Reviving Low-Temperature Performance of Lithium Batteries by Emerging Electrolyte Systems

Although lithium batteries have been successfully commercialized in the past two decades,they are particularly sensitive to ultralow temperatures.For most batteries,capacities and powers are lost at sub-zero temperatures,mainly due to the increased electrolyte viscosity,insufficient ionic conduction,slow charge-transfer kinetics,and reduced ion diffusing constant.In this review,we sorted out the critical factors leading to the poor low-temperature performance of electrolytes,and the comprehensive research progress of emerging electrolyte systems for the ultra-low temperature lithium battery is classified and highlighted.We further provide a systematic summary of the advanced characterization and computational simulation for low-temperature electrolyte systems to guide researchers in screening the low-temperature electrolytes,monitoring solvation/desolvation behavior,and investigating reaction mechanisms.Besides their fundamental significance,our review might also forge a new opportunity and prospects in the effective design of electrolytes for the ultralow temperature application of energy storage devices.

Disproportionation Reactions of HIO and NaIO in Static and Dynamic Systems

The paper refers to disproportionation of HIO and NaIO in aqueous media, in static and dynamic systems. The results of calculations, realized according to GATES/GEB principles, with use of an iterative computer program, are presented graphically. An example of the computer program with all physicochemical knowledge involved in the related algorithm is attached herewith.

General Relation Valid for Electrolytic Systems

A simple general relation P = Q + R + 1 between the number P of kinds of species, the number Q of charge and elemental/core balances and the number R of independent equilibrium constants is deduced, and its validity is confirmed for non-redox and redox electrolytic systems, of different degree of complexity.

Comparative Balancing of Non-Redox and Redox Electrolytic Systems and Its Consequences

In this paper, it is proved that linear combination 2·f(O)?- f(H) of elemental balances: f(O) for O and f(H) for H is linearly independent on charge and elemental/core balances for all redox systems of any degree of complexity;it is the primary form of the Generalized Electron Balance (GEB), , considered as the Approach II to GEB. The Approach II is equivalent to the Approach I based on the principle of common pool of electrons. Both Approaches are illustrated on an example of titration of acidified (H2SO4) solution of H2C2O4 with KMnO4. It is also stated, on an example of titration of the same solution with NaOH, that 2·f(O)?- f(H) is a linear combination of charge and elemental/core balances, i.e. it is not an independent balance when related to the non-redox system. These properties of 2·f(O)?- f(H) can be extended on redox and non-redox systems, of any degree of complexity, i.e. the linear independency/dependency of 2·f(O)?- f(H) on other balances related to a system in question is a criterion distinguishing redox and non-redox systems. The GEB completes the set of (charge and concentration) balances and a set of expressions for independent equilibrium constants needed for modeling the related redox system.

Formulation of Titration Curves for Some Redox Systems

The formalism realised according to the Generalised Approach to Electrolytic Systems (GATES) is presented and applied to typical redox systems known from the laboratory practice. In any redox system, the Generalized Electron Balance (GEB), perceived as the law of the matter conservation, is derivable from linear combination 2·f(O) – f(H) of elemental balances: f(O) for oxygen and f(H) for hydrogen. It is an equation linearly independent from other (charge and concentration) balances referred to an electrolytic redox system (aqueous media) of any degree of complexity, and named as the primary form of GEB and then denoted as pr-GEB. A compact equation for GEB is obtained from linear combination of 2·f(O) – f(H) with other (charge and concentration) balances. For a non-redox electrolytic system, of any degree of complexity, the balance 2·f(O) – f(H) is not an independent equation. In the derivation of GEB, all known components (species) of the system tested, taken in their real (i.e., hydrated) form, are involved in the balances, and none simplifying assumptions are needed. The redox systems are simulated with use of an iterative computer program.

Generalized Electron Balance for Dynamic Redox Systems in Mixed-Solvent Media

A complex example of electrolytic redox system involving 47 species, 3 electron-active elements and five (3 am-phiprotic + 2 aprotic) co-solvents, is presented. Mixed solvates of the species thus formed are admitted in the system considered. It is proved that the Generalized Electron Balance (GEB) in its simplest form obtained according to the Approach II to GEB is identical with the one obtained for aqueous media and binary-solvent system, and is equivalent to the Approach I to GEB.

Compact Formulation of Redox Systems According to GATES/GEB Principles

The Generalized Electron Balance (GEB), together with charge balance and concentration balances, completes the set of equations needed for resolution of electrolytic redox systems. The general formulae for GEB were obtained according to Approach II to GEB, i.e., on the basis of the equation 2?f(O) ? f(H) obtained from elemental balances: f(H) for H, and f(O) for O. Equivalency of the Approach II and the Approach I to GEB was proved for an aqueous solution and a binary-solvent system. On this basis, a compact form of GEB was derived.

Evaluation of Transition Points between Different Solid Phases in Aqueous Media

A uniform procedure is suggested for calculation of the pHt value(s) separating equilibrium solid phases in pH scale, at an excess of the precipitating agent. The pHt value, related to pairs of precipitates formed from the species ??and ?, fulfils the relation , where F is a constant value involving pKso’s for solubility products (Kso’s) of these precipitates, and the equilibrium data, related to the species composing these precipitates.

Dielectric spectroscopy characterization of Naþ ion-conducting polymer nanocomposite system PEO–PVP–NaIO_(4)–TiO_(2)

We studied the effect of titanium dioxide(TiO_(2))nanoparticles(NPs)on dielectric behavior of Naþion-conducting salt-complexed polymer nanocomposite system formed from a binary polymer blend of poly(ethylene oxide)(PEO)and polyvinyl pyrrolidone(PVP),with the addition of both sodium metaperiodate(NaIO_(4))at concentration 10 wt.%and TiO_(2) NPs of size10 nm,at concentrations 1,2,3,4 and 5 wt.%.Free standing nanocomposite PEO/PVP/NaIO_(4)/TiO_(2) films(150m)were characterized at room-temperature by analyzing their complex electrical impedance and dielectric spectra in the range 1 Hz–1 MHz.At the concentration of 3 wt.%of TiO_(2) NPs,both ion conductivity and dielectric permittivity of the PEO/PVP/NaIO_(4)/TiO_(2) ion-conducting dielectrics reach an enhancement by more than one order of magnitude as compared to nanoadditive-free case.

Crossover effects of transition metal ions in high-voltage lithium metal batteries

Enhancing the cut-off voltage of high-nickel layered oxide cathodes is an efficient way to obtain higher energy density of lithiummetal batteries(LMBs).However,the phase transition of the cathode materials and the uncontrolled decomposition of the electrolytes at high voltage can lead to irreversible dissolution of transition metal ions,which might cause the crossover effects on the lithium metal anodes.Nonetheless,the mechanism and electrolyte dependence of the crossover effects for Li metal anodes are still unclear.Herein,we investigate the crossover effects between LiNi_(0.8)Mn_(0.1)Co_(0.1)O_(2)and Li-metal anode in two electrolyte systems.For ether-based electrolyte,its poor oxidation stability results in massive dissolution of transition metal ions,leading to dendrite growth on anode and rapid cells failure.Conversely,ester-based electrolyte exhibits good electrochemical performances at 4.5 V with little crossover effect.This study provides an idea for electrolyte systems selection for high-voltage LMBs,and verifies that the crossover effect should not be neglected in LMBs.