electrode-free secondary lithium battery is charged at a current density of 0.5C and discharged at a current density of 1C (1C = 170mAh / g) for a cycle, and the charge and discharge voltage range of the battery is controlled to be 2.7V to 3.8V. After the negative electrode-free secondary lithium battery has been charged and discharged for 25 cycles, the current density is 0.1mA / cm 2 The current density was cycled for 3 cycles.
[0074] The above-assembled negative electrode-free secondary lithium battery was subjected to electrochemical testing. The results showed that after 100 cycles of testing, the discharge specific capacity was 57.8 mAh / g, the capacity retention rate was 45.5%, and the average coulombic efficiency was 98.4%, showing better cycle stability than Comparative Examples 1 and 3.
[0075] Example 5
[0076] A method for charging and discharging a negative electrode-free secondary lithium battery comprises the following steps:
[0077] S1: Assembly of negative electrode-free secondary lithium battery:
[0078] The negative electrode current collector, the separator, and the positive electrode sheet coated with the positive electrode material are assembled into an electrode assembly; the electrode assembly is placed in a packaging material and a liquid electrolyte is added to obtain a negative electrode-free secondary lithium battery.
[0079] Among them, lithium iron phosphate is used as the positive electrode material, and the composition of the liquid electrolyte is: lithium bis(trifluoromethanesulfonyl)imide as the lithium salt, a mixture of 1,3-dioxolane and ethylene glycol dimethyl ether as the organic solvent system, and lithium nitrate as the additive; the molar concentration of the lithium salt is 1 mol / L, based on the mass of the liquid electrolyte, the mass proportion of the additive is 2%, and the volume ratio of 1,3-dioxolane and ethylene glycol dimethyl ether is 1:1.
[0080] S2: After the negative electrode-free secondary lithium battery is assembled, it is placed in a constant temperature room at 25°C for 10 hours.
[0081] S3: The non-negative-electrode secondary lithium battery after standing is subjected to formation at a rate of 0.1C.
[0082] S4: The formed negative electrode-free secondary lithium battery is charged at a current density of 0.5C and discharged at a current density of 1C (1C = 170mAh / g) for a cycle, and the charge and discharge voltage range of the battery is controlled to be 2.7V to 3.8V. After the negative electrode-free secondary lithium battery has been charged and discharged for 25 cycles, the current density is 0.05mA / cm 2 The current density was cycled for 1 cycle.
[0083] The above-assembled negative electrode-free secondary lithium battery was subjected to electrochemical testing. The results showed that after 100 cycles of testing, the discharge specific capacity was 66.7 mAh / g, the capacity retention rate was 49%, and the average coulombic efficiency was 98.7%, showing better cycle stability than Comparative Examples 1 and 3.
[0084] Comparative Example 1
[0085] A method for charging and discharging a negative electrode-free secondary lithium battery comprises the following steps:
[0086] S1: Assembly of negative electrode-free secondary lithium battery:
[0087] The negative electrode current collector, the separator, and the positive electrode sheet coated with the positive electrode material are assembled into an electrode assembly; the electrode assembly is placed in a packaging material and a liquid electrolyte is added to obtain a negative electrode-free secondary lithium battery.
[0088] Among them, lithium iron phosphate is used as the positive electrode material, and the composition of the liquid electrolyte is: lithium bis(trifluoromethanesulfonyl)imide as the lithium salt, a mixture of 1,3-dioxolane and ethylene glycol dimethyl ether as the organic solvent system, and lithium nitrate as the additive; the molar concentration of the lithium salt is 1 mol / L, based on the mass of the liquid electrolyte, the mass proportion of the additive is 2%, and the volume ratio of 1,3-dioxolane and ethylene glycol dimethyl ether is 1:1.
[0089] S2: After the negative electrode-free secondary lithium battery is assembled, it is placed in a constant temperature room at 25°C for 10 hours.
[0090] S3: The non-negative-electrode secondary lithium battery after standing is subjected to formation at a rate of 0.1C.
[0091] S4: The formed negative electrode-free secondary lithium battery is charged at a current density of 0.5C and discharged at a current density of 1C (1C=170mAh / g) for continuous cycling, and the charge and discharge voltage range of the battery is controlled to be 2.7V to 3.8V.
[0092] The above-assembled negative electrode-free secondary lithium battery was subjected to electrochemical testing. The results showed that after 100 cycles of testing, the discharge specific capacity was 53.1 mAh / g, the capacity retention rate was 38.8%, and the average coulombic efficiency was 98.5%, which showed poor cycle stability compared with Examples 1 to 5.
