Electrolytes For Lithium Batteries Research Articles

Low-temperature crystal structures of the solvent dimethyl carbonate

Dimethyl carbonate (DMC) is an important industrial solvent but is additionally a common component of liquid lithium-ion battery electrolytes. Pure DMC has a melting point of 277 K, so encountering solidification under outdoor climatic conditions is very likely in many locations around the globe. Even eutectic, ethylene carbonate:dimethyl carbonate commercial LiPF6 salt electrolyte formulations can start to solidify at temperatures around 260 K with obvious consequences for their performance. No structures for crystalline DMC are currently available which could be a hindrance for in situ battery studies at reduced temperatures. A time-of-flight neutron powder diffraction study of the phase behavior and crystal structures of deuterated DMC was undertaken to help fill this knowledge gap. Three different orthorhombic crystalline phases were found with a previously unreported low-temperature phase transition around 50–55 K. The progression of Pbca → Pbcm → Ibam space groups follow a sequence of group–subgroup relationships with the final Ibam structure being disordered around the central carbon atom.

Bisphenol-Derived Single-Ion Conducting Multiblock Copolymers as Lithium Battery Electrolytes: Impact of the Bisphenol Building Block

Bisphenol-Derived Single-Ion Conducting Multiblock Copolymers as Lithium Battery Electrolytes: Impact of the Bisphenol Building Block

Entropy-Driven Liquid Electrolytes for Lithium Batteries.

Developing liquid electrolytes with higher kinetics and enhanced interphase stability is one of the key challenges for lithium batteries. However, the poor solubility of lithium salts in solvents sets constraints that compromises the electrolyte properties. Here, it is shown that introducing multiple salts to form a high-entropy solution, alters the solvation structure, which can be used to raise the solubility of specific salts and stabilize electrode-electrolyte interphases. The prepared high-entropy electrolytes significantly enhance the cycling and rate performance of lithium batteries. For lithium-metal anodes the reversibility exceeds 99%, which extends the cycle life of batteries even under aggressive cycling conditions. For commercial batteries, combining a graphite anode with a LiNi0.8 Co0.1 Mn0.1 O2 cathode, more than 1000 charge-discharge cycles are achieved while maintaining a capacity retention of more than 90%. These performance improvements with respect to regular electrolytes are rationalized by the unique features of the solvation structure in high-entropy electrolytes. The weaker solvation interaction induced by the higher disorder results in improved lithium-ion kinetics, and the altered solvation composition leads to stabilized interphases. Finally, the high-entropy, induced by the presence of multiple salts, enables a decrease in melting temperature of the electrolytes and thus enables lower battery operation temperatures without changing the solvents.

2D Layered Nanomaterials as Fillers in Polymer Composite Electrolytes for Lithium Batteries

AbstractPolymer composite electrolytes (PCEs), i.e., materials combining the disciplines of polymer chemistry, inorganic chemistry, and electrochemistry, have received tremendous attention within academia and industry for lithium‐based battery applications. While PCEs often comprise 3D micro‐ or nanoparticles, this review thoroughly summarizes the prospects of 2D layered inorganic, organic, and hybrid nanomaterials as active (ion conductive) or passive (nonion conductive) fillers in PCEs. The synthetic inorganic nanofillers covered here include graphene oxide, boron nitride, transition metal chalcogenides, phosphorene, and MXenes. Furthermore, the use of naturally occurring 2D layered clay minerals, such as layered double hydroxides and silicates, in PCEs is also thoroughly detailed considering their impact on battery cell performance. Despite the dominance of 2D layered inorganic materials, their organic and hybrid counterparts, such as 2D covalent organic frameworks and 2D metal–organic frameworks are also identified as tuneable nanofillers for use in PCE. Hence, this review gives an overview of the plethora of options available for the selective development of both the 2D layered nanofillers and resulting PCEs, which can revolutionize the field of polymer‐based solid‐state electrolytes and their implementation in lithium and post‐lithium batteries.

