Advanced Lithium-ion Batteries Research Articles

Encapsulating ultrafine cobalt sulfides into multichannel carbon nanofibers for superior Li-ion energy storage

Developing high-capacity anode materials based on metal sulfides is of great importance for building advanced lithium-ion batteries (LIBs). Herein, we demonstrate rational encapsulation of cobalt sulfide (CoSx) nanoparticles into multichannel carbon nanofibers (CoSx/MCF) with substantially improved Li+ reactivity and durability. The unique multichannel and conductive carbon scaffold not only affords boosted electron/Li + transportation pathways for fast redox reaction with CoSx, but also stabilizes the electrode structure by buffering the volume change of CoSx. Impressively, the CoSx/MCF composite could serve as flexible anodes to deliver a high reversible capacity of 737 mAh g−1 at 0.2 A g−1 after 100 cycles, superior rate capacity of 374 mAh g−1 at 5 A g−1, and excellent operating stability over 1000 cycles. Practical feasibility is also demonstrated by a full cell based on the high-capacity CoSx/MCF anode and Li[Ni0.8Co0.1Mn0.1]O2 cathode. The present study may provide insights for the facile synthesis of advanced anode materials for high-performance LIBs.

Free-standing ultrathick LiMn2O4@single-wall carbon nanotubes electrode with high areal capacity

The ever-increasing demands for advanced lithium-ion batteries with high energy density have greatly stimulated the pursuit of thick electrodes with high active material loading. However, it is not feasible to prepare thick electrodes with traditional coating methods due to mechanical instability. Herein, using single-wall carbon nanotubes (SWCNT) as conductive carbon and binder, free-standing LiMn2O4 thick electrodes (F-LMO) with ultrahigh-mass loading up to ∼190 mg cm−2 were prepared by vacuum filtration combined with freeze-drying. The thick electrodes with ∼30 mg cm−2 mass loading achieved a high specific capacity of 106.7 mAh g−1 with a good capacity retention of 94% over 50 cycles at 0.5 C, which was superior to the traditional coating electrodes (∼20 mg cm−2) of 99.3 mAh g−1 with 95% because of the enhanced electronic conductivity originated from SWCNT. In addition, the high active material ratio of 97.5 wt%, near-theoretical reversible capacity, and high mass loading gave ultrathick F-LMO electrodes (600 μm) of ∼190 mg cm−2 with a remarkable areal capacity of 20 mAh cm−2. Moreover, the concentration polarization that occurred in the thick F-LMO electrodes under high current density was discussed via electrochemical stimulation.

Ultra-fine Sb2S3 particles encapsulated in activated-carbon: A high-performance anode for Li-ion batteries

The low electronic conductivity and severe volume change hinder the commercialization of Sb2S3 anode, despite many efforts have been made to improve its electrochemical properties in the past decades. Many of these methods are complicated and different kinds of chemicals are required. Herein, a facile high-temperature melting method was employed to prepare high-performance Sb2S3 anode with nanosizing bulk natural stibnite and wrapping activated carbon. The activated carbon can provide nano-pores that absorb the molten Sb2S3. This structure can not only promote electronic conductivity but also provide accommodation for the volume change of Sb2S3 nanoparticles. More importantly, compared to other methods such as the hydrothermal method, the advantage of this method is that natural stibnite (95 wt% Sb2S3) was directly used as the Sb2S3 source without other synthetic or purification processes. Benefiting from these merits, the Sb2S3 composite anode exhibits good cyclic stability and excellent rate property, which delivers a high capacity of over 450 mAh g−1 even at a current density of 5 A g−1, proving that the Sb2S3 composite can serve as a promising anode for advanced lithium-ion batteries.

Metal‐ organic frameworks and their derivatives as anode material in lithium‐ion batteries: Recent advances towards novel configurations

Lithium-ion batteries (LIBs) have drawn extensive research interests due to their noticeably enhanced gravimetric energy density relative to other chemical batteries. The potential utility of metal-organic frameworks (MOFs) and their derivatives has recently been recognized as highly effective anode components for LIBs because they can be tuned to select specific metal sites and/or to adjust pore sizes. In this work, their electrochemical performance as anodic materials is carefully evaluated with respect to lithium-ions storage capacity, energy/power, stability, and flexibility. Furthermore, through the coordination of the organic linker and metal center, MOFs can benefit from enhanced catalytic activities in the design of advanced LIBs. For future research for next-generation LIBs, scientific focus should be placed on the development of diverse features of MOF-based composites such as core-shell MOFs, mono/bi-metal doped MOFs, dual organic linker-based MOFs, MOFs@MOFs core shell structure, and dual organic ligands-based MOF. As such, MOF-based LIB electrode materials are expected to expand their utility with the improvement in topology and functionality in association with the dimensionality, pore size, and surface area.

