Project description:The performance of all-solid-state lithium metal batteries (SSLMBs) is affected by the presence of electrochemically inactive (i.e., electronically and/or ionically disconnected) lithium metal and solid electrolyte interphase (SEI), which are jointly termed inactive lithium. However, the differentiation and quantification of inactive lithium during cycling are challenging, and their lack limits the fundamental understanding of SSLMBs failure mechanisms. To shed some light on these crucial aspects, here, we propose operando nuclear magnetic resonance (NMR) spectroscopy measurements for real-time quantification and evolution-tracking of inactive lithium formed in SSLMBs. In particular, we examine four different sulfide-based solid electrolytes, namely, Li10GeP2S12, Li9.54Si1.74P1.44S11.7Cl0.3, Li6PS5Cl and Li7P3S11. We found that the chemistry of the solid electrolyte influences the activity of lithium. Furthermore, we demonstrate that electronically disconnected lithium metal is mainly found in the interior of solid electrolytes, and ionically disconnected lithium metal is found at the negative electrode surface. Moreover, by monitoring the Li NMR signal during cell calendar ageing, we prove the faster corrosion rate of mossy/dendritic lithium than flat/homogeneous lithium in SSLMBs.
Project description:Metal negative electrodes that alloy with lithium have high theoretical charge storage capacity and are ideal candidates for developing high-energy rechargeable batteries. However, such electrode materials show limited reversibility in Li-ion batteries with standard non-aqueous liquid electrolyte solutions. To circumvent this issue, here we report the use of non-pre-lithiated aluminum-foil-based negative electrodes with engineered microstructures in an all-solid-state Li-ion cell configuration. When a 30-μm-thick Al94.5In5.5 negative electrode is combined with a Li6PS5Cl solid-state electrolyte and a LiNi0.6Mn0.2Co0.2O2-based positive electrode, lab-scale cells deliver hundreds of stable cycles with practically relevant areal capacities at high current densities (6.5 mA cm-2). We also demonstrate that the multiphase Al-In microstructure enables improved rate behavior and enhanced reversibility due to the distributed LiIn network within the aluminum matrix. These results demonstrate the possibility of improved all-solid-state batteries via metallurgical design of negative electrodes while simplifying manufacturing processes.
Project description:All-solid-state lithium-ion batteries with argyrodite solid electrolytes have been developed to attain high conductivities of 10-3 S cm-1 in studies aiming at fast ionic conductivity of electrolytes. However, no matter how high the ionic conductivity of the electrolyte, the design of the cathode composite is often the bottleneck for high performance. Thus, optimization of the composite cathode formulation is of utmost importance. Unfortunately, many reports limit their studies to only a few parameters of the whole electrode formulation. In addition, different measurement setups and testing conditions employed for all-solid-state batteries make a comparison of results from mutually independent studies quite difficult. Therefore, a detailed investigation on different key parameters for preparation of cathodes employed in all-solid-state batteries is presented here. Employing a rational approach for optimization of composite cathodes using solid sulfide electrolytes elucidated the influence of different parameters on the cycling performance. First, powder electrodes made without binders are investigated to optimize several parameters, including the active materials' particle morphology, the nature and amount of the conductive additive, the particle size of the solid electrolyte, as well as the active material-to-solid electrolyte ratio. Finally, cast electrodes are examined to determine the influence of a binder on cycling performance.
Project description:Anode-free lithium batteries without lithium metal excess are a practical option to maximize the energy content beyond the conventional design of Li-ion and Li metal batteries. However, their performance and reliability are still limited by using low-capacity oxygen-releasing intercalation cathodes and flammable liquid electrolytes. Herein, we propose quasi-solid-state anode-free batteries containing lithium sulfide-based cathodes and non-flammable polymeric gel electrolytes. Such batteries exhibit an energy density of 1323 Wh L-1 at the pouch cell level. Moreover, the lithium sulfide-based anode-free cell chemistry endows intrinsic safety thanks to a lack of uncontrolled exothermic reactions of reactive oxygen and excess Li inventory. Furthermore, the non-flammable gel electrolyte, developed from MXene-doped fluorinated polymer, inhibits polysulfide shuttling, hinders Li dendrite formation and further secures cell safety. Finally, we demonstrate the improved cell safety against mechanical, electrical and thermal abuses.
Project description:Given the inherent performance limitations of intercalation-based lithium-ion batteries, solid-state conversion batteries are promising systems for future energy storage. A high specific capacity and natural abundancy make iron disulfide (FeS2 ) a promising cathode-active material. In this work, FeS2 nanoparticles were prepared solvothermally. By adjusting the synthesis conditions, samples with average particle diameters between 10 nm and 35 nm were synthesized. The electrochemical performance was evaluated in solid-state cells with a Li-argyrodite solid electrolyte. While the reduction of FeS2 was found to be irreversible in the initial discharge, a stable cycling of the reduced species was observed subsequently. A positive effect of smaller particle dimensions on FeS2 utilization was identified, which can be attributed to a higher interfacial contact area and shortened diffusion pathways inside the FeS2 particles. These results highlight the general importance of morphological design to exploit the promising theoretical capacity of conversion electrodes in solid-state batteries.
