Solvation Chemistry Research Articles

High-Performance K Metal Batteries Enabled by Regulating an Electrolyte Solvation Structure

Batteries using a potassium metal (K-metal) anode are attention to a new type of low-cost and high-energy storage devices. However, the thermodynamic instability of the K-metal anode in organic electrolyte solutions causes uncontrolled growth of dendrites and parasitic reactions, which leads rapid capacity loss and low Coulombic efficiency.[1-4] In this presentation, I will introduce the advanced electrolyte using dual-salt for regulated solvation chemistry showing an improved the K-metal anode stability. Experimental and theoretical studies supported the details of solvation chemistry and results. Incorporating dual-salt into the electrolyte solution decreased the number of free solvent molecules surrounding the K+ leading to facile K+ desolvation as well as lowering the exchange current density improving the uniform K electrodeposition. Moreover, the modified electrolyte mitigates decomposition of the solvent molecules and leads to form enhanced mechanical rigidity of the SEI layer on the surface of the K–metal electrode with larger fraction of KF compound. Compared to previous studies, the K-metal anode using modified electrolyte shows long cycling stability at fast charge-discharge capability in symmetrical K | K cells. Even under high current density, the modified electrolyte ensures high areal capacity and an unprecedented lifespan with stable Coulombic efficiency for the K-metal full battery employing a sulfurized polyacrylonitrile cathode. M. Park, Y. Jeong, M. H. Alfaruqi, Y. Liu, X. Xu, S. Xiong, M.–G. Jung, H.–G. Jung, J. Kim, J.–Y. Hwang, Y.–K. Sun. Stable Solid Electrolyte Interphase for Long–Life Potassium Metal Batteries, ACS Energy Lett. 7 (2022) 401–409.Kim, W. Song, D.–Y. Son, L. K. One, Y. Qi. Lithium–Ion Batteries: Outlook on Present, Future, and Hybridized Technologies. J. Mater. Chem. A 7 (2019) 2942–2964.–H. Kim, G.–T. Park, B.–K. Son, G. W. Nam, J. Liu, L.–Y. Kuo, P. Kaghazchi, C. S. Yoon, Y.–K. Sun. Heuristic Solution for Achieving Long–Term Cycle Stability for Ni–Rich Layered Cathodes at Full Depth of Discharge, Nat. Energy 5 (2020) 860.–Y. Hwang, S.–T. Myung, Y.–K. Sun. Recent Progress in Rechargeable Potassim Batteries, Adv. Funct. Mater. 28 (2018) 1802938.

(Invited) Computationally Guided Design of Sustainable Chemistry for Low-Cost Battery Technologies

The ever-growing demand for storing electrical energy generated from intermittent source of renewable energy (e.g., sun, wind etc.) has necessitated development of new low-cost, safe, and sustainable battery systems that go beyond the conventional Li-ion technology. In this context, electrochemistry based on aluminum and iron – third and fourth most abundant elements on earth, respectively – offer the most promise. Unfortunately, long-standing issues with electrolyte design, cyclability, dendrite proliferation, and parasitic side-reactions has precluded deployment of rechargeable Al- or Fe- batteries. Most of the daunting issues stalling progress stem from dearth of atomic-scale understanding of solvation chemistry, ion-transport, chemical reactions, and material evolution in the bulk electrolyte, as well as electrode/electrolyte interfaces. In this talk, I will demonstrate how a synergistic integration of first-principles calculations, ab initio/classical reactive molecular dynamics simulations, electrochemical experiments, and spectroscopic measurements can pave the path towards advancing such understanding; and accelerate design of low-cost battery technologies. Specifically, I will showcase two recent successes of this approach, which led to (a) design of low-cost, fire-resistant inorganic molten-salt electrolytes containing AlnCl3n+1 – species, which allow fast de-solvation of Al3+ ions and prevent dendrite formation – both central for fast-charging Al-chalcogen batteries (200 C) with high cycle life, and (b) demonstration of a novel bi-directional Fe(OH)2/FeOOH redox chemistry facilitated by sulfate intercalation in Fe(OH)2, which drastically impairs parasitic hydrogen evolution, and Fe3O4 formation – consequently, enhancing capacity and cycle life of alkaline batteries. I will discuss these results in the context of accelerating design of new sustainable high-performance battery technologies for grid-storage.

Self-Purifying Primary Solvation Sheath Enables Stable Electrode-Electrolyte Interfaces for Nickel-Rich Cathodes.

