Due to the non-flammable nature of water-based electrolytes, aqueous lithium-ion batteries are resistant to catching fire. However, they are not immune to the risk of explosion, since the sealing ...structure adopted by current batteries limits the dissipation of heat and pressure within the cells. Here, we report a safe aqueous lithium-ion battery with an open configuration using water-in-salt electrolytes and aluminum oxide coated anodes. The design can inhibit the self-discharge by substantially suppressing the oxygen reduction reaction on lithiated anodes and enable good cycle performance over 1000 times. Our study may open a pathway towards safer lithium-ion battery designs.
In carbonate electrolytes, the organic–inorganic solid electrolyte interphase (SEI) formed on the Li‐metal anode surface is strongly bonded to Li and experiences the same volume change as Li, thus it ...undergoes continuous cracking/reformation during plating/stripping cycles. Here, an inorganic‐rich SEI is designed on a Li‐metal surface to reduce its bonding energy with Li metal by dissolving 4m concentrated LiNO3 in dimethyl sulfoxide (DMSO) as an additive for a fluoroethylene‐carbonate (FEC)‐based electrolyte. Due to the aggregate structure of NO3− ions and their participation in the primary Li+ solvation sheath, abundant Li2O, Li3N, and LiNxOy grains are formed in the resulting SEI, in addition to the uniform LiF distribution from the reduction of PF6− ions. The weak bonding of the SEI (high interface energy) to Li can effectively promote Li diffusion along the SEI/Li interface and prevent Li dendrite penetration into the SEI. As a result, our designed carbonate electrolyte enables a Li anode to achieve a high Li plating/stripping Coulombic efficiency of 99.55 % (1 mA cm−2, 1.0 mAh cm−2) and the electrolyte also enables a Li||LiNi0.8Co0.1Mn0.1O2 (NMC811) full cell (2.5 mAh cm−2) to retain 75 % of its initial capacity after 200 cycles with an outstanding CE of 99.83 %.
An inorganic‐rich solid electrolyte interphase (SEI) has been constructed on Li metal to promote dense Li growth with a Coulombic efficiency of 99.55 % in the carbonate electrolyte. It was synthesized on the surface of the Li‐metal anode using concentrated LiNO3 in dimethyl sulfoxide (DMSO) as an additive in the FEC‐based electrolyte, which participates in the primary Li+ solvation shell and promotes the reduction of NO3− ions to form the inorganic‐rich SEI.
Layered metal oxides have been widely used as the best cathode materials for commercial lithium-ion batteries and are being intensively explored for sodium-ion batteries. However, their application ...to potassium-ion batteries (PIBs) is hampered because of the poor cycling stability and low rate capability due to the larger ionic size of K+ than of Li+ or Na+. Herein, a facile self-templated strategy was used to synthesize unique P2-type K0.6CoO2 microspheres that consist of aggregated primary nanoplates as PIB cathodes. The unique K0.6CoO2 microspheres with aggregated structure significantly enhanced the kinetics of the K+ intercalation/deintercation and also minimized the parasitic reactions between the electrolyte and K0.6CoO2. The P2-K0.6CoO2 microspheres demonstrated a high reversible capacity of 82 mAh g–1 at 10 mA g–1, high rate capability of 65 mAh g–1 at 100 mA g–1, and long cycle life (87% capacity retention over 300 cycles). The high reversibility of the P2-K0.6CoO2 full cell paired with a hard carbon anode further demonstrated the feasibility of PIBs. This work not only successfully demonstrates exceptional performance of P2-type K0.6CoO2 cathodes and microspheres K0.6CoO2∥hard carbon full cells, but also provides new insights into the exploration of other layered metal oxides for PIBs.
Organic compounds are desirable alternatives for sustainable lithium‐ion battery electrodes. However, the electrochemical properties of state‐of‐the‐art organic electrodes are still worse than ...commercial inorganic counterparts. Here, a new chemistry is reported based on the electrochemical conversion of nitro compounds to azo compounds for high performance lithium‐ion batteries. 4‐Nitrobenzoic acid lithium salt (NBALS) is selected as a model nitro compound to systemically investigate the structure, lithiation/delithiation mechanism, and electrochemical performance of nitro compounds. NBALS delivers an initial capacity of 153 mAh g−1 at 0.5 C and retains a capacity of 131 mAh g−1 after 100 cycles. Detailed characterizations demonstrate that during initial electrochemical lithiation, the nitro group in crystalline NBALS is irreversibly reduced into an amorphous azo compound. Subsequently, the azo compound is reversibly lithiated/delithiated in the following charge/discharge cycles with high electrochemical performance. The lithiation/delithiation mechanism of azo compounds is also validated by directly using azo compounds as electrode materials, which exhibit similar electrochemical performance to nitro compounds, while having a much higher initial Coulombic efficiency. Therefore, this work proves that nitro compounds can be electrochemically converted to azo compounds for high performance lithium‐ion batteries.