[0093] Comparative Example 2
[0094] A method for charging and discharging a negative electrode-free secondary lithium battery comprises the following steps:
[0095] S1: Assembly of negative electrode-free secondary lithium battery:
[0096] The negative electrode current collector, the separator, and the positive electrode sheet coated with the positive electrode material are assembled into an electrode assembly; the electrode assembly is placed in a packaging material and a liquid electrolyte is added to obtain a negative electrode-free secondary lithium battery.
[0097] Among them, lithium iron phosphate is used as the positive electrode material, and the composition of the liquid electrolyte is: lithium bis(trifluoromethanesulfonyl)imide as the lithium salt, a mixture of 1,3-dioxolane and ethylene glycol dimethyl ether as the organic solvent system, and lithium nitrate as the additive; the molar concentration of the lithium salt is 1 mol / L, based on the mass of the liquid electrolyte, the mass proportion of the functional additive is 2%, and the volume ratio of 1,3-dioxolane and ethylene glycol dimethyl ether is 1:1.
[0098] S2: After the negative electrode-free secondary lithium battery is assembled, it is placed in a constant temperature room at 25°C for 10 hours.
[0099] S3: The non-negative-electrode secondary lithium battery after standing is subjected to formation at a rate of 0.1C.
[0100] S4: The formed negative electrode-free secondary lithium battery is charged at a current density of 0.5C and discharged at a current density of 1C (1C = 170mAh / g) for a cycle, and the charge and discharge voltage range of the battery is controlled to be 2.7V to 3.8V. After the negative electrode-free secondary lithium battery has been charged and discharged for 25 cycles, the current density is 0.03mA / cm 2 The current density was cycled for 1 cycle.
[0101] The above-assembled negative electrode-free secondary lithium battery was subjected to electrochemical testing. The results showed that after 100 cycles of testing, the discharge specific capacity was 69.3 mAh / g, the capacity retention rate was 49.2%, and the average coulombic efficiency was 98.6%, which showed poor cycle stability compared with Examples 1 to 2.
[0102] Comparative Example 3
[0103] A method for charging and discharging a negative electrode-free secondary lithium battery comprises the following steps:
[0104] S1: Assembly of negative electrode-free secondary lithium battery:
[0105] The negative electrode current collector, the separator, and the positive electrode sheet coated with the positive electrode material are assembled into an electrode assembly; the electrode assembly is placed in a packaging material and a liquid electrolyte is added to obtain a negative electrode-free secondary lithium battery.
[0106] Among them, lithium iron phosphate is used as the positive electrode material, and the composition of the liquid electrolyte is: lithium bis(trifluoromethanesulfonyl)imide as the lithium salt, a mixture of 1,3-dioxolane and ethylene glycol dimethyl ether as the organic solvent system, and lithium nitrate as the additive; the molar concentration of the lithium salt is 1 mol / L, based on the mass of the liquid electrolyte, the mass proportion of the functional additive is 2%, and the volume ratio of 1,3-dioxolane and ethylene glycol dimethyl ether is 1:1.
[0107] S2: After the negative electrode-free secondary lithium battery is assembled, it is placed in a constant temperature room at 25°C for 10 hours.
[0108] S3: The non-negative-electrode secondary lithium battery after standing is subjected to formation at a rate of 0.1C.
[0109] S4: The formed negative electrode-free secondary lithium battery is charged at a current density of 0.5C and discharged at a current density of 1C (1C = 170mAh / g) for a cycle, and the charge and discharge voltage range of the battery is controlled to be 2.7V to 3.8V. After the negative electrode-free secondary lithium battery has been charged and discharged for 25 cycles, the current density is 0.2mA / cm 2 The current density was cycled for 1 cycle.
[0110] The above-assembled negative electrode-free secondary lithium battery was subjected to electrochemical testing. The results showed that after 100 cycles of testing, the discharge specific capacity was 59.9 mAh / g, the capacity retention rate was 43.4%, and the average coulombic efficiency was 98.7%, which showed poor cycle stability compared with Examples 1 to 5.
[0111] Comparative Example 4
[0112] A method for charging and discharging a negative electrode-free secondary lithium battery comprises the following steps:
[0113] S1: Assembly of negative electrode-free secondary lithium battery:
[0114] The negative electrode current collector, the separator, and the positive electrode sheet coated with the positive electrode material are assembled into an electrode assembly; the electrode assembly is placed in a packaging material and a liquid electrolyte is added to obtain a negative electrode-free secondary lithium battery.
