Solid-state Li Batteries Research Articles

Built-in elasticity-rigidity balanced polymer electrolyte in solid-state Li-batteries with high-loading cathode

Solid-state lithium batteries (SSLBs) using polymer electrolytes have attracted increasing attention owing to their intrinsic flexibility and high energy density. However, due to the lack of permeability like liquid electrolytes, polymer electrolytes equipped with high-loading electrodes are usually limited by the high polarization and rapid capacity decay. Herein, an elasticity-rigidity balanced polymer electrolyte (ERBE) was designed by the in-situ crosslinking polymerization, where poly(ethylene glycol) diacrylate (PEGDA) works as crosslinking elasticity agents, poly(vinylidene carbonate) (PVC) acts as main structure support. Benefiting from the structural design, ERBE electrolyte features high compression strength of 96.1 MPa and volume compression ratio up to 73.9 %. The ERBE also exhibits room-temperature ionic conductivity of 2.31 × 10−4 S cm−1 and high Li-ions transfer number of 0.69. The LiFePO4||Li cells equipped with ERBE electrolyte can maintain over 3000 cycles with 70.1 % capacity retention at 1 C and 25 °C. Even at the cathode mass loading up to 78 mg cm−2, it can deliver a high discharge capacity of 11.98 mAh cm−2 at 25 °C. Such an integrated in-situ polymer electrolyte provides strong support for solving the problems of rigidity or elasticity insufficiency and dendrite growth, and holds promising applications in wide-temperature, high-energy-density solid-state batteries.

Efficient Co-ZrO2 electrocatalyst achieves high-performance solid-state lithium-sulfur batteries

Abstract Li-S batteries are recognized as a promising secondary battery system because of their high energy density, low cost, and environmental friendliness. However, the development of Li-S batteries is mainly limited by issues such as electrode volume expansion, lithium polysulfide (LiPSs) shuttle, and slow redox reaction kinetics of sulfur. Here, a kind of solid-state Li-S battery with in situ solidified solid-state electrolytes (SSEs) is reported, which dramatically reduces the electrode/electrolyte interfacial impedance. In addition, electrospinning is used to fabricate a macroporous carbon nanofibers film (MP-CNFs) loaded with dispersed Co-ZrO2 nanodot electrocatalyst as the cathode host. The in-situ gel electrolyte can be easily infiltrated into the porous carbon nanofibers and contact the Co-ZrO2 catalyst, thus fully exerting its catalytic and conversion effects on LiPSs. The results indicate that solid-state Li-S batteries exhibit a high initial capacity of 795.5 mA h·g−1 and a capacity retention rate of ∼100% after 200 cycles at 1 C.

Homogenizing Interfacial Stress by Nanoporous Metal Current Collector to Enable Stable All-Solid-State Li Metal Battery

All-solid-state lithium-metal batteries are prone to shorting due to lithium penetration through the electrolyte layer. Li experiences creep during compression which creates stress in the electrolyte layer. Uneven deposition and stripping of Li further exaggerate the heterogeneity of stress distribution. To overcome this challenge, we design a current collector for Li metal. Its specific properties can homogenize interfacial stress distribution and prevent the solid electrolyte layer from developing additional defects that encourage penetration by Li metal during processes of fabrication and electrochemical cycling. Compared with a conventional current collector, our current collector effectively enhances the critical current density (1.7 vs. 0.5 mA/cm2) and extends cycle life (> 360 vs. 12 hours) for Li/Li symmetric cells. This development provides a chemistry-agnostic approach to improving the cycle life of solid-state Li batteries.

Capacity Degradation of Zero-Excess All-Solid-State Li Metal Batteries Using a Poly(ethylene oxide) Based Solid Electrolyte.

Solid-state polymer electrolytes (SPEs), such as poly(ethylene oxide) (PEO), have good flexibility when compared to ceramic-type solid electrolytes. Therefore, it could be an ideal solid electrolyte for zero-excess all-solid-state Li metal battery (ZESSLB), also known as anode-free all-solid-state Li battery, development by offering better contact to the Cu current collector. However, the low Coulombic efficiencies observed from polymer type solid-state Li batteries (SSLBs) raise the concern that PEO may consume the limited amount of Li in ZESSLB to fail the system. Here, we designed ZESSLBs by using all-ceramic half-cells and an extra PEO electrolyte interlayer to study the reactivity between PEO and freshly deposited Li under a real battery operating conduction. By shuttling active Li back from the anode to the cathode, the PEO SPEs can be separated from the ZESSLBs for experimental studies without the influence from cathode materials or possible contamination from the usage of Li foil as the anode. Electrochemical cycling of ZESSLBs shows that the capacities of ZESSLBs with solvent-free and solvent-casted PEO SPEs significantly degraded compared to the ones with Li metal as the anode for the all-solid-state Li batteries. The fast capacity degradation of ZESSLBs using different types of PEO SPEs is evidenced to be associated with Li reacting with PEO, residual solvent, and water in PEO and dead Li formation upon the presence or absence of residual solvent. The results suggest that avoiding direct contact between the PEO electrolyte and deposited lithium is necessary when there is only a limited amount of Li available in ZESSLBs.

