Construction of 3D Electronic/Ionic Conduction Networks for All-Solid-State Lithium Batteries

Construction of ion-electron conduction network on FeS2 as high-performance cathodes enables all-solid-state lithium batteries

The all-solid-state lithium batteries (ASSLBs) with high energy density are considered to be one of the most promising candidates for next-generation lithium battery systems. Nevertheless, the low ionic and electronic conduction inside the cathode and the poor interfacial contact of the cathode/electrolyte seriously impede the large-scale application of ASSLBs. In this work, a novel multiple ion-electron conductive network is constructed on the FeS2 cathode to realize a high-energy all-solid-state battery. The internal disordered carbon matrix acts as electronic network to accelerate the electronic transmission. Meanwhile, reduced graphene oxide (rGO) tightly wrapping FeS2/C microspheres' surface serves as external electronic pathway. Moreover, the in-situ formed Li7P3S11 electrolyte infiltrates into the nanoparticles to improve lithium-ion transport kinetics. Therefore, the dual-carbon framework and Li7P3S11 coating layer strategies significantly enhance ion-electron transport kinetics and improve interfacial contact during cycling. As expected, the FeS2@C/rGO@Li7P3S11 cathode exhibits excellent rate capability and cycling stability, showing a reversible discharge capacity of 350.3 mAh/g at 0.5C after 200 cycles. More importantly, ex-situ XPS and dQ/dV results reveal that the synergistic effect of dual-carbon frameworks and Li7P3S11 coating layer not only provides fast electron-ion transfer channels, but also wraps the reaction products with poor electrochemical activity such as Fe0, FeSy, and S to accelerate the reaction kinetics and strengthens the reaction reversibility. This work provides valuable insights for improving the electrochemical performance and understanding the reaction mechanism of the conversion-type metal sulfide cathodes in ASSLBs.

Design Strategies of Li-Si Alloy Anode for Mitigating Chemo-Mechanical Degradation in Sulfide-Based All-Solid-State Batteries

Composite anodes of Li3 PS4  glass+Li-Si alloy (Type 1) and Li3 N+LiF+Li-Si alloy (Type 2) are prepared for all-solid-state batteries with Li3 PS4 (LPS) glass electrolyte and sulfur/LPS glass/carbon composite cathode. Using a three-electrode system, the anode and cathode potentials are separated, and their polarization resistances are individually traced. Even under high-cutoff-voltage conditions (3.7 V), Type 1 and 2 cells are stably cycled without voltage noise for >200 cycles. Although cathode polarization resistance drastically increases after 3.7 V charge owing to LPS oxidation, LPS redox behavior is fairly reversible upon discharge-charge unlike the non-composite alloy anode cell. Time-of-flight secondary ion mass spectrometry analysis reveals that the enhanced cyclability is attributed to uniform Li-Si alloying throughout the composite anode, providing more pathways for lithium ions even when these ions are over-supplied via LPS oxidation. These results imply that LPS-based cells can be reversibly cycled with LPS redox even under high-cutoff voltages, as long as non-uniform alloying (lithium dendrite growth) is prevented. Type 1 and 2 cells exhibit similar performance and stability although reduction product is formed in Type 1. This work highlights the importance of alloy anode design to prevent chemo-mechanical failure when cycling the cell outside the electrochemical stability window.

Rationally Designed Solution-Processible Conductive Carbon Additive Coating for Sulfide-based All-Solid-State Batteries

Sulfide-based all-solid-state batteries (ASSBs) have emerged as promising candidates for next-generation energy storage systems owing to their superior safety and energy density. A conductive agent is necessarily added in the cathode composite of ASSBs to facilitate electron transport therein, but it causes the decomposition of the solid electrolyte and ultimately the shortening of lifetime. To resolve this dilemmatic situation, herein, we report a rationally designed solution-processible coating of zinc oxide (ZnO) onto vapor-grown carbon fiber as a conductive agent to reduce the contact between the carbon additive and the solid electrolyte and still maintain electron pathways to the active material. ASSBs with the carbon additive with an optimal coating of ZnO have markedly improved cycling performance and rate capability compared to those with the bare conductive agent, which can be attributed to hindering the decomposition of the solid electrolytes. The results highlight the usefulness of controlling the interparticle contacts in the composite cathodes in addressing the challenging interfacial degradation of sulfide-based ASSBs and improving their key electrochemical properties.