[0115] Among them, lithium iron phosphate is used as the positive electrode material, and the composition of the liquid electrolyte is: lithium bis(trifluoromethanesulfonyl)imide as the lithium salt, a mixture of 1,3-dioxolane and ethylene glycol dimethyl ether as the organic solvent system, and lithium nitrate as the additive; the molar concentration of the lithium salt is 1 mol / L, based on the mass of the liquid electrolyte, the mass proportion of the functional additive is 2%, and the volume ratio of 1,3-dioxolane and ethylene glycol dimethyl ether is 1:1.
[0116] S2: After the negative electrode-free secondary lithium battery is assembled, it is placed in a constant temperature room at 25°C for 10 hours.
[0117] S3: The non-negative-electrode secondary lithium battery after standing is subjected to formation at a rate of 0.1C.
[0118] S4: The formed negative electrode-free secondary lithium battery is charged at a current density of 0.5C and discharged at a current density of 1C (1C = 170mAh / g) for a cycle, and the charge and discharge voltage range of the battery is controlled to be 2.7V to 3.8V. After the negative electrode-free secondary lithium battery has been charged and discharged for 25 cycles, the current density is 0.1mA / cm 2 The current density was cycled for 5 cycles.
[0119] The above-assembled negative electrode-free secondary lithium battery was subjected to electrochemical testing. The results showed that after 100 cycles of testing, the discharge specific capacity was 67.7 mAh / g, the capacity retention rate was 49.7%, and the average coulombic efficiency was 98.9%, which showed poor cycle stability compared with Examples 1 to 2.
[0120] Figure 1 The graph of the change of discharge specific capacity of the negative electrode-free secondary lithium battery in Examples 1 to 5 and Comparative Examples 1 to 4 during the cycle at a 0.5C charge rate and a 1C discharge rate is shown. Figure 1 It can be seen that the specific capacity of Comparative Example 1 gradually decreases with the increase in the number of cycles, indicating that the negative electrode-free secondary lithium battery is affected by factors such as the accumulation of dead lithium and interfacial side reactions during long-term cycling, resulting in active lithium loss and increased polarization. Examples 1 to 5 have delayed the attenuation of the specific capacity to a certain extent, especially when the number of cycles is relatively high. The negative electrode-free secondary lithium battery after adopting the charge and discharge method of the present application still maintains a relatively high discharge specific capacity. This shows that the charging method of the present application helps to maintain the reversibility of active lithium and slow down the growth of battery polarization, thereby improving the cycle stability of the negative electrode-free secondary lithium battery.
[0121] Figure 2 The graph of the change of coulombic efficiency during the cycle of the negative electrode-free secondary lithium battery in Examples 1 to 5 and Comparative Examples 1 to 4 at a charge rate of 0.5C and a discharge rate of 1C is shown. Figure 2 It can be seen that although certain fluctuations occur in some cycle stages of Examples 1 to 5, the overall coulombic efficiency is maintained at a high level. This shows that the charge and discharge method of the present application can inhibit the accumulation of side reactions to a certain extent, slow down the irreversible loss of lithium, and thus extend the cycle life of the negative electrode-free secondary lithium battery.
[0122] Figure 3 This is a graph showing the change in current and voltage over time for the negative electrode-free secondary lithium battery in Comparative Example 1 of this application after 100 cycles. Figure 3 It can be seen that in the comparative example 1, during the continuous cycle, the current of each charge and discharge cycle remains unchanged, the voltage change trend is relatively consistent, and the specific capacity decay of the negative electrode-free secondary lithium battery accelerates rapidly with the progress of the cycle.
[0123] Figure 4 This is a graph showing the change in current and voltage over time for a negative electrode-free secondary lithium battery after 100 cycles in Example 2 of this application. Figure 4 It can be seen that the voltage curve shows a significant decrease in charge and discharge voltage polarization, which helps to alleviate the polarization accumulation caused by continuous cycling, reduce the growth of lithium dendrites and the impact of interface side reactions, and the negative electrode-free secondary lithium battery after adopting the charge and discharge method of the present application has a high voltage stability in long-term cycling. This shows that the charge and discharge method of the present application can effectively regulate the interface state, delay the battery performance degradation, and thus extend the cycle life of the negative electrode-free secondary lithium battery.
[0124] The performance test results of Examples 1 to 5 and Comparative Examples 1 to 4 are shown in Table 1:
[0125] Table 1
[0126]
[0127]
[0128] As can be seen from Table 1, compared with Comparative Example 1, Examples 1 to 5 can slow down the attenuation of the battery specific capacity to a certain extent, especially at a high number of cycles. Among them, the capacity retention rate of Example 1 after 100 cycles is 50.6%, and the capacity retention rate of Example 2 after 100 cycles is 51.7%, while the cycle stability of Comparative Example 1 is poor, and its capacity retention rate after 100 cycles is only 38.8%. This shows that the charge and discharge method of the present application helps to maintain the reversibility of active lithium, slow down the growth of battery polarization, and thus improve the cycle stability of the battery.
