Challenges for Safe Electrolytes Applied in Lithium-Ion Cells-A Review

Low-Temperature In Situ Lithiation Construction of a Lithiophilic Particle-Selective Interlayer for Solid-State Lithium Metal Batteries

Unexpected interface resistance and lithium dendrite puncture hinder the application of garnet-type solid-state electrolytes in high-energy-density systems. Different from the previous high-temperature (>180 °C) molten lithium that promotes the alloying reaction between the coating layer and Li to enhance the interface contact, herein, we introduce liquid-metal-like SbCl3 to construct a three-dimensional Li+ directional-selection interlayer by in situ low-temperature lithiation (80 °C). An interlayer with a more negative interface energy composed of SbLi3 and LiCl exhibits a superior affinity with Li and LGLZO, which reduces the interface resistance and suppresses the growth of Li dendrites by an insulated electron. The introduction of the SbCl3 modification layer into Li/Li symmetric cells enables charge/discharge at a current density of 6.0 mA cm-2 and operation for more than 1000 h under 2.0 mA cm-2 at room temperature. The full cells with the LiFePO4 cathode exhibit a high residual capacity of 144.8 mAh g-1 at 0.5 C after 1000 cycles and excellent cycling stability with a retention ratio of 94.7% at 1 C after 600 cycles. The low-temperature lithiation method based on an energy-saving perspective should be applied to other types of solid-state electrolyte modification strategies.

Stable Operation Induced by Plastic Crystal Electrolyte Used in Ni-Rich NMC811 Cathodes for Li-Ion Batteries

The LiNi0.8Mn0.1Co0.1O2 (NMC811) cathode material has been of significant consideration owing to its high energy density for Li-ion batteries. However, the poor cycling stability in a carbonate electrolyte limits its further development. In this work, we report the excellent electrochemical performance of the NMC811 cathode using a rational electrolyte based on organic ionic plastic crystal N-ethyl-N-methyl pyrrolidinium bis(fluorosulfonyl)imide C2mpyr[FSI], with the addition of (1:1 mol) LiFSI salt. This plastic crystal electrolyte (PC) is a thick viscous liquid with an ionic conductivity of 2.3 × 10-3 S cm-1 and a high Li+ transference number of 0.4 at ambient temperature. The NMC811@PC cathode delivers a discharge capacity of 188 mA h g-1 at a rate of 0.2 C with a capacity retention of 94.5% after 200 cycles, much higher than that of using a carbonate electrolyte (54.3%). Moreover, the NMC811@PC cathode also exhibits a superior high-rate capability with a discharge capacity of 111.0 mA h g-1 at the 10 C rate. The significantly improved cycle performance of the NMC811@PC cathode can be attributed to the high Li+ conductivity of the PC electrolyte, the stable Li+ conductive CEI film, and the maintaining of particle integrity during long-term cycling. The admirable electrochemical performance of the NMC811|C2mpyr[FSI]:[LiFSI] system exhibits a promising application of the plastic crystal electrolyte for high voltage layered oxide cathode materials in advanced lithium-ion batteries.

Interfacial Designs of MXenes for Mild Aqueous Zinc-Ion Storage

Limited Li resources, high cost, and safety risks of using organic electrolytes have stimulated a strong motivation to develop non-Li aqueous batteries. Aqueous Zn-ion storage (ZIS) devices offer low-cost and high-safety solutions. However, their practical applications are at the moment restricted by their short cycle life arising mainly from irreversible electrochemical side reactions and processes at the interfaces. This review sums up the capability of using 2D MXenes to increase the reversibility at the interface, assist the charge transfer process, and thereby improve the performance of ZIS. First, they discuss the ZIS mechanism and irreversibility of typical electrode materials in mild aqueous electrolytes. Then, applications of MXenes in different ZIS components are highlighted, including as electrodes for Zn2+ intercalation, protective layers of Zn anode, hosts for Zn deposition, substrates, and separators. Finally, perspectives are put forward on further optimizing MXenes to improve the ZIS performance.

PEO-Based Block Copolymer Electrolytes Containing Double Conductive Phases with Improved Mechanical and Electrochemical Properties

In this work, the advanced all solid-state block copolymer electrolytes (SBCPEs) for lithium-ion batteries with double conductive phases, poly(ethylene oxide)-b-poly(trimethyl-N-((2-(dimethylamino)ethyl methacrylate)-7-propyl)-ammonium bis(trifluoromethanesulfonyl) imide) (PEO-b-PDM-dTFSI)/LiTFSI, were fabricated, in which the charged PDM-dTFSI block contained double quaternary ammonium cations and the PEO block was doped with LiTFSI. The disordered (DIS) and ordered lamellae (LAM) phase structures were achieved by adjusting the composition of the block copolymer and the doping ratio r. In addition, the presence of the hard PDM-dTFSI block and the formation of the LAM phase structure resulted in a good mechanical strength of the solid PEO-b-PDM-dTFSI/LiTFSI electrolyte, and it could maintain a high level of 10⁴ Pa at 100 °C, which was around 10,000 times stronger than that of the PEO/LiTFSI electrolyte. Based on the good mechanical and electrochemical properties, the PEO-b-PDM-dTFSI/LiTFSI SBCPE exhibited excellent long-term galvanostatic cycle performance, indicating the strong ability to suppress lithium dendrites.