Germanium-Free Dense Lithium Superionic Conductor and Interface Re-Engineering for All-Solid-State Lithium Batteries against High-Voltage Cathode

Li₁₀GeP₂S₁₂ (LGPS) solid electrolyte is not affordable due to the high cost of Ge metal, making it economically unviable despite being a lithium superionic conductor. The synthesis of such solid electrolytes is much more time- and energy-consuming and needs an inert environment. Here, we report Si (silicon)-based composition [Li₁₀SiP₂S₁₂ (LSiPS)] to make it cost-effective through microwave heating (MW). The total time for synthesis processes, including ball milling, heating rate, and heating dwell time, is ∼120 min, much less than the previous reports. We have also avoided vacuum sealing/Ar-purging to reduce the synthesis cost further. During MW heating, the densification process dominates over coarsening, resulting in a dense nanoflake morphology with a finer crystallite size. The synthesized LSiPS has a high fraction (∼89%) of more conducting tetragonal phase as identified by NMR analysis. Further, we modified the interface between the Li anode and LSiPS by forming a lithiophobic and lithiophilic kind of gradient interlayer to reduce the reduction of LSiPS and suppress the side reactions. The interface modification resulted in a better Li/LSiPS/Li cyclic performance for 1800 h at 0.2 mA/cm² and 500 h at 1.0 mA/cm². All-solid-state lithium-metal batteries (ASSLIB) have been developed against a high-voltage cathode (LCMO-coated LCO) and showed an excellent cycling performance with a reversible capacity of ∼110 mAh/g after 300 cycles.

Long-Cycling All-Solid-State Batteries Achieved by 2D Interface between Prelithiated Aluminum Foil Anode and Sulfide Electrolyte

All-solid-state batteries (ASSBs) with alloy anodes are expected to achieve high energy density and safety. However, the stability of alloy anodes is largely impeded by their large volume changes during cycling and poor interfacial stability against solid-state electrolytes. Here, a mechanically prelithiation aluminum foil (MP-Al-H) is used as an anode to construct high-performance ASSBs with sulfide electrolyte. The dense Li-Al layer of the MP-Al-H foil acts as a prelithiated anode and forms a 2D interface with sulfide electrolyte, while the unlithiated Al layer acts as a tightly bound current collector and ensures the structural integrity of the electrode. Remarkably, the MP-Al-H anode exhibits superior lithium conduction kinetics and stable interfacial compatibility with Li₆ PS₅ Cl (LPSCl) and Li₁₀ GeP₂ S₁₂ electrolytes. Consequently, the symmetrical cells using LPSCl electrolyte can work at a high current density of 7.5 mA cm^-2 and endure for over 1500 h at 1 mA cm^-2 . Notably, ≈100% capacity is retained for the MP-Al-H||LPSCl||LiCoO₂ full cell with high area loadings of 18 mg cm^-2 after 300 cycles. This work offers a pathway to improve the interfacial and performance issues for the application of ASSBs.

