A near dimensionally invariable high-capacity positive electrode material

Interpretable Surrogate Learning for Electronic Material Generation

Despite many accessible AI models that have been developed, it is an open challenge to fully exploit interpretable insights to enable effective materials design and develop materials with desired properties for target applications. Here, we introduce an interpretable surrogate learning framework that can actively design and generate electronic materials (EMGen), akin to producing updated materials with requirements by screening all possible elements and fractions. Taking the materials system with required band gaps as a case study, EMGen exhibits a benchmarking predictive error and a running time of 1.7 min for designing and producing a structure with a desired band gap. Using EMGen, we establish a large hybrid functional band gap database, and more uplifting is that the proposed EMGen effectively designs GaxOy with a wide band gap (>5.0 eV) for deep ultraviolet (DUV) optoelectronic devices, enabling a breakthrough extension of the applicability of GaxOy films in photodetectors to DUV light below 240 nm. The augmented band gap also helps improve the breakdown voltage and the heat resilience performance of the amorphous GaxOy film, thereby achieving considerable potential within the realm of power electronics applications. The proposed EMGen, as a specialized, interpretable AI model for the generation of electronic materials, is demonstrated to be an essential tool for on-demand semiconductor materials design.

MXene Electrodes for All Strain-Free Solid-State Batteries

All-solid-state batteries with nonflammable inorganic solid electrolytes are the key to addressing the safety issues of lithium-ion batteries with flammable organic liquid electrolytes. However, conventional electrode materials suffer from substantial volume changes during Li+ (de)intercalation, leading to mechanical failure of interfaces between electrode materials and solid electrolytes and then severe performance degradation. In this study, we report strain-free charge storage via the interfaces between transition metal carbides (MXenes) and solid electrolytes, where MXene shows negligible structural changes during Li+ (de)intercalation. Operando scanning electron transmission microscopy with electron energy-loss spectroscopy reveals the pillar effect of trapped Li+ in the interlayer spaces of MXene to achieve the strain-free features. An all strain-free solid-state battery, which consists of a strain-free Ti3C2Tx negative electrode and a strain-free disordered rocksalt Li8/7Ti2/7V4/7O2 positive electrode, demonstrates long-term stable operation while preserving the interfacial contact between electrode materials and solid electrolytes.

Polymeric Electronic Shielding Layer Enabling Superior Dendrite Suppression for All-Solid-State Lithium Batteries

LiBH4 is one of the most promising candidates for use in all-solid-state lithium batteries. However, the main challenges of LiBH4 are the poor Li-ion conductivity at room temperature, excessive dendrite formation, and the narrow voltage window, which hamper practical application. Herein, we fabricate a flexible polymeric electronic shielding layer on the particle surfaces of LiBH4. The electronic conductivity of the primary LiBH4 is reduced by 2 orders of magnitude, to 1.15 × 10-9 S cm-1 at 25 °C, due to the high electron affinity of the electronic shielding layer; this localizes the electrons around the BH4- anions, which eliminates electronic leakage from the anionic framework and leads to a 68-fold higher critical electrical bias for dendrite growth on the particle surfaces. Contrary to the previously reported work, the shielding layer also ensures fast Li-ion conduction due to the fast-rotational dynamics of the BH4- species and the high Li-ion (carrier) concentration on the particle surfaces. In addition, the flexibility of the layer guarantees its structural integrity during Li plating and stripping. Therefore, our LiBH4-based solid-state electrolyte exhibits a high critical current density (11.43 mA cm-2) and long cycling stability of 5000 h (5.70 mA cm-2) at 25 °C. More importantly, the electrolyte had a wide operational temperature window (-30-150 °C). We believe that our findings provide a perspective with which to avoid dendrite formation in hydride solid-state electrolytes and provide high-performance all-solid-state lithium batteries.

