"Win-Win"Scenario of High Energy Density and Long Cycling Life in a Novel Na_(3.9)MnCr_(0.9)Zr_(0.1)(PO_(4))_(3)Cathode

The development of high-energy and long-lifespan NASICON-type cathode materials for sodium-ion batteries has always been a research hotspot but a daunting challenge.Although Na_(4)MnCr(PO_(4))_(3)has emerged as one of the most promising high-energy-density cathode materials owing to its three-electron reactions,it still suffers from serious structural distortion upon repetitive charge/discharge processes caused by the Jahn-Teller active Mn^(3+).Herein,the selective substitution of Cr by Zr in Na_(4)MnCr(PO_(4))_(3)was explored to enhance the structural stability,due to the pinning effect of Zr ions and the≈2.9-electron reactions,as-prepared Na_(3.9)MnCr_(0.9)Zr_(0.1)(PO_(4))_(3)/C delivers a high capacity retention of 85.94%over 500 cycles at 5 C and an ultrahigh capacity of 156.4 mAh g^(-1)at 0.1 C,enabling the stable energy output as high as 555.2 Wh kg^(-1).Moreover,during the whole charge/discharge process,a small volume change of only 6.7%was verified by in situ X-ray diffraction,and the reversible reactions of Cr^(3+)/Cr^(4+),Mn^(3+)/Mn^(4+),and Mn^(2+)/Mn^(3+)redox couples were identified via ex situ X-ray photoelectron spectroscopy analyses.Galvanostatic intermittent titration technique tests and density functional theory calculations further demonstrated the fast reaction kinetics of the Na_(3.9)MnCr_(0.9)Zr_(0.1)(PO_(4))_(3)/C electrode.This work offers new opportunities for designing high-energy and high-stability NASICON cathodes by ion doping.

Research on Preparation and Electrochemical Performance of the High Compacted Density Ni-Co-Mn Ternary Cathode Materials

The high compacted density LiNi0.5-xCo0.2Mn0.3MgxO2 cathode material for lithium-ion batteries was synthesized by high temperature solid-state method, taking the Mg element as a doping element and the spherical Ni0.5Co0.2Mn0.3 (OH)2, Li2CO3 as raw materials. The effects of calcination temperature on the structure and properties of the products were investigated. The structure and morphology of cathode materials powder were analyzed by X-ray diffraction spectroscopy (XRD) and scanning electronmicroscopy (SEM). The electrochemical properties of the cathode materials were studied by charge-discharge test and cyclic properties test. The results show that LiNi0.4985Co0.2Mn0.3 Mg0.0015O2 cathode material prepared at calcination temperature 930°C has a good layered structure, and the compacted density of the electrode sheet is above 3.68 g/cm3. The discharge capacity retention rate is more than 97.5% after 100 cycles at a charge-discharge rate of 1C, displaying a good cyclic performance.

Modification strategies improving the electrochemical and structural stability of high-Ni cathode materials

With the increasing spotlight in electric vehicles,there is a growing demand for high-energy-density batteries to enhance driving range.Consequently,several studies have been conducted on high-energy-density LiNi_(x)Co_(y)Mn_(z)O_(2)cathodes.However,there is a limit to permanent performance deterioration because of side reactions caused by moisture in the atmosphere and continuous microcracks during cycling as the Ni content to express high energy increases and the content of Mn and Co that maintain structural and electrochemical stabilization decreases.The direct modification of the surface and bulk regions aims to enhance the capacity and long-term performance of high-Ni cathode materials.Therefore,an efficient modification requires a study based on a thorough understanding of the degradation mechanisms in the surface and bulk region.In this review,a comprehensive analysis of various modifications,including doping,coating,concentration gradient,and single crystals,is conducted to solve degradation issues along with an analysis of the overall degradation mechanism occurring in high-Ni cathode materials.It also summarizes recent research developments related to the following modifications,aims to provide notable points and directions for post-studies,and provides valuable references for the commercialization of stable high-energy-density cathode materials.

