An effective way to inhibit lithium dendrites - high concentration LiFSI electrolyte

With the development of science and technology, human demand for energy is increasing day by day. Currently, commercial lithium-ion batteries (theoretical capacity 372 mAh/g) can no longer meet this demand, and the development of high-capacity density batteries has become a research hotspot.
Lithium metal has a high theoretical specific capacity (3860 mAh / g) and has great application potential in the field of energy storage. However, the growth of lithium dendrites not only reduces the battery performance, but also is prone to short circuits, posing a safety hazard. 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 schemes, such as preparation of three-dimensional lithium intercalation substrates, 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 influence of different electrolyte environments on the growth of lithium dendrites. It is proposed that the high concentration of LiFSI ether electrolyte can effectively inhibit the growth of lithium dendrites on copper current collectors even without lithium intercalation matrix. At the same time, battery coulombic efficiency has also improved significantly.
Figure 1. Schematicillustrations of battery configurations. a) State-of-the-art Li-ion battery, ie, Cu|C6||LiFePO4|Al. b) Anode-free battery,ie,Cu||LiFePO4|Al.
The Cu-LiFePO4 battery was used as the research system, and 1 M LiPF6-EC/DMC (1/2 v/v) ester electrolyte and 4 MLiFSI-DME ether electrolyte were used for comparison. The experimental results show that the battery resistance increases obviously in the ester electrolyte environment as the number of cycles increases, while the resistance increases in the 4 MLiFSI-DME ether electrolyte environment.
Moreover, in the 4 MLiFSI-DME environment, the average coulombic efficiency was greater than 99% after multiple cycles. Even at a current density of 2 mA cm-2, the Coulomb efficiency is close to 100%.
In addition, the study found that Coulomb efficiency can also be improved by adjusting the test conditions. When lithium is deposited at 0.2 mA cm-2 and 2 mA cm-2 is removed, the average coulombic efficiency is 99.6%, which is higher than the Coulomb efficiency which has been cycled at 0.2 mA cm-2/2 mA cm-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 differentcycles whencharged/discharged at 0.2 mA cm?2. All data Were collectedatdischarged state of the cells.
Figure 3. Electrochemical performance of anode-freeCu||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 two electrolytes. 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) Capacityretention 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 withlow-rate (C/5) charging and high-rate (2 C b) CEof Cu||Li cells. A capacity of 0.5 mAh cm?2 was used to plate the Limetal, which wassubsequently 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 the reasons by characterization, which has guiding significance for the research and large-scale production of lithium metal batteries.
Relevant research results were published in the famous publication 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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