Abstract
High nickel content in LiNi
x
Co
y
Mn
z
O
2
(NCM, x ≥ 0.8, x + y + z = 1) layered cathode material allows high specific energy density in lithium-ion batteries (LIBs). However, Ni-rich NCM ...cathodes suffer from performance degradation, mechanical and structural instability upon prolonged cell cycling. Although the use of single-crystal Ni-rich NCM can mitigate these drawbacks, the ion-diffusion in large single-crystal particles hamper its rate capability. Herein, we report a strategy to construct an in situ Li
1.4
Y
0.4
Ti
1.6
(PO
4
)
3
(LYTP) ion/electron conductive network which interconnects single-crystal LiNi
0.88
Co
0.09
Mn
0.03
O
2
(SC-NCM88) particles. The LYTP network facilitates the lithium-ion transport between SC-NCM88 particles, mitigates mechanical instability and prevents detrimental crystalline phase transformation. When used in combination with a Li metal anode, the LYTP-containing SC-NCM88-based cathode enables a coin cell capacity of 130 mAh g
−1
after 500 cycles at 5 C rate in the 2.75-4.4 V range at 25 °C. Tests in Li-ion pouch cell configuration (i.e., graphite used as negative electrode active material) demonstrate capacity retention of 85% after 1000 cycles at 0.5 C in the 2.75-4.4 V range at 25 °C for the LYTP-containing SC-NCM88-based positive electrode.
Ni-rich layered oxides are extensively employed as a promising cathode material in lithium ion batteries (LIBs) due to their high energy density and reasonable cost. However, the hierarchical ...structure of secondary particles with grain boundaries inevitably induces the structural collapse and severe electrode/electrolyte interface parasitic reactions as the intergranular crack arises from the anisotropic shrink and expansion. Herein, the single-crystalline LiNi0.83Co0.11Mn0.06O2 (SC-NCM) with primary particles of 3–6 μm diameter is developed and comprehensively investigated, which exhibits superior cycling performance at both room temperature and elevated temperature (55 °C) as well as significantly improved structural integrity after long-term cycling. Remarkably, the SiO-C||SC-NCM pouch-type full cell with a practical loading (8.7 mAh cm−2) delivers a capacity retention of 84.8 % at 45 °C after 600 cycles at a current rate of 1C (1C = 200 mA g−1), retaining a high specific energy density of 225 Wh/kg. Using a combination of X-ray photoelectron spectroscopy, time-of-flight secondary-ion mass spectrometry and scanning transmission electron microscopy, we reveal that SC-NCM particles with micron-sizes effectively mitigate the undesired electrode/electrolyte side interactions and prevent the generation of intergranular cracks, thereby alleviating irreversible structural degradation. The strategy of developing single-crystalline micron-sized particles may offer a new path for maintaining the structural stability and improving cycling life of Ni-rich layered NCM cathodes even under high temperature.
Integrated single-crystalline Ni-rich NCM cathode is rationally designed and successfully fabricated, which effectively mitigate undesired electrode/electrolyte interactions, avoid intergranular cracks, and significantly alleviate irreversible phase transformation. Investigation of the relationship between phase transformation and intergranular crack unambiguously reveals that the enhanced prolonged cyclic life and thermal stability are attributed to the intrinsic structure of single-crystalline Ni-rich NCM. Display omitted
•The single-crystalline Ni-rich NCM with 3-6 μm diameter is developed and systematically investigated for the first time.•The pouch-type full cell with a practical loading (8.7mAh/cm) delivers capacity retention of 84.8% at 45°C after 600 cycles.•SC-NCM exhibits superior cycling performance at both 25 and 55 °C as well as enhanced thermal stability.•SC-NCM effectively mitigate undesired side interactions and significantly prevent the generation of intergranular cracks.
Rechargeable lithium‐metal batteries (LMBs) are regarded as the “holy grail” of energy‐storage systems, but the electrolytes that are highly stable with both a lithium‐metal anode and high‐voltage ...cathodes still remain a great challenge. Here a novel “localized high‐concentration electrolyte” (HCE; 1.2 m lithium bis(fluorosulfonyl)imide in a mixture of dimethyl carbonate/bis(2,2,2‐trifluoroethyl) ether (1:2 by mol)) is reported that enables dendrite‐free cycling of lithium‐metal anodes with high Coulombic efficiency (99.5%) and excellent capacity retention (>80% after 700 cycles) of Li||LiNi1/3Mn1/3Co1/3O2 batteries. Unlike the HCEs reported before, the electrolyte reported in this work exhibits low concentration, low cost, low viscosity, improved conductivity, and good wettability that make LMBs closer to practical applications. The fundamental concept of “localized HCEs” developed in this work can also be applied to other battery systems, sensors, supercapacitors, and other electrochemical systems.