Sb-Cu alloy cathode with a novel lithiation mechanism of ternary intermetallic formation: Enabling high energy density and superior rate capability of liquid metal battery

Antimony(Sb) is an attractive cathode for liquid metal batteries(LMBs) because of its high theoretical voltage and low cost.The main obstacles associated with the Sb-based cathodes are unsatisfactory energy density and poor rate-capability.Herein,we propose a novel Sb_(64)Cu_(36)cathode that effectively tackles these issues.The Sb_(64)Cu_(36)(melting point:525℃) cathode presents a novel lithiation mechanism involving sequentially the generation of Li_(2)CuSb,the formation of Li_(3)Sb,and the conversion reaction of Li_(2)CuSb to Li_(3)Sb and Cu.The generated intermetallic compounds show a unique microstructure of the upper floated Li_(2)CuSb layer and the below cross-linked structure with interpenetrated Li_(2)CuSb and Li_(3)Sb phases.Compared with Li_(3)Sb,the lower Li migration energy barrier(0.188 eV) of Li_(2)CuSb significantly facilitates the lithium diffusion across the intermediate compounds and accelerates the reaction kinetics.Consequently,the Li‖Sb_(64)Cu_(36)cell delivers a more excellent electrochemical performance(energy density:353 W h kg^(-1)at 0.4 A cm^(-2);rate capability:0.59 V at 2.0 A cm^(-2)),and a much lower energy storage cost of only 38.45 $ kW h^(-1)than other previously reported Sb-based LMBs.This work provides a novel cathode design concept for the development of high-performance LMBs in applications for large-scale energy storage.

A defective iron-based perovskite cathode for high-performance IT-SOFCs:Tailoring the oxygen vacancies using Nb/Ta co-doping

The sluggish kinetics of the electrochemical oxygen reduction reaction(ORR)in intermediatetemperature solid oxide fuel cells(IT-SOFCs)greatly limits the overall cell performance.In this study,an efficient and durable cathode material for IT-SOFCs is designed based on density functional theory(DFT)calculations by co-doping with Nb and Ta the B-site of the SrFeO_(3-δ)perovskite oxide.The DFT calculations suggest that Nb/Ta co-doping can regulate the energy band of the parent SrFeO_(3-δ)and help electron transfer.In symmetrical cells,such cathode with a SrFe_(0.8)Nb_(0.1)Ta_(0.1)O_(3-δ)(SFNT)detailed formula achieves a low cathode polarization resistance of 0.147Ωcm^(2) at 650℃.Electron spin resonance(ESR)and X-ray photoelectron spectroscopy(XPS)analysis confirm that the co-doping of Nb/Ta in SrFeO_(3-δ)B-site increases the balanced concentration of oxygen vacancies,enhancing the electrochemical performance when compared to 20 mol%Nb single-doped perovskite oxide.The cathode button cell with NiSDC|SDC|SFNT configuration achieves an outstanding peak power density of 1.3 W cm^(-2)at 650℃.Moreover,the button cell shows durability for 110 h under 0.65 V at 600℃ using wet H_(2) as fuel.

Mg/Fe site-specific dual-doping to boost the performance of cobalt-free nickle-rich layered oxide cathode for high-energy lithium-ion batteries

Layer-type LiNi0.9Mn0.1O2is promising to be the primary cathode material for lithium-ion batteries(LIBs)due to its excellent electrochemical performance.Unfortunately,the cathode with high nickel content suffers from severely detrimental structural transformation that causes rapid capacity attenuation.Herein,site-specific dual-doping with Fe and Mg ions is proposed to enhance the structural stability of LiNi0.9Mn0.1O2.The Fe3+dopants are inserted into transition metal sites(3b)and can favorably provide additional redox potential to compensate for charge and enhance the reversibility of anionic redox.The Mg ions are doped into the Li sites(3a)and serve as O_(2)^(-)-Mg^(2+)-O_(2)^(-)pillar to reinforce the electrostatic cohesion between the two adjacent transition-metal layers,which further suppress the cracking and the generation of harmful phase transitions,ultimately improving the cyclability.The theoretical calculations,including Bader charge and crystal orbital Hamilton populations(COHP)analyses,confirm that the doped Fe and Mg can form stable bonds with oxygen and the electrostatic repulsion of O_(2)^(-)-O_(2)^(-)can be effectively suppressed,which effectively mitigates oxygen anion loss at the high delithiation state.This dual-site doping strategy offers new avenues for understanding and regulating the crystalline oxygen redox and demonstrates significant potential for designing high-performance cobalt-free nickel-rich cathodes.

