Improved performances of lithium carbonate coated graphite in the piperidinium-based hybrid electrolyte for lithium-ion battery

The lithium carbonate (Li₂CO₃)-coated carbon microbead composites (LCO/CMB-T) with the coating amount of 1.07, 2.88, and 7.39% are prepared by the impregnation process (IP). Three LCO/CMB-T samples are first used in the piperidinium-based hybrid electrolyte. It is found that the long charge–discharge cycles did not result in the decomposition or exfoliation of Li₂CO₃ coating. They can effectively prevent graphite electrode from exfoliation and suppress the graphite/electrolyte interfacial reaction. In three tested samples (IP-1.07%, IP-2.88% and IP-7.39% for short), the IP-2.88% sample showed the best cell performances and the highest capacity retention (82.9%) after 50 cycles. This work gives a new design method for the application of graphite materials in the ionic liquid-based electrolyte.     

Fluoroethylene Carbonate Enabling a Robust LiF‐rich Solid Electrolyte Interphase to Enhance the Stability of the MoS2 Anode for Lithium‐Ion Storage

As a high‐capacity anode for lithium‐ion batteries (LIBs), MoS₂ suffers from short lifespan that is due in part to its unstable solid electrolyte interphase (SEI). The cycle life of MoS₂ can be greatly extended by manipulating the SEI with a fluoroethylene carbonate (FEC) additive. The capacity of MoS₂ in the electrolyte with 10 wt % FEC stabilizes at about 770 mAh g^?1 for 200 cycles at 1 A g^?1, which far surpasses the FEC‐free counterpart (ca. 40 mAh g^?1 after 150 cycles). The presence of FEC enables a robust LiF‐rich SEI that can effectively inhibit the continual electrolyte decomposition. A full cell with a LiNi_0.5Co_0.3Mn_0.2O₂ cathode also gains improved performance in the FEC‐containing electrolyte. These findings reveal the importance of controlling SEI formation on MoS₂ toward promoted lithium storage, opening a new avenue for developing metal sulfides as high‐capacity electrodes for LIBs.     

Propylene sulfite as film-forming electrolyte additive in lithium ion batteries

Propylene sulfite (PS) has been studied as a film-forming electrolyte additive for use in lithium ion battery electrolytes. Even small amounts in the order of 5 vol.% PS suppress propylene carbonate (PC) co-intercalation into graphite. In addition, a 1 M LiClO₄/PC/PS (95:5 by volume) electrolyte is characterised by a high oxidation stability at a LiMn₂O₄ cathode.     

Effect of CO2-induced side reactions on the deposition in the non-aqueous Li-air batteries

This paper presents a non-aqueous Li-air battery model that considers the side reactions of lithium carbonate (Li₂CO₃) formation from both electrolyte decomposition and carbon dioxide (CO₂) in the ambient air. The deposition and decomposition behaviors of discharge products, the voltage, and capacity evolutions during the cycling operation of the Li-air batteries are investigated. The deposition behavior analysis implies that the Li₂CO₃ generated by electrolyte decomposition is mainly distributed near the separator side, while it is dominantly generated by Li-O₂/CO₂ reaction near the air side. The formation of Li₂CO₃ by side reactions makes the Li-air batteries exhibit a peak discharge deposition inside the cathode. Moreover, Li₂CO₃ is difficult to decompose and gradually accumulates with cycles, especially near the air side. The severe accumulation of Li₂CO₃ near the air side significantly reduces the O₂ diffusion into the electrode, which induces severe cycling performance decay of the Li-air batteries. According to the distribution and evolution of the deposition, three simple hierarchical cathode structures with high porosities near the air side are finally studied. The simulation results indicate that the increase of the local porosity near the air side substantially improves the cycling performance of the Li-air batteries.

