Health diagnosis and recuperation of aged Li-ion batteries with data analytics and equivalent circuit modeling.

Battery health assessment and recuperation play crucial roles in the utilization of second-life Li-ion batteries. However, due to ambiguous aging mechanisms, it is challenging to estimate battery health and devise an effective strategy for cell rejuvenation. This paper presents aging and reconditioning experiments of 62 commercial lithium iron phosphate cells, which allow us to use machine learning models to predict cycle life and identify important indicators of recoverable capacity. An average test error of 16.84% ± 1.87% (mean absolute percentage error) for cycle life prediction is achieved by gradient boosting regressor. Some of the recoverable lost capacity is found to be attributed to the non-uniformity in electrodes. An experimentally validated equivalent circuit model is built to demonstrate how such non-uniformity can be accumulated, and how it can give rise to recoverable capacity loss. Furthermore, Shapley additive explanations (SHAP) analysis also reveals that battery operation history significantly affects the capacity recovery.

Mixed Ionically/Electronically Conductive Double-Phase Interface Enhanced Solid-State Charge Transfer for a High-Performance All-Solid-State Li-S Battery.

An all-solid-state lithium-sulfur battery (ASSLSB) is a promising candidate for post-Li-ion battery technologies with high energy densities and good safety performance. However, the intrinsic insulating nature of sulfur requires triple-phase contact with an ionic conductor and an electronic conductor for electrochemical reactions, which decreases the amount of active surface and lowers the charge-transfer efficiency. In this work, a double-phase interface constructed from a mixed ionic/electronic conductor is proposed to enhance the solid-state electrochemical reaction of sulfur. By employing lithium lanthanum titanium oxide/carbon (LLTO/C) nanofibers with mixed ionic/electronic conductivity, enhanced charge-transfer behavior is realized at the sulfur-LLTO/C double-phase interface, compared to the traditional triple-phase interface. As a result, high sulfur utilization and excellent rate performance are achieved. And the facilitated charge transfer shows great potential to lower the operating temperature and improve the sulfur content for practical applications of ASSLSBs. Cycle performance is also enhanced due to the suppressed shuttle effect of polysulfides by the incorporation of the LLTO/C nanofibers.

Stabilizing a Lithium Metal Battery by an In Situ Li2S-modified Interfacial Layer via Amorphous-Sulfide Composite Solid Electrolyte.

A novel strategy has been proposed to produce in situ Li2S at the interfacial layer between lithium anode and the solid electrolyte, by using an amorphous-sulfide-LiTFSI-poly(vinylidene difluoride) (PVDF) composite solid electrolyte (SLCSE). Besides retarding the decomposition of PVDF in CSE, the Li2S-modified interfacial layer (SMIL) also improves the wettability between lithium metal and SLCSE which in turn optimizes the lithium deposition process. Our density functional theory calculation results reveal that the migration energy barrier of Li passing through SMIL is much lower than that of Li passing through LiF-modified interfacial layer (FMIL) formed from the decomposition of PVDF. The as-prepared SLCSE shows a Li ionic transference number of 0.44 and Li ion conductivity of 3.42 × 10-4 S/cm at room temperature, and the Li||SLCSE||LiFePO4 cell exhibits an outstanding rate performance with a capacity of 153, 144, 131, and 101 mAh/g at a current density of 0.05, 0.10, 0.25, and 0.50 mA/cm2, respectively.

Thermal Conductive 2D Boron Nitride for High-Performance All-Solid-State Lithium-Sulfur Batteries.

Polymer-based solid-state electrolytes are shown to be highly promising for realizing low-cost, high-capacity, and safe Li batteries. One major challenge for polymer solid-state batteries is the relatively high operating temperature (60-80 °C), which means operating such batteries will require significant ramp up time due to heating. On the other hand, as polymer electrolytes are poor thermal conductors, thermal variation across the polymer electrolyte can lead to nonuniformity in ionic conductivity. This can be highly detrimental to lithium deposition and may result in dendrite formation. Here, a polyethylene oxide-based electrolyte with improved thermal responses is developed by incorporating 2D boron nitride (BN) nanoflakes. The results show that the BN additive also enhances ionic and mechanical properties of the electrolyte. More uniform Li stripping/deposition and reversible cathode reactions are achieved, which in turn enable all-solid-state lithium-sulfur cells with superior performances.

Synergistic Effect of Salinized Quinone for Entrapment of Polysulfides for High-Performance Li-S Batteries.

Lithium-sulfur (Li-S) batteries have attracted considerable attention in the energy storage field due to their high theoretical energy density and low price. However, the dissolution of polysulfides and the "shuttle effect" lead to serious capacity degradation, which greatly hinders the industrial application of Li-S batteries. Herein, we propose a bifunctional quinone-type salt to anchor polysulfides and suppress their dissolution for use in high-performance Li-S batteries. We find that the tetrahydroxy-1,4-benzoquinone disodium salt dimer (TBS-dimer) does not dissolve in organic electrolytes and can be generated at 400 °C. The abundant reactive keto groups and double bonds result in the TBS-dimers having numerous "hot spots" for capturing sulfur (TBS/S-400) in the three-dimensional space of the molecule. The insolubility and abundant active sites of the organic salt remarkably suppress the dissolution of lithium polysulfides. As a result, the TBS/S-400 composite delivers a capacity decay rate of only 0.023% per cycle over 600 cycles at 2 C. The use of organic salts to effectively suppress the dissolution of lithium polysulfides opens a new avenue for the practical applications of high-performance Li-S batteries.