Mo-Incorporated Magnetite Fe3 O4 Featuring Cationic Vacancies Enabling Fast Lithium Intercalation for Batteries

Transition metal oxides (TMOs) as high-capacity electrodes have several drawbacks owing to their inherent poor electronic conductivity and structural instability during the multi-electron conversion reaction process. In this study, the authors use an intrinsic high-valent cation substitution approach to stabilize cation-deficient magnetite (Fe₃ O₄ ) and overcome the abovementioned issues. Herein, 5 at% of Mo⁴⁺ -ions are incorporated into the spinel structure to substitute octahedral Fe³⁺ -ions, featuring ≈1.7 at% cationic vacancies in the octahedral sites. This defective Fe_2.93 ▫_0.017 Mo_0.053 O₄ electrode shows significant improvements in the mitigation of capacity fade and the promotion of rate performance as compared to the pristine Fe₃ O₄ . Furthermore, physical-electrochemical analyses and theoretical calculations are performed to investigate the underlying mechanisms. In Fe_2.93 ▫_0.017 Mo_0.053 O₄ , the cationic vacancies provide active sites for storing Li⁺ and vacancy-mediated Li⁺ migration paths with lower energy barriers. The enlarged lattice and improved electronic conductivity induced by larger doped-Mo⁴⁺ yield this defective oxide capable of fast lithium intercalation. This is confirmed by a combined characterization including electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), galvanostatic intermittent titration technique (GITT) and density functional theory (DFT) calculation. This study provides a valuable strategy of vacancy-mediated reaction to intrinsically modulate the defective structure in TMOs for high-performance lithium-ion batteries.

Grain Boundary Engineering in Ta-Doped Garnet-Type Electrolyte for Lithium Dendrite Suppression

Solid-state lithium batteries (SSLBs) based on Ta-doped Li_6.5La₃Zr_1.5Ta_0.5O₁₂ (LLZTO) suffer from lithium dendrite growth, which hinders their practical application. Herein, first principles simulations indicate that the Ta element prefers to segregate along grain boundaries in the form of Ta₂O₅ precipitates due to a high energy difference induced by Ta doping. Grain boundary engineering is employed to regulate the distribution of the Ta element and enhance the density of LLZTO by introducing the La₂O₃ additive. The sufficient La₂O₃ additive reacts with the Ta₂O₅ precipitates, while the residual La₂O₃ nanoparticles fill up void defects, promoting the homogeneous distribution of the Ta element and improving the relative density to ∼98%. Critical current density of the symmetric Li battery reaches 2.12 mA·cm^-2 at room temperature with the solid-state electrolyte (LLZTO + 5 wt % La₂O₃), which increases by 41% compared to pure LLZTO. SSLBs with the LiFePO₄ cathode achieve a stable cycling performance with a discharge capacity of 138.6 mA·h·g^-1 after 400 cycles at 0.2 C. This work provides theoretical insights into the distribution of Ta-doped LLZTO and inhibits lithium dendrite growth through grain boundary engineering.

Grain Boundary Engineering Enabled High-Performance Garnet-Type Electrolyte for Lithium Dendrite Free Lithium Metal Batteries

Solid-state lithium metal batteries (SSLMBs) are attracting increasing attentions as one of the promising next-generation technologies due to their high-safety and high-energy density. Their practical application, however, is hindered by lithium dendrite growth and propagation in solid-state electrolytes (SSEs). Herein, an in situ grain boundary modification strategy relying on the reaction between Li₂ TiO₃ (LTO) and Ta-substituted garnet-type electrolyte (LLZT) is developed, which forms LaTiO₃ along with lesser amounts of LTO/Li₂ ZrO₃ at the grain boundaries (GBs). The second phases of LTO/Li₂ ZrO₃ inhibit abnormal grain growth. The presence of LaTiO₃ at the GBs reduces electronic conductivity and improves mechanical strength, which can hinder dendrite formation and block lithium dendrite penetration through the LLZT. Moreover, the adjacent grains by LaTiO₃ build a continuous Li⁺ transport path, providing a homogeneous Li⁺ flux throughout the whole LLZT-4LTO. As a result, symmetric cells of Li | LLZT-4LTO | Li shows a high critical current density of 1.8 mA cm^-2 and a long cycling stability up to 2000 h at 0.3 mA cm^-2 . Moreover, the high-voltage full cells demonstrate remarkable cycling stability and rate performance. It is believed that this novel grain boundary modification strategy can shed light on the constructing of high-performance SSEs for practical SSLMBs.