     

A pentafluorophenylboron oxalate additive in non-aqueous electrolytes for lithium batteries

A novel compound named pentafluorophenylboron oxalate (PFPBO) has been synthesized. PFPBO has a unique molecular structure containing a boron atom center with electron deficiency and an oxalate group. It is found that when PFPBO is used as additive, the solubility of lithium fluoride (LiF) or lithium oxide (Li₂O, Li₂O₂) in propylene carbonate (PC) and dimethyl carbonate (DMC) solvents can be increased dramatically. The new electrolytes show high ionic conductivity, high lithium ion transference number and good compatibility with LiMn₂O₄ cathode and MCMB anode. PFPBO was synthesized with the designed structure to act as a bi-functional additive: boron-based anion receptor (BBAR) additive and stable solid electrolyte interphase (SEI) formation additive in PC-based electrolytes. The results show it does possess these two desired functionalities.     

Highly Oxidative-Resistant Cyano-Functionalized Lithium Borate Salt for Enhanced Cycling Performance of Practical Lithium-Ion Batteries

Lithium difluoro(oxalato) borate (LiDFOB) has been widely investigated in lithium-ion batteries (LIBs) owing to its advantageous thermal stability and excellent aluminum passivation property. However, LiDFOB tends to suffer from severe decomposition and generate a lot of gas species (e.g., CO₂). Herein, a novel cyano-functionalized lithium borate salt, namely lithium difluoro(1,2-dihydroxyethane-1,1,2,2-tetracarbonitrile) borate (LiDFTCB), is innovatively synthesized as a highly oxidative-resistant salt to alleviate above dilemma. It is revealed that the LiDFTCB-based electrolyte enables LiCoO₂/graphite cells with superior capacity retention at both room and elevated temperatures (e.g., 80 % after 600 cycles) with barely any CO₂ gas evolution. Systematic studies reveal that LiDFTCB tends to form thin and robust interfacial layers at both electrodes. This work emphasizes the crucial role of cyano-functionalized anions in improving cycle lifespan and safety of practical LIBs.     

Strategies of Removing Residual Lithium Compounds on the Surface of Ni‐Rich Cathode Materials†

Ni‐rich cathode materials have become one of the most promising cathode materials for advanced high‐energy Li‐ion batteries (LIBs) owing to their high specific capacity. However, Ni‐rich cathode materials are sensitive to the trace H₂O and CO₂ in the air, and tend to react with them to generate LiOH and Li₂CO₃ at the particle surface region (named residual lithium compounds, labeled as RLCs). The RLCs will deteriorate the comprehensive performances of Ni‐rich cathode materials and make trouble in the subsequent manufacturing process of electrode, including causing low initial coulombic efficiency and poor storage property, bringing about potential safety hazards, and gelatinizing the electrode slurry. Therefore, it is of considerable significance to remove the RLCs. Researchers have done a lot of work on the corresponding field, such as exploring the formation mechanism and elimination methods. This paper investigates the origin of the surface residual lithium compounds on Ni‐rich cathode materials, analyzes their adverse effects on the performance and the subsequent electrode production process, and summarizes various kinds of feasible methods for removing the RLCs. Finally, we propose a new research direction of eliminating the lithium residuals after comparing and summing up the above. We hope this work can provide a reference for alleviating the adverse effects of residual lithium compounds for Ni‐rich cathode materials’ industrial production.     

A Designed Durable Electrolyte for High-Voltage Lithium-Ion Batteries and Mechanism Analysis

Rechargeable lithium-ion batteries (LIBs) dominate the energy market, from electronic devices to electric vehicles, but pursuing greater energy density remains challenging owing to the limited electrode capacity. Although increasing the cut-off voltage of LIBs (>4.4 V vs. Li/Li⁺) can enhance the energy density, the aggravated electrolyte decomposition always leads to a severe capacity fading and/or expiry of the battery. Herein, a new durable electrolyte is reported for high-voltage LIBs. The designed electrolyte is composed of mixed linear alkyl carbonate solvent with certain cyclic carbonate additives, in which use of the ethylene carbonate (EC) co-solvent was successfully avoided to suppress the electrolyte decomposition. As a result, an extremely high cycling stability, rate capability, and high-temperature storage performance were demonstrated in the case of a graphite|LiNi_0.6Co_0.2Mn_0.2O₂ (NCM622) battery at 4.45 V when this electrolyte was used. The good compatibility of the electrolyte with the graphite anode and the mitigated structural degradation of the NCM622 cathode are responsible for the high performance at high potentials above 4.4 V. This work presents a promising application of high-voltage electrolytes for pursuing high energy LIBs and provides a straightforward guide to study the electrodes/electrolyte interface for higher stability.     

