Reducing voltage hysteresis of metal oxide anodes to achieve high energy efficiency for Li-ion batteries

In the past two decades,a lot of high-capacity conversion-type metal oxides have been intensively studied as alternative anode materials for Li-ion batteries with higher energy density.Unfortunately,their large voltage hysteresis(0.8-1.2 V) within reversed conversion reactions results in huge round-trip inefficiencies and thus lower energy efficiency(50%-75%) in full cells than those with graphite anodes.This remains a long-term open question and has been the most serious drawback toward application of metal oxide anodes.Here we clarify the origins of voltage hysteresis in the typical SnO2anode and propose a universal strategy to minimize it.With the established in situ phosphating to generate metal phosphates during reversed conversion reactions in synergy with boosted reaction kinetics by the added P and Mo,the huge voltage hysteresis of 0.9 V in SnO_(2),SnO_(2)-Mo,and 0.6 V in SnO2-P anodes is minimized to 0.3 V in a ternary SnO_(2)-Mo-P(SOMP) composite,along with stable high capacity of 936 mA h g^(-1)after 800 cycles.The small voltage hysteresis can remain stable even the SOMP anode operated at high current rate of10 A g^(-1)and wide-range temperatures from 60 to 30℃,resulting in a high energy efficiency of88.5% in full cells.This effective strategy to minimize voltage hysteresis has also been demonstrated in Fe2O3,Co3O4-basded conversion-type anodes.This work provides important guidance to advance the high-capacity metal oxide anodes from laboratory to industrialization.

Effects of stress dependent electrochemical reaction on voltage hysteresis of lithium ion batteries

Intercalation of lithium ions into the electrodes of lithium ion batteries is affected by the stress of active materials, leading to energy dissipation and stress dependent voltage hysteresis. A reaction-diffusion-stress coupling model is established to investigate the stress effects under galvanostatic and potentiostatic operations. It is found from simulations that the stress hysteresis contributes to the voltage hysteresis and leads to the energy dissipation. In addition, the stress induced voltage hysteresis is small in low rate galvanostatic operations but extraordinarily significant in high rate cases. In potentiostatic operations, the stresses and stress induced overpotentials increase to a peak value very soon after the operation commences and decays all the left time. Therefore,a combined charge-discharge operation is suggested, i.e., first the galvanostatic one and then the potentiostatic one. This combined operation can not only avoid the extreme stress during operations so as to prevent electrodes from failure but also reduce the voltage hysteresis and energy dissipation due to stress effects.

Characteristics and mechanisms of subthreshold voltage hysteresis in 4H-SiC MOSFETs

In order to investigate the characteristics and mechanisms of subthreshold voltage hysteresis(ΔV_(th,sub)) of 4 H-SiC metal-oxide-semiconductor field-effect transistors(MOSFETs),4 H-SiC planar and trench MOSFETs and corresponding P-type planar and trench metal-oxide-semiconductor(MOS) capacitors are fabricated and characterized.Compared with planar MOSFEF,the trench MOSFET shows hardly larger ΔV_(th,sub) in wide temperature range from 25 0 C to 300 0 C.When operating temperature range is from 25 ℃ to 300 ℃,the off-state negative V_(gs) of planar and trench MOSFETs should be safely above-4 V and-2 V,respectively,to alleviate the effect of ΔV_(th,sub) on the normal operation.With the help of P-type planar and trench MOS capacitors,it is confirmed that the obvious ΔV_(th,sub) of 4 H-SiC MOSFET originates from the high density of the hole interface traps between intrinsic Fermi energy level(E_(i)) and valence band(E_(v)).The maximumΔV_(th,sub) of trench MOSFET is about twelve times larger than that of planar MOSFET,owing to higher density of interface states(D_(it)) between E_(i) and E_(v).These research results will be very helpful for the application of 4 H-SiC MOSFET and the improvement of ΔV_(th,sub) of 4 H-SiC MOSFET,especially in 4 H-SiC trench MOSFET.