Local Volume Conservation in Concentrated Electrolytes Is Governing Charge Transport in Electric Fields

While ion transport processes in concentrated electrolytes, e.g., based on ionic liquids (IL), are a subject of intense research, the role of conservation laws and reference frames is still a matter of debate. Employing electrophoretic NMR, we show that momentum conservation, a typical prerequisite in molecular dynamics (MD) simulations, is not governing ion transport. Involving density measurements to determine molar volumes of distinct ion species, we propose that conservation of local molar species volumes is the governing constraint for ion transport. The experimentally quantified net volume flux is found to be zero, implying a nonzero local momentum flux, as tested in pure ILs and IL-based electrolytes for a broad variety of concentrations and chemical compositions. This constraint is consistent with incompressibility, but not with a local application of momentum conservation. The constraint affects the calculation of transference numbers as well as comparisons of MD results to experimental findings.

Lignin as Polymer Electrolyte Precursor for Stable and Sustainable Potassium Batteries

Potassium batteries show interesting peculiarities as large-scale energy storage systems and, in this scenario, the formulation of polymer electrolytes obtained from sustainable resources or waste-derived products represents a milestone activity. In this study, a lignin-based membrane is designed by crosslinking a pre-oxidized Kraft lignin matrix with an ethoxylated difunctional oligomer, leading to self-standing membranes that are able to incorporate solvated potassium salts. The in-depth electrochemical characterization highlights a wide stability window (up to 4 V) and an ionic conductivity exceeding 10^-3  S cm^-1 at ambient temperature. When potassium metal cell prototypes are assembled, the lignin-based electrolyte attains significant electrochemical performances, with an initial specific capacity of 168 mAh g^-1 at 0.05 A g^-1 and an excellent operation for more than 200 cycles, which is an unprecedented outcome for biosourced systems in potassium batteries.

Polymer Electrolytes for Lithium-Ion Batteries Studied by NMR Techniques

This review is devoted to different types of novel polymer electrolytes for lithium power sources developed during the last decade. In the first part, the compositions and conductivity of various polymer electrolytes are considered. The second part contains NMR applications to the ion transport mechanism. Polymer electrolytes prevail over liquid electrolytes because of their exploitation safety and wider working temperature ranges. The gel electrolytes are mainly attractive. The systems based on polyethylene oxide, poly(vinylidene fluoride-co-hexafluoropropylene), poly(ethylene glycol) diacrylate, etc., modified by nanoparticle (TiO₂, SiO₂, etc.) additives and ionic liquids are considered in detail. NMR techniques such as high-resolution NMR, solid-state NMR, magic angle spinning (MAS) NMR, NMR relaxation, and pulsed-field gradient NMR applications are discussed. ¹H, ⁷Li, and ¹⁹F NMR methods applied to polymer electrolytes are considered. Primary attention is given to the revelation of the ion transport mechanism. A nanochannel structure, compositions of ion complexes, and mobilities of cations and anions studied by NMR, quantum-chemical, and ionic conductivity methods are discussed.

Temperature Sensor Based on Periodically Tapered Optical Fibers

In this paper, the fabrication and characterization of a temperature sensor based on periodically tapered optical fibers (PTOF) are presented. The relation between the geometry of the sensors and sensing ability was investigated in order to find the relatively simple structure of a sensor. Four types of PTOF structures with two, four, six and eight waists were manufactured with the fusion splicer. For each PTOF type, the theoretical free spectral range (FSR) was calculated and compared with measurements. The experiments were conducted for a temperature range of 20–70 °C. The results proved that the number of the tapered regions in PTOF is crucial, because some of the investigated structures did not exhibit the temperature response. The interference occurring inside the structures with two and four waists was found be too weak and, therefore, the transmission dip was hardly visible. We proved that sensors with a low number of tapered regions cannot be considered as a temperature sensor. Sufficiently more valuable results were obtained for the last two types of PTOF, where the sensor’s sensitivity was equal to 0.07 dB/°C with an excellent linear fitting (R² > 0.99). The transmission dip shift can be described by a linear function (R² > 0.97) with a slope α > 0.39 nm/°C.