LiNbO3-coated LiCoO2 as cathode material for all solid-state lithium secondary batteries

The further enhancement of high-rate capabilities for all solid-state lithium secondary batteries is reported. A LiNbO₃ layer of nanometer thickness was interposed between LiCoO₂ and sulfide solid electrolyte as buffer layer. This greatly reduced the interfacial resistance in the cathode and enhanced the high-rate capabilities of solid-state lithium batteries, providing good prospects for practical application of lithium secondary batteries free from safety issues.     

Solubilization of SEI lithium salts in alkylcarbonate solvents

The SEI (Solid Electrolyte Interphase) at the surface of electrodes in lithium-ion batteries is composed of various lithium compounds, organic or mineral, which have a direct impact on cycling performance. The main lithium species constituting the SEI and selected in this study are lithium fluoride LiF, lithium carbonate Li₂CO₃, lithium hydroxide LiOH, lithium oxide Li₂O, lithium methoxide LiOCH₃ and lithium ethoxide LiOC₂H₅. Their solubilities were determined in ethylene, propylene, dimethyl, diethyl and vinylene carbonates (EC, PC, DMC, DEC and VC) and in one of their mixtures commonly used in lithium-ion batteries (EC/PC/3DMC) by mean of atomic absorption spectroscopy (AAS). These solutions were also investigated by EIS (Electrochemical Impedance Spectroscopy) and conductimetry measurements. Results show that while solubilization properties differ between LiF and other lithium compounds considered, their association pattern in solution is identical and solutions are mainly constituted of quadrupolar aggregates.     

Synergistic effect of fluorinated solvent and Mg2+ enabling 4.6 V LiCoO2 performances

Increasing the charging cut-off potential of lithium cobalt oxide (LiCoO₂, LCO) can effectively improve the energy density of the lithium-ion batteries, which are the mainstream energy storage devices used in 3C electronic products. However, the continuous decomposition of the electrolyte and dissolution of Co from the electrode will occur at high-potential operation, which deteriorate the performances of LCO. Here, a cathode-electrolyte interface (CEI) layer containing MgF₂ is constructed to enhance the electrochemical stability of LCO at 4.6 V (vs. Li⁺/Li). The Mg²⁺ added to the cathode gradually releases into the electrolyte during cycling, which forms a stable MgF₂-rich protective layer. In addition, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropylether (TTE) is added to the electrolyte acting as a F source to increase the content of MgF₂ in the CEI layer. The MgF₂-rich CEI layer effectively suppresses the decomposition of electrolyte components and the dissolution of Co of LCO, which makes the Li||LiCoO₂ (Li||LCO) cell cycled stably at 3∼4.6 V (vs. Li⁺/Li) in 200 cycles with a retention of 83.9%.     

Amorphous Zr(OH)_4 coated LiNi_(0.915)Co_(0.075)Al_(0.01)O_2 cathode material with enhanced electrochemical performance for lithium ion batteries

LiNi_(0.915)Co_(0.075)Al_(0.01)O_2(NCA) with Zr(OH)_4 coating is demonstrated as high performance cathode material for lithium ion batteries(LIBs). The coated materials are synthesized via a simple dry coating method of NCA with Zr(OH)_4 powders, and then characterized with scanning electron microscopy(SEM), transmission electron microscopy(TEM) and X-ray photoelectron spectroscopy(XPS). Experimental results show that amorphous Zr(OH)_4 powders have been successfully coated on the surface of spherical NCA particles, exhibiting improved electrochemical performance. 0.50 wt% Zr(OH)_4 coated NCA delivers a capacity of 197.6 mAh/g at the first cycle and 154.3 mAh/g after 100 cycles with a capacity retention of 78.1% at 1 C rate. In comparison, the pure NCA shows a capacity of 194.6 mAh/g at the first cycle and 142.5 mAh/g after 100 cycles with a capacity retention of 73.2% at 1 C rate. Electrochemical impedance spectroscopy(EIS) results show that the coated material exhibits a lower resistance, indicating that the coating layer can efficiently suppress transition metals dissolution and decrease the side reactions at the surface between the electrode and electrolyte. Therefore, surface coating with amorphous Zr(OH)_4 is a simple and useful method to enhance the electrochemical performance of NCA-based materials for the cathode of LIBs.     

