Chongyin Yang

Zn/MnO2 Battery Chemistry With H+ and Zn2+ Coinsertion

Rechargeable aqueous Zn/MnO2 battery chemistry in a neutral or mildly acidic electrolyte has attracted extensive attention recently because all the components (anode, cathode, and electrolyte) in a Zn/MnO2 battery are safe, abundant, and sustainable. However, the reaction mechanism of the MnO2 cathode remains a topic of discussion. Herein, we design a highly reversible aqueous Zn/MnO2 battery where the binder-free MnO2 cathode was fabricated by in situ electrodeposition of MnO2 on carbon fiber paper in mild acidic ZnSO4+MnSO4 electrolyte. Electrochemical and structural analysis identify that the MnO2 cathode experience a consequent H+ and Zn2+ insertion/extraction process with high reversibility and cycling stability. To our best knowledge, it is the first report on rechargeable aqueous batteries with a consequent ion-insertion reaction mechanism.

High power rechargeable magnesium/iodine battery chemistry

Rechargeable magnesium batteries have attracted considerable attention because of their potential high energy density and low cost. However, their development has been severely hindered because of the lack of appropriate cathode materials. Here we report a rechargeable magnesium/iodine battery, in which the soluble iodine reacts with Mg2+ to form a soluble intermediate and then an insoluble final product magnesium iodide. The liquid–solid two-phase reaction pathway circumvents solid-state Mg2+ diffusion and ensures a large interfacial reaction area, leading to fast reaction kinetics and high reaction reversibility. As a result, the rechargeable magnesium/iodine battery shows a better rate capability (180 mAh g−1 at 0.5 C and 140 mAh g−1 at 1 C) and a higher energy density (∼400 Wh kg−1) than all other reported rechargeable magnesium batteries using intercalation cathodes. This study demonstrates that the liquid–solid two-phase reaction mechanism is promising in addressing the kinetic limitation of rechargeable magnesium batteries.

Stabilizing high voltage LiCoO2 cathode in aqueous electrolyte with interphase-forming additive

Aqueous lithium ion batteries (ALIBs) receive increasing attention due to their intrinsic non-flammable nature. Their practical application, however, has been prevented by the poor electrochemical stability of aqueous electrolytes, which severely restricts the choice of anode and cathode materials for such batteries and leads to low energy densities. It has been demonstrated that “water-in-salt” electrolytes can provide an expanded voltage window of ∼3.0 V, which can accommodate electrode materials that were otherwise forbidden in conventional aqueous electrolytes. In this study, we showed that the presence of an additive could further stabilize the aqueous electrolyte at a high voltage cathode surface. By forming a cathode electrolyte interphase (CEI) through electrochemical oxidation of tris(trimethylsilyl) borate (TMSB), we successfully stabilized LiCoO2 in water-in-salt electrolyte at a high cut-off voltage that corresponds to 0.7e electron charge transfer. To the best of our knowledge, this is also the first electrolyte additive known to form an interphase in aqueous electrolytes. The formed CEI significantly suppressed electrolyte oxidation as well as cobalt dissolution from LiCoO2 into electrolytes, allowing LiCoO2 to be stably charged/discharged at a higher cut-off voltage with a high capacity utilization of 170 mA h g−1. When paired with an Mo6S8 anode, the 2.5 V aqueous full cell delivered a high energy density of 120 W h kg−1 for 1000 cycles with an extremely low capacity decay rate of 0.013% per cycle.

Unique aqueous Li-ion/sulfur chemistry with high energy density and reversibility

Significance Sulfur as an anode coupled with a lithium-ion intercalation cathode in the superconcentrated aqueous electrolyte creates a unique Li-ion/sulfur chemistry, realizing the highest energy density ever achieved in aqueous batteries, along with high safety and excellent cycle-life. Mechanism investigation finds that the reversible sulfur lithiation/delithiation in such an aqueous electrolyte proceeds with fast kinetics that significantly differ from that in nonaqueous systems, whereas polysulfides’ insolubility in such an aqueous electrolyte essentially eliminates the parasitic shuttling. The excellent performances of Li-ion/sulfur cells not only find an application of “water-in-salt” electrolyte for beyond Li-ion chemistries, more importantly, an alternative pathway is provided to solve the “polysulfide shuttling” that has been plaguing the sulfur chemistries in nonaqueous electrolytes. Leveraging the most recent success in expanding the electrochemical stability window of aqueous electrolytes, in this work we create a unique Li-ion/sulfur chemistry of both high energy density and safety. We show that in the superconcentrated aqueous electrolyte, lithiation of sulfur experiences phase change from a high-order polysulfide to low-order polysulfides through solid–liquid two-phase reaction pathway, where the liquid polysulfide phase in the sulfide electrode is thermodynamically phase-separated from the superconcentrated aqueous electrolyte. The sulfur with solid–liquid two-phase exhibits a reversible capacity of 1,327 mAh/(g of S), along with fast reaction kinetics and negligible polysulfide dissolution. By coupling a sulfur anode with different Li-ion cathode materials, the aqueous Li-ion/sulfur full cell delivers record-high energy densities up to 200 Wh/(kg of total electrode mass) for >1,000 cycles at ∼100% coulombic efficiency. These performances already approach that of commercial lithium-ion batteries (LIBs) using a nonaqueous electrolyte, along with intrinsic safety not possessed by the latter. The excellent performance of this aqueous battery chemistry significantly promotes the practical possibility of aqueous LIBs in large-format applications.

