Sodium‐ion batteries have been considered one of the most promising power sources beyond Li‐ion batteries. Although the Na metal anode exhibits a high theoretical capacity of 1165 mAh g−1, its ...application in Na batteries is largely hindered by dendrite growth and low coulombic efficiency. Herein, it is demonstrated that an electrolyte consisting of 1 m sodium tetrafluoroborate in tetraglyme can enable excellent cycling efficiency (99.9%) of a Na metal anode for more than 1000 cycles. This high reversibility of a Na anode can be attributed to a stable solid electrolyte interphase formed on the Na surface, as revealed by cryogenic transmission electron microscopy and X‐ray photoelectron spectroscopy (XPS). These electrolytes also enable excellent cycling stability of Na||hard‐carbon cells and Na||Na2/3Co1/3Mn2/3O2 cells at high rates with very high coulombic efficiencies.
The excellent coulombic efficiency of Na in 1 m NaBF4/TEGDME electrolyte and the first observation of nanoscale chemical and structural heterogeneity of a solid electrolyte interphase formed on a Na surface in an ether‐based electrolyte using cryogenic transmission electron microscopy are reported. High stability of Na||hard‐carbon and Na||Na2/3Co1/3Mn2/3O2 cells is also observed.
Electrochemically driven functioning of a battery inevitably induces thermal and mechanical effects, which in turn couple with the electrochemical effect and collectively govern the performance of ...the battery. However, such a coupling effect, whether favorable or detrimental, has never been explicitly elucidated. Here we use in situ transmission electron microscopy to demonstrate such a coupling effect. We discover that thermally perturbating delithiated LiNi
Mn
Co
O
will trigger explosive nucleation and propagation of intragranular cracks in the lattice, providing us a unique opportunity to directly visualize the cracking mechanism and dynamics. We reveal that thermal stress associated with electrochemically induced phase inhomogeneity and internal pressure resulting from oxygen release are the primary driving forces for intragranular cracking that resembles a "popcorn" fracture mechanism. The present work reveals that, for battery performance, the intricate coupling of electrochemical, thermal, and mechanical effects will surpass the superposition of individual effects.
Large‐scale electrical energy storage has become more important than ever for reducing fossil energy consumption in transportation and for the widespread deployment of intermittent renewable energy ...in electric grid. However, significant challenges exist for its applications. Here, the status and challenges are reviewed from the perspective of materials science and materials chemistry in electrochemical energy storage technologies, such as Li‐ion batteries, sodium (sulfur and metal halide) batteries, Pb‐acid battery, redox flow batteries, and supercapacitors. Perspectives and approaches are introduced for emerging battery designs and new chemistry combinations to reduce the cost of energy storage devices.
The different applications of energy storage, different technologies, and the cost requirements from the kilowatt to gigawatt scale are compared. Li‐ion batteries have attracted attention for transportation storage, while many other technologies are considered for stationary applications.
Lithium ion capacitors (LICs) can generally deliver higher energy density than supercapacitors (SCs) and have much higher power density and longer cycle life than lithium ion batteries (LIBs). Due to ...their great potential to bridge the gap between SCs and LIBs, LICs are becoming important electrochemical energy storage systems in the field of energy storage and conversion. Although it is generally accepted that pre-lithiation technologies are indispensable for the operation of LICs, no comprehensive overview of the existing pre-lithiation technologies has been conducted. In this progress report, we first classify LICs according to their energy storage mechanisms and discuss the multiple roles that the pre-lithiation technologies play for improving the performance of LICs. Then, we present the existing pre-lithiation methods used in LICs in detail and the current research progress is summarized. Finally, we provide a comprehensive comparison of the current pre-lithiation methods and propose the prospects and challenges of these methods from both a fundamental and a practical point of view. The broader impact of pre-lithiation technologies on next-generation LIBs is also discussed. This progress report aims at providing the fundamental knowledge necessary to researchers who are new to studying LICs and also serves as a guideline for senior researchers in the fields of LICs and LIBs for future research directions.
This review summarizes the progress of pre-lithiation technologies involving the fundamental research and practical application of LICs.
Abstract
It is classically well perceived that cathode–air interfacial reactions, often instantaneous and thermodynamic non-equilibrium, will lead to the formation of interfacial layers, which ...subsequently, often vitally, control the behaviour and performance of batteries. However, understanding of the nature of cathode–air interfacial reactions remain elusive. Here, using atomic-resolution, time-resolved in-situ environmental transmission electron microscopy and atomistic simulation, we reveal that the cathode–water interfacial reactions can lead to the surface passivation, where the resultant conformal LiOH layers present a critical thickness beyond which the otherwise sustained interfacial reactions are arrested. We rationalize that the passivation behavior is dictated by the Li
+
-water interaction driven Li-ion de-intercalation, rather than a direct cathode–gas chemical reaction. Further, we show that a thin disordered rocksalt layer formed on the cathode surface can effectively mitigate the surface degradation by suppressing chemical delithiation. The established passivation paradigm opens new venues for the development of novel high-energy and high-stability cathodes.
The Li-rich, Mn-rich (LMR) layered structure materials exhibit very high discharge capacities exceeding 250 mAh g–1 and are very promising cathodes to be used in lithium ion batteries. However, ...significant barriers, such as voltage fade and low rate capability, still need to be overcome before the practical applications of these materials. A detailed study of the voltage/capacity fading mechanism will be beneficial for further tailoring the electrode structure and thus improving the electrochemical performances of these layered cathodes. Here, we report detailed studies of structural changes of LMR layered cathode LiLi0.2Ni0.2Mn0.6O2 after long-term cycling by aberration-corrected scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS). The fundamental findings provide new insights into capacity/voltage fading mechanism of LiLi0.2Ni0.2Mn0.6O2. Sponge-like structure and fragmented pieces were found on the surface of cathode after extended cycling. Formation of Mn2+ species and reduced Li content in the fragments leads to the significant capacity loss during cycling. These results also imply the functional mechanism of surface coatings, for example, AlF3, which can protect the electrode from etching by acidic species in the electrolyte, suppress cathode corrosion/fragmentation, and thus improve long-term cycling stability.
