Zinc-ion batteries are under current research focus because of their uniqueness in low cost and high safety. However, it is still desirable to improve the rate performance by improving the Zn (de)intercalation kinetics and long-cycle stability by eliminating the dendrite formation problem. Herein, the first paradigm of a high-rate and ultrastable flexible quasi-solid-state zinc-ion battery is constructed from a novel 2D ultrathin layered zinc orthovanadate array cathode, a Zn array anode supported by a conductive porous graphene foam, and a gel electrolyte. The nanoarray structure for both electrodes assures the high rate capability and alleviates the dendrite growth. The flexible Zn-ion battery has a depth of discharge of ≈100% for the cathode and 66% for the anode, and delivers an impressive high-rate of 50 C (discharge in 60 s), long-term durability of 2000 cycles at 20 C, and unprecedented energy density ≈115 Wh kg , together with a peak power density ≈5.1 kW kg (calculation includes masses of cathode, anode, and current collectors). First principles calculations and quantitative kinetics analysis show that the high-rate and stable properties are correlated with the 2D fast ion-migration pathways and the introduced intercalation pseudocapacitance.

The synaptic activities in the nervous system is the basis of memory and learning behaviors, and the concept of biological synapse has also spurred the development of neuromorphic engineering. In recent years, the hardware implementation of the biological synapse has been achieved based on CMOS circuits, resistive switching memory, and field effect transistors with ionic dielectrics. However, the artificial synapse with regulatable plasticity has never been realized of the device level. Here, an artificial dynamic synapse based on twisted bilayer graphene is demonstrated with tunable plasticity. Due to the ambipolar conductance of graphene, both behaviors of the excitatory synapse and the inhibitory synapse could be realized in a single device. Moreover, the synaptic plasticity could also be modulated by tuning the carrier density of graphene. Because the artificial synapse here could be regulated and inverted via changing the bottom gate voltage, the whole process of synapse development could be imitated. Hence, this work would offer a broad new vista for the 2D material electronics and guide the innovation of neuro-electronics fundamentally.

Application of high-voltage spinel LiNi 0.5 Mn 1.5 O 4 cathode material is the closest and the most realistic approach to meeting the midterm goal of lithium-ion batteries for electric vehicles (EVs) and plug-in hybrid electric vehicles (HEVs). However, this application has been hampered by long-standing issues, such as capacity degradation and poor first-cycle Coulombic efficiency of LiNi 0.5 Mn 1.5 O 4 cathode material. Although it is well-known that the structure of LiNi 0.5 Mn 1.5 O 4 into which Li ions are reversibly intercalated plays a critical role in the above issues, performance degradation related to structural changes, particularly in the first cycle, are not fully understood. Here, we report detailed investigations of local atomic-level and average structure of LiNi 0.5 Mn 1.5 O 4 during first cycle (3.5−4.9 V) at room temperature. We observed two types of local atomic-level migration of transition metals (TM) ions in the cathode of a well-prepared LiNi 0.5 Mn 1.5 O 4 //Li half-cell during first charge via an aberration-corrected scanning transmission electron microscopy (STEM). Surface regions (∼2 nm) of the cycled LiNi 0.5 Mn 1.5 O 4 particles show migration of TM ions into tetrahedral Li sites to form a Mn 3 O 4 -like structure. However, subsurface regions of the cycled particles exhibit migration of TM ions into empty octahedral sites to form a rocksalt-like structure. The migration of these TM ions are closely related to dissolution of Ni/Mn ions and building-up of charge transfer impedance, which contribute significantly to the capacity degradation and the poor first-cycle Coulombic efficiency of spinel LiNi 0.5 Mn 1.5 O 4 cathode material. Accordingly, we provide suggestions of effective stabilization of LiNi 0.5 Mn 1.5 O 4 structure to obtain better electrochemical performance.