Herein, we optimize the primary solvation sheath to investigate the fundamental correlation between battery performance and electrode-electrolyte interfacial properties through electrolyte solvation chemistry. Experimental and theoretical analyses reveal that the primary solvation sheath with a self-purifying feature can "positively" scavenge both the HF and PF5 (hydrolysis of ion-paired LiPF6), stabilize the PF6 anion-derived electrode-electrolyte interfaces, and thus boost the cycling performances. Being attributed with these superiorities, the NCM811//Li Li metal battery (LMB) with the electrolyte containing the optimized solvation sheath delivers 99.9% capacity retention at 2.5 C after 250 cycles. To circumvent the impact of excess Li content of Li metal on the performance of NCM811 cathode, the as-fabricated NCM811//graphite Li ion battery (LIB) also delivers a high-capacity retention of 90.1% from the 5th to the 100th cycle at 1 C. This work sheds light on the strong ability of the primary solvation sheath to regulate cathode interfacial properties.

Electrolyte‐Mediated Misconception of Carbon‐Based Electrode Performance and Beyond in Metal‐Ion Batteries

AbstractA half‐cell that is composed of electrode and metal (e.g., lithium) is the most classical model for examining electrode performance in battery community, by which the voltage versus capacity profile is the important indicator. However, it is found that these results are not all reliable, as a misconception of electrode performance can be caused once the electrolyte is chemically unstable. As a paradigm, it is demonstrated that the diethyl carbonate (DEC) solvent can chemically react with lithium metal to form insoluble and soluble by‐products, which can accumulate on the lithium anode to influence the lithium potential and/or migrate to the counter electrode to proceed with the uncompleted electrochemical reactions. The resultant voltage‐capacity profile cannot reflect the actual electrode performance, such as the lithium storing capability within the graphite. The reason for this phenomenon is elucidated based on solvation chemistry, particularly the mechanism of mitigating it by introducing ethylene carbonatesolvent to form new hydrogen bonds. The viewpoint is further verified by employing the full cell and also extended in sodium and potassium batteries. This study shows the necessity of discerning the reliability of electrode performance and also sheds light on the importance of designing a compatible electrolyte to examine electrode performance.

Microscopic-Level Insights into Solvation Chemistry for Nonsolvating Diluents Enabling High-Voltage/Rate Aqueous Supercapacitors.

Localized "water-in-salt" (LWIS) electrolytes are promising candidates for the next generation of high-voltage aqueous electrolytes with low viscosity/salt beyond high-salt electrolytes. An effective yet high-function diluent mainly determines the properties of LWIS electrolytes, being a key issue. Herein, the donor number of solvents is identified to serve as a descriptor of interaction intensity between solvents and salts to screen the organic diluents having few impacts on the solvation microenvironment and intrinsic properties of the original high-salt electrolyte, further leading to the construction of a novel low-viscosity electrolyte with a low dosage of the LiNO3 salt and well-kept intrinsic Li+-NO3--H2O clusters. Nonsolvating diluents, especially acetonitrile (AN) that has never been reported previously, are presented with the capability of constructing a LWIS electrolyte with nonflammability, electrode-philic features, lower viscosity, decreased salt dosage, and a greatly enhanced ion diffusion coefficient by about 280 times. This strongly relies on a huge difference of about 5000 times in coordination and solubility between AN and H2O toward LiNO3 (0.05 vs 25 mol kgsolvent-1) and the moderate interaction between AN and H2O. Multi-spectroscopic techniques and molecular dynamics simulations uncover the solvation chemistry at the microscopic level and the interplay among cations, anions, and H2O without/with AN. The identified unique diluting and nonsolvating effects of AN reveal well-maintained cation-anion-H2O clusters and enhanced intermolecular hydrogen bonding between AN and H2O, further reinforcing the H2O stability and expanding the voltage window up to 3.28 V. This is a breakthrough that is far beyond high-viscosity/salt electrolytes for high-voltage and high-rate aqueous supercapacitors.

