Successfully commercialized poly(ethylene oxide) (PEO)based solid polymer batteries (SPBs) are expected to continuously play a key role in the next generation of high-energy density lithium-ion battery technologies. However, the introduction of high-voltage cathodes, accompanied by safety concerns such as PEO decomposition and the associated gas release, is worthy of more attention. This study employs in situ DEMS to study the gassing behavior of LiCoO 2 |PEO-LiTFSI|Li SPBs. The experiments, together with theory calculations, reveal that a surface catalytic effect of LiCoO 2 is the root cause of the unexpected H 2 gas release of PEO-based SPBs at 4.2 V. The surface coating of LiCoO 2 with a stable solid electrolyte Li 1.4 Al 0.4 Ti 1.6 (PO 4 ) 3 (LATP) can mitigate such a surface catalytic effect and therefore extend the stable working voltage to >4.5 V. The crossover effect of HTFSI, which is generated at the cathode side due to oxidation/dehydration of PEO and reacts with lithium at the anode side, is proposed to explain the H 2 generation behavior.
Solid state lithium batteries are widely accepted as promising candidates for next generation of various energy storage devices with the probability to realize improved energy density and superior safety performances. However, the interface between electrode and solid electrolyte remain a key issue that hinders practical development of solid state lithium batteries. In this review, we specifically focus on the interface between solid electrolytes and prevailing cathodes. The basic principles of interface layer formation are summarized and three kinds of interface layers can be categorized. For typical solid state lithium batteries, a most common and daunting challenge is to achieve and sustain intimate solid-solid contact. Meanwhile, different specific issues occur on various types of solid electrolytes, depending on the intrinsic properties of adjacent solid components. Our discussion mostly involves following electrolytes, including solid polymer electrolyte, inorganic solid oxide and sulfide electrolytes as well as composite electrolytes. The effective strategies to overcome the interface instabilities are also summarized. In order to clarify interfacial behaviors fundamentally, advanced characterization techniques with time, and atomic-scale resolution are required to gain more insights from different perspectives. And recent progresses achieved from advanced characterization are also reviewed here. We highlight that the cooperative characterization of diverse advanced characterization techniques is necessary to gain the final clarification of interface behavior, and stress that the combination of diverse interfacial modification strategies is required to build up decent cathode-electrolyte interface for superior solid state lithium batteries.
Due to their numerous advantages, such as high specific capacity, lithiumsulfur batteries (Li-S batteries) have attracted much attention as nextgeneration energy storage systems. To meet future needs for commercial application, Li-S batteries will require both improved cycle life and high energy density. It is of critical importance to understand the fundamental mechanisms in Li-S systems to further improve the overall battery performance. Various advanced characterization techniques, over the past few years, have proven their important role in promoting the mechanism understanding for Li-S batteries. Here, the recent progress of mechanism understanding, including redox reactions, Li polysulfides dissolution, etc., in Li-S systems based on the advanced characterization techniques is reviewed. Special focus is placed on how these advanced characterization techniques are being employed and what characteristic or capability they possess. The importance of the combination of multiple characterization techniques, differences between ex situ and in situ experimental methods, as well as effects of characterization conditions in Li-S batteries are also discussed.
The
reactivity of garnet solid electrolytes toward humid air hinders
their practical application despite their attractive, superior properties
such as high Li+ conductivity and wide electrochemical
window. Sealing garnets with organic solvents can not only prevent
them from reacting with humid air but also render them compatible
with other processing technologies. Therefore, the chemical and structural
stability of garnets in organic solvents must be studied. In this
study, we selected several commonly used organic solvents with different
representative functional groups to investigate their stability with
garnets and reaction mechanisms. The experiments and theoretical calculations
revealed that all of the solvents reacted with garnets through Li–H
exchange, and solvent acidity determined the reaction strength. Furthermore,
the solvent acidity was closely correlated to the functional groups
connected to H atoms, which can affect charge distribution. Solvents
or the tautomer of the solvents with hydroxyl groups such as alcohol,
acetone, and N-methyl pyrrolidone, which are relatively
more acidic, can lead to a violent reaction with changes in the lattice
parameters of garnets. Ether compounds and saturated aliphatic hydrocarbons
with relatively low acidity are highly stable against garnets. The
proposed reaction mechanisms and rules may help in selecting appropriate
solvents for different applications of garnets.
Li(Ni0.6Co0.2Mn0.2)O2 has been surface-modified by the lithium-ion conductor Li1.4)Al0.4)Ti1.6)(PO4)3 via a facile mechanical fusion method. The annealing temperature during coating process shows a strong impact on the surface morphology and chemical composition of Li(Ni0.6Co0.2Mn0.2)O2. The 600-°C annealed material exhibits the best cyclic stability at high charging cut-off voltage of 4.5 V (versus Li
+
/Li) with the capacity retention of 90.9% after 100 cycles, which is much higher than that of bare material (79%). Moreover, the rate capability and thermal stability are also improved by Li1.4)Al0.4)Ti1.6)(PO4)3 coating. The enhanced performance can be attributed to the improved stability of interface between Li(Ni0.6Co0.2Mn0.2)O2 and electrolyte by Li1.4)Al0.4)Ti1.6)(PO4)3 modification. The results of this work provide a possible method to design reliable cathode materials to achieve high energy density and long cycle life.
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