Preparation and characterization of LLZO-LATP composite solid electrolyte for solid-state lithium-ion battery

All-solid-state lithium-ion batteries (ASSLB) demonstrate significant advancements in energy density and safety comparing the traditional lithium-ion batteries, which using liquid electrolyte. The performance of ASSLBs strongly depends on the characteristics of solid electrolyte materials. Currently, Li1.3Al0.3Ti1.7(PO4)3 (LATP) and Li7La3Zr2O12 (LLZO) have the best individual performances in the field of solid ceramic electrolytes. The purpose of this study is to investigate the characteristics of the LLZO-LATP composite electrolyte sintering at various temperatures. The dense LLZO-LATP solid composited electrolyte with acceptable electrochemical performance is successfully prepared using planetary ball-mill method. The phase and morphology of the samples were assisted by X-ray diffraction and Field-emission scanning electron microscopy. The LLZO-LATP composite sintered at 800 °C has less chemical reaction with small amount of second phase with high sintering density of 88.4%. The ionic conductivity of LLZO-LATP sintered at 800 °C is 1.3 × 10−6 Scm−1. This study addresses the lowering of sintering temperature of a composite solid electrolyte with two different structure electrolyte materials, is informative for its future research and to be promising in solid-state batteries.

Rational design of an in-build quasi-solid-state electrolyte for high-performance lithium-ion batteries with the silicon-based anode

Design and optimization of the electrolyte are essential for improving electrochemical performances of high-energy–density lithium-ion batteries (LIBs) with silicon-based anodes. However, the dramatic volume change of silicon and the repeated destruction of the solid electrolyte interphase (SEI) film bring formidable challenges for electrolyte exploitation. Herein, a quasi-solid-state electrolyte is proposed via in situ polymerization with 1,3,5-trioxane (TXE) as the monomer, lithium bistrifluoromethanesulfonimide (LiTFSI) and lithium difluoro(oxalato) borate (LiDFOB) as lithium salts, which delivers excellent ionic conductivity and sufficient anion transference number. By half-cell evaluation with the quasi-solid-state electrolyte, the in situ generated polymer skeleton and modified SEI film effectively suppressed the volume expansion of silicon-graphite (Si-Gr) anode to 26.7% after 300 cycles, significantly lower than 60.7% for conventional liquid electrolytes. Furthermore, the LiNi0.6Co0.2Mn0.2O2||Si-Gr full-cell test demonstrates that the quasi-solid-state electrolyte can also protect the cathode structure and inhibit the dissolution and shuttling of transition metals. Ultimately, capacity retention of the full cell is up to 86.0% after 200 cycles with high average coulombic efficiency (99.79%) at 25 °C, and the electrolyte further enhances its cycling stability at high temperature (60 °C). This work proposes a straightforward strategy for the comprehensive enhancement of battery safety and electrochemical performance with Si-based anodes.

Solvation structure and dynamics of a small ion in an organic electrolyte

Organic carbonates are commonly used as electrolytes in commercial lithium-ion batteries. A detailed interpretation of the solvation structure and dynamics of the electrolyte around ions is necessary to understand the charge/discharge process in batteries. This work combines infrared absorption spectroscopy with quantum chemical calculations and molecular dynamics simulations to decipher the solvation structure of propylene carbonate, a cyclic carbonate, around the dissolved thiocyanate ion. Two dimensional infrared spectroscopy and polarization-selective pump probe spectroscopies have been utilized to extract the timescales of solvent fluctuation and the solute reorientational dynamics. The similarity in the slow timescales for the solute and the solvent dynamics signifies that similar processes control both dynamics.