Fluorinated soft carbon as an ultra-high energy density potassium-ion battery cathode enabled by a ternary phase K_(x)FC

Fluorinated carbons(CFx)have been widely applied as lithium primary batteries due to their ultra-high energy density.It will be a great promise if CFx can be rechargeable.In this study,we rationally tune the C-F bond strength for the alkaline intercalated CFx via importing an electronegative weaker element K instead of Li.It forms a ternary phase K_(x)FC instead of two phases(LiF+C)in lithium-ion batteries.Meanwhile,we choose a large layer distance and more defects CFx,namely fluorinated soft carbon,to accommodate K.Thus,we enable CFx rechargeable as a potassium-ion battery cathode.In detail fluorinated soft carbon CF_(1.01) presents a reversible specific capacity of 339 mA h g^(-1)(797 Wh kg^(-1))in the 2nd cycle and maintains 330 mA h g^(-1)(726 Wh kg^(-1))in the 15th cycle.This study reveals the importance of tuning chemical bond stability using different alkaline ions to endow batteries with rechargeability.This work provides good references for focusing on developing reversible electrode materials from popular primary cell configurations.

Determinations of plasma density and decay time in the hollow cathode discharge by microwave transmission

The microwave （MW） transmission method is employed to measure both the plasma density and the plasma decay time in the hollow cathode discharge （HCD） in argon at low pressure. The plasma density in DC-driven or pulsed HCD is on the order of 1012 cm-3, which can block the X-band MW effectively. In the case of pulsed HCD, the MW transmittance shows the same waveform as the pulsed current during the rising edge if the driving frequency is low, but with a longer delay during the falling edge. The MW transmittance reaches a constant low level when the driving frequency is high enough. The plasma decay time in the HCD system is measured to be about 100 μs around a pressure of 120 Pa. The ambipolar diffusion is considered to be the major mechanism in the decay process.

Lithium-ion full cell with high energy density using nickel-rich LiNi_(0.8)Co_(0.1)Mn_(0.1)O_2 cathode and SiO-C composite anode

A high-energy-density Li-ion battery with excellent rate capability and long cycle life was fabricated with a Ni-rich layered LiNi_(0.8)Co_(0.1)Mn_(0.1)O_2 cathode and Si O-C composite anode. The LiNi_(0.8)Co_(0.1)Mn_(0.1)O_2 and Si O-C exhibited excellent electrochemical performance in both half and full cells. Specifically, when integrated into a full cell configuration, a high energy density(280 Wh·kg^(-1)) with excellent rate capability and long cycle life was attained. At 0.5 C, the full cell retained 80% of its initial capacity after 200 charge/discharge cycles, and 60% after 600 cycles, indicating robust structural tolerance for the repeated insertion/extraction of Li^+ ions. The rate performance showed that, at high rate of 1 C and 2 C, 96.8% and 93% of the initial capacity were retained, respectively. The results demonstrate strong potential for the development of high energy density Li-ion batteries for practical applications.

Surface-engineering of layered LiNi_(0.815)Co_(0.15)Al_(0.035)O_2 cathode material for high-energy and stable Li-ion batteries

Surface engineering is an effective strategy to restrain the generation of rocksalt NiO phase on surface of layered LiNi0.815Co0.15Al0.035O2（NCA） primary nanoparticles, a representative Ni-rich layered oxides cathode materials. Herein, we demonstrate the kilogram-scale synthesis of few-layer reduced graphene oxide（rGO） conformably coated NCA primary nanoparticles cathode materials by a mechanical wet ball-milling strategy. The lightening rGO coating layer effectively avoids the direct contact of electrolyte and NCA with rapid electrons transfer. As a result, the as-obtained NCA@rGO hybrids with only 1.0 wt% rGO content can deliver a high specific capacity（196 mAh g-1 at 0.2 C） and fast charge/discharge capability（127 mAh g-1 at 5 C）, which is much higher than the corresponding NCA nanoparticles（95 mAh g-1 at 5 C）. Even after100 cycles at 1 C, 91.7% of initial reversible capacity is still maintained. Furthermore, a prismatic pouch cell（240 mAh） is also successfully assembled with the commercial graphite anode.