A novel “localized high‐concentration electrolyte,” which consists of 1.2 m lithium bis(fluorosulfonyl)imide in a mixture of dimethyl carbonate/bis(2,2,2‐trifluoroethyl) ether (1:2 by mol), enables dendrite‐free cycling of lithium‐metal anodes with high Coulombic efficiency of 99.3% and excellent capacity retention (>80% after 700 cycles) of Li||LiNi1/3Mn1/3Co1/3O2 batteries.
The lithium (Li) metal battery (LMB) is one of the most promising candidates for next‐generation energy storage systems. However, it is still a significant challenge to operate LMBs with high voltage ...cathodes under high rate conditions. In this work, an LMB using a nickel‐rich layered cathode of LiNi0.76Mn0.14Co0.10O2 (NMC76) and an optimized electrolyte 0.6 m lithium bis(trifluoromethanesulfonyl)imide + 0.4 m lithium bis(oxalato)borate + 0.05 m LiPF6 dissolved in ethylene carbonate and ethyl methyl carbonate (4:6 by weight) demonstrates excellent stability at a high charge cutoff voltage of 4.5 V. Remarkably, these Li||NMC76 cells can deliver a high discharge capacity of >220 mA h g−1 (846 W h kg−1) and retain more than 80% capacity after 1000 cycles at high charge/discharge current rates of 2C/2C (1C = 200 mA g−1). This excellent electrochemical performance can be attributed to the greatly enhanced structural/interfacial stability of both the Ni‐rich NMC76 cathode material and the Li metal anode using the optimized electrolyte.
Excellent rate capability and cycling performance in a high voltage lithium (Li) metal battery (LMB) composed of Ni‐rich layered LiNi0.76Mn0.14Co0.10O2 (NMC76) and Li metal are enabled by the formation of stable electrode/electrolyte interfaces in an optimized dual‐salt electrolyte with additive. The Li||NMC76 cell demonstrates a capacity retention above 80% after 1000 cycles at 400 mA g−1 between 2.7–4.5 V.
Silicon anodes are regarded as one of the most promising alternatives to graphite for high energy‐density lithium‐ion batteries (LIBs), but their practical applications have been hindered by high ...volume change, limited cycle life, and safety concerns. In this work, nonflammable localized high‐concentration electrolytes (LHCEs) are developed for Si‐based anodes. The LHCEs enable the Si anodes with significantly enhanced electrochemical performances comparing to conventional carbonate electrolytes with a high content of fluoroethylene carbonate (FEC). The LHCE with only 1.2 wt% FEC can further improve the long‐term cycling stability of Si‐based anodes. When coupled with a LiNi0.3Mn0.3Co0.3O2 cathode, the full cells using this nonflammable LHCE can maintain >90% capacity after 600 cycles at C/2 rate, demonstrating excellent rate capability and cycling stability at elevated temperatures and high loadings. This work casts new insights in electrolyte development from the perspective of in situ Si/electrolyte interphase protection for high energy‐density LIBs with Si anodes.
A nonflammable localized high‐concentration electrolyte (LHCE) with a small amount of fluoroethylene carbonate significantly enhances the performances of silicon anodes. The concept of forming locally highly‐coordinated lithium ion‐solvent solvates and a robust salt‐derived “lithium fluoride‐rich” solid electrolyte interphase on Si anodes from the LHCE offers a promising avenue to overcome the challenges of Si anodes in lithium ion batteries.
To enable next-generation high-energy-density lithium (Li)-metal batteries (LMBs), an electrolyte that has simultaneous high Li-metal Coulombic efficiency (CE) and high anodic stability on cathodes ...is of significant importance. Sulfones are known for strong resistance against oxidation, yet their application in LMBs is restricted because of their poor compatibility with Li-metal anodes, high viscosity, and poor wettability. Here, we demonstrate that a high Li CE over 98% can be achieved in concentrated sulfone-based electrolytes. Furthermore, the viscosity and wettability issues of sulfones are resolved by the addition of a fluorinated ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, to form a localized high-concentration electrolyte (LHCE), which not only provides further improvement in Li CE (98.8%) but also remains anodically stable with high-voltage cathodes, suppresses Al corrosion, and enables LMBs to operate in a wide temperature range. As a result, significantly improved cycling performance of LMBs has been realized with sulfone-based LHCE.
