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"High voltages"
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Fluorinated ether electrolyte with controlled solvation structure for high voltage lithium metal batteries
The development of new solvents is imperative in lithium metal batteries due to the incompatibility of conventional carbonate and narrow electrochemical windows of ether-based electrolytes. Whereas the fluorinated ethers showed improved electrochemical stabilities, they can hardly solvate lithium ions. Thus, the challenge in electrolyte chemistry is to combine the high voltage stability of fluorinated ethers with high lithium ion solvation ability of ethers in a single molecule. Herein, we report a new solvent, 2,2-dimethoxy-4-(trifluoromethyl)-1,3-dioxolane (DTDL), combining a cyclic fluorinated ether with a linear ether segment to simultaneously achieve high voltage stability and tune lithium ion solvation ability and structure. High oxidation stability up to 5.5 V, large lithium ion transference number of 0.75 and stable Coulombic efficiency of 99.2% after 500 cycles proved the potential of DTDL in high-voltage lithium metal batteries. Furthermore, 20 μm thick lithium paired LiNi
0.8
Co
0.1
Mn
0.1
O
2
full cell incorporating 2 M LiFSI-DTDL electrolyte retained 84% of the original capacity after 200 cycles at 0.5 C.
The development of lithium-metal batteries is limited by the low thermodynamic and/or low voltage stability of conventional electrolytes. Here, the authors combined the high voltage stability of fluorinated ethers with high Li
+
solvation ability of ethers in a single molecule and realized highly stable lithium-metal batteries.
Journal Article
Strong Lewis-acid coordinated PEO electrolyte achieves 4.8 V-class all-solid-state batteries over 580 Wh kg−1
Polyethylene oxide (PEO) based electrolytes critically govern the security and energy density of solid-state batteries, but typically suffer from poor oxidation resistance at high voltages, which limits the energy density of batteries. Here, we report a Lewis-acid coordinated strategy to significantly improve the cyclic stability of 4.8 V-class PEO-based battery. The introduced Mg
2+
and Al
3+
with strong electron-withdrawing capability weaken the electron density of ether oxygen (EO) chains via chelation in the coordination structure, resulting in a locally limited interaction between the EO chains and the surface of cathodes at high state of charge. The batteries using Lewis-acid coordinated electrolytes and Ni-rich cathodes achieve high voltage stability of 4.8 V over 300 cycles. Further, the realization of industrial-scale electrolyte membranes, and Ah-level pouch cells over 586 Wh kg
‒1
with good cyclic stability, suggests the potential of our strategy in practical applications of all-solid-state batteries.
This work reports a Lewis-acid coordinated strategy to improve stability of a 4.8 V-class PEO-based battery. The batteries using Lewis-acid coordinated electrolytes and Ni-rich cathodes achieve high voltage stability of 4.8 V over 300 cycles.
Journal Article
Engineering a passivating electric double layer for high performance lithium metal batteries
In electrochemical devices, such as batteries, traditional electric double layer (EDL) theory holds that cations in the cathode/electrolyte interface will be repelled during charging, leaving a large amount of free solvents. This promotes the continuous anodic decomposition of the electrolyte, leading to a limited operation voltage and cycle life of the devices. In this work, we design a new EDL structure with adaptive and passivating properties. It is enabled by adding functional anionic additives in the electrolyte, which can selectively bind with cations and free solvents, forming unique cation-rich and branch-chain like supramolecular polymer structures with high electrochemical stability in the EDL inner layer. Due to this design, the anodic decomposition of ether-based electrolytes is significantly suppressed in the high voltage cathodes and the battery shows outstanding performances such as super-fast charging/discharging and ultra-low temperature applications, which is extremely hard in conventional electrolyte design principle. This unconventional EDL structure breaks the inherent perception of the classical EDL rearrangement mechanism and greatly improve electrochemical performances of the device.
Developing an electrolyte that is compatible with both high-voltage cathodes and Li metal anodes has always been challenging. Here, the authors created a new strategy by engineering a passivating electric double layer to achieve a fast-charging and lowtemperature high voltage lithium metal batteries.