Non-coordinating flame retardants with varied vapor pressures enabling biphasic fire-extinguishing electrolyte for high safety lithium-ion batteries

Safety issues of LIBs are closely related to flammable carbonate electrolytes. Traditional strategies for nonflammable electrolytes involve soluble and coordinative flame retardants with limited choices, which interact with lithium ions and lead to deteriorated electrochemical performance. Meanwhile, single dosage of flame retardants fails to suppress ignition of both gas and liquid phases during thermal runaway (TR) of LIBs, thus generating multi-stage fire. Here, we introduce two flame retardants with high and low vapor pressure into carbonate electrolyte through a bridge co-solvent to obtain a non-flammable electrolyte with biphasic fire extinguishing capability. The designed electrolyte not only affords excellent electrochemical performance, but also simultaneously suppresses the combustion of flammable gases and liquid electrolytes. The Li[Ni0.78Co0.10Mn0.12]O2 | graphite pouch cell (2.90 Ah) empowered with such electrolyte exhibits outstanding cycling stability (87.5 % retention after 1000 cycles at 0.5 C) and shows only smoke under the severe nail penetration test as well as maximum temperature of TR reduced by 300 °C. What’s more, the onset time of TR is delayed by 86 s under thermal abuse test. Furthermore, the pouch cell after 1000 cycles remains flameless under the nail penetration test. This work provides a promising path for expanding the selectivity of flame retardants and offers new strategy for designing advanced non-flammable electrolytes for safe LIBs.

Exploring the use of oligomeric carbonates as porogens and ion-conductors in phase-separated structural electrolytes for Lithium-ion batteries

Phase-separated structural battery electrolytes (SBEs) have the potential to enhance the mechanical stability of the electrolyte while maintaining a high ion conduction. This can be achieved via polymerization-induced phase separation (PIPS), which creates a two-phase system with a liquid electrolyte percolating a mesoporous thermoset. While previous studies have used commercially available liquid electrolytes, this study investigates the use of novel oligomeric carbonates to enhanced the safety of the SBEs. Increasing the carbonate chain length significantly enhances the thermal stability of the SBEs. Tuning the molecular structure of the liquid electrolyte has a significant effect on the PIPS process and SBE morphology. Using a combination of analyses on a series of wet and dried SBEs, the complex interplay between the phases is interpreted. When an increased pore size is achieved, it leads to a lower MacMullin number (NM). A conductivity of 2 × 10−5 S/cm with a NM=13 could be achieved, while maintaining a thermal stability up to 150 °C. The present study demonstrates a versatile approach to tailor this type of electrolyte.

Solution NMR of Battery Electrolytes: Assessing and Mitigating Spectral Broadening Caused by Transition Metal Dissolution.

NMR spectroscopy is a powerful tool that is commonly used to assess the degradation of lithium-ion battery electrolyte solutions. However, dissolution of paramagnetic Ni2+ and Mn2+ ions from cathode materials may affect the NMR spectra of the electrolyte solution, with the unpaired electron spins in these paramagnetic solutes inducing rapid nuclear relaxation and spectral broadening (and often peak shifts). This work establishes how dissolved Ni2+ and Mn2+ in LiPF6 electrolyte solutions affect 1H, 19F, and 31P NMR spectra of pristine and degraded electrolyte solutions, including whether the peaks from degradation species are at risk of being lost and whether the spectral broadening can be mitigated. Mn2+ is shown to cause far greater peak broadening than Ni2+, with the effect of Mn2+ observable at just 10 μM. Generally, 19F peaks from PF6 - degradation species are most affected by the presence of the paramagnetic metals, followed by 31P and 1H peaks. Surprisingly, when NMR solvents are added to acquire the spectra, the degree of broadening is heavily solvent-dependent, following the trend of solvent donor number (increased broadening with lower solvent donicity). Severe spectral broadening is shown to occur whether Mn is introduced via the salt Mn(TFSI)2 or is dissolved from LiMn2O4. We show that the weak 19F and 31P peaks in spectra of electrolyte samples containing micromolar levels of dissolved Mn2+ are broadened to an extent that they are no longer visible, but this broadening can be minimized by diluting electrolyte samples with a suitably coordinating NMR solvent. Li3PO4 addition to the sample is also shown to return 19F and 31P spectral resolution by precipitating Mn2+ out of electrolyte samples, although this method consumes any HF in the electrolyte solution.

