No abstract

No abstract

A principle of suppressing Li dendrite in solid-state electrolytes is proposed and demonstrated using LiF-rich SEI experimentally.

All-ceramic cathode-electrolyte with a low interfacial resistance can be realized by thermally soldering LiCoO 2 and Li 7 La 3 Zr 2 O 12 (LLZO) together with Li 2.3Àx C 0.7+x B 0.3Àx O 3 solid electrolyte interphase through the reaction between the Li 2.3 C 0.7 B 0.3 O 3 solder and the Li 2 CO 3 layers that can be spontaneously coated on both LLZO and LiCoO 2. The all-solid-state Li/LLZO/LiCoO 2 battery with such an all-ceramic cathode/electrolyte exhibits high cycling stability and high rate performance.

All-solid-state lithium-sulfur batteries (ASSLSBs) using highly conductive sulfide-based solid electrolytes suffer from low sulfur utilization, poor cycle life, and low rate performance due to the huge volume change of the electrode and the poor electronic and ionic conductivities of S and Li2S. The most promising approach to mitigate these challenges lies in the fabrication of a sulfur nanocomposite electrode consisting of a homogeneous distribution of nanosized active material, solid electrolyte, and carbon. Here, we reported a novel bottom-up method to synthesize such a nanocomposite by dissolving Li2S as the active material, polyvinylpyrrolidone (PVP) as the carbon precursor, and Li6PS5Cl as the solid electrolyte in ethanol, followed by a coprecipitation and high-temperature carbonization process. Li2S active material and Li6PS5Cl solid electrolyte with a particle size of ∼4 nm were uniformly confined in a nanoscale carbon matrix. The homogeneous nanocomposite electrode consisting of different nanoparticles with distinct properties of lithium storage capability, mechanical reinforcement, and ionic and electronic conductivities enabled a mechanical robust and mixed conductive (ionic and electronic conductive) sulfur electrode for ASSLSB. A large reversible capacity of 830 mAh/g (71% utilization of Li2S) at 50 mA/g for 60 cycles with a high rate performance was achieved at room temperature even at a high loading of Li2S (∼3.6 mg/cm(2)). This work provides a new strategy to design a mechanically robust, mixed conductive nanocomposite electrode for high-performance all-solid-state lithium sulfur batteries.

that the Li dendrites also form in 70Li 2 S-30P 2 S 5 glass, 75Li 2 S-25P 2 S 5 glass, 80Li 2 S-20P 2 S 5 glass-ceramic, and polycrystalline β-Li 3 PS 4 . [13][14][15] The formation of Li dendrites leads to rapid short circuit of the Li/electrolyte/Li (Li-Li) cells at current densities larger than 1 mA cm −2 . [13,15] It should be noted that even in the conventional liquid electrolyte (1 m LiPF 6 in EC/ DMC), the lithium metal anode is still able to cycle hundreds of hours at 2 mA cm −2 without shorting. [16] This indicates that sulfide electrolytes tend to promote, rather than suppress, dendrite formation when compared with liquid electrolytes. However, until now, there is still no effective approach to suppress the Li dendrite growth in sulfide electrolytes because the mechanism for the "unexpected" dendrite formation is unclear. To the best of our knowledge, there is only one report on the suppression of the lithium dendrite formation in sulfide electrolyte by optimizing the processing conditions. [15] It was shown that hot pressing 75Li 2 S-25P 2 S 5 solid electrolyte can help to increase the critical current density (at which current the cell will be short circuited by dendrite formation) because of the formation of a highly conductive thio-LISICON phase and the improvement of adhesion between particles. However, the critical current density for the hot-pressed 75Li 2 S-25P 2 S 5 solid electrolyte is still limited to 1 mA cm −2 , much lower than that in the liquid-electrolyte Li batteries. It is fair to conclude that, similar as in the liquidelectrolyte lithium-metal batteries, the main challenge to utilize lithium anode with sulfide solid electrolytes is how to effectively suppress the dendrite formation at a large current.It has been known that the sulfide solid electrolytes have a limited thermodynamic electrochemical stability window around 1.7-2.1 V. [17][18][19] Therefore, the interfacial stability between Li metal and sulfide electrolytes is achieved by forming solid electrolyte interphase (SEI) as a passivating layer. The composition of the SEI mainly includes Li 3 P, Li 2 S, and other Li-containing compounds depending on the composition of the electrolyte. [17,18,[20][21][22] Since the Li dendrites have to grow through the SEI, the composition of the SEI should play an important role in the dendrite formation. It is therefore hypothesized that the dendrite formation in sulfide electrolytes can be suppressed by tuning the composition of the electrolyte.In this work, we demonstrated that the formation of Li dendrites in Li 2 S-P 2 S 5 glass can be suppressed by incorporating LiI into the electrolyte. Our interest in glass-type electrolyte Solid electrolytes have been considered as a promising approach for Li dendrite prevention because of their high mechanical strength and high Li transference number. However, recent reports indicate that Li dendrites also form in Li 2 S-P 2 S 5 based sulfide electrolytes at current densities much lower than that in the conventional liquid electrolytes. The methods of...

No abstract

Engineering a stable solid electrolyte interphase (SEI) is critical for suppression of lithium dendrites. However, the formation of a desired SEI by formulating electrolyte composition is very difficult due to complex electrochemical reduction reactions. Here, instead of trial-anderror of electrolyte composition, we design a Li-11 wt % Sr alloy anode to form a SrF 2 -rich SEI in fluorinated electrolytes. Density functional theory (DFT) calculation and experimental characterization demonstrate that a SrF 2 -rich SEI has a large interfacial energy with Li metal and a high mechanical strength, which can effectively suppress the Li dendrite growth by simultaneously promoting the lateral growth of deposited Li metal and the SEI stability. The Li−Sr/Cu cells in 2 M LiFSI-DME show an outstanding Li plating/stripping Coulombic efficiency of 99.42% at 1 mA cm −2 with a capacity of 1 mAh cm −2 and 98.95% at 3 mA cm −2 with a capacity of 2 mAh cm −2 , respectively. The symmetric Li−Sr/Li−Sr cells also achieve a stable electrochemical performance of 180 cycles at an extremely high current density of 30 mA cm −2 with a capacity of 1 mAh cm −2 . When paired with LiFePO 4 (LFP) and LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811) cathodes, Li−Sr/LFP cells in 2 M LiFSI-DME electrolytes and Li−Sr/NMC811 cells in 1 M LiPF 6 in FEC:FEMC:HFE electrolytes also maintain excellent capacity retention. Designing SEIs by regulating Li-metal anode composition opens up a new and rational avenue to suppress Li dendrites.