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An effective way to inhibit lithium dendrites - high concent

Number of visits: Date:2018-05-18 11:39:54
An effective way to inhibit lithium dendrites - high concentration of LiFSI electrolyte

With the development of science and technology, the demand for energy by humans is increasing day by day. Currently, commercial lithium-ion batteries (the theoretical capacity of 372 mAh/g) cannot meet this demand. The development of high-capacity-density batteries has become a research hotspot.
 
Lithium metal has a high theoretical specific capacity (3860 mAh/g), which has great potential for application in energy storage. However, the growth of lithium dendrites not only reduces the battery performance, but also causes short circuit easily, which may cause safety hazards. These problems have seriously hindered the development and practical application of lithium metal batteries.
 
In order to solve the above problems, scientists have proposed various solutions, such as the preparation of three-dimensional lithium intercalation, lithium metal surface coating, and membrane modification. However, these methods increase the overall weight of the battery, and the preparation process is cumbersome, which is not conducive to commercial production.
 
Recently, Qian et al. compared the effects of different electrolyte environments on the growth of lithium dendrites, and proposed that under high LiFSI ether electrolyte environments, the growth of lithium dendrites on copper current collectors can be effectively suppressed even without a lithium intercalation matrix. At the same time, the battery coulombic efficiency has also improved significantly.
 
 
Figure 1. Schematicillustrations of battery configurations. a) State-of-the-art Li-ion battery, i.e., Cu|C6||LiFePO4|Al.b) Anode-free battery, i.e., Cu||LiFePO4|Al.
 
The experiment uses Cu-LiFePO4 battery as the research system, and 1 M LiPF6-EC/DMC (1/2 v/v) ester electrolyte and 4 MLiFSI-DME ether electrolyte are used for comparison. The experimental results show that with the increase of the number of cycles, the battery resistance increases significantly in the environment of ester electrolytes, while the resistance increase is small in the environment of 4 MLiFSI-DME ether electrolytes.
 
And in the 4 MLiFSI-DME environment, the average Coulomb efficiency is more than 99% after multiple cycles. Even at a current density of 2 mA cm-2, the Coulomb efficiency is still close to 100%.
 
In addition, the study found that Coulomb efficiency can also be improved by adjusting test conditions. When lithium is deposited at 0.2 mA cm-2 and 2 mA cm-2 is removed, the average Coulomb efficiency can reach 99.6%, which is higher than the Coulomb efficiency that has been cycled at 0.2 mA cm-2/2 mAcm-2.
 
Figure 2. Nyquistplot of anode-free Cu||LiFePO4 cells with either 1 M LiPF6-EC/DMC (dashed line) or 4 M LiFSI-DME (solid line) after different cycles when when charged/discharged at 0.2 mA cm−2. All data Are collectedatdischarged state of the cells.
 
 
Figure 3. Electrochemical performance of anode-free Cu||LiFePO4 cells with either 1 M LiPF6-EC/DMC or 4 M LiFSI-DME.a) Charge/discharge voltageprofiles for the first three cycles with the twoelectrolytes. b) Capacity retention and CE Of the cells with the twoelectrolytes as a function of cycle numberwhen charged/discharged at 0.2 mA cm−2(open symbols: charge capacity, filled symbols:discharge capacity). c) Capacity retention of the cells with 4 M LiFSI-DME charged/discharged At differentcurrent densities.
 
 
 
Figure 4. Cycling performance of Cu||Li and Cu||LiFePO4cells with 4 M LiFSI-DME cycled at different current densities. a) Li||LiFePO4cell cycled with low-rate (C/5) charging and high-rate (2 C ) discharging. b) CEof Cu||Li cells. A capacity of 0.5 mAh cm−2 was used to plate the Limetal, which was subsequently stripped by cycling to 1.0 V versus Li/Li+.c) Charge/discharge voltage profiles for the first 30 cycles of the anode-freecells (Cu||LiFePO4) with 4 MLiFSI-DME cycled at different current densities. d) Discharge capacity and CE of anode-free Cu||LiFePO4cells charged at 0.2 mA cm−2 anddischarged at either 0.2 or 2.0 mAcm−2 (open symbols: charge capacity, filled symbols: dischargecapacity).
 
In summary, this work proposes an electrolyte that can effectively inhibit the growth of lithium dendrites, and explains its causes through characterization, which has guiding significance for the research and large-scale production of lithium metal batteries.
 
Relevant research results were published in the famous journal Advanced Functionalmaterials (DOI:10.1002/adfm.201602353.) JiangfengQian, Brian D. Adams, Jianming Zheng, Ji-Guang Zhang et al. Anode-Free RechargeableLithium Metal Batteries.Adv.Funct. Mater. 2016 .).

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