Trimethoxyboroxine as an electrolyte additive to enhance the 4.5 ​V cycling performance of a Ni-rich layered oxide cathode

Ni-rich layered oxides are attractive cathode materials for advanced lithium-ion batteries (LIBs) due to their high energy density. However, their large-scale application is seriously hindered by their interfacial instability, especially at a high cut-off potential. Here, we demonstrate that trimethoxyboroxine (TMOBX) is an effective film-forming additive to address the interfacial instability of LiNi0.8Co0.1Mn0.1O2 (NCM811) material at a high cut-off voltage of 4.5 ​V. We find that TMOBX decomposes before carbonate solvent and forms a thin cathode electrolyte interphase (CEI) layer on the surface of the NCM811 material. This TMOBX-formed CEI significantly suppresses electrolyte decomposition at a high potential and inhibits the dissolution of transition metals from NCM811 during cycling. In addition, electron-deficient borate compounds coordinate with anions (PF6−, F−, etc.) and H2O in the battery, further improving the battery's stability. As a result, adding 1.0 ​wt% of TMOBX boosts the capacity retention of a Li||NCM811 ​cell from 68.72% to 86.60% after 200 cycles at 0.5C in the range of 2.8–4.5 ​V.

Structure modification of Ni-rich layered oxide cathode toward advanced lithium-ion batteries

Structure modification of Ni-rich layered oxide cathode toward advanced lithium-ion batteries

Garnet solid electrolyte blended LiNi0.6Mn0.2Co0.2O2 as high-voltage stable cathodes for advanced lithium-ion batteries

Ni-rich LiNi1-xCox/2Mnx/2O2 layered materials have been widely adopted as cathodes for current electric vehicles (EVs) due to their high gravimetric and volumetric energy densities. However, their high-voltage instability (e.g., > 4.3 VvsLi) limited their usable capacities corresponding to about 60 – 70 % of theoretical capacities. The major problems of high-voltage operation stem from instability of Ni3+/4+ at cathode-electrolyte interphase (CEI) in contact with electrolytes. Here we propose garnet-type Li6.7La3Zr1.7Ta0.3O12 (LLZT) solid-electrolyte-blended LiNi0.6Mn0.2Co0.2O2 (NMC) as high-voltage stable cathodes. The LLZT not only passivates the CEI but scavenges protons and moisture in electrolytes. From well-balanced ionic and electronic transport properties, 5 wt% LLZT blended NMC cathodes delivered enhanced electrochemical performances in full-cells. Unlike other complicated coating processes, our proposed solid-electrolyte blending approach can be readily implementable in commercial Li-ion batteries due to its manufacturing friendliness, energy saving, and cost effectiveness.

Mechanical properties of cathode materials for lithium-ion batteries

<h2>Summary</h2> Mechanochemical degradation processes such as the fracture of cathode particles play a major role in limiting the service life of advanced lithium-ion batteries (LIBs). In order to help alleviate the degradation of battery performance, it is necessary to measure the relationship between the degradation of the mechanical properties of cathodes and their concomitant degradation of electrochemical performance. In this review, measurements of the mechanical properties of LIB cathode materials are summarized from the literature, along with the range of experimental methods used in their determination. Dimensional changes that accompany charge and discharge are compared for active materials of olivine, spinel, and layered atomic structures. The sensitivity of indentation hardness, Young's modulus and fracture strength to grain size, porosity, state of charge and charge/discharge history are critically reviewed and discussed with reference to the behavior of conventional, electrically inactive solids. This approach allows for the identification of microstructural properties that dictate the mechanical properties of LIB cathode materials.

