Luyuan Paul Wang

Recent developments in electrode materials for sodium-ion batteries

The rapid consumption of non-renewable resources has resulted in an ever-increasing problem of CO2 emissions that has motivated people for investigating the harvesting of energy from renewable alternatives (e.g. solar and wind). Efficient electrochemical energy storage devices play a crucial role in storing harvested energies in our daily lives. For example, rechargeable batteries can store energy generated by solar cells during the daytime and release it during night-time. In particular, lithium-ion batteries (LIBs) have received considerable attention ever since their early commercialization in 1990s. However, with initiatives by several governments to build large-scale energy grids to store energy for cities, problems such as the high cost and limited availability of lithium starts to become major issues. Sodium, which also belongs to Group 1 of the periodic table, has comparable electrochemical properties to Lithium, and more importantly it is considerably more accessible than lithium. Nonetheless, research into sodium-ion batteries (NIBs) is currently still in its infancy compared to LIBs, although great leaps and bounds have been made recently in terms of research and development into this technology. Here in this review, we summarize the recent advancements made, also covering the prospective materials for both the battery cathode and anode. Additionally, opinions on possible solutions through correlating trends in recent papers will be suggested.

Large exchange bias after zero-field cooling from an unmagnetized state

Exchange bias (EB) is usually observed in systems with an interface between different magnetic phases after field cooling. Here we report an unusual phenomenon in which a large EB can be observed in Ni-Mn-In bulk alloys after zero-field cooling from an unmagnetized state. We propose that this is related to the newly formed interface between different magnetic phases during the initial magnetization process. The magnetic unidirectional anisotropy, which is the origin of the EB effect, can be created isothermally below the blocking temperature.

Exchange bias and its training effect in the martensitic state of bulk polycrystalline Ni49.5Mn34.5In16

Exchange bias phenomena are observed in the bulk polycrystalline Ni49.5Mn34.5In16 alloy in which ferromagnetic and antiferromagnetic phases coexist in the martensitic state. Both the exchange bias field and coercivity are strongly dependent on temperature. The training effect of the exchange bias is found to be very small in the present alloy and can be explained by the depinning of uncompensated antiferromagnet spins. These results suggest that the ferromagnetic and antiferromagnetic domains couple at the interfaces and as a result induce the exchange bias. Such behavior is an addition to the multifunctional properties of the Ni49.5Mn34.5In16 ferromagnetic shape memory alloy.

High-performance hybrid electrochemical capacitor with binder-free Nb2O5@graphene

Hybrid electrochemical capacitors (HECs) are capable of storing more energy than supercapacitors while providing more power compared to lithium-ion batteries (LIBs). The development of Li-intercalating materials is critical to organic electrolyte based HECs, which generally give larger potential output than aqueous electrolyte based HECs. This article reports on a simple binder-free Nb2O5@graphene composite that exhibited excellent HEC performance as compared with other Li intercalating electrode materials. The composite exhibited enhanced cyclability with a capacity retention of 91.2% compared to 74.4% of the pure Nb2O5 half-cell when tested at a rate of 2000 mA g−1 (10 C). The composite displayed a lower polarization effect when cycled at increasing scan rates (1–10 mV s−1). The enhanced rate capability could be ascribed to the use of a highly conductive graphene support. As a result, the HEC composed of the Nb2O5@graphene composite and activated carbon (AC) delivered a maximum energy and power density of 29 W h kg−1 and 2.9 kW kg−1. The performance is better than most reported HECs with other Li-intercalating electrode materials.

Reserving Interior Void Space for Volume Change Accommodation: An Example of Cable-Like MWNTs@SnO2@C Composite for Superior Lithium and Sodium Storage.

Reserving interior void space in the cable‐like structure of multiwalled carbon nanotubes‐in‐SnO2‐in‐carbon layer (MWNTs@SnO2@C) is reported for the first time. Such a design enables the structure performing excellent for Li and Na storage, which benefit from the good electrical conductivity of MWNTs and carbon layer as well as the reserved void space to accommodate the volume changes of SnO2.

Strong thermal-history-dependent magnetoresistance behavior in Ni49.5Mn34.5In16

The thermal-history-dependent (THD) isothermal magnetoresistance (MR) behavior of Ni49.5Mn34.5In16 metamagnetic shape memory alloy is investigated. Irreversibility in isothermal MR is observed in reverse martensitic transformation temperature range, while an intriguing “overshooting” phenomenon is observed in forward martensitic transformation temperature range, showing a strong thermal-history dependence of MR behavior. Such a THD MR behavior can be explained in terms of phase coexistence, THD metastable phase, and magnetic-field-induced phase transition.

Novel Preparation of N‐Doped SnO2 Nanoparticles via Laser‐Assisted Pyrolysis: Demonstration of Exceptional Lithium Storage Properties

Laser pyrolyzed SnO2 nanoparticles with an option of nitrogen (N) doping are prepared using a cost-effective method. The electrochemical performance of N-doped samples is tested for the first time in Li-ion batteries where the sample with 3% of N-dopant exhibits optimum performance with a capacity of 522 mAh gactive material-1 that can be obtained at 10 A g-1 (6.7C).

Origin of the colossal dielectric permittivity and magnetocapacitance in LuFe2O4

We report the detailed study on the colossal dielectric constant and magnetocapacitance of LuFe2O4. The experimental results indicate that the large dielectric constant of LuFe2O4 is originated from two sources, (1) Maxwell Wagner-type contributions of depletion layers at grain boundaries and the interfaces between sample and contacts, (2) AC response of the constant phase element in the bulk. A detailed equivalent circuit analysis indicates that the conductivity variation can be responsible for the observed “magnetocapacitance.”

A second-order ferromagnetic transition in the martensitic state of Ni49.5Mn32.5Cu4Sn14: A critical behavior study

A second-order ferromagnetic transition is observed in the martensitic state of Ni49.5Mn32.5Cu4Sn14 alloy and the critical behavior around the transition is investigated by dc magnetization measurements. With the help of modified Arrott plots, Kouvel–Fisher method, and Widom scaling relation, the values of TcM (ferromagnetic transition temperature in the martensite), and critical exponents: β (associated with the spontaneous magnetization), γ (relevant to the initial susceptibility), and δ (associated with the critical magnetization isotherm) are obtained. The scaling plots show that the obtained values of the critical exponents are reliable. The values of the critical exponents of Ni49.5Mn32.5Cu4Sn14 are different from those predicted by several theoretical models, i.e., mean-field theory, three-dimensional Heisenberg model, and three-dimensional Ising model. The magnetic interactions exhibit two different behaviors: long-range magnetic interaction below TcM and local magnetic interaction above TcM. The ...

Nonconventional magnetism in pristine and alkali doped In2O3: density functional study

Using In2O3 as a host matrix, extensive calculations based on density functional theory have been carried out to understand the electronic and magnetic properties of native defects, alkali and alkaline-earth metal substitutions as disputed in recent theoretical and experimental studies. Our calculations show that the magnetism in undoped In2O3 is originated from In vacancies (VIn) instead of O vacancies. The ferromagnetic (FM) coupling between the moments introduced by VIn is found strong enough to achieve room temperature ferromagnetism. Moreover, FM coupling is also strongly favored in alkali metal doping cases with negative formation energy. For all XIn (XIn=VIn, LiIn, NaIn, and KIn) doped In2O3, the induced magnetic moments are mainly localized on the first shell of O atoms around XIn sites. The FM coupling between the moments induced by XIn defects is activated by intra- and intercorrelation of the XIn–6ONN complexes. A XIn–ONN–InNN–ONN–XIn chain is required to mediate the long-range FM coupling. How...