Virtues of Cold Isostatic Pressing for Preparation of All-Solid-State-Batteries with Poly(Ethylene Oxide)

All-solid-state-batteries (ASSBs) necessitate the preparation of a solid electrolyte and an electrode couple with individually dense and compact structures with superior interfacial contact to minimize overall cell resistance. A conventional preparation method of solid polymer electrolyte (SPE) with polyethylene-oxide (PEO) generally consists in employing uni-axial hot press (HP) to densify SPE. However, while uni-axial press with moderate pressure effectively densifies PEO with Li salts, excessive pressure also unavoidably results in perpendicular elongation and deformation for polymer matrix. In this research, to overcome this limitation for the uni-axial press technique, a cold isostatic press (CIP) is applied to the fabrication of ASSB with PEO and LiFePO4 . CIP effectively and uniformly applies pressure as high as 500 MPa without deformation. Characterizations confirm that CIP treated SPE has enhanced mechanical puncture strength, increasing from 499.3±22.6 to 539.3±22.6 g, and ionic conductivity, increasing from 1.04×10-4 to 1.91×10-4  S cm-1 at 50 °C. ASSB treated by CIP demonstrates remarkably enhanced rate capability and cyclability compared with the cell processed by HP, which is further evidenced by improvement of the apparent Li ion diffusion constant based on Sand equation analysis. The improvement enabled by CIP treatment originates from the superior interface uniformity between electrodes and SPE and from the densification of the LiFePO4 and SPE composite electrode.

Structural Design Principle of Rocksalt Oxides for Li-Excess Cathode Materials

Li-excess oxide cathodes have received increasing attention due to their high capacity derived from accumulated cation and anion redox activity. However, Li-excess layered oxides suffer from capacity and voltage decay due to the irreversible phase transition, while cation-disordered cathodes also have the problems of poor cycling stability and rate capability. The rocksalt oxides with a layered-disordered coexistence nanostructure can combine the advantages of both phases such as the inherent high capacity of Li-excess oxides, good rate capability of the layered phase, and structural stability resulting from the intergrown disordered phase. Herein, for rational design, we developed a descriptor by correlating the ionic radius and electronic configuration to predict layered, cation-disordered, and coexistent structures of Li-excess cathode materials. Accordingly, we experimentally synthesized Li1.2Ni0.4Mn0.2Nb0.2O2 oxide with a coexistent structure in which the layered and disordered phases are well combined in the nanoscale region, achieving a high capacity (312 mAh g-1) with good cycling stability and rate capability. The design principle with composition predicting structure provides a valuable strategy in controllably designing and preparing Li-excess cathode materials.

Toward Sustainable All Solid-State Li-Metal Batteries: Perspectives on Battery Technology and Recycling Processes

Lithium (Li)-based batteries are gradually evolving from the liquid to the solid state in terms of safety and energy density, where all solid-state Li-metal batteries (ASSLMBs) are considered the most promising candidates. This is demonstrated by the Bluecar electric vehicle produced by the Bolloré Group, which is utilized in car-sharing services in several cities worldwide. Despite impressive progress in the development of ASSLMBs, their avenues for recycling them remain underexplored, and combined with the current explosion of spent Li-ion batteries, they should attract widespread interest from academia and industry. Here, the potential challenges of recycling ASSLMBs as compared to Li-ion batteries are analyzed and the current progress and prospects for recycling ASSLMBs are summarized and analyzed. Drawing on the lessons learned from Li-ion battery recycling, it is important to design sustainable recycling technologies before ASSLMBs gain widespread market adoption. A battery-recycling-oriented design is also highlighted for ASSLMBs to promote the recycling rate and maximize profitability. Finally, future research directions, challenges, and prospects are outlined to provide strategies for achieving sustainable development of ASSLMBs.

Interelectrode Talk in Solid-State Lithium-Metal Batteries

Solid-state lithium-metal batteries have been identified as a strategic research direction for the electric vehicle industry because of their promising high energy density and potential characteristic safety. However, the intrinsic mechanical properties of solid materials cause inevitable electro-chemo-mechanical failure of electrodes and electrolytes during charging and discharging; these failure mechanisms include lithium penetration and formation of cracks and voids, which pose a serious challenge for the long cycle life of solid-state lithium-metal batteries. Here, a short overview of the recent advances with a view to understand this challenge is provided. Furthermore, new insights into the cross-talk behavior between the cathode and lithium-metal anode are provided based on the non-uniform Li+ flux inducing interactional electro-chemo-mechanical failure. Furthermore, guidelines for designing stable solid-state lithium-metal batteries and research directions to figure out the interelectrode-talk-related electro-chemo-mechanical failure mechanism are presented, which can be significant for accelerating the development of solid-state lithium batteries.