Theoretical and Experimental Sets of Choice Anode/Cathode Architectonics for High-Performance Full-Scale LIB Built-up Models

To control the power hierarchy design of lithium-ion battery(LIB)builtup sets for electric vehicles(EVs),we offer intensive theoretical and experimental sets of choice anode/cathode architectonics that can be modulated in full-scale LIB built-up models.As primary structural tectonics,heterogeneous composite superstructures of full-cell-LIB(anode//cathode)electrodes were designed in closely packed flower agave rosettes TiO2@C(FRTO@C anode)and vertical-star-tower LiFePO4@C(VST@C cathode)building blocks to regulate the electron/ion movement in the three-dimensional axes and orientation pathways.The superpower hierarchy surfaces and multi-directional orientation components may create isosurface potential electrodes with mobile electron movements,in-to-out interplay electron dominances,and electron/charge cloud distributions.This study is the first to evaluate the hotkeys of choice anode/cathode architectonics to assemble different LIB-electrode platforms with high-mobility electron/ion flows and high-performance capacity functionalities.Density functional theory calculation revealed that the FRTO@C anode and VST-(i)@C cathode architectonics are a superior choice for the configuration of full-scale LIB built-up models.The integrated FRTO@C//VST-(i)@C full-scale LIB retains a huge discharge capacity(~94.2%),an average Coulombic efficiency of 99.85%after 2000 cycles at 1 C,and a high energy density of 127 Wh kg?1,thereby satisfying scale-up commercial EV requirements.

Iodine Promoted Ultralow Zn Nucleation Overpotential and Zn-Rich Cathode for Low-Cost, Fast-Production and High-Energy Density Anode-Free Zn-Iodine Batteries

The anode-free design is a promising strategy to increase the energy density of aqueous Zn metal batteries(AZMBs).However,the scarcity of Zn-rich cathodes and the rapid loss of limited Zn greatly hinder their commercial applications.To address these issues,a novel anode-free Zniodine battery(AFZIB)was designed via a simple,low-cost and scalable approach.Iodine plays bifunctional roles in improving the AFZIB overall performance:enabling high-performance Zn-rich cathode and modulating Zn deposition behavior.On the cathode side,the ZnI_(2) serves as Zn-rich cathode material.The graphene/polyvinyl pyrrolidone heterostructure was employed as an efficient host for ZnI_(2) to enhance electron conductivity and suppress the shuttle effect of iodine species.On the anode side,trace I_(3)^(−) additive in the electrolyte creates surface reconstruction on the commercial Cu foil.The in situ formed zincophilic Cu nanocluster allows ultralow-overpotential and uniform Zn deposition and superior reversibility(average coulombic efficiency>99.91% over 7,000 cycles).Based on such a configuration,AFZIB exhibits significantly increased energy density(162 Wh kg^(−1)) and durable cycle stability(63.8% capacity retention after 200 cycles)under practical application conditions.Considering the low cost and simple preparation methods of the electrode materials,this work paves the way for the practical application of AZMBs.

Comparative Study of Two Carbon Fiber Cathodes and Theoretical Analysis in Microbial Fuel Cells on Ocean Floor

Cathode activity plays an important role in the improvement of the microbial fuel cells on ocean floor （BMFCs）. A comparison study between Rayon-based （CF-R） and PAN-based carbon fiber （CF-P） cathodes is conducted in the paper. The two carbon fibers were heat treated to improve cell performance （CF-R-H ＆ CF-P-H）, and were used to build a new BMFCs structure with a foamy carbon anode. The maximum power density was 112.4mWm-2 for CF-R-H, followed by 66.6mWm-2 for CF-R, 49.7 mWm-2 for CF-P-H and 21.6mWm-2 for CF-P respectively. The higher specific area and deep groove make CF-R have a better power output than with CF-P. Meanwhile, heat treatment of carbon fiber can improve cell power, nearly two-fold higher than heat treatment of plain fiber. This improvement may be due to the quinones group formation to accelerate the reduction of oxygen and electron transfer on the fiber surface in the three phase boundary after heat treatment. Compared to PAN-based carbon fiber, Rayon-based carbon fiber would be preferentially selected as cathode in novel BMFCs design due to its high surface area, low cost and higher power. The comparison research is significant for cathode material selection and cell design.

A Bifunctional-Modulated Conformal Li/Mn-Rich Layered Cathode for Fast-Charging,High Volumetric Density and Durable Li-Ion Full Cells