A new chemistry is unveiled to electrochemically convert nitro compounds into azo compounds, which act as active materials to reversibly react with lithium ions. The discovery of nitro and azo compounds for organic electrodes offers new opportunities for high‐performance lithium‐ion batteries.
High electrochemical reversibility of the TiS2 anode in “Water-in-Salt” electrolyte (21m LiTFSI in H2O) is demonstrated for the first time. The wide electrochemical window and low chemical activity ...of H2O in the “Water-in-Salt” electrolyte not only significantly enhanced the electrochemical reversibility of TiS2 but also effectively suppressed the hydrolysis side reaction in the aqueous electrolyte. Paired with a LiMn2O4 cathode, the LiMn2O4/TiS2 full cell delivers a relatively high discharge voltage of 1.7 V and an energy density of 78Whkg−1 as well as a satisfactory rate performance.
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•“Water-in-Salt” electrolyte featured with wide electrochemical window.•TiS2 can be used as an anode in aqueous Li-ion battery for the first time.•LiMn2O4/TiS2 full cell delivers a high energy density of 78Whkg−1.
Electrolytes that are able to reversibly deposit/strip Mg are crucial for rechargeable Mg batteries. The most studied complex electrolytes based on Lewis acid‐base chemistry are expensive, difficult ...to be synthesized, and show limited anodic stability. Conventional electrolytes using simple salts such as Mg(TFSI)2 can be readily synthesized, but Mg deposition/stripping in these simple salt electrolytes is accompanied by a large overpotential due to the formation of a surface layer on the Mg metal with a low Mg ion conductivity. Here the overpotential for Mg deposition/stripping in a simple salt, Mg(TFSI)2‐1,2‐dimethoxyethane (DME), electrolyte is significantly reduced by adding a small concentration of iodine (≤50 × 10−3m) as an additive. Mechanism studies demonstrate that an Mg ion conductive solid MgI2 layer is formed on the surface of the Mg metal and acts as a solid electrolyte interface. With the Mg(TFSI)2‐DME‐I2 electrolyte, a very small voltage hysteresis is achieved in an Mg‐S full cell.
A solid electrolyte interphase (SEI) layer is formed due to the reaction of iodine with Mg, whose main component is magnesium iodide. This SEI layer dramatically decreases the overpotential of Mg deposition/stripping, hence enabling the usage of simple electrolyte Mg(TFSI)2‐1,2‐dimethoxyethane (DME) in full cells. For the first time, the SEI concept is successfully used in Mg batteries to address the interfacial kinetics problem.
Magnesium redox chemistry is a very appealing “beyond Li ion chemistry” for realizing high energy density batteries due to the high capacity, low reduction potential, and most importantly, highly ...reversible and dendrite-free Mg metal anode. However, the progress of rechargeable Mg batteries has been greatly hindered by shortage of electrolytes with wide stability window, high ionic conductivity, and good compatibility with cathode materials. Unlike solid electrolyte interphase on Li metal anode, surface film formed by electrolyte decomposition in Mg batteries was considered to block Mg ion transport and passivate Mg electrode. For this reason, the attention of the community has been mainly focusing on surface layer free electrolytes, while reductively unstable salts/solvents are barely considered, despite many of them possessing all the necessary properties for good electrolytes. Here, for the first time, we demonstrate that the surface film formed by electrolyte decomposition can function as a solid electrolyte interphase (SEI). Using Mg/S chemistry as a model system, the SEI formation mechanism on Mg metal anode was thoroughly examined using electrochemical methods and surface chemistry characterization techniques such as EDX and XPS. On the basis of these results, a comprehensive view of the Mg/electrolyte interface that unifies both the SEI mechanism and the passivation layer mechanism is proposed. This new picture of surface layer on Mg metal anode in Mg batteries not only revolutionizes current understanding of Mg/electrolyte interface but also opens new avenues for electrolyte development by uncovering the potential of those reductively unstable candidates through interface design.
Recent breakthroughs in aqueous electrolytes made highly safe 3.0 V class aqueous Li-ion batteries possible. However, the formed solid-electrolyte interphase therein still cannot effectively support ...the desired energy-dense anode and cathode materials. In this work, we report a new class of electrolytes, by hybridizing aqueous with non-aqueous solvents, that inherits the non-flammability and non-toxicity characteristics from aqueous and better electrochemical stability from non-aqueous systems. The secondary interphasial ingredient (alkylcarbonate) introduced by non-aqueous component helps to expand the electrochemical window of the hybridized electrolyte to 4.1 V, which supports the operation of a 3.2 V aqueous Li-ion battery based on Li4Ti5O12 and LiNi0.5Mn1.5O4 to deliver a high energy density of 165 Wh/kg for >1,000 cycles. The understanding of how a better interphase could be tailored by regulating the inner-Helmholtz interfacial structures of the hybridized electrolyte provides important guidelines for designing future electrolytes and interphases for new battery chemistries.
