Solid composite electrolytes (SCEs) that combine the advantages of solid polymer electrolytes (SPEs) and inorganic ceramic electrolytes (ICEs) present acceptable ionic conductivity, high mechanical strength, and favorable interfacial contact with electrodes, which greatly improve the electrochemical performance of all-solid-state batteries compared to single SPEs and ICEs. However, there are many challenges to overcome before the practical application of SCEs, including the low ionic conductivity less than 10-3 S cm-1 at ambient temperature, poor interfacial stability, and high interfacial resistance, which greatly restrict the room temperature performance. Herein, the advances of SCEs applied in all-solid-state lithium batteries are presented, including the Li ion migration mechanism of SCEs, the strategies to enhance the ionic conductivity of SCEs by various morphologies of ICEs, and construction methods of the low resistance and stable interfaces of SCEs with both cathode and anode. Finally, some typical applications of SCEs in lithium batteries are summarized and future development directions are prospected. This work presents how it is quite significant to further enhance the ionic conductivity of SCEs by developing the novel SPEs with the special morphology of ICEs for advanced all-solid-state lithium batteries.

https://onlinelibrary.wiley.com/doi/epdf/10.1002/advs.201903088

Progress and Perspective of Ceramic/Polymer Composite Solid Electrolytes for Lithium Batteries

Voltage fade is a major problem in battery applications for high-energy lithium- and manganese-rich (LMR) layered materials. As a result of the complexity of the LMR structure, the voltage fade mechanism is not well understood. Here we conduct both in situ and ex situ studies on a typical LMR material (Li1.2Ni0.15Co0.1Mn0.55O2) during charge–discharge cycling, using multi-length-scale X-ray spectroscopic and three-dimensional electron microscopic imaging techniques. Through probing from the surface to the bulk, and from individual to whole ensembles of particles, we show that the average valence state of each type of transition metal cation is continuously reduced, which is attributed to oxygen release from the LMR material. Such reductions activate the lower-voltage Mn3+/Mn4+ and Co2+/Co3+ redox couples in addition to the original redox couples including Ni2+/Ni3+, Ni3+/Ni4+ and O2−/O−, directly leading to the voltage fade. We also show that the oxygen release causes microstructural defects such as the formation of large pores within particles, which also contributes to the voltage fade. Surface coating and modification methods are suggested to be effective in suppressing the voltage fade through reducing the oxygen release.Voltage decay is a major problem in applications of high-energy Li- and Mn-rich layer-structured battery materials. Here, the authors report the evolution of redox couples as the origin of the voltage decay and discuss strategies to suppress the problem.

(Invited) Evolution of Redox Couples in Li- and Mn-Rich Cathode Materials and Mitigation of Voltage Fade by Reducing Oxygen Release

Due to higher energy density, high-voltage all-solid-state lithium batteries (ASSLBs) have attracted increasing attention. However, they require solid-state electrolytes (SSEs) with wide electrochemical stability windows (ESW, typically >4.2 V) and high-stability against the Li anode. Nevertheless, poly(ethylene oxide) (PEO), the most widely used solid polymer electrolyte (SPE), can’t tolerate a high-voltage over 4 V. Whether the main chain (–C–O–C–) or the terminal hydroxide group (–OH) is the limiting factor for the narrow ESW remains unknown. Herein, poly(ethylene glycol) (PEG) and poly(ethylene glycol)dimethyl ether (PEGDME) with different terminal groups are selected to answer this question. The results show that the reactive terminal –OH group is the limiting factor towards applicability against high voltage and the Li anode. Replacing –OH with more stable –OCH3 can significantly extend the ESW from 4.05 to 4.3 V, while improving the Li-anode compatibility as well (Li–Li symmetric cells stably run for 2500 h at 0.2 mA cm−2). Its practical application is further proved by developing PEGDME-based ASSLB pouch cells. The 0.53 mA cm−2 Li–LiFePO4 and 0.47 mA h cm−2 Li–LiNi0.5Mn0.3Co0.2O2 cells demonstrated high capacity retention of 97% and 90% after 210 cycles and 110 cycles, respectively. This work offers a new strategy for PEO-based high-voltage ASSLB development by changing the unstable terminal groups.

Determining the limiting factor of the electrochemical stability window for PEO-based solid polymer electrolytes: main chain or terminal –OH group?

