Toward the Integration of a Silicon/Graphite Anode-Based Lithium-Ion Battery in Photovoltaic Charging Battery Systems.

Solar photovoltaic (PV) energy generation is highly dependent on weather conditions and only applicable when the sun is shining during the daytime, leading to a mismatch between demand and supply. Merging PVs with battery storage is the straightforward route to counteract the intermittent nature of solar generation. Capacity (or energy density), overall efficiency, and stability at elevated temperatures are among key battery performance metrics for an integrated PV-battery system. The performance of high-capacity silicon (Si)/graphite (Gr) anode and LiNi0.6Mn0.2Co0.2O2 (NMC622) cathode cells at room temperature, 45, and 60 °C working temperatures for PV modules are explored. The electrochemical performance of both half and full cells are tested using a specially formulated electrolyte, 1 M LiPF6 in ethylene carbonate: diethyl carbonate, with 5 wt % fluoroethylene carbonate, 2 wt % vinylene carbonate, and 1 wt % (2-cyanoethyl)triethoxysilane. To demonstrate solar charging, perovskite solar cells (PSCs) are coupled to the developed batteries, following the evaluation of each device. An overall efficiency of 8.74% under standard PV test conditions is obtained for the PSC charged lithium-ion battery via the direct-current-direct-current converter, showing the promising applicability of silicon/graphite-based anodes in the PV-battery integrated system.

Production of high-energy Li-ion batteries comprising silicon-containing anodes and insertion-type cathodes.

Rechargeable Li-based battery technologies utilising silicon, silicon-based, and Si-derivative anodes coupled with high-capacity/high-voltage insertion-type cathodes have reaped significant interest from both academic and industrial sectors. This stems from their practically achievable energy density, offering a new avenue towards the mass-market adoption of electric vehicles and renewable energy sources. Nevertheless, such high-energy systems are limited by their complex chemistry and intrinsic drawbacks. From this perspective, we present the progress, current status, prevailing challenges and mitigating strategies of Li-based battery systems comprising silicon-containing anodes and insertion-type cathodes. This is accompanied by an assessment of their potential to meet the targets for evolving volume- and weight-sensitive applications such as electro-mobility.

From Solid-Solution Electrodes and the Rocking-Chair Concept to Today's Batteries.

Lithium-ion batteries (LIBs) have become ubiquitous power sources for small electronic devices, electric vehicles, and stationary energy storage systems. Despite the success of LIBs which is acknowledged by their increasing commodity market, the historical evolution of the chemistry behind the LIB technologies is laden with obstacles and yet to be unambiguously documented. This Viewpoint outlines chronologically the most essential findings related to today's LIBs, including commercial electrode and electrolyte materials, but furthermore also depicts how the today popular and widely emerging solid-state batteries were instrumental at very early stages in the development of LIBs.

Understanding the Electrode/Electrolyte Interface Layer on the Li-Rich Nickel Manganese Cobalt Layered Oxide Cathode by XPS.

Layered lithium-rich nickel manganese cobalt oxide (LR-NMC) represents one of the most promising cathode materials for application in high energy density lithium-ion batteries. The extraordinary capacity delivered derives from a combination of both cationic and anionic redox processes. However, the latter ones lead to oxygen evolution which triggers structural degradation and electrode/electrolyte interface (EEI) instability that hinders the use of LR-NMC in practical application. In this work, we investigate the surface chemistry of LR-NMC and its evolution upon different conditions to give further insights into the processes occurring at the EEI. X-ray photoelectron spectroscopy studies reveal that once the organic component of the layer is formed, it remains stable independently on the higher cutoff voltage applied, while continuous growth of inorganics along with oxygen evolution occurs. The results performed on lithiated and delithiated LR-NMC surfaces indicate an instability of the EEI layer formed at high voltages, which undergoes a partial decomposition. Furthermore, the tris(pentafluorophenyl)borane electrolyte additive simultaneously prevents excess LiF formation and changes the chemical composition of the EEI layer. The latter is characterized by a higher amount of poly(ethylene oxide) oligomer species and LixPOyFz formation. In addition, the presence of boron-containing compounds in the EEI layer cannot be excluded, which may be also responsible of the increased thickness of the EEI layer. Finally, fast kinetics at elevated temperatures exacerbate the salt decomposition which results in the formation of an EEI which is thicker and richer in LiF.