Project description:Solid-state lithium metal batteries have attracted broad interest as a promising energy storage technology because of the high energy density and enhanced safety that are highly desired in the markets of consumer electronics and electric vehicles. However, there are still many challenges before the practical application of the new battery. One of the major challenges is the poor interface between lithium metal electrodes and solid electrolytes, which eventually lead to the exceptionally high internal resistance of the cells and limited output. The interface issue arises largely due to the poor contact between solid and solid, and the mechanical/electrochemical instability of the interface. In this work, an in situ "welding" strategy is developed to address the interfacial issue in solid-state batteries. Microliter-level of liquid electrolyte is transformed into an organic-inorganic composite buffer layer, offering a flexible and stable interface and promoting enhanced electrochemical performance. Symmetric lithium-metal batteries with the new interface demonstrate good cycling performance for 400 h and withstand the current density of 0.4 mA cm-2. Full batteries developed with lithium-metal anode and LiFePO4 cathode also demonstrate significantly improved cycling endurance and capacity retention.
Project description:All-solid-state lithium-based batteries with inorganic solid electrolytes are considered a viable option for electrochemical energy storage applications. However, the application of lithium metal is hindered by issues associated with the growth of mossy and dendritic Li morphologies upon prolonged cell cycling and undesired reactions at the electrode/solid electrolyte interface. In this context, alloy materials such as lithium-indium (Li-In) alloys are widely used at the laboratory scale because of their (electro)chemical stability, although no in-depth investigations on their morphological stability have been reported yet. In this work, we report the growth of Li-In dendritic structures when the alloy material is used in combination with a Li6PS5Cl solid electrolyte and Li(Ni0.6Co0.2Mn0.2)O2 positive electrode active material and cycled at high currents (e.g., 3.8 mA cm-2) and high cathode loading (e.g., 4 mAh cm-2). Via ex situ measurements and simulations, we demonstrate that the irregular growth of Li-In dendrites leads to cell short circuits after room-temperature long-term cycling. Furthermore, the difference between Li and Li-In dendrites is investigated and discussed to demonstrate the distinct type of dendrite morphology.
Project description:The next generation of all-solid-state lithium-ion batteries (ASLIBs) based on solid-state sulfide electrolytes (SSEs) is closest to commercialization. Understanding the overall safety behavior of SSE-ASLIBs is necessary for their product design and commercialization. However, their safety behavior in real-life situations, such as battery exposure to high temperature, overcharge, mechanical rupture, and air exposure, remains largely unknown. Herein, we report preliminary but needed evidence of (i) significantly improved resistance to electrical shorting at high temperatures, (ii) reduced heat generation when subjected to excessive heat, (iii) tolerable harmful gas generation when subjected to air exposure followed by high-temperature heating, and (iv) high-voltage charge stability when a battery is overcharged (5.5 V charge) in SSE-based ASLIBs compared to commercial liquid electrolyte-based LIBs (LE-LIBs). Furthermore, the result shows that SSEs can self-induce a fast and effective battery shut-down capability in ASLIBs and avoid thermal runaway upon mechanical damage and exposure to air.
Project description:Li6.3La3Zr1.65W0.35O12 (LLZO)-Li6PS5Cl (LPSC) composite electrolytes and all-solid-state cells containing LLZO-LPSC were fabricated by cold pressing at room temperature. The LPSC:LLZO ratio was varied, and the microstructure, ionic conductivity, and electrochemical performance of the corresponding composite electrolytes were investigated; the ionic conductivity of the composite electrolytes was three or four orders of magnitude higher than that of LLZO. The high conductivity of the composite electrolytes was attributed to the enhanced relative density and the rule of mixture for soft LPSC particles with high lithium-ion conductivity (~10-4 S·cm-1). The specific capacities of all-solid-state cells (ASSCs) consisting of a LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode and the composite electrolytes of LLZO:LPSC = 7:3 and 6:4 were 163 and 167 mAh·g-1, respectively, at 0.1 C and room temperature. Moreover, the charge-discharge curves of the ASSCs with the composite electrolytes revealed that a good interfacial contact was successfully formed between the NCM811 cathode and the LLZO-LPSC composite electrolyte.
Project description:Sulfide ionic conductors are promising candidates as solid electrolytes for all-solid-state batteries due to their high conductivity. However, interfacial instability between cathodes and sulfide electrolytes still remains a challenge because sulfides are highly reactive. To suppress undesirable side reactions at the cathode/sulfide electrolyte interface, the surface of the cathode has been modified using stable coating materials. Herein, a precursor based (PB) surface modification using Ta and W is introduced as an effective approach for the formation of a suitable cathode coating layer. Through heat-treatment of the PB surface modification, the source materials (Ta or W) coated on the precursors diffused into the cathode and acted as a dopant. Formation of the surface coating layer was confirmed by X-ray photoelectron spectroscopy (XPS) depth profiles and scanning transmission electron microscopy (STEM) images. The PB surface modified electrodes showed higher capacity, improved rate capability and enhanced cyclic performance compared to those of the pristine electrode. The impedance value of the cells dominantly decreased after cycling due to the modification effect. Moreover, considering the XPS analysis, undesirable reaction products that formed upon cycling were reduced by PB surface modification. These results indicate that PB surface modification using Ta and W effectively suppresses undesirable side reactions and stabilizes the cathode/sulfide electrolyte interface, which is a synergic effect of the doping and coating attributed to Ta and W.