Design of Cathode Coating Using Niobate and Phosphate Hybrid Material for Sulfide-Based Solid-State Battery

Coating the surface of the cathode active material of all-solid-state batteries with sulfide-based solid electrolytes is key for improving and enhancing the battery performance. Although lithium niobate (LiNbO₃) is one of the most representative coating materials, its low durability at a highly charged potential and high temperature is an impediment to the realization of high-performance all-solid-state batteries. In this study, we developed new hybrid coating materials consisting of lithium niobate (Li-Nb-O) and lithium phosphate (Li-P-O) and investigated the influence of the ratio of P/(Nb + P) on the durability performance. The cathode half-cells, using a sulfide-based solid electrolyte Li₆PS₅Cl/cathode active material, LiNi_0.5Co_0.2Mn_0.3O₂, coated with the new hybrid coating materials of LiP_xNb_1-xO₃ (x = 0-1), were exposed to harsh conditions (60 °C and 4.55 V vs Li/Li⁺) for 120 h as a degradation test. P substitution resulted in higher durability and lower interfacial resistance. In particular, the hybrid coating with x = 0.5 performed better, in terms of capacity retention and interfacial resistance, than those with other compositions of niobate and phosphate. The coated cathode active materials were analyzed using various analytical techniques such as scanning electron microscopy/energy-dispersive X-ray spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy (XAS) to elucidate the improvement mechanism. Moreover, the degraded cathodes were observed using time-of-flight secondary-ion mass spectrometry, TEM/electron diffraction, and XAS. These analyses revealed that the Nb-O-P coordination in the hybrid coating material captured O by P. The coordination suppressed the release of O from the coating layer as a decomposition side reaction to realize a higher durability than that of LiNbO₃.

Microscopic Degradation Mechanism of Argyrodite-Type Sulfide at the Solid Electrolyte-Cathode Interface

Interfacial engineering of sulfide-based solid electrolyte/lithium-transition-metal oxide active materials in all-solid-state battery cathodes is vital for cell performance parameters, such as high-rate charge/discharge, long lifetime, and wide temperature range. A typical interfacial engineering method is the surface coating of the cathode active material with a buffer layer, such as LiNbO₃. However, cell performance reportedly degrades under harsh environments even with a LiNbO₃ coating, such as high temperatures and high cathode potentials. Therefore, we investigated the interfacial degradation mechanism focusing on the solid electrolyte side for half cells employing the cathode mixture of argyrodite-type Li₆PS₅Cl/LiNbO₃-coated LiNi_0.5Co_0.2Mn_0.3O₂ exposed at 60 °C and 4.25 and 4.55 V vs Li/Li⁺ using transmission electron microscopy/electron diffraction (TEM/ED) and X-ray absorption spectroscopy (XAS). The TEM/ED results indicated that the ED pattern of the argyrodite structure disappeared and changed to an amorphous phase as the cells degraded. Moreover, the crystal phases of LiCl and Li₂S appeared simultaneously. Finally, XAS analysis confirmed the decrease in the PS₄ units of the argyrodite structure and the increase in local P-S-P domains with delithiation from the interfacial solid electrolyte, corresponding to the TEM/ED results. In addition, the formation of P-O bonds was confirmed during degradation at higher cathode potentials, such as 4.55 V vs Li/Li⁺. These results indicate that the degradation of this interfacial region determines the cell performance.

Nanoscale domain imaging of Li-rich disordered rocksalt-type cathode materials with X-ray spectroscopic ptychography

Lithium-rich disordered rocksalt-type cathode materials are promising for high-capacity and high-power lithium-ion batteries. Many of them are synthesized by mechanical milling and may have heterogeneous structures and chemical states at the nanoscale. In this study, we performed X-ray spectroscopic ptychography measurements of Li-rich disordered rocksalt-type oxide particles synthesized by mechanical milling before and after delithiation reaction at the vanadium K absorption edge, and visualized their structures and chemical state with a spatial resolution of ∼100 nm. We classified multiple domains with different chemical states via clustering analysis. A comparison of the domain distribution trends of the particles before and after the delithiation reaction revealed the presence of domains, suggesting that the delithiation reaction was suppressed.