Confronting the Challenges of Next-Generation Silicon Anode-Based Lithium-Ion Batteries: Role of Designer Electrolyte Additives and Polymeric Binders.

Silicon has emerged as the next-generation anode material for high-capacity lithium-ion batteries (LIBs). It is currently of scientific and practical interest to encounter increasingly growing demands for high energy/power density electrochemical energy-storage devices for use in electric vehicles (xEVs), renewable energy sources, and smart grid/utility applications. Improvements to existing conventional LIBs are required to provide higher energy, longer cycle lives. This is attributed to its unparalleled theoretical capacity (4200 mAh g-1 for Li4.4 Si), which is approximately 10 times higher than that of a state-of-the-art graphitic anode (372 mAh g-1 for LiC6 ), with a suitable operating voltage, natural abundance, environmental benignity, nontoxicity, high safety, and so forth. However, despite the overwhelming beneficial features, the practical integration of LIBs containing a silicon anode beyond the commercial niche is hampered by unavoidable challenges, such as excessive volume changes during the (de-)alloying process, inherently low electrical and ionic conductivities, an unstable solid-electrolyte interphase, and electrolyte drying out. Among various extenuating strategies, non-electrode factors encompassing electrolyte additives and polymeric binders are regarded as the most economical, and effective approaches towards circumventing these disadvantages are in short supply. With the aim of providing an in-depth insight into rapidly growing accounts of electrolyte additives and binders for use with silicon anode-based LIBs, this Review assesses the current state of the art of research and thereby examines opportunities to open up new avenues for the practical realization of these silicon anode-based LIBs.

Ultrahigh Performance All Solid-State Lithium Sulfur Batteries: Salt Anion's Chemistry-Induced Anomalous Synergistic Effect.

With a remarkably higher theoretical energy density compared to lithium-ion batteries (LIBs) and abundance of elemental sulfur, lithium sulfur (Li-S) batteries have emerged as one of the most promising alternatives among all the post LIB technologies. In particular, the coupling of solid polymer electrolytes (SPEs) with the cell chemistry of Li-S batteries enables a safe and high-capacity electrochemical energy storage system, due to the better processability and less flammability of SPEs compared to liquid electrolytes. However, the practical deployment of all solid-state Li-S batteries (ASSLSBs) containing SPEs is largely hindered by the low accessibility of active materials and side reactions of soluble polysulfide species, resulting in a poor specific capacity and cyclability. In the present work, an ultrahigh performance of ASSLSBs is obtained via an anomalous synergistic effect between (fluorosulfonyl)(trifluoromethanesulfonyl)imide anions inherited from the design of lithium salts in SPEs and the polysulfide species formed during the cycling. The corresponding Li-S cells deliver high specific/areal capacity (1394 mAh gsulfur-1, 1.2 mAh cm-2), good Coulombic efficiency, and superior rate capability (∼800 mAh gsulfur-1 after 60 cycles). These results imply the importance of the molecular structure of lithium salts in ASSLSBs and pave a way for future development of safe and cost-effective Li-S batteries.

Electrolyte Additives for Room-Temperature, Sodium-Based, Rechargeable Batteries.

Owing to resource abundance, and hence, a reduction in cost, wider global distribution, environmental benignity, and sustainability, sodium-based, rechargeable batteries are believed to be the most feasible and enthralling energy-storage devices. Accordingly, they have recently attracted attention from both the scientific and industrial communities. However, to compete with and exceed dominating lithium-ion technologies, breakthrough research is urgently needed. Among all non-electrode components of the sodium-based battery system, the electrolyte is considered to be the most critical element, and its tailored design and formulation is of top priority. The incorporation of a small dose of foreign molecules, called additives, brings vast, salient benefits to the electrolytes. Thus, this review presents progress in electrolyte additives for room-temperature, sodium-based, rechargeable batteries, by enlisting sodium-ion, Na-O2 /air, Na-S, and sodium-intercalated cathode type-based batteries.

Electrolyte Additives for Lithium Metal Anodes and Rechargeable Lithium Metal Batteries: Progress and Perspectives.