2D Materials for All-Solid-State Lithium Batteries

Although one of the most mature battery technologies, lithium-ion batteries still have many aspects that have not reached the desired requirements, such as energy density, current density, safety, environmental compatibility, and price. To solve these problems, all-solid-state lithium batteries (ASSLB) based on lithium metal anodes with high energy density and safety have been proposed and become a research hotpot in recent years. Due to the advanced electrochemical properties of 2D materials (2DM), they have been applied to mitigate some of the current problems of ASSLBs, such as high interface impedance and low electrolyte ionic conductivity. In this work, the background and fabrication method of 2DMs are reviewed initially. The improvement strategies of 2DMs are categorized based on their application in the three main components of ASSLBs: The anode, cathode, and electrolyte. Finally, to elucidate the mechanisms of 2DMs in ASSLBs, the role of in situ characterization, synchrotron X-ray techniques, and other advanced characterization are discussed.

Facile Method for the Formation of Intimate Interfaces in Sulfide-Based All-Solid-State Batteries

Sulfide-based inorganic solid electrolytes have been considered promising candidates for all-solid-state batteries owing to their high ionic conductivity. Compared with oxide-based inorganic solid electrolytes which require high-temperature sintering, the intrinsic deformability of sulfide electrolytes enables the fabrication of all-solid-state batteries by a simple cold pressing method. Nevertheless, the performance of sulfide-based all-solid-state batteries is still unsatisfactory, owing to the insufficient interfacial properties within the composite electrodes. Using cold pressing alone, it is challenging to form intimate contacts with rigid oxide-based cathode materials. Here, we demonstrate a mild-temperature pressing (MP) method for the fabrication of all-solid-state batteries. The mild temperature (85 °C) increases the deformability of the sulfide and therefore helps to form more enhanced interfacial contacts in the composite cathode without side reactions. Compared with the conventional cold pressing cell, the MP cell possesses more favorable contacts, resulting in higher capacity, cyclability, and rate capability. In addition, we demonstrate that the charge-transfer resistance in composite cathodes dominates the electrochemical performance of all-solid-state batteries.

Grain Boundary Design of Solid Electrolyte Actualizing Stable All-Solid-State Sodium Batteries

Advanced inorganic solid electrolytes (SEs) are critical for all-solid-state alkaline metal batteries with high safety and high energy densities. A new interphase design to address the urgent interfacial stability issues against all-solid-state sodium metal batteries (ASSMBs) is proposed. The grain boundary phase of a Mg²⁺ -doped Na₃ Zr₂ Si₂ PO₁₂ conductor (denoted as NZSP-xMg) is manipulated to introduce a favorable Na_{3-2 δ} Mg_δ PO₄ -dominant interphase which facilitates its intimate contact with Na metal and works as an electron barrier to suppress Na metal dendrite penetration into the electrolyte bulk. The optimal NZSP-0.2Mg electrolyte endows a low interfacial resistance of 93 Ω cm² at room temperature, over 16 times smaller than that of Na₃ Zr₂ Si₂ PO₁₂ . The Na plating/stripping with small polarization is retained under 0.3 mA cm^-2 for more than 290 days (7000 h), representing a record high cycling stability of SEs for ASSMBs. An all-solid-state NaCrO₂ //Na battery is accordingly assembled manifesting a high capacity of 110 mA h g^-1 at 1 C for 1755 cycles with almost no capacity decay. Excellent rate capability at 5 C is realized with a high Coulombic efficiency of 99.8%, signifying promising application in solid-state electrochemical energy storage systems.

