Rechargeable Lithium Batteries Research Articles

Preparation and application of polyacrylonitrile electrospun nanofiber-based all-solid-state composite electrolyte for lithium metal battery

The demand for lithium-ion batteries that are both safe and high-energy is growing. Liquid electrolytes are used in traditional lithium rechargeable batteries, which pose security hazards such as volatilization, flammability, and explosion. Most of the safety problems associated with liquid electrolytes could be addressed by solid-state electrolytes. This research firstly incorporated Li6.4La3Zr1.4Ta0.6O12 (LLZTO) ceramic nanoparticle filler into electrospun polyacrylonitrile (PAN) to obtain a composite nanofiber membrane, and then added it to polyethylene oxide (PEO) polymer as a nano-polymer filler to create an all-solid-state electrolyte. By incorporating the PAN/LLZTO composite nanofiber membrane, the resulting electrolyte gains a sturdy framework that enhances its overall mechanical strength (7.8 MPa) to prevent the growth of lithium dendrites during cycling. In addition, the addition of LLZTO particles can help promote chain segment motion in a PEO matrix by increasing the ratios of amorphous to crystalline phase, which is beneficial for the rapid migration of lithium ions in the electrolyte membrane. At the same time, the interaction between LLZTO and DMF solvent can also generate an alkaline atmosphere and then promotes the cyclization of PAN, thus enhancing the ionic conductivity of the electrolyte (6.5 × 10−5cm−1 at 30 °C). The Li/Li symmetric battery assembled with the PEO-PAN/LLZTO composite electrolyte can stable cycling for 800 h at different current densities, and the Li/LiFePO4 battery can still maintain a high Coulomb efficiency of 99.7% after even 400 cycles under 1C. The research will lead to a promising electrolyte candidate for all-solid-state lithium metal batteries.

Li3PO4-Coated Graphite Anode for Thermo-Electrochemically Stable Lithium-Ion Batteries

Extensive research on electrode materials has been sparked by the rising demand for high-energy-density rechargeable lithium-ion batteries (LIBs). Graphite is a crucial component of LIB anodes, as more than 90% of the commercialized cathodes are coupled with the graphite anode. For the advanced graphite anode, the fast charge–discharge electrochemical performance and the thermal stability need to be further improved in order to meet the growing demand. Herein, a graphite anode material’s thermo-electrochemical stability was improved by the surface coating of lithium phosphate (Li3PO4; LPO). The graphite anode with a well-dispersed LPO-coating layer (graphite@LPO) demonstrated significant improvement in the cycle and rate performances. The graphite@LPO sample showed a capacity retention of 67.8% after 300 cycles at 60 °C, whereas the pristine graphite anode failed after 225 cycles, confirming the ameliorated thermo-electrochemical stability and cyclability by LPO coating. The improved thermo-electrochemical stability of the graphite@LPO anode was validated by the full-cell tests as well. The performance enhancement by LPO-coating is due to the suppression of the growth of the surface film and charge-transfer resistances during the repeated cycling, as evidenced by the electrochemical impedance spectroscopy analysis.

IoT-Based Smart Battery Management and Monitoring System for Electric Vehicles

The growing popularity of electric vehicles on a worldwide scale leads to further research to monitor their performance. The use of Internet of Things (IoT) technology will make it easier to integrate the automated real-time monitoring system with the current electric vehicle technology. The great majority of electric vehicles use rechargeable lithium-ion batteries. Use of lithium-ion batteries creates an overcharging situation in the battery, which significantly decreases battery life. It also increases the possibility of disastrous safety risks due to fire. This paper develops an IoT-based battery management system to minimize hazardous situations. The battery monitoring system (BMS) notifies the user about the condition of the battery in real time.

Synergetic modulation on solvation structure and electrode interface to achieve lithium-ion batteries cycled at ultra-low temperature

The performance of rechargeable lithium-ion batteries (LIBs) in cold environments remains a challenge due to the insufficient ionic conductivity of electrolyte and lithium plating at graphite anodes. Herein, we demonstrate that the synergistic effect of ether-based electrolyte and niobium oxide with high intercalation potential can significantly improve the low-temperature charging/discharging performance of LIBs. Theoretical calculations and in-situ characterizations prove that the weak desolvation energy of electrolyte and the strong binding energy Li+-O bridging coordination synergistically accelerate the interfacial reaction kinetics. The full cells by coupling the niobium oxide anode with LiFePO4 cathode show 95.6% of the initial capacity after 500 cycles at −30 °C, and exhibit excellent rechargeability at −50 °C. This work verifies that the synergism of solvating power of solvent and Li+ intercalation behavior is crucial in low-temperature LIBs.