EC modified PEO/PVDF-LLZO composite electrolytes for solid state lithium metal batteries

The polymer-ceramic composite electrolytes have great application potential for next-generation solid state lithium batteries, as they have the merits to eliminate the problem of liquid organic electrolytes and enhancing chemical/electrochemical stability. However, polymer-ceramic composite electrolytes show poor ionic conductivity, which greatly hinders their practical applications. In this work, the addition of plasticizer ethylene carbonate (EC) into polymer-ceramic composite electrolyte for lithium batteries effectively promotes the ionic conductivity. A high ionic conductivity can be attained by adding 40 wt% EC to the polyethylene oxide (PEO)/polyvinylidene fluoride (PVDF)-Li7La3Zr2O12 (LLZO) based polymer-ceramic composite electrolytes, which is 2.64 × 10−4 S cm−1 (tested at room temperature). Furthermore, the cell assembled with lithium metal anode, this composite electrolyte， and LiFePO4 cathode can work more than 80 cycles at room temperature (tested at 0.2 C). The battery delivers a high reversible specific capacity after 89 cycles, which is 119 mAh g−1.

Composition and Structure Design of Poly(vinylidene fluoride)‐Based Solid Polymer Electrolytes for Lithium Batteries

AbstractSolid‐state lithium batteries have become the focus of the next‐generation high‐safety lithium batteries due to their dimensional, thermal, and electrochemical stability. Thus, the progress of solid electrolytes with satisfactory comprehensive performances has become the key to promoting the development of solid batteries. Herein, poly(vinylidene fluoride) (PVDF) solid polymer electrolytes (SPEs) possess excellent flexibility, mechanical property, and high electrochemical and thermal stability, which show huge application potentiality in solid‐state lithium batteries and obtain extensive research. But the PVDF SPEs have been suffering from low ionic conductivity, high crystallinity, and low reactive sites. The development of PVDF‐based composite solid polymer electrolytes (CSPEs) has been confirmed to be a forceful strategy to optimize the performance of electrolytes. In this review, based on different design strategies, the recent progress of PVDF‐based SPEs is introduced in detail, especially in the mechanism of ionic conductivity enhancement and interface regulation by modified fillers. Besides, the applications of PVDF‐based SPEs in Li‐S and Li‐O2 battery systems are also introduced. Finally, this review presents some insights for promoting the development of high‐performance PVDF‐based SPEs.

Advanced Composite Solid Electrolytes for Lithium Batteries: Filler Dimensional Design and Ion Path Optimization.

Composite solid electrolytes are considered to be the crucial components of all-solid-state lithium batteries, which are viewed as the next-generation energy storage devices for high energy density and long working life. Numerous studies have shown that fillers in composite solid electrolytes can effectively improve the ion-transport behavior, the essence of which lies in the optimization of the ion-transport path in the electrolyte. The performance is closely related to the structure of the fillers and the interaction between fillers and other electrolyte components including polymer matrices and lithium salts. In this review, the dimensional design of fillers in advanced composite solid electrolytes involving 0D-2D nanofillers, and 3D continuous frameworks are focused on. The ion-transport mechanism and the interaction between fillers and other electrolyte components are highlighted. In addition, sandwich-structured composite solid electrolytes with fillers are also discussed. Strategies for the design of composite solid electrolytes with high room temperature ionic conductivity are summarized, aiming to assist target-oriented research for high-performance composite solid electrolytes.

Self-Healing Polymer Electrolytes for Next-Generation Lithium Batteries

The integration of polymer materials with self-healing features into advanced lithium batteries is a promising and attractive approach to mitigate degradation and, thus, improve the performance and reliability of batteries. Polymeric materials with an ability to autonomously repair themselves after damage may compensate for the mechanical rupture of an electrolyte, prevent the cracking and pulverization of electrodes or stabilize a solid electrolyte interface (SEI), thus prolonging the cycling lifetime of a battery while simultaneously tackling financial and safety issues. This paper comprehensively reviews various categories of self-healing polymer materials for application as electrolytes and adaptive coatings for electrodes in lithium-ion (LIBs) and lithium metal batteries (LMBs). We discuss the opportunities and current challenges in the development of self-healable polymeric materials for lithium batteries in terms of their synthesis, characterization and underlying self-healing mechanism, as well as performance, validation and optimization.