Hydrolysis lignin-based organic electrode material for primary lithium batteries

The possibility of using hydrolysis lignin as a cathode material for primary lithium batteries has been demonstrated for the first time. The electroconductivity, morphology, and element composition of hydrolysis lignin have been investigated by means of the methods of impedance spectroscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The main parameters and the behavior of lignin-based lithium batteries were studied using two electrolyte systems: 1 M LiBF₄ in γ-butyrolacton and 1 M LiClO₄ in propylene carbonate. The chemical composition of cathode materials upon battery discharge down to 0.9 V was studied by the methods of X-ray photoelectron spectroscopy and infrared spectroscopy. The suggestions on possible electrochemical reactions occurring in the lithium/hydrolysis lignin system were made on the basis of the products composition analysis.     

In situ analysis of interfacial reactions between negative MCMB,lithium electrodes,and gel polymer electrolyte

The interfacial properties of mesocarbon-microbeads (MCMB) and lithium electrodes during charge process in poly (vinylidenefluoride-co-hexafluoropropylene)-based gel electrolyte were investigated by in situ Raman microscopy, in situ Fourier transform-infrared (FTIR) spectroscopic methods, and charge–discharge, electrochemical impedance spectroscopy techniques. For MCMB electrode, the series phase transitions from initial formation of the dilute stage 1 graphite intercalation compound (GIC) to a stage 4 GIC, then through a stage 3 to stage 2, and finally to stage 1 GIC was proved by in situ Raman spectroscopic measurement. The formation of solid electrolyte interface (SEI) films formed on MCMB and metal lithium electrode was studied by in situ reflectance FTIR spectroscopic method. At MCMB electrode surface, the solvent (mostly ethylene carbonate) decomposed during charging process and ROCO₂Li may be the product. ROCO₂Li, ROLi, and Li₂CO₃ were the main composites of SEI film formed on lithium electrode, not on electrodeposited lithium electrode or lithium foil electrode.     

On the gassing behavior of lithium-ion batteries with NCM523 cathodes

Gas evolution has a profound effect on the functioning of state-of-the-art lithium-ion batteries. On one hand, it is the natural concomitant of solid electrolyte interphase (SEI) formation on the anode (reduction of electrolyte components). On the other hand, because of the demand for high terminal voltages, it is also the consequence of electrolyte and/or cathode material oxidation. Overall, gassing happens on the expense of Coulombic efficiency and additionally raises safety issues. Herein, the gassing behavior of one of the most important commercialized cathode materials, namely Ni-rich Li_1 + x Ni_0.5Co_0.2Mn_0.3O₂ (NCM523 with 0.01 < x < 0.05), is reported for the first time. We analyze the generation pattern of the most typical gases H₂, C₂H₄, CO₂, and CO during 30 cycles by means of differential electrochemical mass spectrometry combined with Fourier transform infrared spectroscopy. In a long-term test of an NCM523/graphite cell, we monitor its potential-resolved gas evolution and evaluate the total amount of gas from cycle to cycle. An explanation on the characteristic features of pressure versus time curves during cycling is given by combining the spectrometric and total gas pressure data. With additional information from graphite/lithium cells, the identity of gases formed during SEI formation is revealed.     

An Approach towards Synthesis of Nanoarchitectured LiNi1/3Co1/3Mn1/3O2 Cathode Material for Lithium Ion Batteries

To explore advanced cathode materials for lithium ion batteries (LIBs), a nanoarchitectured LiNi_1/3Co_1/3Mn_1/3O₂ (LNCM) material is developed using a modified carbonate coprecipitation method in combination with a vacuum distillation‐crystallisation process. Compared with the LNCM materials produced by a traditional carbonate coprecipitation method, the prepared LNCM material synthesized through this modified method reveals a better hexagonal layered structure, smaller particle sizes (ca. 110.5 nm), and higher specific surface areas. Because of its unique structural characteristics, the as‐prepared LNCM material demonstrates excellent electrochemical properties including high rate capability and good cycleability when it is utilized as a cathode in the lithium ion battery (LIB).     