B-doped and La4NiLiO8-coated Ni-rich cathode with enhanced structural and interfacial stability for lithium-ion batteries

Ni-rich layered oxides are considered promising cathodes for advanced lithium-ion batteries (LIBs) in the future, owing to their high capacity and low cost. However, the issues on structural and interfacial stability of Ni-rich cathodes still pose substantial obstacles in the practical application of advanced LIBs. Here, we employ a one-step method to synthesize a B-doped and La4NiLiO8-coated LiNi0.825Co0.115Mn0.06O2 (BL-1) cathode with reliable structure and interface, for the first time. The La4NiLiO8 coating layer can prevent cathodes from electrolyte assault and facilitate Li+ diffusion kinetics. Moreover, B-doping can effectively restrain the pernicious H2-H3 phase transition and adjust the orientation of primary particles to a radial alignment, which is obstructive to the arise of microcracks induced by the change of anisotropic volume. Specifically, when tested in pouch cells, the BL-1cathode exhibits outstanding capacity retention of 93.49% after 500 cycles at 1C. This dual-modification strategy dramatically enhances the stability of the structure and interface for Ni-rich cathode materials, consequently accelerating the commercialization process of high-energy–density LIBs.

Efficient Lithium Storage of Si‐Based Anode Enabled by a Dual‐Component Protection Strategy

Si, as a highly competitive anode material for lithium‐ion batteries (LIBs), has gained enormous commercial interests due to its high theoretical capacity, low delithiation potential, and natural abundance. However, its poor cycling stability/electron conductivity seriously restrains its practical applications. To address this problem well, herein, a scalable spray‐drying method is explored to construct an ultrahigh stable 3D Si‐based composite (designed as Si@C‐MX) anode, where the Ti3C2Tx MXene nanosheets (NSs) crump the nano‐Si coated uniformly with an ultrathin carbon layer. Synergistically, the coating carbon layer and Ti3C2Tx NSs as the conductive elastomer constrain/buffer the volume expansion of nano‐Si, avoid direct contact with the electrolyte, build a continuous electronic network for rapid electron transport, and meanwhile improve mechanical properties of the electrodes. Thanks to the dual protection (i.e., carbon coating and Ti3C2Tx NSs) strategy, the resultant Si@C‐MX anode exhibits large reversible capacities, superior rate capability, and long‐duration cycle stability. Additionally, the Si@C‐MX‐based full batteries delivered an energy density of 371.8 Wh kg−1 based on the whole device at 123.9 W kg−1 and a desirable capacity retention with cycling, which convincingly highlights its promising application in advanced LIBs.

Surface Coupling between Mechanical and Electric Fields Empowering Ni-Rich Cathodes with Superior Cyclabilities for Lithium-Ion Batteries.

Ni‐rich cathodes with high energy densities are considered as promising candidates for advanced lithium‐ion batteries, whereas their commercial application is in dilemma due to dramatic capacity decay and poor structure stability stemmed from interfacial instability, structural degradation, and stress–strain accumulation, as well as intergranular cracks. Herein, a piezoelectric LiTaO3 (LTO) layer is facilely deposited onto Li[Ni x CoyMn1− x − y ]O2 (x = 0.6, 0.8) cathodes to induce surface polarized electric fields via the intrinsic stress–strain of Ni‐rich active materials, thus modulating interfacial Li+ kinetics upon cycling. Various characterizations indicate that the electrochemical performances of LTO‐modified cathodes are obviously enhanced even under large current density and elevated temperature. Intensive explorations from in situ X‐ray diffraction technique, finite element analysis, and first‐principle calculation manifest that the improvement mechanism of LTO decoration can be attributed to the enhanced structural stability of bulk material, suppressed stress accumulation, and regulated ion transportation. These findings provide deep insight into surface coupling strategy between mechanical and electric fields to regulate the interfacial Li+ kinetics behavior and enhance structure stability for Ni‐rich cathodes, which will also arouse great interest from scientists and engineers in multifunctional surface engineering for electrochemical systems.