Journal Article
Electronic structure formed by Y2O3-doping in lithium position assists improvement of charging-voltage for high-nickel cathodes
High-capacity power battery can be attained through the elevation of the cut-off voltage for LiNi
0.83
Co
0.12
Mn
0.05
O
2
high-nickel material. Nevertheless, unstable lattice oxygen would be released during the lithium deep extraction. To solve the above issues, the electronic structure is reconstructed by substituting Li
+
ions with Y
3+
ions. The dopant within the Li layer could transfer electrons to the adjacent lattice oxygen. Subsequently, the accumulated electrons in the oxygen site are transferred to nickel of highly valence state under the action of the reduction coupling mechanism. The modified strategy suppresses the generation of oxygen defects by regulating the local electronic structure, but more importantly, it reduces the concentration of highly reactive Ni
4+
species during the charging state, thus avoiding the evolution of an unexpected phase transition. Strengthening the coupling strength between the lithium layers and transition metal layers finally realizes the fast-charging performance improvement and the cycling stability enhancement under high voltage.
Authors report on restructuring the electronic structure of a high-nickel material by substituting Li
+
ions with Y
3+
ions. This strategy suppresses the generation of oxygen defects with a reduction coupling mechanism improving high-voltage stability.
Journal Article
Stabilizing effects of atomic Ti doping on high-voltage high-nickel layered oxide cathode for lithium-ion rechargeable batteries
High-voltage high-nickel lithium layered oxide cathodes show great application prospects to meet the ever-increasing demand for further improvement of the energy density of rechargeable lithium-ion batteries (LIBs) mainly due to their high output capacity. However, severe bulk structural degradation and undesired electrode-electrolyte interface reactions seriously endanger the cycle life and safety of the battery. Here, 2 mol% Ti atom is used as modified material doping into LiNi
0.6
Co
0.2
Mn
0.2
O
2
(NCM) to reform LiNi
0.6
Co
0.2
Mn
0.18
Ti
0.02
O
2
(NCM-Ti) and address the long-standing inherent problem. At a high cut-off voltage of 4.5 V, NCM-Ti delivers a higher capacity retention ratio (91.8% vs. 82.9%) after 150 cycles and a superior rate capacity (118 vs. 105 mAh·g-1) at the high current density of 10 C than the pristine NCM. The designed high-voltage full battery with graphite as anode and NCM-Ti as cathode also exhibits high energy density (240 Wh·kg-1) and excellent electrochemical performance. The superior electrochemical behavior can be attributed to the improved stability of the bulk structure and the electrode-electrolyte interface owing to the strong Ti-O bond and no unpaired electrons. The
in-situ
X-ray diffraction analysis demonstrates that Ti-doping inhibits the undesired H2-H3 phase transition, minimizing the mechanical degradation. The
ex-situ
TEM and X-ray photoelectron spectroscopy reveal that Ti-doping suppresses the release of interfacial oxygen, reducing undesired interfacial reactions. This work provides a valuable strategic guideline for the application of high-voltage high-nickel cathodes in LIBs.
Journal Article
Boron-doped sodium layered oxide for reversible oxygen redox reaction in Na-ion battery cathodes
Na-ion cathode materials operating at high voltage with a stable cycling behavior are needed to develop future high-energy Na-ion cells. However, the irreversible oxygen redox reaction at the high-voltage region in sodium layered cathode materials generates structural instability and poor capacity retention upon cycling. Here, we report a doping strategy by incorporating light-weight boron into the cathode active material lattice to decrease the irreversible oxygen oxidation at high voltages (i.e., >4.0 V vs. Na
+
/Na). The presence of covalent B–O bonds and the negative charges of the oxygen atoms ensures a robust ligand framework for the NaLi
1/9
Ni
2/9
Fe
2/9
Mn
4/9
O
2
cathode material while mitigating the excessive oxidation of oxygen for charge compensation and avoiding irreversible structural changes during cell operation. The B-doped cathode material promotes reversible transition metal redox reaction enabling a room-temperature capacity of 160.5 mAh g
−1
at 25 mA g
−1
and capacity retention of 82.8% after 200 cycles at 250 mA g
−1
. A 71.28 mAh single-coated lab-scale Na-ion pouch cell comprising a pre-sodiated hard carbon-based anode and B-doped cathode material is also reported as proof of concept.
