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Abstract: In this paper, we report the electrochemical characteristics of a novel cathode material, Li2CoPO4F, prepared by solid-state reactions. The solid-state reaction mechanism involved in synthesizing the Li2CoPO4F also is analyzed in this paper. When cycled between 2.0V and 5.0V during cyclic voltammetry measurements, the Li2CoPO4F samples present one, fully reversible anodic reaction at 4.81V. When cycled between 2.0V and 5.5V, peaks occurring at 4.81V and 5.12V in the first anodic scan evolved to one broad oxidative, mound-like pattern in subsequent cycles. Correspondingly, the X-ray diffraction (XRD) pattern of the Li2CoPO4F electrode discharged from 5.5V to 2.0V is slightly different from the patterns exhibited by a fresh sample and the sample discharged from 5.0V to 2.0V. This difference may correspond to a structural relaxation that appears above 5V. In the constant current cycling measurements, the Li2CoPO4F samples exhibited a capacity as high as 109mAhg−1 and maintained a good cyclability between 2.0V and 5.5V vs. Li/Li+. XRD measurements confirmed that the discharged state is Li2CoPO4F. Combining these XRD results and electrochemical data proved that up to 1mol Li+ is extractable when charged to 5.5V. [ABSTRACT FROM AUTHOR]

Rechargeable lithium (Li) metal batteries with conventional LiPF 6 -carbonate electrolytes have been reported to fail quickly at charging current densities of about 1.0 mA cm −2 and above. In this work, we demonstrate the rapid charging capability of Li||LiNi 0.8 Co 0.15 Al 0.05 O 2 (NCA) cells can be enabled by a dual-salt electrolyte of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium bis(oxalato)borate (LiBOB) in a carbonate solvent mixture. The cells using the LiTFSI-LiBOB dual-salt electrolyte significantly outperform those using the LiPF 6 electrolyte at high charging current densities. At the charging current density of 1.50 mA cm −2 , the Li||NCA cells with the dual-salt electrolyte can still deliver a discharge capacity of 131 mAh g −1 and a capacity retention of 80% after 100 cycles. The Li||NCA cells with the LiPF 6 electrolyte start to show fast capacity fading after the 30th cycle and only exhibit a low capacity of 25 mAh g −1 and a low retention of 15% after 100 cycles. The reasons for the good chargeability and cycling stability of the cells using the LiTFSI-LiBOB dual-salt electrolyte can be attributed to the good film-formation ability of the electrolyte on the Li metal anode and the highly conductive nature of the sulfur-rich interphase layer. [ABSTRACT FROM AUTHOR]

The practical application of lithium (Li) metal anode in rechargeable Li batteries is hindered by both the growth of Li dendrites and the low Coulombic efficiency (CE) during repeated charge/discharge cycles. Recently, we have discovered that CsPF 6 as an electrolyte additive can significantly suppress Li dendrite growth and lead to highly compacted and well aligned Li nanorod structures during Li deposition on copper substrates. In this paper, the effect of CsPF 6 additive on the performance of rechargeable Li metal batteries with lithium iron phosphate (LFP) cathode is further studied. Li|LFP coin cells with CsPF 6 additive in electrolytes show well protected Li anode surface, decreased resistance, enhanced rate capability and extended cycling stability. In Li|LFP cells, the electrolyte with CsPF 6 additive shows excellent long-term cycling stability (at least 500 cycles) at a charge current density of 0.5 mA cm −2 without internal short circuit. At high charge current densities, the effect of CsPF 6 additive becomes less significant. Future work needs to be done to protect Li metal anode, especially at high charge current densities and for long cycle life. [ABSTRACT FROM AUTHOR]