A Reconfigurable Two-WSe2 -Transistor Synaptic Cell for Reinforcement Learning.

Reward-modulated spike-timing-dependent plasticity (R-STDP) is a brain-inspired reinforcement learning (RL) rule, exhibiting potential for decision-making tasks and artificial general intelligence. However, the hardware implementation of the reward-modulation process in R-STDP usually requires complicated Si complementary metal-oxide-semiconductor (CMOS) circuit design that causes high power consumption and large footprint. Here, a design with two synaptic transistors (2T) connected in a parallel structure is experimentally demonstrated. The 2T unit based on WSe2 ferroelectric transistors exhibits reconfigurable polarity behavior, where one channel can be tuned as n-type and the other as p-type due to nonvolatile ferroelectric polarization. In this way, opposite synaptic weight update behaviors with multilevel (>6 bit) conductance states, ultralow nonlinearity (0.56/-1.23), and large Gmax /Gmin ratio of 30 are realized. By applying positive/negative reward to (anti-)STDP component of 2T cell, R-STDP learning rules are realized for training the spiking neural network and demonstrated to solve the classical cart-pole problem, exhibiting a way for realizing low-power (32 pJ per forward process) and highly area-efficient (100 µm2 ) hardware chip for reinforcement learning.

MoO2@C modified separator as an interlayer for high performance lithium-sulfur batteries.

Lithium-sulfur batteries have attracted much attention as a promising next-generation energy storage system due to their high theoretical specific capacity and energy density. However, lithium-sulfur batteries are still facing some problems that hinder their large-scale commercial application. High conductivity molybdenum dioxide coated with carbon composite (MoO2@C) were introduced to coat the separator to study its application in lithium sulfur batteries. Molybdenum dioxide coated with carbon composite nanoparticles were synthesized by hydrothermal method and high-temperature calcination and then was coated on the separator with acetylene black. The coating layer can take advantage of the synergetic effect of physical barrier and chemical adsorption to reduce the loss of active substances. The electrochemical performance of the battery has been improved by applying MoO2@C in lithium-sulfur separator. The first discharge specific capacity is 917 mA h g-1 under the current density of 1.0 A g-1, after 300 cycles, the capacity is 618 mA h g-1; after 200 cycles under the current density of 2.0 A g-1, the reversible specific capacity can still maintain 551 mA h g-1.

MoO2 nanoparticles embedded in N-doped hydrangea-like carbon as a sulfur host for high-performance lithium-sulfur batteries.

Lithium-sulfur batteries are considered to be promising energy storage devices owing to their high energy density, relatively low price and abundant resources. However, the low utilization of insulated active materials and shuttle effect have severely hindered the further development of lithium-sulfur batteries. Herein, MoO2 nanoparticles embedded in N-doped hydrangea-like carbon have been synthesized by liquid-phase reaction followed by an annealing process and used as a sulfur host. The nitrogen-doped carbon matrix improves electrical conductivity and provides pathways for smooth electron and Li ion transfer to uniformly dispersed sulfur. Meanwhile, MoO2 nanoparticles can absorb polysulfide ions by forming strong chemical bonds, which can effectively alleviate the polysulfide shuttling effect. These results showed a good rate performance: 1361, 1071, 925, 815 and 782 mA h g-1 at the current densities of 0.1, 0.2, 0.5, 1 and 2 A g-1, and capacity retention of 85% after 300 cycles at 1 A g-1. The excellent performance was due to the synergistic effects of the polar MoO2 and nitrogen-doped carbon matrix, which can effectively restrain and reutilize active materials by absorbing polysulfides and catalyzing the transformation of polysulfides.

A rational design of the coupling mechanism of physical adsorption and chemical charge effect for high-performance lithium-sulfur batteries.

Lithium sulfur batteries are considered as potential energy storage systems for electrical devices owing to their high energy density, low cost, and environmental friendliness. However, the hasty capacity fading originating from the solution and migration of polysulfides is the major obstacle for their industrial application. The polysulfide adsorption and repulsion effect achieved by adding an extra coating layer on the side of the cathode and separator have been separately proved to be effective in mitigating the shuttle effect. Herein, a cooperative coated separator, which employs a hybrid carbon matrix as the coated material, including an appropriate ratio of N-doped activated conductive carbon and commercial acetylene black, and sulfonated polystyrene as the binder, is established to prevent the migration of polysulfides and serves as a secondary current collector to reutilize the active materials for high-performance lithium sulfur batteries. The research results showed that the coated separator with 50 wt% N-doped activated conductive carbon as the coating material and sulfonated polystyrene as the binder showed highlighted cycle performance, and 731 mA h g-1 was maintained after 150 cycles at 800 mA g-1(the capacity retention was 86.0%). The superior performance may be because the coated separator can efficiently restrain the polysulfides by physical and chemical effects and also reject the polysulfides by the anion electrostatic effect. In summary, this study provides a new cooperative way to address the shuttle effect and promotes the development of lithium sulfur batteries.