[0129] The average coulombic efficiency of Example 2 and Example 5 after 100 cycles is 98.7%, while the average coulombic efficiency of Comparative Example 1 after 100 cycles is 98.5%. This shows that the charge and discharge method of the present application can inhibit the accumulation of side reactions to a certain extent, slow down the irreversible loss of lithium, and thus extend the cycle life of the battery.
[0130] The capacity retention rate of Example 2 after 100 cycles is 51.7%, while the capacity retention rates of Comparative Examples 1 to 4 after 100 cycles are all lower than 51.7%. This further illustrates that the charge and discharge method of the present application helps to maintain the reversibility of active lithium, slow down the growth of battery polarization, and thus improve the cycle stability of the battery.
[0131] The above embodiments are only used to illustrate the technical solutions of the present application and are not intended to limit the present application. Although the present application has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent replacements of the technical solutions of the present application should not depart from the spirit and scope of the technical solutions of the present application.
Claims
1. A method for charging and discharging a negative electrode-free secondary lithium battery, characterized in that: The following steps are involved: The negative electrode-free secondary lithium battery is left to stand at room temperature; forming the negative electrode-free secondary lithium battery after standing still; The formed negative electrode-free secondary lithium battery is subjected to a first round of constant current charge and discharge cycle; The negative electrode-free secondary lithium battery after the first round of constant current charge and discharge cycle is subjected to a second round of constant current charge and discharge cycle at a first current density, wherein the number of cycles of the second round of constant current charge and discharge cycle is 1 to 3, wherein the first current density is 0.05 mA / cm 2 Up to 0.1 mA / cm 2 .
2. The method for charging and discharging a negative electrode-free secondary lithium battery according to claim 1, wherein: The standing time is 10 hours to 24 hours.
3. The method for charging and discharging a negative electrode-free secondary lithium battery according to claim 1, wherein: The number of cycles of the first round of constant current charge and discharge cycle is 10 to 50, and the charge and discharge voltage is 2.7V to 3.8V.
4. The method for charging and discharging a negative electrode-free secondary lithium battery according to claim 1, wherein: The assembly method of the negative electrode-free secondary lithium battery comprises: Assembling the negative electrode current collector, the separator, and the positive electrode sheet coated with the positive electrode material into an electrode assembly; The electrode assembly is placed in a packaging material and a liquid electrolyte is added to obtain the negative electrode-free secondary lithium battery.
5. The method for charging and discharging a negative electrode-free secondary lithium battery according to claim 4, wherein: The positive electrode material includes lithium iron phosphate, the liquid electrolyte includes an organic solvent, a lithium salt and an additive, wherein the lithium salt includes lithium bis(trifluoromethanesulfonyl)imide, the organic solvent includes 1,3-dioxolane and ethylene glycol dimethyl ether, and the additive includes lithium nitrate.
6. The method for charging and discharging a negative electrode-free secondary lithium battery according to claim 5, wherein: The molar concentration of the lithium bis(trifluoromethanesulfonyl)imide is 0.5 mol / L to 3 mol / L; based on the mass of the liquid electrolyte, the mass proportion of the lithium nitrate is 1% to 3%; and the volume ratio of the 1,3-dioxolane to the ethylene glycol dimethyl ether is 1:
1.
7. The method for charging and discharging a negative electrode-free secondary lithium battery according to claim 4, wherein: The positive electrode material includes a high-nickel ternary material, and the liquid electrolyte includes an organic solvent, a lithium salt, and an additive, wherein the lithium salt includes lithium difluorooxalatoborate and lithium tetrafluoroborate, and the organic solvent includes fluoroethylene carbonate and diethyl carbonate.
8. The method for charging and discharging a negative electrode-free secondary lithium battery according to claim 7, wherein: The molar content of the lithium salt is 0.6 mol / L to 2 mol / L; and the volume ratio of the fluoroethylene carbonate to the diethyl carbonate is 2:
1.
9. The method for charging and discharging a negative electrode-free secondary lithium battery according to claim 4, wherein: The negative electrode current collector includes at least one of copper foil, copper mesh, foam copper, nickel foil, iron foil, carbon paper or carbon cloth.
10. A negative electrode-free secondary lithium battery, characterized in that: The negative electrode-free secondary lithium battery is prepared by the charge and discharge method of the negative electrode-free secondary lithium battery according to any one of claims 1 to 9.
Citation Information
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