Bio-Based Binder Development for Lithium-Ion Batteries.

The development of rechargeable lithium-ion battery (LIB) technology has facilitated the shift toward electric vehicles and grid storage solutions. This technology is currently undergoing significant development to meet industrial applications for portable electronics and provide our society with "greener" electricity. The large increase in LIB production following the growing demand from the automotive sector has led to the establishment of gigafactories worldwide, thus increasing the substantial consumption of fossil-based and non-sustainable materials, such as polyvinylidene fluoride and/or styrene-butadiene rubber as binders in cathode and anode formulations. Furthermore, the use of raw resources, such as Li, Ni, and Mn in cathode active materials and graphite and nanosilicon in anodes, necessitates further efforts to enhance battery efficiency. To foster a global sustainable transition in LIB manufacturing and reduce reliance on non-sustainable materials, the implementation of bio-based binder solutions for electrodes in LIBs is crucial. Bio-based binders such as cellulose, lignin, alginate, gums, starch, and others can address environmental concerns and can enhance LIBs' performance. This review aims to provide an overview of the current progress in the development and application of bio-based binders for LIB electrode manufacturing, highlighting their significance toward sustainable development.

A flame retardant and flexible gel polymer electrolytes for high temperature lithium metal batteries

In recent years, rechargeable lithium-ion batteries (LIBs) have been extensively studied and applied in portable electronics, electric vehicles, and new energy storage devices. Gel polymer electrolytes (GPEs), currently a research hotspot, inherit the high ionic conductivity of liquid electrolytes and great mechanical properties and safety of solid electrolytes, exhibiting great application potential. Herein, we demonstrate a flexible flame retardant GPE (PPC37) that forms a polymer network through intermolecular hydrogen bonding. During the charge–discharge cycle, the formation of a LiF-rich solid electrolyte interface (SEI) facilitates the uniform electrochemical deposition of Li+ and achieves a long life cycle without dendrites. PPC37 possesses high ionic conductivity (1.06 mS cm−1 at 25 °C) and robust mechanical properties (198% fracture length and 2.43 MPa fracture strength). The Li|PPC37|LiFePO4 batteries presented great cycling stability with an initial capacity of 151.9 mAh/g and a discharge capacity retention of 86.4% after 500 cycles at a high current density of 3C at 55 °C. The excellent thermal stability, interfacial stability, flame retardancy, flexibility and electrochemical stability demonstrated with PPC37 demonstrate the safety of high-temperature batteries, indicating their great application potential in flexible electronic devices and high-temperature environments.

Long‐Life, High‐Rate Rechargeable Lithium Batteries Based on Soluble Bis(2‐pyrimidyl) Disulfide Cathode

AbstractOrganosulfides are promising candidates as cathode materials for the development of electric vehicles and energy storage systems due to their low‐cost and high capacity properties. However, they generally suffer from slow kinetics because of the large rearrangement of S−S bonds and structural degradation upon cycling in batteries. In this paper, we reveal that soluble bis(2‐pyrimidyl) disulfide (Pym2S2) can be a high‐rate cathode material for rechargeable lithium batteries. Benefiting from the superdelocalization of pyrimidyl group, the extra electrons prefer to be localized on the π* (pyrimidyl group) than σ* (S−S bond) molecular orbitals initially, generating the anion‐like intermedia of [Pym2S2]2− and thus decreasing the dissociation energy of the S−S bond. It makes the intrinsic energy barrier of dissociative electron transfer depleted, therefore the lithium half cell exhibits 2000 cycles at 5 C. This study provides a distinct pathway for the design of high‐rate, long‐cycle‐life organic cathode materials.

Long-Life, High-Rate Rechargeable Lithium Batteries Based on Soluble Bis(2-pyrimidyl) Disulfide Cathode.