High-Voltage Aqueous Magnesium Ion Batteries

Nonaqueous rechargeable magnesium (Mg) batteries suffer from the complicated and moisture-sensitive electrolyte chemistry. Besides electrolytes, the practicality of a Mg battery is also confined by the absence of high-performance electrode materials due to the intrinsically slow Mg2+ diffusion in the solids. In this work, we demonstrated a rechargeable aqueous magnesium ion battery (AMIB) concept of high energy density, fast kinetics, and reversibility. Using a superconcentration approach we expanded the electrochemical stability window of the aqueous electrolyte to 2.0 V. More importantly, two new Mg ion host materials, Li superconcentration approach we expanded the electrochemical stability window of the aqueous electrolyte to 2.0 V. More importantly, two new Mg ion host materials, Li3V2(PO4)3 and poly pyromellitic dianhydride, were developed and employed as cathode and anode electrodes, respectively. Based on comparisons of the aqueous and nonaqueous systems, the role of water is identified to be critical in the Mg ion mobility in the intercalation host but remaining little detrimental to its non-diffusion controlled process. Compared with the previously reported Mg ion cell delivers an unprecedented high power density of 6400 W kg ion cell delivers an unprecedented high power density of 6400 W kg while retaining 92% of the initial capacity after 6000 cycles, pushing the Mg ion cell to a brand new stage.

Non-flammable electrolyte enables Li-metal batteries with aggressive cathode chemistries

Rechargeable Li-metal batteries using high-voltage cathodes can deliver the highest possible energy densities among all electrochemistries. However, the notorious reactivity of metallic lithium as well as the catalytic nature of high-voltage cathode materials largely prevents their practical application. Here, we report a non-flammable fluorinated electrolyte that supports the most aggressive and high-voltage cathodes in a Li-metal battery. Our battery shows high cycling stability, as evidenced by the efficiencies for Li-metal plating/stripping (99.2%) for a 5 V cathode LiCoPO4 (~99.81%) and a Ni-rich LiNi0.8Mn0.1Co0.1O2 cathode (~99.93%). At a loading of 2.0 mAh cm−2, our full cells retain ~93% of their original capacities after 1,000 cycles. Surface analyses and quantum chemistry calculations show that stabilization of these aggressive chemistries at extreme potentials is due to the formation of a several-nanometre-thick fluorinated interphase.A fluorinated electrolyte forms a few-nanometre-thick interface both at the anode and the cathode that stabilizes lithium-metal battery operation with high-voltage cathodes.

Intercalation of Bi nanoparticles into graphite results in an ultra-fast and ultra-stable anode material for sodium-ion batteries

Sodium ion batteries (SIBs) have been revived as important alternative energy storage devices for large-scale energy storage, which requires SIBs to have a long cycling life and high power density. However, the scarcity of suitable anode materials hinders their application. Herein, we report a bismuth intercalated graphite (Bi@Graphite) anode material, which is substantially different from the previously reported metal@Graphene. In Bi@Graphite, the Bi nanoparticles between graphite interlayers enhance the capacity, while the graphite sheath provides a robust fast electronic connection for long cycling stability. The Bi@Graphite possesses a safe average storage potential of approximately 0.5 V vs. Na/Na+, delivers a capacity of ∼160 mA h g−1 at 1C (160 mA g−1), exhibits outstanding cycling stability (ca. 90% capacity retention for 10 000 cycles at 20C), and can maintain 70% capacity at 300C (∼110 mA h g−1 at 48 A g−1), which is equivalent to full charge/discharge in 12 s. Bi@Graphite demonstrates the highest rate-capability ever reported among all anodes for SIBs. Detailed characterization results indicate that the unique Bi nanoparticle-in-graphite structure and the fast kinetics of ether co-intercalation into graphite are responsible for these significant improvements, which could translate into SIBs with excellent power densities.

Author Correction: Non-flammable electrolyte enables Li-metal batteries with aggressive cathode chemistries

In the version of this Article originally published, in the first paragraph of the Methods, HFE was incorrectly given as 2,2,2-Trifluoroethyl-3ʹ,3ʹ,3ʹ,2ʹ,2ʹ-pentafluoropropyl ether; it should have been 1,1,2,2-tetrafluoroethyl-2ʹ,2ʹ,2ʹ-trifluoroethyl ether. This has now been corrected in the online versions of the Article.