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•A new hybrid aqueous/non-aqueous electrolyte (HANE) is demonstrated•HANE inherits merits from electrolytes of both aqueous and non-aqueous natures•Investigated the evolution of inner-Helmholtz interface under different potentials•The interphase chemistry allows a 3.2 V Li4Ti5O12/LiNi0.5Mn1.5O4 full cell
A new class of electrolyte is created by hybridizing aqueous and non-aqueous components. Named hybrid aqueous/non-aqueous electrolyte (HANE), it bridges the once-clear demarcation between aqueous and non-aqueous electrolytes and inherits merits from both. A Li-ion battery based on Li4Ti5O12/LiNi0.5Mn1.5O4 was demonstrated to deliver performances comparable with those of the state-of-the-art non-aqueous Li-ion batteries, as represented by the high working voltage of 3.2 V, energy density of 165 Wh/kg, and cycling stability beyond 1,000 cycles. The correlation established between solvation structure in HANE and the resultant interphase on anode surfaces provides insights for how to design a better interphase by regulating the inner-Helmholtz regions.
Hybrid aqueous/non-aqueous electrolyte (HANE) inherits the merits from both aqueous (non-flammability) and non-aqueous (high electrochemical stability) systems. Its unique assembly at the inner-Helmholtz interface leads to an interphasial chemistry that supports a 3.2 V Li4Ti5O12/LiNi0.5Mn1.5O4 full aqueous Li-ion battery with performances comparable with state-of-the-art Li-ion batteries.
Although recent efforts have expanded the stability window of aqueous electrolytes from 1.23 V to >3 V, intrinsically safe aqueous batteries still deliver lower energy densities (200 Wh/kg) compared ...with state-of-the-art Li-ion batteries (∼400 Wh/kg). The essential origin for this gap comes from their cathodic stability limit, excluding the use of the most ideal anode materials (graphite, Li metal). Here, we resolved this “cathodic challenge” by adopting an “inhomogeneous additive” approach, in which a fluorinated additive immiscible with aqueous electrolyte can be applied on anode surfaces as an interphase precursor coating. The strong hydrophobicity of the precursor minimizes the competitive water reduction during interphase formation, while its own reductive decomposition forms a unique composite interphase consisting of both organic and inorganic fluorides. Such effective protection allows these high-capacity/low-potential anode materials to couple with different cathode materials, leading to 4.0 V aqueous Li-ion batteries with high efficiency and reversibility.
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•A new aqueous solid-electrolyte-interphase (SEI) is engineered•This SEI stabilized graphite and lithium-metal anodes in aqueous electrolyte•4.0 V class aqueous LIBs with high energy density and safety are enabled
Constrained by the narrow electrochemical stability window of water (1.23 V under thermodynamic equilibria), aqueous batteries have always been considered subpar to their non-aqueous counterparts in terms of energy density, although the latter bear the intrinsic disadvantages of being flammable, toxic, and sensitive to ambient atmosphere. Here, we report a unique strategy of stabilizing lithium metal or graphite in an aqueous electrolyte, so that a series of 4 V class aqueous Li-ion chemistries could be enabled. Such aqueous Li-ion batteries, expected to offer energy densities approaching those of non-aqueous Li-ion batteries, but without the safety concern of the latter, represent a significant advance on the fundamental level of battery materials.
4.0 V aqueous LIBs of both high energy density and high safety are made possible by a new interphase formed from an “inhomogeneous additive” approach that effectively stabilizes graphite or lithium-metal anode materials.
A system of electrolytes using water as a solvent was successfully used to support a typical lithium-ion battery chemistry that operates at 3.7V–4.2 V using standard ultraviolet-cured acrylic-based ...polymers as hydrophobic barriers. The aqueous electrolyte is contained in a system of poly(ethylene glycol) acrylate polymers crosslinked to produce an electrolyte gel that has electrochemical properties similar to that of the liquid phase component. The electrolyte gels have elastic moduli in the kPa range, making them soft enough to tolerant flexing, cutting, and blunt force impacts while keeping the electrodes covered and safe from shorting. While batteries based on water-in-salt electrolyte provides intrinsic safety that is otherwise unavailable from typical non-aqueous electrolytes, acrylate-based aqueous gel electrolytes offer the potential of large-scale manufacturing owing to the relatively low volatility of the electrolyte components and the low complexity of the proposed manufacturing process.
•UV-cured gel electrolytes were used to construct a 4 V lithium ion battery.•The main gel electrolyte was water-based, making the battery safe.•Gel electrolytes had conductivity ≥0.3 mS/cm.•Gel electrolytes exhibited favorable impedance characteristics.•Battery cells used graphite anodes and LiCoO2 cathodes.
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