Safety and cycling stability enhancement of cellulose paper-based lithium-ion battery separator by aramid nanofibers

Commercial polyolefin separators suffer from poor electrolyte wettability and low thermal stability, which give rise to unsatisfied electrochemical performance and severe safety hazards for lithium-ion batteries (LIBs). Herein, a novel paper-based composite separator composed of electrolyte-affinitive cellulose fibers (CFs) and thermally stable aramid nanofibers (ANFs) was successfully fabricated through the traditional papermaking method. The ANFs as a functional nanofiller played crucial roles in improving the defects of pure CF separator including large-sized pores, low mechanical strength and high flammability. Specifically, the CF/ANF composite separator with 20 wt% ANFs (CF/ANF-20) possessed narrow micropores, satisfied tensile strength (33 MPa), excellent thermal resistance (without dimensional shrinkage up to 200 °C) and flame retardancy, which greatly enhanced the safe operation of battery. Moreover, inheriting from the highly porous structure and exceptional electrolyte affinity of CF separator, the CF/ANF-20 composite separator exhibited appropriate porosity and superior electrolyte wettability, which brought about a high electrolyte uptake (157%), thus endowing it with better ionic conductivity (0.75 mS cm−1) and lower interfacial resistance compared to commercial polypropylene separator. Accordingly, the LiFePO4/Li half cells using CF/ANF-20 separator delivered outstanding rate capability and stable cycling performance. All results indicate that the CF/ANF-20 separator shown great balance between the electrochemical performance and safety is an intriguing candidate for advanced LIBs.

A newly-developed heat-resistance polyimide microsphere coating to enhance the thermal stability of commercial polyolefin separators for advanced lithium-ion battery

Polymer separators with high-temp dimensional stability is strongly demanded for high-safety lithium-ion batteries (LIBs). In this study, a novel polyimide (PI) microsphere coating slurry was prepared and then plated on Celgard polypropylene (PP) separator, producing PP@PI microsphere composite separator with excellent thermal stability, flame retardancy, high liquid retention capacity and high ionic conductivity by a simple blade-coating process. The results show that the thermal stability and liquid retention capacity of the PP@PI microsphere composite separator are significantly improved. Compared with the pure commercial PP separator which sharply shrank at 150 °C, the PI microsphere composite separator shows negligible shrinkage over 150 °C. The obtained PP@PI microsphere composite separators exhibited excellent thermal stability and fire-resistance properties. At the same time, the peel strength of composite separator reached 138.6 N·m−1, with excellent adhesion. The surface density of PP@PI microsphere composite separator is 16.62 g·m−2, which is lower than 30.22 g·m−2 of ceramic coated composite separator. Electrochemical characterizations indicate that the discharge capacity and capacity retention rate of the battery assembled with PP@PI microsphere composite separator are significantly higher than those assembled with the pure PP separator. The half-cell assembled with this composite separator shows a high capacity of 144.3 mAh·g−1 at 5C, which is much higher than the 117.8 mAh·g−1 of the commercial PP separator equipped battery. Moreover, the lithium-ion batteries assembled with the PP@PI microsphere composite separator show excellent cycle stability after 200 cycles at 1C. More importantly, the lithium-ion battery assembled with PP@PI microsphere composite separator has excellent safety at high temperature. These features demonstrate the potential of PP@PI microspheres composite membrane as high-security separator for LIBs.

Modification-scavenging hydroxyl groups of natural mineral fiber separators to boost initial coulombic efficiency of lithium-ion battery

The recently reported inorganic separator is promising for advanced lithium-ion batteries (LIBs) with excellent electrochemical performance and high safety. However, then with most of inorganic separators suffered from low initial Coulombic efficiency (ICE). In this work, the chrysotile fiber (CF) separator was researched as a hydroxyl-rich inorganic separator, and the relationship between the hydroxyl groups on the surface of the CF separators and the ICE of batteries was studied. It was found that the rich hydroxyl groups on the surface of the CF separators induced the decomposition of LiPF6, thus leading to low ICE. Modified CF separators (LSO) were prepared by acid leaching and lithium ions modification. Modification-scavenging the hydroxyl groups on the surface of the CF separators can effectively promote the ICE of the Li|LiFePO4 cell (93%). Furthermore, the Li|LiFePO4 cell with LSO exhibited an excellent rate performance and high-rate cycle stability (109.4 mAh g−1 at 5C after 1000 cycles). This work provided a new strategy for improving electrochemical performance that reducing the number of hydroxyl groups on the surface of natural mineral fibers is effective to improve the ICE of inorganic separators.