Heteroatom Doping: An Effective Way to Boost Sodium Ion Storage

The recent discovery of highly conductive solid-state electrolytes (SSEs) has led to tremendous progress in the development of all-solid-state batteries (ASSBs). Though promising, they still face barriers that limit their practical application, such as poor interfacial stability, scalability challenges and production safety. Additionally, efforts to develop sustainable manufacturing of lithium ion batteries are still lacking, with no prevailing strategy developed yet to handle recyclability of ASSBs. To date, most SSE research has been largely focused on the discovery of novel electrolytes. Recent review articles have extensively examined a broad spectrum of these SSEs using evaluation factors such as conductivity and chemical stability. Recognizing this, in this Review we seek to evaluate SSEs beyond conventional factors and offer a perspective on various bulk, interface and nanoscale phenomena that require urgent attention within the scientific community. We provide a realistic assessment of the current state-of-the-art characterization techniques and evaluate future full cell ASSB prototyping strategies. We hope to offer rational solutions to overcome some major fundamental obstacles faced by the ASSB community, as well as potential strategies toward a sustainable ASSB recycling model.

/pdf/from-nanoscale-interface-characterization-to-sustainable-562jvv2w2i.pdf

From nanoscale interface characterization to sustainable energy storage using all-solid-state batteries

Lithium-ion batteries have dominated the high performance and mobile market for last decade. Despite their dominance in many areas, the development of current commercial lithium-ion batteries is experiencing bottlenecks, limited by safety risks such as: leakage, burning, and even explosions due to the low-boiling point organic liquid electrolytes. Solid electrolyte is a promising option to solve or mitigate those issues. Among all solid electrolytes, polymer based solid electrolytes have the advantages of low flammability, good flexibility, excellent thermal stability, and high safety. Numerous researchers have focused on implementing solid polymer based Li-ion batteries with high performance. Nevertheless, low Li-ion conductivity and poor mechanical properties are still the main challenges in its commercial development. In order to tackle the issues and improve the overall performance, composites with external particles are widely investigated to form a polymer-based composite electrolyte. In light of their work, this review discusses the progress of polymer-based composite lithium ion's solid electrolytes. In particular, the structures, ionic conductivities, electrochemical/chemical stabilities, and fabrications of solid polymer electrolytes are introduced in the text and summarized at the end. On the basis of previous work, the perspectives of solid polymer electrolytes are provided especially toward the future of lithium ion batteries.

/pdf/review-on-polymer-based-composite-electrolytes-for-lithium-2ftvum11u3.pdf

Review on Polymer-Based Composite Electrolytes for Lithium Batteries

Hybridizing poly(vinylidene fluoride-co-hexafluoropropylene) with Li6.5La3Zr1.5Ta0.5O12 as a lithium-ion electrolyte for solid state lithium metal batteries

3D Cube-Maze-Like Li-Rich Layered Cathodes Assembled from 2D Porous Nanosheets for Enhanced Cycle Stability and Rate Capability of Lithium-Ion Batteries

Three-dimensional hierarchical graphene and CNT-coated spinel ZnMn2O4 as a high-stability anode for lithium-ion batteries

Iron-based sulfides have been deemed as an appealing anode material for lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs) for their high theoretical capacity and low cost. However, their practical application is limited by drastic volume expansion during cycling and low-intrinsic electronic conductivity. In this work, we report a FeS2/Fe7S8-rGO composite synthesized via a facile solvothermal method as an LIB/SIB anode. The FeS2/Fe7S8-rGO anode exhibits an excellent Li-storage capacity of 514 mAh g-1 at 2.0 A g-1 after 3000 cycles and a Na-storage capacity of 650 mAh g-1 at 0.2 A g-1 after 250 cycles, respectively. The rGO matrix is deemed responsible for providing good electron conduction and alleviating volume expansion during cycling. The electrokinetic analysis confirms a large portion of intercalational pseudocapacitance as a major contribution to the superior rate performance. In situ X-ray diffraction further reveals details of a combined intercalational and conversional Li-ion storage mechanisms in this Fe-sulfide-based anode. Finally, density functional theory calculations suggest that there exists a synergistic effect at the heterointerface between FeS2 and Fe7S8 to promote electrokinetics.

Zhiyu Ding

Papers

Review on Polymer-Based Composite Electrolytes for Lithium Batteries

Hybridizing poly(vinylidene fluoride-co-hexafluoropropylene) with Li6.5La3Zr1.5Ta0.5O12 as a lithium-ion electrolyte for solid state lithium metal batteries

3D Cube-Maze-Like Li-Rich Layered Cathodes Assembled from 2D Porous Nanosheets for Enhanced Cycle Stability and Rate Capability of Lithium-Ion Batteries

Three-dimensional hierarchical graphene and CNT-coated spinel ZnMn2O4 as a high-stability anode for lithium-ion batteries

Binary Iron Sulfide as a Low-Cost and High-Performance Anode for Lithium-/Sodium-Ion Batteries