Electrochemical and Mechanical Performance According to Regulating Sintering Time of Cubic Li6.1Ga0.3La3Zr2O12 Solid Electrolyte

The solid-state electrolyte is a promising candidate to replace the liquid electrolytes in lithium ion batteries, although it has a fatal drawback of inferior ionic conductivity. Garnet-type LiLaZrO can be regarded as a favorable material for all-solid-state lithium batteries since it has better lithium ion kinetics, nonflammability, and outstanding electrochemical/thermal stability. The grain size is closely related to the microstructure, affecting the electrochemical and mechanical properties. Here, we control the grain size by adjusting the sintering time and demonstrate that Li6.1Ga0.3La3Zr2O12 (LGLZO) sintered at 1250 °C for 10 h delivers relative density of 97.5 ± 0.5%, hardness of 9.1 ± 0.46 GPa, ionic conductivities of 8.9 × 10–4 S/cm (Au/LGLZO/Au symmetric cell) and 4.2 × 10–5 S/cm (Li/LGLZO/Li symmetric cell), and critical current density of 0.58 mA/cm2, which are superior to those of LGLZO sintered for 20 h. Therefore, we can conclude that regulating sintering time is a simple and easy approach for high performance all-solid-state lithium ion batteries.

Revealing Surfactant Effect of Trifluoromethylbenzene in Medium-Concentrated PC Electrolyte for Advanced Lithium-Ion Batteries.

Despite wide-temperature tolerance and high-voltage compatibility, employing propylene carbonate (PC) as electrolyte in lithium-ion batteries (LIBs) is hampered by solvent co-intercalation and graphite exfoliation due to incompetent solvent-derived solid electrolyte interphase (SEI). Herein, trifluoromethylbenzene (PhCF3 ), featuring both specific adsorption and anion attraction, is utilized to regulate the interfacial behaviors and construct anion-induced SEI at low Li salts' concentration (<1m). The adsorbed PhCF3 , showing surfactant effect on graphite surface, induces preferential accumulation and facilitated decomposition of bis(fluorosulfonyl)imide anions (FSI- ) based on the adsorption-attraction-reduction mechanism. As a result, PhCF3 successfully ameliorates graphite exfoliation-induced cell failure in PC-based electrolyte and enables the practical operation of NCM613/graphite pouch cell with high reversibility at 4.35V (96% capacity retention over 300 cycles at 0.5C). This work constructs stable anion-derived SEI at low concentration of Li salt by regulating anions-co-solvents interaction and electrode/electrolyte interfacial chemistries.

Weak Solvent–Solvent Interaction Enables High Stability of Battery Electrolyte

Electrolytes play an important role in transporting metal ions (e.g., Li+) in metal ion batteries, while understanding the relationship between the electrolyte properties and behaviors is still challenging. Herein, we detect the existence of weak solvent–solvent interactions in electrolytes by nuclear magnetic resonance (NMR), particularly discovering that such interactions have a significant function of stabilizing the electrolytes, which has never been reported before. As a paradigm, we renovated the understanding of the role of ethylene carbonate (EC) solvent in the lithium-ion battery electrolyte. We find that the EC solvent can stabilize the linear carbonate solvent electrolyte, particularly the diethyl carbonate (DEC) electrolyte, by the weak intermolecular interactions, enhancing the energy difference between the orbitals of the Li+(EC)x(DEC)y complex, in turn demonstrating strong capability against reduction. Our viewpoint was further demonstrated in other metal ion batteries (e.g., Na+, K+), whose discovery is significant for designing electrolytes and in-depth understanding of the battery performance.