Lithium metal (Li0 ) rechargeable batteries (LMBs), such as systems with a Li0 anode and intercalation and/or conversion type cathode, lithium-sulfur (Li-S), and lithium-oxygen (O2 )/air (Li-O2 /air) batteries, are becoming increasingly important for electrifying the modern transportation system, with the aim of sustainable mobility. Although some rechargeable LMBs (e.g. Li0 /LiFePO4 batteries from Bolloré Bluecar, Li-S batteries from OXIS Energy and Sion Power) are already commercially viable in niche applications, their large-scale deployment is hampered by a number of formidable challenges, including growth of lithium dendrites, electrolyte instability towards high voltage intercalation-type cathodes, the poor electronic and ionic conductivities of sulfur (S8 ) and O2 , as well as their corresponding reduction products (e.g. Li2 S and Li2 O), dissolution, and shuttling of polysulfide (PS) intermediates. This leads to a short lifecycle, low coulombic/energy efficiency, poor safety, and a high self-discharge rate. The use of electrolyte additives is considered one of the most economical and effective approaches for circumventing these problems. This Review gives an overview of the various functional additives that are being applied and aims to stimulate new avenues for the practical realization of these appealing devices.

Lithium Azide as an Electrolyte Additive for All-Solid-State Lithium-Sulfur Batteries.

Of the various beyond-lithium-ion battery technologies, lithium-sulfur (Li-S) batteries have an appealing theoretical energy density and are being intensely investigated as next-generation rechargeable lithium-metal batteries. However, the stability of the lithium-metal (Li°) anode is among the most urgent challenges that need to be addressed to ensure the long-term stability of Li-S batteries. Herein, we report lithium azide (LiN3 ) as a novel electrolyte additive for all-solid-state Li-S batteries (ASSLSBs). It results in the formation of a thin, compact and highly conductive passivation layer on the Li° anode, thereby avoiding dendrite formation, and polysulfide shuttling. It greatly enhances the cycling performance, Coulombic and energy efficiencies of ASSLSBs, outperforming the state-of-the-art additive lithium nitrate (LiNO3 ).

Polymer-Rich Composite Electrolytes for All-Solid-State Li-S Cells.

Polymer-rich composite electrolytes with lithium bis(fluorosulfonyl)imide/poly(ethylene oxide) (LiFSI/PEO) containing either Li-ion conducting glass ceramic (LICGC) or inorganic Al2O3 fillers are investigated in all-solid-state Li-S cells. In the presence of the fillers, the ionic conductivity of the composite polymer electrolytes (CPEs) does not increase compared to the plain LiFSI/PEO electrolyte at various tested temperatures. The CPE with Al2O3 fillers improves the stability of the Li/electrolyte interface, while the Li-S cell with a LICGC-based CPE delivers high sulfur utilization of 1111 mAh g-1 and areal capacity of 1.14 mAh cm-2. In particular, the cell performance gets further enhanced when combining these two CPEs (Li | Al2O3-CPE/LICGC-CPE | S), reaching a capacity of 518 mAh g-1 and 0.53 mAh cm-2 with Coulombic efficiency higher than 99% at the end of 50 cycles at 70 °C. This study shows that the CPEs can be promising electrolyte candidates to develop safe and high-performance all-solid-state Li-S batteries.

Comprehensive Insights into the Thermal Stability, Biodegradability, and Combustion Chemistry of Pyrrolidinium-Based Ionic Liquids.

The use of ionic liquids (ILs) as advanced electrolyte components in electrochemical energy-storage devices is one of the most appealing and emerging options. However, although ILs are hailed as safer and eco-friendly electrolytes, to overcome the limitations imposed by the highly volatile/combustible carbonate-based electrolytes, full-scale and precise appraisal of their overall safety levels under abuse conditions still needs to be fully addressed. With the aim of providing this level of information on the thermal and chemical stabilities, as well as actual fire hazards, herein, a detailed investigation of the short- and long-term thermal stabilities, biodegradability, and combustion behavior of various pyrrolidinium-based ILs, with different alkyl chain lengths, counteranions, and cations, as well as the effect of doping with lithium salts, is described.

In-Depth Interfacial Chemistry and Reactivity Focused Investigation of Lithium-Imide- and Lithium-Imidazole-Based Electrolytes.