Organosulfides are promising candidates as cathode materials for the development of electric vehicles and energy storage systems due to their low-cost and high capacity properties. However, they generally suffer from slow kinetics because of the large rearrangement of S-S bonds and structural degradation upon cycling in batteries. In this paper, we reveal that soluble bis(2-pyrimidyl) disulfide (Pym2 S2 ) can be a high-rate cathode material for rechargeable lithium batteries. Benefiting from the superdelocalization of pyrimidyl group, the extra electrons prefer to be localized on the π* (pyrimidyl group) than σ* (S-S bond) molecular orbitals initially, generating the anion-like intermedia of [Pym2 S2 ]2- and thus decreasing the dissociation energy of the S-S bond. It makes the intrinsic energy barrier of dissociative electron transfer depleted, therefore the lithium half cell exhibits 2000 cycles at 5 C. This study provides a distinct pathway for the design of high-rate, long-cycle-life organic cathode materials.

Perspective on the use of methanogens in lithium recovery from brines.

Methanogenic archaea stand out as multipurpose biocatalysts for different applications in wide-ranging industrial sectors due to their crucial role in the methane (CH4) cycle and ubiquity in natural environments. The increasing demand for raw materials required by the manufacturing sector (i.e., metals-, concrete-, chemicals-, plastic- and lubricants-based industries) represents a milestone for the global economy and one of the main sources of CO2 emissions. Recovery of critical raw materials (CRMs) from byproducts generated along their supply chain, rather than massive mining operations for mineral extraction and metal smelting, represents a sustainable choice. Demand for lithium (Li), included among CRMs in 2023, grew by 17.1% in the last decades, mostly due to its application in rechargeable lithium-ion batteries. In addition to mineral deposits, the natural resources of Li comprise water, ranging from low Li concentrations (seawater and freshwater) to higher ones (salt lakes and artificial brines). Brines from water desalination can be high in Li content which can be recovered. However, biological brine treatment is not a popular methodology. The methanogenic community has already demonstrated its ability to recover several CRMs which are not essential to their metabolism. Here, we attempt to interconnect the well-established biomethanation process with Li recovery from brines, by analyzing the methanogenic species which may be suitable to grow in brine-like environments and the corresponding mechanism of recovery. Moreover, key factors which should be considered to establish the techno-economic feasibility of this process are here discussed.

Effect of laser repetition rate parameter in pulsed Laser ablation for synthesis Li4Ti5O12 polyether sulfone nanocomposite for optoelectronic applications

We examine Li4Ti5O12 (LTO) anode component inserted into PES produced by pulsed laser ablation in liquid media method with adjustable its particle size by tuning laser repetition rate, followed by post irradiation, to investigate the capability for using in Rechargeable lithium-ion batteries applications. Thermal analysis illustrates how material characteristics change with temperature. X-ray diffraction (XRD), Fourier transform infrared (FT-IR), and energy dispersive spectra (EDS) are used to assess the compound's phase composition, optical characteristics, and elemental analyses. Without any usual peaks for other impurities, notably rutile and anatase TiO2, the XRD pattern showed a cubic spinel structure with high crystallinity of just LTO structure. The sample's component elements are confirmed by the EDS spectra since only the peaks for the impurities Ti and O could be seen in the spectra. FT-IR revealed that the broad absorption bands appeared at wave numbers in the figure print region because of the stretching vibrations of the octahedral groups (MO6) lattice. The XPS survey spectra reveal the presence of Li, Ti, O, C, and S. TGA revealed that the interaction of hydroxyl groups of PES with functional groups of LTO via hydrogen bonding may result in a temperature shift of breakdown. Electrical conductivity measurements were conducted at various frequencies and temperatures. The generated samples' real and imaginary parts of dielectric parameter characteristics were tested at frequencies ranging from 0.1 to 3 M Hz and temperatures ranging from 200 to 500 K. The temperature variation of the real component of the dielectric constant indicates that these compounds have high electromagnetic absorption and wideband electrical activity.