Lithium-and manganese-rich(LMR)layered cathode materials hold the great promise in designing the next-generation high energy density lithium ion batteries.However,due to the severe surface phase transformation and structure collapse,stabilizing LMR to suppress capacity fade has been a critical challenge.Here,a bifunctional strategy that integrates the advantages of surface modification and structural design is proposed to address the above issues.A model compound Li_(1.2)Mn_(0.54)Ni_(0.13)Co_(0.13)O_(2)(MNC)with semi-hollow microsphere structure is synthesized,of which the surface is modified by surface-treated layer and graphene/car-bon nanotube dual layers.The unique structure design enabled high tap density(2.1 g cm^(−3))and bidirectional ion diffusion pathways.The dual surface coatings covalent bonded with MNC via C-O-M linkage greatly improves charge transfer efficiency and mitigates electrode degradation.Owing to the synergistic effect,the obtained MNC cathode is highly conformal with durable structure integrity,exhibiting high volumetric energy density(2234 Wh L^(−1))and predominant capacitive behavior.The assembled full cell,with nanograph-ite as the anode,reveals an energy density of 526.5 Wh kg^(−1),good rate performance(70.3%retention at 20 C)and long cycle life(1000 cycles).The strategy presented in this work may shed light on designing other high-performance energy devices.

Preparation and properties of Os–Ir–Al alloy for impregnated tungsten cathodes

Os–Ir–Al alloy was fabricated by powder metallurgy technique.IrAl and OsIr interalloys were synthesized to reduce the Al evaporation and ensure the composition of the ternary alloy.Analysis on microstructures shows that each component is distributed homogeneously,and the green density reaches 94.9%.Ba–W cathodes with Os–Ir–Al alloy magnetic sputtered on the tips are prepared and directly current density tests are carried out on these cathodes.It is found that at 1,050℃,the average zero field emission density of the cathode reaches up to 20 Aácm-2.The improvements of cathodic current density and stability may indicate the prosperous application of Os–Ir–Al alloy on cathode.

Dendrite-structured FeF_(2) consisting of closely linked nanoparticles as cathode for high-performance lithium-ion capacitors

Lithium-ion capacitors(LICs)are regarded as a good choice for next-generation energy storage devices,which are expected to exhibit high energy densities,high power densities,and ultra-long cycling stability.Nevertheless,only a few battery-type cathode materials with limited kinetic properties can be employed in LICs,and their electrochemical properties need to be optimized urgently.Here,we exploit a new dendrite-structured FeF_(2) consisting of closely linked primary nanoparticles using a facile solvothermal method combined with the subsequent annealing treatment.This particular architecture has favorable transport pathways for both lithium ions and electrons and exhibits an ultrafast chargedischarge capability with high reversible capacities.Furthermore,a well-designed LIC employing the prepared dendrite-structured FeF_(2) as the battery-type cathode and commercialized activated carbon(AC)as supercapacitor-type anode was constructed in an organic electrolyte containing Li ions.The LIC operates at an optimal voltage range of 1.1-3.8 V and shows a maximum high energy density of 152 W h kg^(-1) and a high power density of 4900 W kg^(-1) based on the total mass of cathode and anode.Long-term cycling stability(85%capacity retention after 2000 cycles)was achieved at 1 A g^(-1).This work suggests that the dendrite-structured FeF_(2) is a prime candidate for high-performance LICs and accelerates the development of hybrid ion capacitor devices.

Concentrated ternary ether electrolyte allows for stable cycling of a lithium metal battery with commercial mass loading high-nickel NMC and thin anodes

A new concentrated ternary salt ether-based electrolyte enables stable cycling of lithium metal battery(LMB)cells with high-mass-loading(13.8 mg cm^(−2),2.5 mAh cm^(−2))NMC622(LiNi_(0.6)Co_(0.2)Mn_(0.2)O_(2))cathodes and 50μm Li anodes.Termed“CETHER-3,”this electrolyte is based on LiTFSI,LiDFOB,and LiBF4 with 5 vol%fluorinated ethylene carbonate in 1,2-dimethoxyethane.Commer-cial carbonate and state-of-the-art binary salt ether electrolytes were also tested as baselines.With CETHER-3,the electrochemical performance of the full-cell battery is among the most favorably reported in terms of high-voltage cycling stability.For example,LiNi_(x)Mn_(y)Co_(1-x-y)O_(2)(NMC)-Li metal cells retain 80%capacity at 430 cycles with a 4.4 V cut-off and 83%capacity at 100 cycles with a 4.5 V cut-off(charge at C/5,discharge at C/2).According to simulation by density functional theory and molecular dynamics,this favorable performance is an outcome of enhanced coordination between Li^(+)and the solvent/salt molecules.Combining advanced microscopy(high-resolution transmission electron microscopy,scanning electron microscopy)and surface science(X-ray photoelectron spectroscopy,time-of-fight secondary ion mass spectroscopy,Fourier-transform infrared spectroscopy,Raman spectroscopy),it is demonstrated that a thinner and more stable cathode electrolyte interphase(CEI)and solid electrolyte interphase(SEI)are formed.The CEI is rich in lithium sulfide(Li_(2)SO_(3)),while the SEI is rich in Li_(3)N and LiF.During cycling,the CEI/SEI suppresses both the deleterious transformation of the cathode R-3m layered near-surface structure into disordered rock salt and the growth of lithium metal dendrites.