A comparative and in-depth investigation on the reactivity of various Li-based electrolytes and of the solid electrolyte interface (SEI) formed at graphite electrode is carried out using X-ray photoelectron spectroscopy (XPS), chemical simulation test, and differential scanning calorimetry (DSC). The electrolytes investigated include LiX (X = PF6, TFSI, TDI, FSI, and FTFSI), dissolved in EC-DMC. The reactivity and SEI nature of electrolytes containing the relatively new imide (LiFSI and LiFTFSI) and imidazole (LiTDI) salts are evaluated and compared to those of well-researched LiPF6(-) and LiTFSI-based electrolytes. The thermal reactivity of LixC6 in the various electrolytes is found to be in the order of LiFSI > LiTDI > LiTFSI > LiFTFSI > LiPF6 and LiFSI > LiFTFSI > LiPF6 > LiTFSI > LiTDI in terms of onset exothermic temperature and total heat generated, respectively. Surface and depth-profiling XPS analysis of the SEI formed with the diverse electrolyte formulations provide insight into the differences and similarities (composition, thickness, and evolution, etc.) emanating from the structure of the various salt anions.

Comprehensive Insights into the Reactivity of Electrolytes Based on Sodium Ions.

We report a systematic investigation of Na-based electrolytes that comprise various NaX [X=hexafluorophosphate (PF6 ), perchlorate (ClO4 ), bis(trifluoromethanesulfonyl)imide (TFSI), fluorosulfonyl-(trifluoromethanesulfonyl)imide (FTFSI), and bis(fluorosulfonyl)imide (FSI)] salts and solvent mixtures [ethylene carbonate (EC)/dimethyl carbonate (DMC), EC/diethyl carbonate (DEC), and EC/propylene carbonate (PC)] with respect to the Al current collector stability, formation of soluble degradation compounds, reactivity towards sodiated hard carbon (Nax -HC), and solid-electrolyte interphase (SEI) layer formation. Cyclic voltammetry demonstrates that the stability of Al is highly influenced by the nature of the anions, solvents, and additives. GC-MS analysis reveals that the formation of SEI telltales depends on the nature of the linear alkyl carbonates and the battery chemistry (Li(+) vs. Na(+) ). FTIR spectroscopy shows that double alkyl carbonates are the main components of the SEI layer on Nax -HC. In the presence of Na salts, EC/DMC and EC/DEC presented a higher reactivity towards Nax -HC than EC/PC. For a fixed solvent mixture, the onset temperature follows the sequence NaClO4

Safer Electrolytes for Lithium-Ion Batteries: State of the Art and Perspectives.

Lithium-ion batteries are becoming increasingly important for electrifying the modern transportation system and, thus, hold the promise to enable sustainable mobility in the future. However, their large-scale application is hindered by severe safety concerns when the cells are exposed to mechanical, thermal, or electrical abuse conditions. These safety issues are intrinsically related to their superior energy density, combined with the (present) utilization of highly volatile and flammable organic-solvent-based electrolytes. Herein, state-of-the-art electrolyte systems and potential alternatives are briefly surveyed, with a particular focus on their (inherent) safety characteristics. The challenges, which so far prevent the widespread replacement of organic carbonate-based electrolytes with LiPF6 as the conducting salt, are also reviewed herein. Starting from rather "facile" electrolyte modifications by (partially) replacing the organic solvent or lithium salt and/or the addition of functional electrolyte additives, conceptually new electrolyte systems, including ionic liquids, solvent-free, and/or gelled polymer-based electrolytes, as well as solid-state electrolytes, are also considered. Indeed, the opportunities for designing new electrolytes appear to be almost infinite, which certainly complicates strict classification of such systems and a fundamental understanding of their properties. Nevertheless, these innumerable opportunities also provide a great chance of developing highly functionalized, new electrolyte systems, which may overcome the afore-mentioned safety concerns, while also offering enhanced mechanical, thermal, physicochemical, and electrochemical performance.

In-depth safety-focused analysis of solvents used in electrolytes for large scale lithium ion batteries.

To better rule out the complex fire risk related to large format lithium ion cells, a detailed and systematic evaluation, both at component and cell levels, could be an invaluable milestone. Therefore, combustion analysis was conducted for major single organic solvents and their mixtures used in lithium ion battery technology, both in oxygen rich and lean environments using a Tewarson calorimeter. Well controlled test conditions have enabled the determination of key parameters governing the fire induced hazards such as flash point, ease of ignition, heat release rate, effective heat of combustion, specific mass loss rate, as well as the assessment of fire induced toxicity. Moreover, a rule of thumb for the screening of new solvents including the safety perspective such as the Boie correlation and N-factor were introduced for predicting the heat of combustion and combustion kinetics, respectively, prior to conducting any experimental work. Fire induced toxicity of single solvents and their mixtures was also briefly examined by performing toxic gas measurements.