Stable Li Metal Anode Enabled by Simultaneous Regulation of Electrolyte Solvation Chemistry and The Solid Electrolyte Interphase

AbstractThe application of Li metal batteries is hindered by the uncontrollable growth of Li dendrites due to the lack of control over Li ion transfer and the formation of solid electrolyte interphase (SEI). Herein, polypropylene (PP) separator modified with acyclic polyaminoborane (PAB, (NH2‐BH2)n) and polyiminoborane (PIB, (NH═BH)n) is developed to regulate electrolyte solvation chemistry and simultaneously facilitate the construction of robust SEI. The mediating effect of PAB and PIB promotes favorable formation of (O)2Li+N to weaken the Li bonds between Li ion and solvent in the electrolyte, which homogenizes Li ion diffusion and reduces the desolvation barrier of Li ions. Additionally, the increase of anions content in the solvation sheath and the reaction between Li metal and PAB and PIB can induce the formation of [LiNBH]n‐enhanced SEI enriched with LiF and Li3N that have Li ion conductivity and mechanical strength to tolerate the volume change of Li metal anode. Therefore, the symmetric cell exhibits a cycling lifetime of over 4000 h.

Anion Receptor Weakens ClO4− Solvation for High‐Temperature Sodium‐Ion Batteries

AbstractSodium‐ion batteries (SIBs) with wide operating temperature are regarded as promising candidates for large‐scale energy storage systems. However, SIBs operating under elevated temperature aggravate the electrolyte decomposition with unstable cathode‐electrolyte interphase (CEI), causing a rapid capacity degradation. Herein, anion receptor tris(pentafluorophenyl)borane (TPFPB) is selected as electrolyte additive to construct robust NaF‐rich CEI. The strong interactions between anion and TPFPB via the electron‐deficient boron atoms weaken ClO4− solvation and promote the coordination capability between solvents and Na+ cations, demonstrating greatly improved oxidative stability. Na3V2(PO4)3 cathode in TPFPB‐containing electrolyte delivers long‐term stability with a capacity retention of 86.9% after 100 cycles at a high cut‐off voltage of 4.2 V (vs. Na+/Na) and a high temperature of 60 °C. Besides, TPFPB also works well with enhanced performance over a temperature range from −30 to 60 °C. This study proposes a prospective method by manipulating the solvation chemistry for constructing high‐temperature rechargeable SIBs.

A Novel Potassium Salt Regulated Solvation Chemistry Enabling Excellent Li-Anode Protection in Carbonate Electrolytes.

In lithium-metal batteries (LMBs), the compatibility of Li anode and conventional lithium hexafluorophosphate-(LiPF6 ) carbonate electrolyte is poor owing to the severe parasitic reactions. Herein, to resolve this issue, a delicately designed additive of potassium perfluoropinacolatoborate (KFPB) is unprecedentedly synthesized. On the one hand, KFPB additive can regulate the solvation structure of the carbonate electrolyte, promoting the formation of Li+ FPB- and K+ PF6 - ion pairs with lower lowest unoccupied molecular orbital (LUMO) energy levels. On the other hand, FPB- anion possesses strong adsorption ability on Li anode. Thus, anions can preferentially adsorb and decompose on the Li-anode surface to form a conductive and robust solid-electrolyte interphase (SEI) layer. Only with a trace amount of KFPB additive (0.03m) in the carbonate electrolyte, Li dendrites' growth can be totally suppressed, and Li||Cu and Li||Li half cells exhibit excellent Li-plating/stripping stability upon cycling. Encouragingly, KFPB-assisted carbonate electrolyte enables high areal capacity LiCoO2 ||Li, LiNi0.8 Co0.1 Mn0.1 O2 (NCM811)||Li, and LiNi0.8 Co0.05 Al0.15 O2 (NCA)||Li LMBs with superior cycling stability, showing its excellent universality. This work reveals the importance of designing novel additives to regulate the solvation structure of carbonate electrolytes in improving its interface compatibility with the Li anode.

Electrolyte solvation chemistry to construct an anion-tuned interphase for stable high-temperature lithium metal batteries

Lithium metal batteries are regarded as promising alternative next-generation energy storage systems. However, the unstable anode interphase results in dendrite growth and irreversible lithium consumption with low Coulombic efficiency (CE). Herein, we rationally design a Li+ coordination structure via electrolyte solvation chemistry. Nitrate anions are aggregated in the solvation sheath, even at low concentration in a solvent with moderate solvation ability, which promotes Li+ desolvation and constructs a nitrate anion-tuned interphase. Meanwhile, a high-donor-number solvent is introduced as an additive to strongly coordinate with Li+, which accelerates the ion-transfer kinetics and rate performance. This not only results in micro-sized lithium deposition and a high CE of 99.5% over 3500 ​h, but also enables superior anode stability even under 50% depth plating/stripping and with a lean electrolyte of 3 ​g ​Ah−1 at 50 ​°C. A lithium–sulfur battery exhibits a prolonged lifespan of 2000 cycles with an average CE of 100%. A full battery using 1x excess lithium exhibits a high capacity near 1600 ​mAh ​gS−1 for 100 cycles without capacity loss. Moreover, a 0.55 ​Ah pouch cell delivers a reversible energy density of 423 ​Wh ​kg−1 based on these electrodes and electrolyte.