Interfacial compatibility design of high-performance electrolytes for SiCO-based all-solid-state lithium battery

Abstract As a new type of Lithium-ion batteries technology, all-solid-state Lithium-ion battery is regarded as one of the cutting-edge directions for new-generation battery technology. The biggest challenge of solid-state Li battery technology is that interface compatibility and stability problems must be solved urgently. In this paper, we specialize in the overall design of solid electrolyte interfacial compatibility and study the interfacial compatibility and stability by calculating the interfacial region interactions, charge transfer, adhesion energy, adsorption energy, interface formation energy, diffusion barrier, and density of states changes through the first nature principle. We conclude that LLZO solid-state electrolytes exhibit excellent interfacial properties, and interfacial compatibility and stability are further improved after doping. This paper shows a theoretical framework for exploiting novel electrolyte materials in all-solid-state battery.

Impact of annealing on the resistance of Li3PO4 electrolyte–LiNi0.5Mn1.5O4 electrode interfaces

The operation of solid-state Li batteries, which are promising power supplies for portable electronic devices and electric vehicles, is accompanied by heating. Therefore, investigating the thermal stability of battery systems is essential. In this study, we report the impact of annealing on the interface of a Li3PO4 electrolyte and LiNi0.5Mn1.5O4 electrode in thin-film batteries. The batteries with the interface annealed at 200 °C show low Li3PO4–LiNi0.5Mn1.5O4 interface resistance of 7.2 Ω cm2. Furthermore, the batteries exhibit stable charge–discharge characteristics with high current density up to 1170 μA cm−2, similar to those of batteries with the non-annealing interface. The batteries with the interface annealed at 450 °C show high Li3PO4–LiNi0.5Mn1.5O4 interface resistance of 490 Ω cm2, resulting in low battery performance. X-ray photoemission spectroscopy indicates that the P in Li3PO4 is reduced by high-temperature annealing, possibly causing the performance degradation of batteries. This study provides an in-depth understanding of the interfaces of solid-state batteries and is expected to facilitate the development of thermally stable batteries.

Grain boundary complexion modification for interface stability in garnet based solid-state Li batteries

The garnet type solid-state electrolyte (SSE) encounters challenges related to poor interfacial contact with Li metal and dendrite penetration problem. This study addresses these issues by manipulating the surface property of garnet-based LLZTO (Li6.5La3Zr1.6Ta0.4O12) SSE. The manipulation is achieved by varying thickness of Al2O3 atomic layer deposition (ALD), followed by sintering. Research results show that the relative density, ionic conductivity, and hardness of LLZTO are improved while electronic conductivity is reduced due to the formation of multiple complexions at grain boundary (GB). The SSE pellets also demonstrate improved wettability with Li metal, leading to stable galvanostatic Li plating/stripping cycling with low polarization, which allows for batter battery performance than pristine one. The concept of modifying SSE through the grain boundary complexion modification by thin ALD coating for enhancing the dendrite tolerance with better electrochemical properties of SSE may open a new direction for solid state battery research.

Garnet-Based Solid-State Li Batteries with High-Surface-Area Porous LLZO Membranes.

Rechargeable garnet-based solid-state Li batteries hold immense promise as nonflammable, nontoxic, and high energy density energy storage systems, employing Li7La3Zr2O12 (LLZO) with a garnet-type structure as the solid-state electrolyte. Despite substantial progress in this field, the advancement and eventual commercialization of garnet-based solid-state Li batteries are impeded by void formation at the LLZO/Li interface at practical current densities and areal capacities beyond 1 mA cm-2 and 1 mAh cm-2, respectively, resulting in limited cycling stability and the emergence of Li dendrites. Additionally, developing a fabrication approach for thin LLZO electrolytes to achieve high energy density remains paramount. To address these critical challenges, herein, we present a facile methodology for fabricating self-standing, 50 μm thick, porous LLZO membranes with a small pore size of ca. 2.3 μm and an average porosity of 51%, resulting in a specific surface area of 1.3 μm-1, the highest reported to date. The use of such LLZO membranes significantly increases the Li/LLZO contact area, effectively mitigating void formation. This methodology combines two key elements: (i) the use of small pore formers of ca. 1.5 μm and (ii) the use of ultrafast sintering, which circumvents ceramics overdensification using rapid heating/cooling rates of ca. 50 °C per second. The fabricated porous LLZO membranes demonstrate exceptional cycling stability in a symmetrical Li/LLZO/Li cell configuration, exceeding 600 h of continuous operation at a current density of 0.1 mA cm-2.