A novel strategy of enhanced thermal performance in air cooled lithium-ion battery by wavy walls

Electric vehicles (EVs) with rechargeable lithium-ion batteries are one of the most appealing choices for electrochemical energy storage to address global energy challenges and environmental concerns caused by rising carbon emissions. However, to maintain the performance and longevity of these high power batteries, a well-planned and effective cooling mechanism is required. Here, a novel air-based battery thermal management system (BTMS) is proposed to realize an improved cooling performance. We examined the thermal performance of an air-cooled lithium-ion battery pack of 3x5 Sony 18650 cells by introducing wavy (undulated) sidewalls for the discharge period of the cells. Influence of air inflow velocity (U0) and number of undulations on wavy wall have been delineated at a discharge rate of 2C and 3C. As obvious, the cooling improves with the increasing U0. Interestingly, a significant reduction (∼ 8-10 K) in the average and maximum cell temperature was seen simply by creating an optimal number of undulations on the walls as compared to the results obtained from straight walls. The highest cooling performance was observed when the undulations form a trough above the cells, however, the highest pressure drop was experienced in such cases. A trade-off between the cooling enhancement and power requirement (∼ pressure drop) has been presented by a performance plot. Finally, the efficacy of system was ensured by changing the number of rows and columns of the cell arrangement in the battery pack. An enhanced heat dissipation and thermal uniformity was seen in all the cases when wall undulations are present.

MoSe2 @rGO as Highly Efficient Host and Catalyst for Li-Organosulfide Battery.

Organosulfides are promising high-capacity cathode materials for rechargeable lithium batteries. However, sluggish kinetics and inferior utilization impede its practical application in batteries. Rationally designing redox mediators and identifying their active moieties remain formidable challenges. Currently, as a rising star of transition metal dichalcogenides, few-layered MoSe2 decorated reduced graphene oxide (rGO) (MoSe2 @rGO) with high electronic conductivity and narrow energy band is used to manipulate electrocatalytic redox kinetics of organosulfides, thereby enhancing the battery performance. Here, an exotic MoSe2 @rGO is reported with Se defects material obtained from 2D MoSe2 growing on rGO for Li-dipentamethylenethiuram tetrasulfide (Li-PMTT) batteries. MoSe2 @rGO with Se defects has a large specific surface area, and sufficient pores, as well as exce llent catalytic ability for organosulfides conversion reactions. Therefore, the PMTT@MoSe2 @rGO cathode delivers a high reversible capacity of 405mAhg-1 in the first cycle at 0.5 C and can maintain 238.3mAhg-1 specific capacity after 300cycles. This work offers an understanding of organosulfides electrochemistry toward fast and durable performance, holding great promise for developing practically feasible lithium-organosulfides battery material designs.

Spontaneous electrochemical stabilization of nanostructured organic electrodes by field-induced charge-transfer

Organic electrodes are promising candidates for the next-generation energy storage system of rechargeable lithium-ion batteries (LIBs) due to their natural abundance and lightweight. However, they have weaknesses: low electrochemical capacity, low capacity retention, and elution of active electrode materials. In this study, the field-induced charge-transfer route and nanostructuring are developed to resolve the poor electrochemical performance. When the 5,10-Dihydro-5,10-dimethylphenazine (DMPZ) with a nanoporous structure is homogeneously mixed with organic and metal nanoparticles (perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA), perylenetetracarboxylic diimide (PTCDI), Flavanthrone, and Aluminum), the organic nanocomposite cathodes exhibit a remarkable enhancement in electrochemical performance: unprecedented cycling stability with capacity retention over 90% up to 600 redox cycles, a high specific capacity of 215 mA·h·g−1 at the current density of 150 mA·g−1, and an excellent rate-capability for the DMPZ and PTCDA nanocomposite cathode. The excellent specific capacity and retention of the redox reaction are due to the fast charge transport through the nanoporous network of the nanocomposites with a high specific surface area. The charge-transfer between the vicinal organic materials with different ionization energies is induced by the charging potential of the redox reaction, which suppresses the elution during the oxidation process and leads to the remarkable cyclability. The all-organic pouch-type full-cell, composed of a PTCDI anode and the nanocomposite cathode, is realized with excellent cyclability of 76% capacity retention at the 200th cycle. This work provides a promising way of developing stable organic electrodes for electrocatalytic applications as well as LIBs.