Graphene-like 2D carbon wrapped porous carbon embedded SnO2/CoSn hybrid nanoparticles with enhanced lithium storage performance

Eliminating the issues caused by large volumetric expansion and low conductivity is a critical tactic for the performance improvement of SnO2 anode materials for lithium-ion batteries. Herein, the issues mentioned above are effectively alleviated and hence the lithium storage performance of the SnO2 is significantly improved through construction of a characteristic nanocomposite. In this nanocomposite the porous carbon embedded SnO2/CoSn hybrid nanoparticles are wrapped in a graphene-like 2-dimensional (2D) carbon nanosheets assembled three-dimensional (3D) carbon matrix. This nanocomposite is referred to as SnO2/CoSn@3DC. The SnO2/CoSn@3DC is demonstrated to integrate the advantages of heterogeneous hybrid nanoparticles, porous carbon and graphene-like 2D carbon nanosheets, therefore showing enhanced electrochemical kinetics and cycling stability. As a result, it delivers 887.1 mAh g − 1 after 110 cycles at 200 mA g − 1 as well as 803.4 mAh g − 1 after 170 cycles at 1000 mA g − 1, therefore exhibiting good potential in application in lithium-ion batteries as advanced anodes. Furthermore, the strategy reported here for preparing SnO2/CoSn@3DC may be extended to prepare other 2D carbon/metallic oxide/alloy composites for advanced lithium-ion battery anodes with various precursors such as ZnSn(OH)6 and FeSn(OH)6 compounds.

Improved Electrochemical Behavior and Thermal Stability of Li and Mn-Rich Cathode Materials Modified by Lithium Sulfate Surface Treatment

High-energy cathode materials that are Li- and Mn-rich lithiated oxides—for instance, 0.35Li2MnO3.0.65LiNi0.35Mn0.45Co0.20O2 (HE-NCM)—are promising for advanced lithium-ion batteries. However, HE-NCM cathodes suffer from severe degradation during cycling, causing gradual capacity loss, voltage fading, and low-rate capability performance. In this work, we applied an effective approach to creating a nano-sized surface layer of Li2SO4 on the above material, providing mitigation of the interfacial side reactions while retaining the structural integrity of the cathodes upon extended cycling. The Li2SO4 coating was formed on the surface of the material by mixing it with nanocrystalline Li2SO4 and annealing at 600 °C. We established enhanced electrochemical behavior with ~20% higher discharge capacity, improved charge-transfer kinetics, and higher rate capability of HE-NCM cathodes due to the presence of the Li2SO4 coating. Online electrochemical mass spectrometry studies revealed lower CO2 and H2 evolution in the treated samples, implying that the Li2SO4 layer partially suppresses the electrolyte degradation during the initial cycle. In addition, a ~28% improvement in the thermal stability of the Li2SO4-treated samples in reactions with battery solution was also shown by DSC studies. The post-cycling analysis allowed us to conclude that the Li2SO4 phase remained on the surface and retained its structure after 100 cycles.

A porous, mechanically strong and thermally stable zeolitic imidazolate framework-8@bacterial cellulose/aramid nanofibers composite separator for advanced lithium-ion batteries

Currently, the commercial polyolefin-based separators suffer from inferior electrolyte wettability and poor thermal resistance, leading to unsatisfied electrochemical performance and severe safety hazards for lithium-ion batteries (LIBs). Herein, a high-performance composite membrane composed of zeolitic imidazolate framework-8@bacterial cellulose (ZIF-8@BC) matrix and aramid nanofibers (ANFs) filler was developed as the LIB separator via the facile in-situ synthesis and subsequent filtration process. The as-prepared ZIF-8@BC/30%ANFs composite separator (with 30 wt% of ANFs) showed high tensile strength (70.7 MPa), outstanding thermal resistance and flame retardancy, which significantly enhanced the safety of LIBs during operation. Moreover, due to the well-developed porous structure and exceptional electrolyte affinity, the ZIF-8@BC/30%ANFs composite separator exhibited good electrolyte wettability and high electrolyte uptake (267.8%), which brought about superior ionic conductivity (1.60 mS cm−1) compared to commercial polypropylene separator. These synergistic advantages eventually endowed the battery with excellent rate capability and cycling performance. Accordingly, the ZIF-8@BC/30%ANFs composite separator is a promising candidate for next-generation LIBs with both high safety and enhanced performance.