Rational Design of an Ionic Liquid‐Based Electrolyte with High Ionic Conductivity Towards Safe Lithium/Lithium‐Ion Batteries

It is a very urgent and important task to improve the safety and high‐temperature performance of lithium/lithium‐ion batteries (LIBs). Here, a novel ionic liquid, 1‐(2‐ethoxyethyl)‐1‐methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (PYR_1(2o2)TFSI), was designed and synthesized, and then mixed with dimethyl carbonate (DMC) as appropriate solvent and LiTFSI lithium salt to produce an electrolyte with high ionic conductivity for safe LIBs. Various characterizations and tests show that the highly flexible ether group could markedly reduce the viscosity and provide coordination sites for Li‐ion, and the DMC could reduce the viscosity and effectively enhance the Li‐ion transport rate and transference number. The electrolyte exhibits excellent electrochemical performance in Li/LiFeO₄ cells at room temperature as well as at a high temperature of 60 °C. More importantly, with the addition of DMC, the IL‐based electrolyte remains nonflammable and appropriate DMC can effectively inhibit the growth of lithium dendrites. Our present work may provide an attractive and promising strategy for high performance and safety of both lithium and lithium‐ion batteries.     

Three new bifunctional additive for safer nickel-cobalt-aluminum based lithium ion batteries

The phosphorus-containing additives can help for forming a stable solid electrolyte interface film on the NCA cathode, thus enhance the thermal stability of the electrolyte and cycle performance of the battery.     

Realizing Stable Carbonate Electrolytes in Li–O2/CO2 Batteries†

The increasing demand for high-energy storage systems has propelled the development of Li-air batteries and Li-O₂/CO₂ batteries to elucidate the mechanism and extend battery life. However, the high charge voltage of Li₂CO₃ accelerates the decomposition of traditional sulfone and ether electrolytes, thus adopting high-voltage electrolytes in Li-O₂/CO₂ batteries is vital to achieve a stable battery system. Herein, we adopt a commercial carbonate electrolyte to prove its excellent suitability in Li-O₂/CO₂ batteries. The generated superoxide can be captured by CO₂ to form less aggressive intermediates, stabilizing the carbonate electrolyte without reactive oxygen species induced decomposition. In addition, this electrolyte permits the Li metal plating/stripping with a significantly improved reversibility, enabling the possibility of using ultra-thin Li anode. Benefiting from the good rechargeability of Li₂CO₃, less cathode passivation, and stabilized Li anode in carbonate electrolyte, the Li-O₂/CO₂ battery demonstrates a long cycling lifetime of 167 cycles at 0.1 mA·cm^–2 and 0.25 mAh·cm^–2. This work paves a new avenue for optimizing carbonate-based electrolytes for Li-O₂ and Li-O₂/CO₂ batteries.      

Application of 7Li NMR to characterize the evolution of intercalated and non-intercalated lithium in LiFePO4-based materials for Li-ion batteries

Different synthesis batches of LiFePO₄/C materials were prepared, and their electrochemical properties as positive cathodes for lithium-ion batteries were evaluated. Using standard solid-state NMR conditions, such as a 7-mm magic-angle-spinning probe performing at low spinning rates, information on both intercalated and non-intercalated (stored on the grain boundaries) lithium was obtained. A sharp signal assigned to non-intercalated lithium could be observed by diluting the active material in silica. Correlations could be, thus, obtained between the amount of each type of lithium and the electrochemical history and state of the material, revealing that the relative amount of surface lithium in a pristine LiFePO₄/C material is rather constant and cannot be used as a criterion for its further specification. However, a drastic increase of this surface lithium was observed in the cathode materials of out-of-order batteries. As the cathode material recovered from the batteries after electrochemical testing was carefully washed before analysis, we can conclude that the non-intercalated lithium is strongly bound to the active material probably inside the so-called solid electrolyte interface layer at the surfaces of LiFePO₄ particles. This work illustrates that solid-state lithium NMR can allow rapid characterization and testing of LiFePO₄/C cathode materials.