Layer-By-Layer (LBL) hybrid MOF coating for graphene-based multilayer composite: Synthesis and application as anode for lithium ion batteries

The hybrid anodic materials with high porosity and low charge resistance exhibit high specific capacity and stable cyclic stability for lithium ion battery (LIBs). For this purpose, three-dimensional hollow material, metal organic framework (MOF-199) was coated over the active surface of oxidized derivative of graphene (Graphene oxide, GO), via layer-by-layer (LBL) coating method. Cupric acetate and benzene-1,3,5-tricarboxylic acid [Cu3(BTC)2], were alternatively coated on the active surface of GO as an anode material, to enhance the structural diversity and reduce the synergistic effect of insertion and extraction of Li+ ions for LIBs. Sharp absorption peaks from 1620 cm−1 to 1360 cm−1 and intense ring bends ∼1000 cm−1 was identified through FTIR. Powder XRD provides the evidence for size reduction of Cu3(BTC)2@GO composite (32.6 nm) comparative to GO (43.7 nm). Outcome of EIS analysis shows the charge transfer resistance of simple GO is 2410 Ω, which is 4 times higher than Rct of Cu3(BTC)2@GO composite (590 Ω). Similarly the Warburg impedance co-efficient for simple GO (448.8 Ωs−1/2) is also higher than Aw of Cu3(BTC)2@GO composite (77.64 Ωs−1/2). The synthesized material show high initial charge/discharge capacity, 1200/1420 mAh/g with 85% Coulombic efficiency and reversible discharge capacity, 1296 mAh/g after 100 cycles at 100 mA/g current density. The 98.9% Coulombic efficiency and 91% retaining capacity of composite at 100th cycle with cyclic stability, provides the phenomenon approach towards the rechargeable LIBs for industrial technology.

Preparation and electrochemical performance of foam–like CeO2 nanofoam as negative electrode material for rechargeable lithium–ion batteries

Oxides of transition metal oxides have been discovered as candidate anode materials for lithium–ion batteries (LIBs) owing to their extraordinary specific capacity. Moreover, to improve the electrochemical performance of energy–storage devices, the use of porous electrode materials is considered one of the most effective strategies. Herein, we report highly porous cerium oxide (CeO2) nanofoam synthesized using a facile and simple solution combustion technique (SCT). In this technique, we use two different fuels to synthesis CeO2. The prepared S–CeO2 nanofoam delivers the highest specific surface area of 142.99 m2 g−1 with a highly enhanced contact area between the electrolyte and electrode. The prepared S–CeO2–based anode offers an initial specific capacity of 1154 mAh g−1 at 100 mA g−1, which is three times higher than that of carbon–based materials. Additionally, the mesoporous S–CeO2 nanofoam exhibits good rate capability at high current densities. These attractive results suggest that S–CeO2 has great potential for use in high–performance LIB applications.

Density Functional Theory Study of Bilayer Borophene-Based Anode Material for Rechargeable Lithium Ion Batteries.

The bilayer borophene has been successfully fabricated in experiments recently and possesses superior antioxidation and robust metallic properties, which holds great promise for the future anode materials of Li-ion batteries. Herein, using first-principles calculations, two bilayer borophenes including P6/mmm or P6̅m2 symmetry groups with or without vacancy defects are comprehensively explored and acted as electrode materials with high performance in Li-ion batteries. The charge density difference, adsorption energies, and Bader charge analysis are calculated and discussed for single lithium adsorbed on bilayer borophene. The results shown that with the increase of lithium concentration, the adsorption energies are rapidly decreased due to the repulsion of boron atoms except for the P6̅m2 systems with double side adsorption and corresponding energies remain the narrow range. Meanwhile, the partial density of states shows metallic character after lithium adsorption and indicates good conductivity for the charge-discharge process. Furthermore, small diffusion barriers, low average open-circuit voltage, can be achieved, and large storage capacity is up to 930.2 mA h/g at the lower lithium content of 0.375. These results propose that bilayer borophene might be a good choice for anode material applications in future Li-ion batteries with fast ion diffusion and high power density.

One pot green synthesis of few-layer graphene (FLG) by simple sonication of graphite and Azardirachta Indica resin in water for high-capacity and excellent cyclic behavior of rechargeable lithium-ion battery

A simple, green, and eco-friend route is employed for the preparation of few-layer graphene using Azardirachta Indica resin (AZIr) in water. In addition, the preparation of the solvent (AZIr) for the exfoliation of graphene involves various steps, including vacuum filtration and surface tension optimization by the capillary rise method. It has been demonstrated that the 4 h sonication effectively exfoliated graphite to form a Few-Layer Graphene (FLG) sheet. Structural, morphological, and surface topographical analysis were performed using X-ray diffraction, Raman spectrum, FTIR spectrum, atomic force microscopy, and Scanning electron microscope. The as-prepared FLG was demonstrated as anode material for lithium-ion batteries¸ exhibiting a high initial capacity of 464 mAh g−1 at 0.1C and excellent cyclic performance of 527 mAh g−1 at 200th cycle with 100 % capacity retention. The maximum capacity of 281 mAh g−1 was achieved when tested at a high current rate of 10C. These results suggest that few-layer graphene is a promising material for high-performance Li-ion battery applications.