Healable and conductive sulfur iodide for solid-state Li-S batteries.

Solid-state Li-S batteries (SSLSBs) are made of low-cost and abundant materials free of supply chain concerns. Owing to their high theoretical energy densities, they are highly desirable for electric vehicles1-3. However, the development of SSLSBs has been historically plagued by the insulating nature of sulfur4,5 and the poor interfacial contacts induced by its large volume change during cycling6,7, impeding charge transfer among different solid components. Here we report an S9.3I molecular crystal with I2 inserted in the crystalline sulfur structure, which shows a semiconductor-level electrical conductivity (approximately 5.9 × 10-7 S cm-1) at 25 °C; an 11-order-of-magnitude increase over sulfur itself. Iodine introduces new states into the band gap of sulfur and promotes the formation of reactive polysulfides during electrochemical cycling. Further, the material features a low melting point of around 65 °C, which enables repairing of damaged interfaces due to cycling by periodical remelting of the cathode material. As a result, an Li-S9.3I battery demonstrates 400 stable cycles with a specific capacity retention of 87%. The design of this conductive, low-melting-point sulfur iodide material represents a substantial advancement in the chemistry of sulfur materials, and opens the door to the practical realization of SSLSBs.

A Novel Approach for Post-Mortem Analysis in All-Solid-State Batteries: Isolating Solid Polymer Electrolytes from Lithium Anodes

Polymeric electrolytes are currently at the forefront of research for the next generation of lithium all-solid-state batteries. Polyethylene oxide (PEO), a commonly used polymer for these batteries, operates at elevated temperatures at which it reacts with active metal electrodes (e.g., lithium). Rich surface chemistry is developed at the Li-PEO interfaces, thereby controlling these batteries’ electrochemical behavior. Interfacial studies are essential to comprehend batteries’ stabilization or capacity fading mechanisms. For that, post-mortem analysis with an emphasis on interfaces is a necessary approach to underpinning these mechanisms. While it can be readily done with liquid electrolytes, post-mortem characterization of similar interfaces with solid electrolytes is hampered by the Li-PEO stack firm adhesion, which is impossible to separate. Here, various methods were attempted to separate polymer electrolytes from metallic anodes after Li symmetric cells’ operation, which is a necessary step for solid-state NMR characterization. By a simple method involving exposure to N2(g) atmosphere, PEO-based solid electrolyte samples were successfully isolated from lithium anodes while preserving their morphology and chemical characteristics to enable their direct analysis. This method’s concept was approved by Solid-state NMR spectroscopy. This work opens the door for post-operative analysis of many kinds of solid-state Li batteries.

Self-Assembly of Ultrathin, Ultrastrong Layered Membranes by Protic Solvent Penetration.

Flexible membranes with ultrathin thickness and excellent mechanical properties have shown great potential for broad uses in solid polymer electrolytes (SPEs), on-skin electronics, etc. However, an ultrathin membrane (<5 μm) is rarely reported in the above applications due to the inherent trade-off between thickness and antifailure ability. We discover a protic solvent penetration strategy to prepare ultrathin, ultrastrong layered films through a continuous interweaving of aramid nanofibers (ANFs) with the assistance of simultaneous protonation and penetration of a protic solvent. The thickness of a pure ANF film can be controlled below 5 μm, with a tensile strength of 556.6 MPa, allowing us to produce the thinnest SPE (3.4 μm). The resultant SPEs enable Li-S batteries to cycle over a thousand times at a high rate of 1C due to the small ionic impedance conferred by the ultrathin characteristic and regulated ionic transportation. Besides, a high loading of the sulfur cathode (4 mg cm-2) with good sulfur utilization was achieved at a mild temperature (35 °C), which is difficult to realize in previously reported solid-state Li-S batteries. Through a simple laminating process at the wet state, the thicker film (tens of micrometers) obtained exhibits mechanical properties comparable to those of thin films and possesses the capability to withstand high-velocity projectile impacts, indicating that our technique features a high degree of thickness controllability. We believe that it can serve as a valuable tool to assemble nanomaterials into ultrathin, ultrastrong membranes for various applications.