Regulating the Solvation Structure of Electrolyte via Dual–Salt Combination for Stable Potassium Metal Batteries

Batteries using potassium metal (K-metal) anode are considered a new type of low-cost and high-energy storage device. However, the thermodynamic instability of the K-metal anode in organic electrolyte solutions causes uncontrolled dendritic growth and parasitic reactions, leading to rapid capacity loss and low Coulombic efficiency of K-metal batteries. Herein, an advanced electrolyte comprising 1M potassium bis(fluorosulfonyl)imide (KFSI) + 0.05M potassium hexafluorophosphate (KPF6 ) dissolved in dimethoxyethane (DME) is introduced as a simple and effective strategy of regulated solvation chemistry, showing an enhanced interfacial stability of the K-metal anode. Incorporating 0.05M KPF6 into the 1M KFSI in DME electrolyte solution decreases the number of solvent molecules surrounding the K ion and simultaneously leads to facile K+ de-solvation. During the electrodeposition process, these unique features can lower the exchange current density between the electrolyte and K-metal anode, thereby improving the uniformity of K electrodeposition, as well as potentially suppressing dendritic growth. Even under a high current density of 4mA cm-2 , the K-metal anode in 0.05M KPF6 -containing electrolyte ensures high areal capacity and an unprecedented lifespan with stable Coulombic efficiency in both symmetrical half-cells and full-cells employing a sulfurized polyacrylonitrile cathode.

Enhanced Anion‐Derived Inorganic‐Dominated Solid Electrolyte Interphases for High‐Rate and Stable Sodium Storage

It is highly desirable for the promising sodium storage possessing high rate and long stable capability, which are mainly hindered by the unstable yet conventional solvent‐derived organic‐rich solid electrolyte interphases. Herein, an electrolyte solvation chemistry is elaborately manipulated to produce an enhanced anion‐derived and inorganic components‐dominated solid electrolyte interphases by introducing a low permittivity (4.33) bis(2,2,2‐trifluoroethyl) ether diluent into the sodium bis(trifluoromethylsulfonyl)imide‐dimethoxyethane‐based high concentration electrolyte to obtain a localized high concentration electrolyte. The bis(2,2,2‐trifluoroethyl) ether breaks the balance of original cation solvation structure and tends to interact with Na+‐coordinated dimethoxyethane solvent rather than Na+ in high concentration electrolyte, leaving an enhanced Coulombic interaction between Na+ and (FSO2)2N−, and more (FSO2)2N− can enter the Na+ solvation shell, forming a further increased number of Na+‐(FSO2)2N−‐dimethoxyethane clusters (from 82.0% for high concentration electrolyte to 94.3% for localized high concentration electrolyte) at a low salt dosage. The preferential reduction of this (FSO2)2N−‐enriched clusters rather than the dimethoxyethane‐dominated Na+ solvation structure produces an enhanced anion‐derived and inorganic components‐dominated solid electrolyte interphases. The reversible charge storage process of Na is decoupled by operando Raman along with a shift of D and G peaks. Benefiting from the enhanced anion‐derived electrode‐electrolyte interface, the commercial hard carbon anode in localized high concentration electrolyte shows a well rate capability (5 A g−1, 70 mAh g−1), cycle performance and stability (85% of initial capacity after 700 cycles) in comparison to that of high concentration electrolyte (68%) and low concentration electrolyte (only 5% after 400 cycles), indicative of uniqueness and superiorities towards stable Na storage.

Regulating the solvation chemistry of non-flammable high voltage electrolyte through salt-solvent ratio modulation

Boosting the energy density and safety issue of lithium-ion batteries has become ever more important to satisfy the diverse applications such as energy storage and mobile electronic devices. Herein, we present a new high voltage polyether-based electrolyte (HVPEE) by solvation structure design that can endure high-voltage operations and also possess non-flammable features. Especially, HVPEEs show better compatibility and stability with electrode than conventional electrolyte. We find that the solvent separated ion pair (SSIP) and contact ion pair (CIP) dominate the ion–solvent structure of HVPEEs, rather than the free solvent and ions. In this way, the oxidative decomposition of HVPEE on the cathode interface can be suppressed significantly due to the reduced highest occupied molecular orbital of SSIP complex structure than that of free TFSI-. As a result, the oxidation voltage can achieve as high as 5.35 V when the ether group/Li is optimized at 10/1 in the HVPEE, enabling the LiFePO4//Li full cells deliver a capacity of 165 mA h g−1 with a capacity retention of 98 % after 200 cycles. Moreover, when the cut-off voltage is 4.5 V, the discharge capacity of the LiNi0.6Mn0.2Co0.2O2//Li full cell can reach 170 mA h g−1.