Electrolyte is very critical to the performance of the high-voltage lithium (Li) metal battery (LMB), which is one of the most attractive candidates for the next-generation high-density ...energy-storage systems. Electrolyte formulation and structure determine the physical properties of the electrolytes and their interfacial chemistries on the electrode surfaces. Localized high-concentration electrolytes (LHCEs) outperform state-of-the-art carbonate electrolytes in many aspects in LMBs due to their unique solvation structures. Types of fluorinated cosolvents used in LHCEs are investigated here in searching for the most suitable diluent for high-concentration electrolytes (HCEs). Nonsolvating solvents (including fluorinated ethers, fluorinated borate, and fluorinated orthoformate) added in HCEs enable the formation of LHCEs with high-concentration solvation structures. However, low-solvating fluorinated carbonate will coordinate with Li
ions and form a second solvation shell or a pseudo-LHCE which diminishes the benefits of LHCE. In addition, it is evident that the diluent has significant influence on the electrode/electrolyte interphases (EEIs) beyond retaining the high-concentration solvation structures. Diluent molecules surrounding the high-concentration clusters could accelerate or decelerate the anion decomposition through coparticipation of diluent decomposition in the EEI formation. The varied interphase features lead to significantly different battery performance. This study points out the importance of diluents and their synergetic effects with the conductive salt and the solvating solvent in designing LHCEs. These systematic comparisons and fundamental insights into LHCEs using different types of fluorinated solvents can guide further development of advanced electrolytes for high-voltage LMBs.
Lithium–sulfur (Li–S) battery is one of the most promising energy storage systems because of its high specific capacity of 1675 mAh g–1 based on sulfur. However, the rapid capacity degradation, ...mainly caused by polysulfide dissolution, remains a significant challenge prior to practical applications. This work demonstrates that a novel Ni-based metal organic framework (Ni-MOF), Ni6(BTB)4(BP)3 (BTB = benzene-1,3,5-tribenzoate and BP = 4,4′-bipyridyl), can remarkably immobilize polysulfides within the cathode structure through physical and chemical interactions at molecular level. The capacity retention achieves up to 89% after 100 cycles at 0.1 C. The excellent performance is attributed to the synergistic effects of the interwoven mesopores (∼2.8 nm) and micropores (∼1.4 nm) of Ni-MOF, which first provide an ideal matrix to confine polysulfides, and the strong interactions between Lewis acidic Ni(II) center and the polysulfide base, which significantly slow down the migration of soluble polysulfides out of the pores, leading to the excellent cycling performance of Ni-MOF/S composite.
With the significant progress made in the development of cathodes in lithium‐sulfur (Li‐S) batteries, the stability of Li metal anodes becomes a more urgent challenge in these batteries. Here the ...systematic investigation of the stability of the anode/electrolyte interface in Li‐S batteries with concentrated electrolytes containing various lithium salts is reported. It is found that Li‐S batteries using LiTFSI‐based electrolytes are more stable than those using LiFSI‐based electrolytes. The decreased stability is because the N–S bond in the FSI− anion is fairly weak and the scission of this bond leads to the formation of lithium sulfate (LiSOx) in the presence of polysulfide species. In contrast, in the LiTFSI‐based electrolyte, the lithium metal anode tends to react with polysulfide to form lithium sulfide (LiSx), which is more reversible than LiSOx formed in the LiFSI‐based electrolyte. This fundamental difference in the bond strength of the salt anions in the presence of polysulfide species leads to a large difference in the stability of the anode‐electrolyte interface and performance of the Li‐S batteries with electrolytes composed of these salts. Therefore, anion selection is one of the key parameters in the search for new electrolytes for stable operation of Li‐S batteries.
The electrolyte selection for lithium‐sulfur batteries is critical to achieve high energy and stable cycling. The stability of concentrated electrolytes containing various lithium salts for lithium‐sulfur batteries is investigated. The anion stability of lithium salt greatly affects the anode/electrolyte interface stability and the electrochemical performance.
Due to the limited oxidation stability (<4 V) of ether oxygen in its polymer structure, polyethylene oxide (PEO)‐based polymer electrolytes are not compatible with high‐voltage (>4 V) cathodes, thus ...hinder further increases in the energy density of lithium (Li) metal batteries (LMBs). Here, a new type of polymer‐in‐“quasi‐ionic liquid” electrolyte is designed, which reduces the electron density on ethereal oxygens in PEO and ether solvent molecules, induces the formation of stable interfacial layers on both surfaces of the LiNi1/3Mn1/3Co1/3O2 (NMC) cathode and the Li metal anode in Li||NMC batteries, and results in a capacity retention of 88.4%, 86.7%, and 79.2% after 300 cycles with a charge cutoff voltage of 4.2, 4.3, and 4.4 V for the LMBs, respectively. Therefore, the use of “quasi‐ionic liquids” is a promising approach to design new polymer electrolytes for high‐voltage and high‐specific‐energy LMBs.
A new type of polymer‐in‐“quasi‐ionic liquid” electrolyte (PQILE) for high‐voltage and long‐term cycling of Li metal batteries is reported. The donation of lone electron pairs of ether oxygen atoms to Li+ cations greatly improves the oxidation stability of PQILE. Li||LiNi1/3Mn1/3Co1/3O2 batteries with optimized PQILE can be stably cycled at 4.4 V for 300 times with a capacity retention of 79.2%.
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