CNTs/LiV3O8/Y2O3 Composites with Enhanced Electrochemical Performances as Cathode Materials for Rechargeable Solid-State Lithium Metal Batteries

Solid-state lithium metal battery (SSLMB) is regarded as a safer energy storage system compared to the liquid one. The performance of the SSLMB depends on the cathode performance and the side reactions derived from the interface of the cathode and the electrolyte, which becomes much severe at high temperatures. Herein, we carried out a facile spray-drying route to prepare a CNTs/LiV₃O₈/Y₂O₃ (M-LVO-Y) composite. The synthesized cathode material exhibits an outstanding Li⁺ storage performance with a high reversible capacity of 279.9 mA h g^-1 at 0.05 A g^-1, excellent power capability (182.5 mA h g^-1 at 2 A g^-1), and a long cycle lifespan of 500 cycles with a capacity retention of 66.5% at a current density of 1 A g^-1. The fabricated rechargeable solid-state Li/M-LVO-Y-2 lithium metal battery (LMB) with a poly(ethylene oxide) (PEO)-based solid polymer electrolyte (SPE) achieves a high discharge capacity of 302.1 mA h g^-1 at 0.05 A g^-1 and a stable cycling performance with the highest capacity of 72.1% after 100 cycles at 0.2 A g^-1 and 80 °C. The above battery performance demonstrates that SSLMBs with the CNTs/LiV₃O₈/Y₂O₃ cathode and the PEO-based SPE film can provide high energy density and are suitable for applying in a high-temperature environment.

Rational Design of an Electron/Ion Dual-Conductive Cathode Framework for High-Performance All-Solid-State Lithium Batteries

All-solid-state lithium batteries (ASSLBs) have been paid increasing attention because of the better security compared with conventional lithium-ion batteries with flammable organic electrolytes. However, the poor ion transport between the cathode materials greatly hinders the capacity performance of ASSLBs. Herein, an electron/ion dual-conductive electrode framework is proposed for superior performance ASSLBs. Highly electronic conductive reduced graphene oxide and carbon nanotubes interconnect with active materials in the cathodes, constructing a three-dimensional continuous electron transport network. The composite electrolyte penetrates into the porous structure of the electrode, forming a consecutive ionic conductive framework. Furthermore, the thin electrolyte film formed on the surface of the cathode effectively lowers the interfacial resistance with the electrolyte membrane. Highly electron/ion conductive electrodes, combined with the polyethylene oxide-Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (PEO-LLZTO) composite electrolyte, show excellent capacity performance for both LiFePO₄ and sulfur (lithium-sulfur battery) active materials. In addition, the LiFePO₄ cathode demonstrates superior capacity performance and rate capability at room temperature. Furthermore, the relationship between the low Coulombic efficiency and Li dendrite growth has been revealed in this work. An effective layer is formed on the surface of Li metal by the simple modification of cupric fluoride (CuF₂), which can stabilize the electrolyte/anode interface. Finally, high-performance ASSLBs with high Coulombic efficiency can be achieved.

In Situ Coating of Li7P3S11 Electrolyte on CuCo2S4/Graphene Nanocomposite as a High-Performance Cathode for All-Solid-State Lithium Batteries

A cathode material, CuCo₂S₄/graphene@10%Li₇P₃S₁₁, is reported for all-solid-state lithium batteries with high performance. The electrical conductivity of CuCo₂S₄ is improved by compounding with graphene. Meanwhile, Li₇P₃S₁₁ electrolyte is coated on the surface of CuCo₂S₄/graphene nanosheets to build an intimate contact interface between the solid electrolyte and the electrode effectively, facilitating lithium-ion conduction. Benefitting from the balanced and efficient electronic and ionic conductions, all-solid-state lithium batteries using CuCo₂S₄/graphene@10%Li₇P₃S₁₁ composite as cathode materials demonstrate superior cycling stability and rate capabilities, exhibiting an initial discharge specific capacity of 1102.25 mAh g^-1 at 50 mA g^-1 and reversible capacity of 556.41 mAh g^-1 at a high current density of 500 mA g^-1 after 100 cycles. These results demonstrate that the CuCo₂S₄/graphene@10%Li₇P₃S₁₁ nanocomposite is a promising active material for all-solid-state lithium batteries with superior performances.