Surface modification of lithium metal anode with lithium silicate-lithium phosphate composite layer for enhanced cycling stability

Lithium metal anode with exceptionally high capacity is very attractive for next-generation anode material of lithium rechargeable batteries, but the safety problems and low Coulombic efficiency have retarded its commercialization. Despite the enormous efforts made to solve the problem of lithium metal anode, its practical use still appears to have a long way to go. In this study, to expedite the problem-solving, we suggest the use of a lithium silicate-lithium phosphate (SP) composite layer to suppress the dendritic growth of lithium and the formation of dead lithium. The composite layer is formed by simply dipping lithium metal in a mixed solution of tetraethyl orthosilicate and phosphoric acid. The synergistic effect of lithium silicate and lithium phosphate – high Li-ion conductivity and high Young's modulus of the inorganic layer – results in enhanced cycling stability of Li || Li symmetric cell and LiFePO4 || Li cell. The change in morphology of the lithium metal anode surface after cycling confirms that the SP layer mitigates the excessive dendritic growth of lithium and dead lithium formation, stabilizing the interface of lithium metal anode/electrolyte.

Mesoporous Cr2O3/MWCNTs/PANI nanocomposite as a high performance anode material for rechargeable lithium ion batteries

Chromium oxide (Cr2O3) has been considered as a promising anode material for lithium-ion batteries (LIBs). However, it is accompanied by a large volumetric expansion which compromises battery performance by damaging internal structure of the material. In this study, dual modification is achieved by developing Cr2O3 nanocomposite with multi-walled carbon nanotubes (MWCNTs) by inexpensive and reproducible co-precipitation method which reduces volume changes by enhancing electronic conductivity and mechanical strength. Meanwhile, polyaniline (PANI) coating was employed by in-situ polymerization of aniline monomer that promotes lithium-ion conductivity and facilitates high electron transportation, thus resulting in excellent stability. This research mainly signifies the effect of PANI coating, where PANI offers conductive contact between active material and electrolyte. The homogenous nanocomposite of Cr2O3-MWCNTs and PANI exhibit good electrochemical performance. A discharge capacity of Cr2O3-MWCNTs(12%)-PANI is found to be 815 mAh g−1 at 100 mA g−1 with coulombic efficiency of 97.5 %. Moreover, the nanocomposite exhibits good rate capability and cyclic stability.

Sodium and potassium ion storage in cation substituted 2D MoWSe2: insights into the effects of upper voltage cut-off

The superior properties, such as large interlayer spacing and the ability to host large alkali-metal ions, of two-dimensional (2D) materials based on transition metal di-chalcogenides (TMDs) enable next-generation battery development beyond lithium-ion rechargeable batteries. In addition, compelling but rarely inspected TMD alloys provide additional opportunities to tailor bandgap and enhance thermodynamic stability. This study explores the sodium-ion (Na-ion) and potassium-ion (K-ion) storage behavior of cation-substituted molybdenum tungsten diselenide (MoWSe2), a TMD alloy. This research also investigates upper potential suspension to overcome obstacles commonly associated with TMD materials, such as capacity fading at high current rates, prolonged cycling conditions, and voltage polarization during conversion reaction. The voltage cut-off was restricted to 1.5 V, 2.0 V, and 2.5 V to realize the material’s Na+ and K+ ion storage behavior. Three-dimensional (3D) surface plots of differential capacity analysis up to prolonged cycles revealed the convenience of voltage suspension as a viable method for structural preservation. Moreover, the cells with higher potential cut-off values conveyed improved cycling stability, higher and stable coulombic efficiency for Na+ and K+ ion half-cells, and increased capacity retention for Na+ ion half-cells, respectively, with half-cells cycled at higher voltage ranges.