Ultra-robust polyimide nanofiber separators with shutdown function for advanced lithium-ion batteries

Safety issues have significantly impeded the development of modern lithium-ion batteries (LIBs), and fabricating advanced separators has been considered as a feasible solution to improve the security of LIBs. Here, we present an advanced polyimide (PI) nanofiber membrane (referred to as PIE) with ultrahigh strength and the shutdown function by optimizing precursor viscosity and nanofibers microstructure. Increasing chain length of the PI backbone and in -situ bonding technique can markedly promote mechanical properties of PI nanofiber separator (strength of pristine PI nonwoven >60 MPa, strength of modified PI nonwoven >90 MPa), which is a new record so far among current PI nanofiber membranes. The present PIE separator displayed superior wettability, heat-resistant, and ion conductivity compared to the commercial Celgard separator. Importantly, the excellent flame resistance and high-temperature shutdown function of PIE separators ensure the security of LIBs. Based on our rational separator design, the PIE separators possessed higher LIB capability (111.3 mAh g −1 at 10 C) than the Celgard separator (90.8 mAh g −1 at 10 C). Moreover, the PIE separator-based LIBs can run stably at 1 C and 5 C for 100 cycles. The present work demonstrated the likelihood of replacing the commercial polyolefin separator with the advanced PI nanofiber membranes. • Advanced PIE separators are prepared by increasing chain length of PI backbone and using in -situ bonding technique. • The strength of as-fabricated PI separators present a highest record so far (pristine PI nonwoven >60 MPa, modified PI nonwoven >90 MPa). • The excellent thermostability, flame resistance, and shutdown function can ensure the safety of LIBs. • PIE separators exhibit superior LIB capability and cycling stability.

Design and Synthesis of Heterometallic Ni–Co Organic Frameworks as Anode Materials for High-Performance Lithium Storage

Reasonable design of high-rate, long-life anode materials is the key to manufacturing advanced lithium-ion batteries. Herein, we synthesized the heterometallic (Ni, Co) 4,4′-biphenyldicarboxylic metal organic framework (NiCo-MOF-1) and heterometallic (Ni, Co) 2,2′-bipyridine-5,5′-dicarboxylic metal organic framework (NiCo-MOF-2) by solvothermal method, and explored the applications as anode materials for lithium-ion batteries in depth. It was demonstrated that the initial discharge/charge specific capacities of NiCo-MOF-1 and NiCo-MOF-2 reached 2.04/1.12 and 1.99/1.11 mAh cm−2 at a current density of 0.1 mA cm−2 and the voltage window of 0.01 ∼ 3.0 V, respectively. Similarly, NiCo-MOF-2 could maintain a specific discharge/charge capacity of 0.65/0.64 mAh cm−2 after 150 cycles, which was higher than that of NiCo-MOF-1 (0.45/0.43 mAh cm−2). In addition, NiCo-MOF-2 delivers outstanding rate performance (0.29/0.29 mAh cm−2 at 1.0 mA cm−2), which came down to the strong conjugated carboxylate π–π interaction and the synergistic effect of nickel and cobalt bimetals. Through the kinetic analysis, the pseudocapacitance contribution was as high as 61.7% at 0.5 mV s−1. Ex-situ XPS verified the coordination mechanism of Li+ and COO− rings with benzene ring in NiCo-MOF-2 thus achieving high lithium storage capacity.

Hydrogen bonds enhanced composite polymer electrolyte for high-voltage cathode of solid-state lithium battery

Polymer electrolyte is one of the important components for developing advanced solid-state lithium batteries (SSLBs). However, the narrow electrochemical stability window restricts the practical application with high-voltage cathodes. Herein, a series of composite solid electrolytes (CSEs), possessing both wide electrochemical stability window (up to 5.0 V vs. Li+/Li) and high ionic conductivity (over 1.35 ×10−3 S/cm at 25 °C), were reported by integrating SiO2 nanoparticles into poly(vinyl ethylene carbonate) polymer electrolyte. The enhanced anti-oxidation performances are mainly caused and confirmed by the local intermolecular interactions of hydrogen bonds in CSE. Based on this CSE, the SSLBs with LiCoO2 cathode present good cycle stability at high voltage, and the capacity retention with 4.5 V cut-off voltage is about 94% after 200 cycles. This work not only proves the importance of intermolecular interactions in CSE, but also provides an effective method for achieving high-energy SSLBs with enhanced interface compatibility between polymer electrolyte and high-voltage cathodes.