Mechanical rolling formation of interpenetrated lithium metal/lithium tin alloy foil for ultrahigh-rate battery anode.

To achieve good rate capability of lithium metal anodes for high-energy-density batteries, one fundamental challenge is the slow lithium diffusion at the interface. Here we report an interpenetrated, three-dimensional lithium metal/lithium tin alloy nanocomposite foil realized by a simple calendering and folding process of lithium and tin foils, and spontaneous alloying reactions. The strong affinity between the metallic lithium and lithium tin alloy as mixed electronic and ionic conducting networks, and their abundant interfaces enable ultrafast charger diffusion across the entire electrode. We demonstrate that a lithium/lithium tin alloy foil electrode sustains stable lithium stripping/plating under 30 mA cm-2 and 5 mAh cm-2 with a very low overpotential of 20 mV for 200 cycles in a commercial carbonate electrolyte. Cycled under 6 C (6.6 mA cm-2), a 1.0 mAh cm-2 LiNi0.6Co0.2Mn0.2O2 electrode maintains a substantial 74% of its capacity by pairing with such anode.

A Cathode-Integrated Sulfur-Deficient Co9S8 Catalytic Interlayer for the Reutilization of "Lost" Polysulfides in Lithium-Sulfur Batteries.

Lithium-sulfur batteries, with their high theoretical energy density and the low material cost of sulfur, are highly promising as a post-lithium ion battery contender. Their current performance is however compromised by sulfur loss and polysulfide shuttle to result in low energy efficiency and poor cycle stability. Herein, a catalytic material (Co9S8- x/CNT, nanoparticles with a metallic Co9S8 core and a sulfur-deficient shell on a CNT support) was applied as an interlayer on the sulfur cathode to retain migratory polysulfides and promote their reutilization. The Co9S8- x/CNT catalyst is highly effective for the conversion of polysulfides to insoluble end products (S or Li2S/Li2S2), and its deployment as a cathode-integrated interlayer was able to retain the polysulfides in the cathode for reuse. The accumulation of polysulfides in the electrolyte and the polysulfide shuttle were significantly reduced as a result. Consequently, a host-free sulfur cathode with the Co9S8- x/CNT interlayer had a low capacity fade rate of 0.049% per cycle for 1000 cycles at a 0.3C rate, a significant improvement of the capacity fade rate without it (0.28% per cycle for 200 cycles). The results here provide not only direct evidence for the contributions of sulfur deficiencies on the catalytic activity of Co9S8 in polysulfide conversion reactions but also the methodology on how the catalyst should be deployed in a Li-S battery for the best catalytic outcome.

Lithium Silicide Surface Enrichment: A Solution to Lithium Metal Battery.

The propensity of lithium dendrite formation during the charging process of lithium metal batteries is linked to inhomogeneity on the lithium surface layer. The high reactivity of lithium and the complex surface structure of the native layer create "hot spots" for fast dendritic growth. Here, it is demonstrated that a fundamental restructuring of the lithium surface in the form of lithium silicide (Lix Si) can effectively eliminate the surface inhomogeneity on the lithium surface. In situ optical microscopic study is carried out to monitor the electrochemical deposition of lithium on the Lix Si-modified lithium electrodes and the bare lithium electrode. It is observed that a much more uniform lithium dissolution/deposition on the Lix Si-modified lithium anode can be achieved as compared to the bare lithium electrode. Full cells paring the modified lithium anode with sulfur and LiFePO4 cathodes show excellent electrochemical performances in terms of rate capability and cycle stability. Compatibility of the anode enrichment method with mass production process also offers a practical way for enabling lithium metal anode for next-generation lithium batteries.

In Situ Observation and Electrochemical Study of Encapsulated Sulfur Nanoparticles by MoS2 Flakes.

Sulfur is an attractive cathode material for next-generation lithium batteries due to its high theoretical capacity and low cost. However, dissolution of its lithiated product (lithium polysulfides) into the electrolyte limits the practical application of lithium sulfur batteries. Here we demonstrate that sulfur particles can be hermetically encapsulated by leveraging on the unique properties of two-dimensional materials such as molybdenum disulfide (MoS2). The high flexibility and strong van der Waals force in MoS2 nanoflakes allows effective encapsulation of the sulfur particles and prevent its sublimation during in situ TEM studies. We observe that the lithium diffusivities in the encapsulated sulfur particles are in the order of 10-17 m2 s-1. Composite electrodes made from the MoS2-encapsulated sulfur spheres show outstanding electrochemical performance, with an initial capacity of 1660 mAh g-1 and long cycle life of more than 1000 cycles.