Interfacial self-healing polymer electrolytes for long-cycle solid-state lithium-sulfur batteries

Coupling high-capacity cathode and Li-anode with solid-state electrolyte has been demonstrated as an effective strategy for increasing the energy densities and safety of rechargeable batteries. However, the limited ion conductivity, the large interfacial resistance, and unconstrained Li-dendrite growth hinder the application of solid-state Li-metal batteries. Here, a poly(ether-urethane)-based solid-state polymer electrolyte with self-healing capability is designed to reduce the interfacial resistance and provides a high-performance solid-state Li-metal battery. With its dynamic covalent disulfide bonds and hydrogen bonds, the proposed solid-state polymer electrolyte exhibits excellent interfacial self-healing ability and maintains good interfacial contact. Full cells are assembled with the two integrated electrodes/electrolytes. As a result, the Li||Li symmetric cells exhibit stable long-term cycling for more than 6000 h, and the solid-state Li-S battery shows a prolonged cycling life of 700 cycles at 0.3 C. The use of ultrasound imaging technology shows that the interfacial contact of the integrated structure is much better than those of traditional laminated structure. This work provides an interesting interfacial dual-integrated strategy for designing high-performance solid-state Li-metal batteries.

Visualization and evaluation of lithium diffusion at grain boundaries in Li0.29La0.57TiO3 solid electrolytes using secondary ion mass spectrometry

Understanding Li diffusion at interfaces in solid-state Li batteries is essential to improving their performance (e.g., rate capabilities and energy densities).

From Non-Aqueous Liquid to Solid-State Li-S Batteries: Design Protocols, Challenges and Solutions

Traditional Lithium-ion batteries may not satisfy the requirements of advanced batteries, demanding higher energy and power density, broader operating temperature ranges, and faster charging speeds. Solid-state Li-S batteries (SSLSBs) offer...

Li3InCl6-Coated High-Voltage Cathodes for Thiophosphate-Based Solid-State Li Batteries

Solid-state Li batteries are pursued as potentially safe and stable high-energy storage systems. However, key issues remain unsolved, impeding the practical realization.[1] One of the fundamental reasons for the failure of these batteries is likely the instability of solid-state electrolytes, such as Li6PS5Cl, towards high voltage cathodes. To mitigate the interface instability issues coating materials that prevent the decomposition of the solid-state electrolytes without limiting the ionic transport across them are thus urgently warranted.[2,3] Halides have been shown to have excellent high voltage stability up to 4.2 V in combination with moderate Li-ion conductivities of the order of magnitude ~10-3 S cm-1.[4]Combining the properties of halides with sulfides, hence, could be a promising strategy to enable room temperature solid-state Li batteries. Therefore, we synthesized nano-sized Li3InCl6 powder by mechanochemistry.Thereafter, Li3InCl6 was coated onto micrometer-sized LiNi0.8Co0.15Al0.05O2 (LIC@NCA) cathode particles using mechanofusion technique. The thickness and uniformity of the coating were investigated using FIB-SEM and TEM. The coating thickness has been found to be as thin as 200 nm nanometers fully covering the NCA particles. Finally, LIC@NCA particles have been tested in a solid-state Li batteries using Li:In-alloy as anode and Li6PS5Cl as SSE. Cells with LIC@NCA show a significant improvement (from 60 mAh/g to 150 mAh/g) in respect of the initial capacity loss and capacity fading compared to the pristine NCA.

On the Chemomechanical Behavior in Solid-State Sodium Sulfur Batteries

Sodium-sulfur batteries are promising for grid energy storage applications thanks to their high theoretical capacity, their abundance in the Earth’s crust and raw materials being cost effective. Unfortunately, their practical application is limited by several technical challenges, especially polysulfide shuttling phenomenon and accompanied volume expansion, which can lead to serious capacity degradation [1]. In this case, solid-state sodium-sulfur battery (S4B) can effectively suppress the shuttle phenomenon [2]. However, the poor triple-phase contact among active material, solid electrolytes and electroconductive agent limits the battery performance. During cycling, the complete conversion of one mole S8 into eight mole Na2S expands its volume by 260 %, and contracts upon dissociation [1].This phenomenon causes the chemo-mechanical failure, results in contact lost within the cathode composite and decreases the reversible capacity. In contrast to solid-state Li-S batteries [3][4], the understanding in case of S4B is lacking. In this study, the battery using composite cathode preparing by ball milling achieved the first discharge capacity of 1640 mAh/g and 50 mA/g current density which is close to the theoretical capacity of sulfur. This is owing to the homogeneous distribution of sulfur within the electrode and intimate contact of sulfur, solid electrolyte, and conductive carbon. Upon cycling the chemo-mechanical impact on the global performance of S4B has been studied using operando XRD, SAXS, WAXS, and electrochemical dilatometry.