Origin and regulation of interfacial instability for nickel-rich cathodes and NASICON-type Li1+xAlxTi2−x(PO4)3 solid electrolytes in solid-state lithium batteries

Li1.3Al0.3Ti1.7(PO4)3 (LATP)-based all-solid-state lithium battery (ASSLB) assembled with Ni-rich layered cathode (NCM), of much interest because of its high energy–density and safety, presents many challenges, one of which is poor interfacial instability resulting in large interfacial resistance. Nevertheless, the mechanism of electrochemical side reactions on the interfacial deterioration hasn’t been much investigated specifically, despite their close relationships in electrochemical performance. Herein, we report that the fundamental origin of interfacial chemical reactions is the migration of Ni2+ from the nickel-rich cathodes to the NCM/LATP interface, for the first time, and the simultaneous chemical reaction with Ti4+ in LATP, followed by the decomposition of LATP. In view of this, an elaborately designed regulation strategy, in-situ construction of the layered perovskite La4NiLiO8 buffer layer, is proposed to effectively reduce the content of Ni2+ on the surface of the nickel-rich cathodes and alleviate the chemical reaction between Ni2+ and Ti4+, thereby improving the interfacial stability between NCM and LATP. As a result, the assembled ASSLBs with the La4NiLiO8 buffer layer exhibit high initial discharge capacity (171.49 mAh/g) and excellent cycling performance with 89.47 % capacity retention after 100 cycles at 0.1C.

Green recycling of short-circuited garnet-type electrolyte for high-performance solid-state lithium batteries

Solid-state lithium batteries (SSLBs) solve safety issues and are potentially energy-dense alternatives to next-generation energy storage systems. Battery green recycling routes are responsible for the widespread use of SSLBs due to minimizing environmental contamination, reducing production costs, and providing a sustainable solution for resources, e.g., saving rare earth elements (La, Ta, etc.). Herein, a solid-state recycling strategy is proposed to achieve green recycling of the crucial component solid-state electrolytes (SSEs) in spent SSLBs. The short-circuited garnet Li6.5La3Zr1.5Ta0.5O12 (LLZTO) is broken into fine particles and mixed with fresh particles to improve sintering activity and achieve high packing density. The continuous Li absorption process promotes sufficient grain fusion and guarantees the transformation from tetragonal phase to pure cubic phase for high-performance recycled LLZTO. The Li-ion conductivity reaches 5.80 × 10-4 S cm−1 with a relative density of 95.9%. Symmetric Li cell with as-recycled LLZTO shows long-term cycling stability for 700 h at 0.3 mA cm−2 without any voltage hysteresis. Full cell exhibits an excellent cycling performance with a discharge capacity of 141.5 mA h g−1 and a capacity retention of 92.1% after 400 cycles (0.2C). This work develops an environmentally friendly and economically controllable strategy to recycle SSE from spent SSLBs, guiding future directions of SSLBs large-scale industrial application and green recycling study.

A localized high concentration carboxylic ester-based electrolyte for high-voltage and low temperature lithium batteries

In this work, a methyl propionate (MP)/fluoroethylene carbonate (FEC)-based localized high concentration electrolyte with lithium difluoro(oxalato)borate (LiDFOB) as the additive is reported. The tuned solvation structure and the addition of LiDFOB enable fast desolvation process of Li+ and good formation of cathode/electrolyte interphase. This optimized electrolyte shows good compatibility with both lithium cobaltate (LCO) cathode and lithium metal anode, enabling 4.5 V Li/LCO cell to cycle 300 cycles at 1C (180 mAh g−1) rate with 87.7 % capacity retention. Even at 10C high-rate cycling, around 75.0 % of initial capacity is also achieved. In addition, it possesses decent conductivity and viscosity at low temperature, demonstrating the great low-temperature performance. It enables the high-loading Li/LCO cell to deliver 136.9 mAh g−1capacity at −70 °C, showing the great discharge performance and application potential at such low temperature. In addition, the cell with this electrolyte could even be cycled at −40 °C with 77.8 % capacity retention after 100 cycles. This work implements the high-voltage, high-rate and low-temperature functions of battery by choosing appropriate electrolyte component and tuning its formulation. This work provides an effective method for designing a multifunctional lithium battery electrolyte.