Influence of Parasitic Parameters on Dynamic Threshold Voltage Hysteresis of Silicon Carbide MOSFETs

Threshold voltage (V_(TH)) hysteresis affects the dynamic characteristics of silicon carbide (SiC) MOSFETs, whichin turn affects reliability of a device. In this paper, a dynamichysteresis curve is proposed as an evaluation method of theinfluence of V_(TH) hysteresis on the switching characteristics ofSiC MOSFETs. This method can eliminate the impact of triggerlevel and obtain the dynamic V_(TH). Furthermore, the influence ofparasitic parameters on dynamic V_(TH) hysteresis is theoreticallyanalyzed. Double pulse tests under different parasitic parametersare performed on three SiC MOSFETs with different gatestructures to verify the analysis. Results show that gate resistance(R_(G)) and source inductance (L_(S)) have more significant effectson dynamic V_(TH) hysteresis compared with gate inductance anddrain inductance. V_(TH) hysteresis phenomenon weakens withincrease of R_(G) or L_(S), which is related to device structure.The results presented in this paper can provide guidance forthe design of circuit parasitic parameters of SiC MOSFETs toregulate V_(TH) hysteresis.

Understanding voltage hysteresis and decay during anionic redox reaction in layered transition metal oxide cathodes:A critical review

The emergence of anionic redox reactions in layered transition metal oxide cathodes provides practical opportunity to boost the energy density of rechargeable batteries.However,the activation of anionic redox reaction in layered oxides has significant voltage hysteresis and decay that reduce battery performance and limit commercialization.Here,we critically review the up-todate development of anionic redox reaction in layered oxide cathodes,summarize the proposed reaction mechanism,and unveil their connection to voltage hysteresis and decay based on the state-of-the-art progress.In addition,advances associated with various modification approaches to mitigate the voltage hysteresis/decay in layered transition metal oxide cathodes are also included.Finally,we conclude with an appraisal of further research directions including rational design of high-performance layered oxide cathodes with reversible anionic redox reactions and suppressed voltage hysteresis/decay.Findings will be of immediate benefit to the development of layered oxide cathodes for high performance rechargeable batteries.

Carbon nanosheets derived from reconstructed lignin for potassium and sodium storage with low voltage hysteresis

Lignin is the second most abundant and the only nature polymer rich in aromatic units.Although aromatic-unit-rich precursors often yield soft carbon after carbonization,the side chains in lignin crosslink with the aromatic units and form a rigid three-dimensional(3D)structure which eventually leads to hard carbons.Through a graphene oxide-catalyzed decomposition and repolymerization process,we successfully reconstructed lignin by partially tailoring the side chains.Compared to directly carbonized lignin,the carbonized reconstructed lignin possesses significantly fewer defects,86%fewer oxygen-functionalities,82%fewer micropores,and narrower interlayer space.These parameters can be tuned by the amount of catalysts(graphene oxide).When tested as anode for K-ion and Na-ion batteries,the carbonized reconstructed lignin delivers notably higher capacity at low-potential range(especially for Na-storage),shows much-improved performance at high current density,and most importantly,reduces voltage hysteresis between discharge and charge process by more than 50%,which is critical to the energy efficiency of the energy storage system.Our study reveals that the voltage hysteresis in K-storage is much severer than that in Na-storage for all samples.For practical K-ion battery applications,the voltage hysteresis deserves more attention in future electrode materials design and the reconstruct ion strategy introduced in this work provides potential low-cost solution.

High lithium storage performance of Ni_(0.5)Fe_(0.5)O_(1-x)Nx thin film with Nio-type crystal structure

The large voltage hysteresis of the NiO anode,which owes much to the intermediate product Li_(2)NiO_(2),is one of the main obstacles to its practical application in lithium-ion batteries.In this work,we show that the incorporation of Fe-and N-ions in the Nio lattice can suppress the formation of intermediate product Li_(2)NiO_(2)and thus greatly reduces the voltage hysteresis of the Nioanode from~1.2 to~0.9 V.In comparison with the pure Nio electrode,the Nio.5Feo.5O1-xNx anode exhibits significantly enhanced reversible specific capacity(959 mAh·g^(-1)at 0.3 A·g^(-1)),cycling stability(capacity retention of 96.1%at 100th cycle relative to the second cycle)and rate capability(442 at 10 A·g^(-1)).These results provide a practical method to enhance the lithium storage performance of the Nio anode and more importantly a new solution to the large voltage hysteresis of conversion-type anodes.