Self-consistent assessment of Li^(+) ion cathodes:Theory vs.experiments

Transition metal oxide cathodes such as layered Li Co O_(2),spinel Li Mn_(2)O_(4) and olivine Li Fe PO4 have been commercialized for several decades and widely used in the rechargeable Li-ion batteries(LIBs).While great theoretical efforts have been made using the density functional theory(DFT)method,leading to insightful understanding covering materials stability and functional properties,the lack of consistency in choices of functionals and/or convergence criteria makes it somewhat difficult to compare results.It is therefore highly useful to assess these established systems towards self-consistency,thus offering a reliable working basis for theoretical formulation of novel cathodes.Here in this work,we have carried out systematic DFT calculations on the basis of recently established framework covering both thermodynamic stability,functional properties and associated mechanisms.Efforts have been made in selfconsistent selection of exchange-correlation(XC)functionals in terms of dependable accuracy with affordable computational cost,which is essential for high-throughput first-principles calculations.The outcome of the current work on three established cathode systems is in very good agreement with experimental data,and the methodology is to provide a solid basis for designing novel cathode materials without using costing non-local exchange-correlation functionals for structure-energy calculations.

Preparation of Li[Ni_(1/3)Co_(1/3)Mn_(1/3)]O_2 powders for cathode material in secondary battery by solid-state method

Employing Li2CO3, NiO, Co3O4, and MnCO3 powders as starting materials, Li[Ni1/3Co1/3Mn1/3]O2 was synthesized by solid-state reaction method. Various grinding aids were applied during milling in order to optimize the synthesis process. After successive heat treatments at 650 and 950 ℃, the prepared powders were characterized by X-ray diffraction (XRD) analysis, scanning electron microscopy, and transmission electron microscopy. The powders prepared by adding salt (NaCl) as grinding aid exhibit a clear R3m layer structure. The powders by other grinding aids like heptane show some impurity peaks in the XRD pattern. The former powders show a uniform particle size distribution of less than 1 μm average size while the latter shows a wide distribution ranging from 1 to 10 μm. Energy dispersive X-ray (EDX) analysiss show that the ratio of Ni, Co, and Mn content in the powder is approximately 1/3, 1/3, and 1/3, respecively. The EDX data indicate no incorporation of sodium or chlorine into the powders. Charge-discharge tests gave an initial discharge capacity of 160 mAh·g-1 for the powders with NaCl addition while 70 mAh·g-1 for the powders with heptane.

Analyses of nonequilibrium transport in atmospheric-pressure direct-current argon discharge under different modes

The key plasma parameters under different discharge modes, such as heavy-particle and electron temperatures, electron number density, and nonequilibrium volume of plasmas, play important roles in various applications of gas discharge plasmas. In this study, a self-consistent two-dimensional nonequilibrium fluid model coupled with an external circuit model is established to reveal the mechanisms related to the discharge modes, including the normal glow, abnormal glow,arc, and glow-to-arc transition modes, with an atmospheric-pressure direct-current(DC) argon discharge as a model plasma system. The modeling results show that, under different discharge modes, the most significant difference between the preceding four discharge modes lies in the current and energy transfer processes on the cathode side. On one hand, the current to the cathode surface is mainly delivered by the ions coming from the plasma column under the glow discharge mode due to the low temperature of the solid cathode, whereas the thermionic and secondary electrons emitted from the hot cathode surface play a very important role under the arc mode with a higher cathode surface temperature and higher ion flux toward the cathode. On the other hand, the energy transfer channel on the cathode side changes from mainly heating the solid cathode under the glow mode to simultaneously heating both the solid cathode and plasma column under the arc mode with an increase in the discharge current. Consequently, the power density in the cathode sheath(P_c) was used as a key parameter for judging different discharge modes, and the range of(0.28–1.2) × 10^(12) W m^(-3) was determined as a critical window of P_c corresponding to the glow-to-arc-mode transition for the atmospheric-pressure DC argon discharge, which was also verified by comparison with the experimental results in this study and the data in the previous literature.