Tailoring solvation chemistry in carbonate electrolytes for all-climate, high-voltage lithium-rich batteries

High-voltage Li-rich layered oxide materials (LLOs) are considered as the promising next-generation cathode materials because of their high energy density and low cost. However, their electrochemical performance continues to deteriorate under high voltages when using traditional lithium hexafluorophosphate (LiPF6)-based carbonate electrolytes, mostly due to the detrimental reactions with free anions, unstable electrode interface and limited Li+ kinetic process. Here, we demonstrate a highly oxidation-resistant carbonate electrolyte by incorporating multifunctional lithium difluoro(oxalato)borate (LiDFOB) and Tris(trimethylsilyl) Phosphite (TMSPi) additives. It is discovered that the introduction of LiDFOB and TMSPi can manipulate the electrolyte solvation structure by reducing the number of coordinated solvent molecules and free PF6−anions at the electrolyte-electrode interface, thus promoting the desolvation process of Li+, suppressing the generation of harmful HF species and conducive to forming a thin and robust cathode electrolyte interphase (CEI) layer. As a result, the Li||LLO cells with dual additives show excellent cycle stability and improved rate capability in a wide temperature ranged from -20 °C to 55 °C, and the retention rate of LLO||graphite pouch cell (2.5 Ah) using EEDB-TMSPi electrolyte is up to 91.1% after 200 cycles. It is anticipated that the work provides a promising strategy for realizing long-cycle stability of layered cathode materials under high-voltage and wide-temperature conditions.

Insights into the solvation chemistry in liquid electrolytes for lithium-based rechargeable batteries.

Lithium-based rechargeable batteries have dominated the energy storage field and attracted considerable research interest due to their excellent electrochemical performance. As indispensable and ubiquitous components, electrolytes play a pivotal role in not only transporting lithium ions, but also expanding the electrochemical stable potential window, suppressing the side reactions, and manipulating the redox mechanism, all of which are closely associated with the behavior of solvation chemistry in electrolytes. Thus, comprehensively understanding the solvation chemistry in electrolytes is of significant importance. Here we critically reviewed the development of electrolytes in various lithium-based rechargeable batteries including lithium-metal batteries (LMBs), nonaqueous lithium-ion batteries (LIBs), lithium-sulfur batteries (LSBs), lithium-oxygen batteries (LOBs), and aqueous lithium-ion batteries (ALIBs), and emphasized the effects of interactions between cations, anions, and solvents on solvation chemistry, and functions of solvation chemistry in different types of electrolytes (strong solvating electrolytes, moderate solvating electrolytes, and weak solvating electrolytes) on the electrochemical performance and redox mechanism in the abovementioned rechargeable batteries. Specifically, the significant effects of solvation chemistry on the stability of electrode-electrolyte interphases, suppression of lithium dendrites in LMBs, inhibition of the co-intercalation of solvents in LIBs, improvement of anodic stability at high cut-off voltages in LMBs, LIBs and ALIBs, regulation of redox pathways in LSBs and LOBs, and inhibition of hydrogen/oxygen evolution reactions in LOBs are thoroughly summarized. Finally, the review concludes with a prospective outlook, where practical issues of electrolytes, advanced in situ/operando techniques to illustrate the mechanism of solvation chemistry, and advanced theoretical calculation and simulation techniques such as "material knowledge informed machine learning" and "artificial intelligence (AI) + big data" driven strategies for high-performance electrolytes have been proposed.

A bio-inspired electrolyte with in situ repair of Zn surface cracks and regulation of Zn ion solvation chemistry to enable long life and deep-cycling zinc metal batteries

A bio-inspired electrolyte was first designed with tetraethyl orthosilicate (TEOS) additive as a “healing agent” to in situ repair the Zn surface crack and modulate the Zn2+ solvation chemistry, rendering long-life and deep-cycling Zn metal anodes.