Nitrile-functionalized Poly(siloxane) as Electrolytes for High-Energy-Density Solid-State Li Batteries.

In the quest to replace liquid Li-ion electrolytes with safer and non-toxic solid counterparts for Li-ion batteries, polysiloxane polymers have attracted considerable attention as they offer low glass transition temperatures, stability with metallic lithium, and versatility in chemical functionalization of the backbone. Herein, we present the synthesis of Li-ion conductive polysiloxane-based polymers functionalized with 60% nitrile groups per chain unit. The synthesis procedure is based on the reaction of poly(dimethylsiloxane-co-methylvinylsiloxane) polymer with 2-cyanoethanethiol, followed by the addition of lithium bis(trifluoromethanesulfonyl)imide. The presented polysiloxane-based polymers exhibit exceptionally high ionic conductivity up to 0.375 mS cm-1 at 60 °C and Li+ ion transfer number of 0.73, one of the highest reported for polymer Li-ion conducting electrolytes. Their electrochemical performance was evaluated in both symmetrical and full-cell configurations to test the utility of synthesized polymers as electrolytes in Li-ion batteries.

A magnetic-assisted construction of functional gradient interlayer for dendrite-free solid-state lithium batteries

Garnet-based solid-state Li batteries are considered as important candidates of the next generation batteries due to their potentially high energy density and reliable safety, however the Li dendrite issue is a serious impediment to their further development. Herein, a functional gradient interlayer (FGIL) is introduced at the interface between the garnet and Li anode, which is formed by the in-situ reaction of molten Li with FeF3 assisted by a magnetic force. The FGIL not only reduces the interfacial impedance, evens out the local current distribution, and prevents the growth of Li dendrites on the electrode surface, but also blocks electron transport and prevents the formation of "Li filaments" inside the electrolyte. Consequently, the Li|LLZTO-FGIL|Li cells have a critical current density of up to 2.3 mA cm−2 and exhibit stable cycling for more than 3400 h at 0.3 mA cm−2.

Progress and Perspective of Controlling Li Dendrites Growth in All‐Solid‐State Li Metal Batteries via External Physical Fields

Li dendrites penetration through solid electrolytes (SEs) challenges the development of solid‐state Li batteries (SSLBs). To date, significant efforts are devoted to understand the mechanistic dynamics of Li dendrites nucleation, growth, and propagation in SEs, and various strategies that aim to alleviate and even inhibit Li dendrite formation have been proposed. Nevertheless, most of these conventional strategies require either additional material processing steps or new materials/layers that eventually increase battery cost and complexity. In contrast, using external fields, such as mechanical force, temperature physical field, electric field, pulse current, and even magnetic field to regulate Li dendrites penetration through SEs, seems to be one of the most cost‐effective strategies. This review focuses on the current research progress of utilizing external physical fields in regulating Li dendrites growth in SSLBs. For this purpose, the mechanical properties of Li and SEs, as well as the experimental results that visually track Li penetration dynamics, are reviewed. Finally, the review ends with remaining open questions in future studies of Li dendrites growth and penetration in SEs. It is hoped this review can shed some light on understanding the complex Li dendrite issues in SSLBs and potentially guide their rational design for further development.

In-situ electrochemical optical techniques in the investigation of lithium interfacial phenomena with a liquid and a solid-state electrolyte

An in-situ electrochemical optical diagnosis is the key to the investigation of electrode interface during a redox reaction. Because the morphology changes particularly, dendrite formation, dendrite shapes, solid electrolyte interface formation and gas generation can be revealed visually. The challenge of ensuring uniform current density on a flat Li anode in a liquid electrolyte is addressed and uniform Li plating is demonstrated. The dendrite shape change under different reduction current density is discussed. The Li dendrite shape change and the performance of Li anodes with a surface lamination of graphite and red phosphate are used as examples to demonstrate the capability of the in-situ optical cell. An in-situ electrochemical optical cell used in the investigation of the increasingly popular solid-state Li batteries has its own challenges. Due to the untransparent nature of a solid-state electrolyte, an optical investigation on a solid-state electrolyte Li battery needs to be done by exposing the cross-section of the cell. In addition, it is very difficult to assemble an optical cell with a brittle and fragile solid-state electrolyte in a glove box. A set of formation and transfer dies, and an optical cell are introduced. The Li dendrite growth at the interface can be observed in a solid-state Li cell.