The irreversible oxygen redox reaction during charging to the high-voltage region causes cathode structural degradation and Na-ion cell capacity fading. Here, the authors report a B-doped cathode active material to mitigate the irreversible oxygen oxidation and increase the cell capacity.
Journal Article
High voltage electrolytes for lithium-ion batteries with micro-sized silicon anodes
Micro-sized silicon anodes can significantly increase the energy density of lithium-ion batteries with low cost. However, the large silicon volume changes during cycling cause cracks for both organic-inorganic interphases and silicon particles. The liquid electrolytes further penetrate the cracked silicon particles and reform the interphases, resulting in huge electrode swelling and quick capacity decay. Here we resolve these challenges by designing a high-voltage electrolyte that forms silicon-phobic interphases with weak bonding to lithium-silicon alloys. The designed electrolyte enables micro-sized silicon anodes (5 µm, 4.1 mAh cm
−2
) to achieve a Coulombic efficiency of 99.8% and capacity of 2175 mAh g
−1
for >250 cycles and enable 100 mAh LiNi
0.8
Co
0.15
Al
0.05
O
2
pouch full cells to deliver a high capacity of 172 mAh g
−1
for 120 cycles with Coulombic efficiency of >99.9%. The high-voltage electrolytes that are capable of forming silicon-phobic interphases pave new ways for the commercialization of lithium-ion batteries using micro-sized silicon anodes.
Micro-sized silicon are promising anode materials due to low-cost and high-energy, yet their application is hindered by inaccessible electrolytes. Here, the authors report sulfolane-based electrolytes that form silicon-phobic interphases and enable high-voltage pouch cells to achieve superior cycle life.
Journal Article
High-voltage and intrinsically safe electrolytes for Li metal batteries
Current electrolytes of mixing different functional solvents inherit both merits and weaknesses of each solvent, thus cannot simultaneously meet all the requirements of high energy, long cycle life, and high safety for Li metal batteries (LMBs). Here, we design a high voltage and safe electrolyte (VSE) by integrating different functional groups into one molecule. The VSE electrolyte has a wide electrochemical stability window of ~5.6 V enabling a Li anode to achieve high Coulombic efficiency of >99.3%, Li | |LiNi
0.8
Co
0.1
Mn
0.1
O
2
coin cell to maintain capacity retention of 92% after 500 cycles, and the 3.5-Ah-grade Li | |LiNi
0.8
Co
0.1
Mn
0.1
O
2
pouch cell to deliver a high energy density of 531 Wh kg
−1
without any flame and expansion after cycled under extreme conditions. The VSE electrolyte even enables 5.0 V Li | |LiNi
0.5
Mn
1.5
O
4
cells to charge/discharge for 200 cycles without capacity decay. This work provides a promising direction for the rational design of high-voltage and intrinsically safe electrolytes for LMBs.
This work provides a high voltage and intrinsically safe electrolyte (VSE) designed by integrating different functional groups into one molecule that enables Li metal batteries to safely operate at high temperatures and achieve a high energy density.
Journal Article
3D printed polyamide membranes for desalination
Commercial reverse osmosis processes for water desalination use membranes made by the polymerization of polyamide at the oil/water interface. Chowdhury et al. show that thinner, smoother membranes can be made with an electrospray technique. Using high voltage, the two precursors are finely sprayed onto a substrate and polymerize on contact. The composition of the resulting membrane can be tuned on the basis of the proportion of the two components. At optimum conditions, the membranes appear to be better at desalination than current commercial reverse osmosis membranes. Science , this issue p. 682 Electrospraying precursors leads to a smoother, more efficient polyamide water purification membrane. Polyamide thickness and roughness have been identified as critical properties that affect thin-film composite membrane performance for reverse osmosis. Conventional formation methodologies lack the ability to control these properties independently with high resolution or precision. An additive approach is presented that uses electrospraying to deposit monomers directly onto a substrate, where they react to form polyamide. The small droplet size coupled with low monomer concentrations result in polyamide films that are smoother and thinner than conventional polyamides, while the additive nature of the approach allows for control of thickness and roughness. Polyamide films are formed with a thickness that is controllable down to 4-nanometer increments and a roughness as low as 2 nanometers while still exhibiting good permselectivity relative to a commercial benchmarking membrane.
Journal Article