A hydrated deep eutectic electrolyte with finely-tuned solvation chemistry for high-performance zinc-ion batteries

A hydrated deep eutectic electrolyte with a water-deficient solvation structure and reduced free water in bulk solution is proposed, resulting in highly reversible and stable Zn anodes.

(Invited) Fire-Extinguishing, Recyclable Liquefied Gas Electrolytes for Temperature-Resilience Lithium Metal Batteries

High energy density, improved safety, temperature resilience and sustainability are desirable properties for lithium battery electrolytes, yet these metrics are rarely achieved simultaneously. Inspired by the compositions of clean fire extinguishing agents, we demonstrate inherently safe liquefied gas electrolytes (LGE) based on 1,1,1,2-tetrafluoroethane (TFE) and pentafluoroethane (PFE) that maintain > 3 mS cm-1 ionic conductivity from –78 to +80 °C. As a result of beneficial solvation chemistry and a fluorine-rich environment, Li cycling at > 99% Coulombic efficiency for over 200 cycles at 3 mA cm-2 and 3 mAh cm-2 was demonstrated in addition to stable cycling of Li/NMC622 full batteries from –60 to +55 °C. Additionally, we demonstrate that the vapor pressure-temperature relationship unique to LGE systems allows for a one-step solvent recycling process, which promises sustainable operation at scale. This work provides a route to sustainable, temperature resilient lithium metal batteries with fire-extinguishing properties that maintain state-of-the-art electrochemical performance.

Weakening the Solvating Power of Solvents to Encapsulate Lithium Polysulfides Enables Long-Cycling Lithium-Sulfur Batteries.

Long cycling lifespan is a prerequisite for practical lithium-sulfur batteries yet is restricted by side reactions between soluble polysulfides and the lithium-metal anode. The regulation on solvation structure of polysulfides renders encapsulating polysulfides electrolytes (EPSE) as a promising solution to suppress the parasitic reactions. The solvating power of the solvents in the outer solvent shell of lithium polysulfides is critical for the encapsulation effect of EPSE. Herein, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether(HFE) is demonstrated as a superior outer-shell solvent to construct EPSE. Based on thelarge steric hindrance of the fluorohydrocarbon chains, the electron-withdrawing perfluoro segment (CF2  further endows HFE with prominently weak solvating power. The HFE-EPSE improves the lifespan from 54 to 135 cycles for lithium-sulfur batteries with an ultrathin lithium-metal anode (50µm) and high-areal-loading sulfur cathode (4.4mg cm-2 ). Furthermore, a 334Wh kg-1 lithium-sulfur pouch cell (2.4 Ah level) with HFE-EPSE stably undergoes 25 cycles. This work demonstrates the role of weakening solvating power of outer-shell solvents to construct superior EPSE and inspires the significance of the solvation chemistry of polysulfides to achieve practical lithium-sulfur batteries.

Unlocking the Low-Temperature Potential of Propylene Carbonate to -30 °C via N-Methylpyrrolidone.

As the one of the core electrolyte solvents for Li-ion batteries, ethylene carbonate (EC) is still irreplaceable for its balance of ionic conductivity and interfacial stability. However, it also defines the boundary for the low-temperature performance of the battery because of its high melting point (36.4 °C). Its immediate sibling, propylene carbonate (PC), has been proposed as its convenient substitute for its much lower melting point (-48.8 °C). Unfortunately, the propylene carbonate-graphite anode interfacial problem has been a puzzle since the days before the advent of the Li-ion battery. Among various strategies to mitigate this issue, blending in selected strong solvents for Li+ to bring down propylene carbonate's presence in the solvation shell has been proven often effective but the mechanism from the interfacial chemistry perspective remains unexplored. Herein, we study a new cosolvent, N-methylpyrrolidone (NMP), for PC-based electrolyte and observe excellent reversibility that approaches the commercial standard, far beyond the similar systems in the past. To understand the mechanism, solvation chemistry analysis and in situ characterizations are undertaken to probe the interfacial chemistry from various standpoints. Based on these results and further theoretical calculation, it is proposed that N-methylpyrrolidone has mediated the reduction process of propylene carbonate to facilitate the growth of a solid electrolyte interphase (SEI) layer akin to ethylene carbonate. Finally, an electrolyte has also been successfully developed based on the NMP/PC couple to outperform the commercial electrolyte by a clear margin when tested in a LiNi0.8Co0.1Mn0.1O2-graphite cell at -30 °C.

Solvation chemistry of electrolytes for stable anodes of lithium metal batteries

Solvation chemistry of electrolytes for stable anodes of lithium metal batteries