Display omitted
•Favorable electrolyte properties and solvation structures in sulfone-based LHCE•Improved Li-metal Coulombic efficiency in LHCE over HCE•Good Al protection for stable high-voltage battery cycling in LHCE
For high-voltage rechargeable lithium (Li)-metal batteries (LMBs), electrolytes with good stabilities on both the highly oxidative cathodes and the highly reductive Li-metal anodes are urgently desired. Sulfones have excellent oxidative stability, yet their high viscosity, poor wettability, and, in particular, incompatibility with Li anodes greatly hinder their applications in LMBs. Here, we demonstrate that a high Li Coulombic efficiency (CE) of 98.2% during repeated Li plating and stripping cycles can be realized in concentrated lithium bis(fluorosulfonyl)imide (LiFSI)-tetramethylene sulfone electrolyte. More importantly, the localized high-concentration electrolyte, formed by the dilution of the high-concentration electrolyte with a non-solvating fluorinated ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, solves the viscosity and wettability issues, further improves Li CE (98.8%), and improves the high-voltage (4.9 V) performance of LMBs with effective Al protection.
High-voltage batteries with Li-metal anodes can offer desirable high energy densities. Despite their excellent oxidative stability, sulfones have various limitations to be useful in Li-metal batteries, in particular their instability with Li metal. Here, we achieved a high Li Coulombic efficiency of nearly 99% in a sulfone-based localized high-concentration electrolyte (LHCE) with the addition of a non-solvating co-solvent. In addition, this co-solvent is highly beneficial for realizing stable battery cycling up to 4.9 V.
The effects of lithium imide and lithium orthoborate dual-salt electrolytes of different salt chemistries in carbonate solvents on the cycling stability of lithium (Li) metal batteries are ...systematically and comparatively investigated. Two imide salts (LiTFSI and LiFSI) and two orthoborate salts (LiBOB and LiDFOB) are chosen for this study and compared with the conventional LiPF6 salt. Density functional theory calculations indicate that the chemical and electrochemical stabilities rank in the following order: LiTFSI-LiBOB > LiTFSI-LiDFOB > LiFSI-LiDFOB > LiFSI-LiBOB. The experimental cycling stability of the Li metal batteries with the electrolytes ranks in the following order: LiTFSI-LiBOB > LiTFSI-LiDFOB > LiFSI-LiDFOB > LiPF6 > LiFSI-LiBOB, which is in well accordance with the calculation results. The LiTFSI-LiBOB can effectively protect the Al substrate and form a more robust surface film on Li metal anode, while the LiFSI-LiBOB results in serious corrosion to the stainless steel cell case and a thicker and looser surface film on Li anode. The key findings of this work emphasize that the salt chemistry is critically important for enhancing the interfacial stability of Li metal anode and should be carefully manipulated in the development of high-performance Li metal batteries.
Nickel–rich layered oxides of LiNi1–x–yCoxMn(Al)yO2 (where 1–x–y>0.6) are considered promising cathode active materials for lithium‐ion batteries (LIBs) due to their high reversible capacity and ...energy density. However, the widespread application of NCM(A) is limited by microstructural degradation caused by the anisotropic shrinkage and expansion of primary particles during the H2→H3 phase transition. In this mini–review, we comprehensively discuss the formation of microcracks, subsequent material degradation, and related alleviation strategies in nickel–rich layered NCM(A). Firstly, theories on microcracks′ formation and evolution mechanisms are presented and critically analyzed. Secondly, recent advancements in mitigation strategies to prevent degradation in Ni–rich NCM/NCA are highlighted. These strategies include doping, surface coating, structural optimization, and morphology engineering. Finally, we provide an outlook and perspective to identify promising strategies that may enable the practical application of Ni–rich NCM/NCA in commercial settings.
Microcracks inevitably form in polycrystalline NCM cathodes during high–voltage operation or prolonged cycling due to internal strain accumulation or phase transition. To address this issue, single or multiple modification strategies such as elemental doping, building single–crystal structures, surface coating, and concentration gradient design can help mitigate microcrack formation and improve cycling capability.
The acoustic characteristics of hydrates are important parameters in geophysical hydrate exploration and hydrate resource estimation. The microscale distribution of hydrate has an important influence ...on the acoustic response of a hydrate-bearing reservoir. Although microscale hydrate distributions can be determined using means such as X-ray computed tomography (X-CT), it is difficult to obtain acoustic parameters for the same sample. In this study, we developed an experimental system that integrated pore-scale visualization and an ultrasonic testing system for methane-hydrate-bearing sediments. Simultaneous X-CT observation and acoustic detection could be achieved in the same hydrate sample, which provided a new method for synchronously monitoring microscale distributions during acoustic testing of natural gas hydrate samples. Hydrate formation experiments were carried out in sandy sediments, during which the acoustic characteristics of hydrate-bearing sediments were detected, while X-ray computed tomography was performed simultaneously. This study found that hydrates formed mainly at the gas–water interface in the early stage, mainly in the pore fluid in the middle stage, and came into contact with sediments in the later stage. The development of this experimental device solved the difficult problem of determining the quantitative relationship between the microscale hydrate distribution and the acoustic properties of the reservoir.
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