Cathode For Rechargeable Lithium Batteries Research Articles

Hypercrosslinked Phenothiazine Polymer as a Low-Cost and Durable Organic Cathode for Rechargeable Lithium Batteries

Hypercrosslinked Phenothiazine Polymer as a Low-Cost and Durable Organic Cathode for Rechargeable Lithium Batteries

Weakly solvated EC-free linear alkyl carbonate electrolytes for Ni-rich cathode in rechargeable lithium battery.

Ethylene carbonate (EC) in the electrolyte is not stable in cells operated at highvoltage (≥4.4V) or with Li metal anode, which greatly reduce the energy density and lifetime of the rechargeable lithium battery. Herein, an EC-free linearalkylcarbonate-based electrolyte is developed, which enables the high-voltage(≥4.4V) and low-temperature (-30°C) application of Ni-rich cathode (LiNi0.8Mn0.1Co0.1O2, NCM811). The EC-free system, consisting of LiPF6 and LiNO3 in ternary linear alkyl carbonates, possesses low viscosity, weakly solvated structure, and high interfacial stability with both the Ni-rich cathode and the Li metal anode to avoid continuous electrode/electrolyte side reactions and metal dissolution from the cathode. As a result, the Li||NCM811 cell delivers remarkable capacity retention of 93± 0.5% at the voltage of 4.4V and 88± 0.6% at 4.5V over 100 cycles. This study provides very encouraging perspective to develop EC-free carbonate-based electrolyte for high-voltage and low-temperature application in high-energy-density rechargeable lithium batteries.

High-Performance Polymeric Lithium Salt Electrode Material from Phenol–Formaldehyde Condensation

In spite of the recent progress made in organic electrode materials, high-performance candidates are still lacking, especially when taking affordability into account. Herein, we report a novel polymeric lithium salt, namely dilithium salt of poly(2,5-dihydroxy-1,4-benzoquinone-3,6-methylene) (Li2PDBM), which can be easily synthesized by phenol-formaldehyde condensation, followed by lithiation in LiOH solution to eliminate the negative effect of phenol groups in PDBM. Benefiting from a high theoretical capacity (327 mA h g-1), structure stability, insolubility, and redox reversibility, Li2PDBM exhibits superior electrochemical performance as a cathode for rechargeable lithium batteries, including a high reversible capacity (256 mA h g-1), a high rate capability (79% @ 2000 mA g-1), and a high cycling stability (77% @ 2000th cycle). Besides the cost-effective electrode material synthesis approach, this work also provides an important mechanistic understanding of the structure-performance relationship of carbonyl-based electrode materials, especially those with -OH or -OM (M = Li, Na, and K) substituents.

Facile Synthesis of Polyphenothiazine as a High-Performance p-Type Cathode for Rechargeable Lithium Batteries.

p-Type electroactive polymers are promising cathodes for dual-ion batteries but cost-effective candidates are still lacking. In this study, the p-type polymer polyphenothiazine (PPTZ) is synthesized by a facile one-step oxidation polymerization from the low-cost phenothiazine (PTZ) monomer. As a cathode for rechargeable lithium batteries, PPTZ shows superior electrochemical performance to previously reported PTZ-based polymers with complicated structures and syntheses. For example, PPTZ has a high reversible capacity of 157 mAh g-1 within 2.5-4.3 V vs. Li+ /Li with an average discharge voltage of 3.5 V, and a high capacity retention of 77 % after 500 cycles. The highly reversible one-electron redox mechanism of PPTZ is also investigated in detail by electrochemical testing, ex situ FT-IR and X-ray photoelectron spectroscopy, and DFT calculations. PPTZ has the potential to serve as an attractive p-type cathode material for practical applications and the facile synthesis may be also extended to other polymer cathodes based on N-heteroaromatic units.

A crosslinking hydrogel binder for high-sulfur content S@pPAN cathode in rechargeable lithium batteries

High-energy density lithium-sulfur (Li-S) batteries have received intensive attention as promising energy storage system. Among diverse sulfur-based cathodes, sulfurized pyrolyzed poly(acrylonitrile) (S@pPAN) cathode delivered superior electrochemical performance. However, the sulfur content of S@pPAN is relatively low (<50 wt%), which significantly limits the energy density. Herein, a hydrogel SA-Cu binder was proposed with a crosslinking network constructed by Cu2+ ions. The introduction of Cu2+ ions enabled excellent electrochemical behaviors of S@pPAN cathode even with high sulfur content of 52.6 wt% via chemical interaction with sulfur and polysulfide. Moreover, a favorable cathode interphase was formed containing electrochemically active and conductive CuSx. S@pPAN/SA-Cu exhibited a high sulfur utilization of 85.3%, long cycling stability over 1000 cycles and remarkable capacity of 1200 mAh gs−1 even at 10 C. Furthermore, ascribed to the improved electrode structure, high-loading electrode (sulfur loading: 4 mg cm−2) displayed stable cycling with areal capacity of 5.26 mAh cm−2 (1315 mAh gs−1) after 40 cycles. This study provides new directions to prepare high-sulfur content and high-loading S@pPAN cathode for higher energy density.

Improved battery performance of Fe-doped LiVPO4F with high capacity and stable cycling

LiVPO4F is considered as an upgrade of current LiFePO4 cathode for rechargeable lithium batteries due to its superior thermal stability and mildly high voltage plateau. However, the low intrinsic electric conductivity and sluggish electrochemical kinetics constrain its battery performance and practical development. Partial substitution of vanadium with iron is designed in this paper given the similarity of LiVPO4F and LiFePO4OH. The phase structure, particle size, battery performance and electrochemical kinetics of LiV1-xFexPO4F (0 ≤ x < 1) are comparatively studied. LiV0.9Fe0.1PO4F is found having the optimal electrochemical performance, and delivers a reversible specific capacity of 132 mA h g−1 and 80 mA h g−1 at C/8 and 6C, respectively. After 300 cycles at 0.5C rate, the capacity slowly reduces from 119 mA h g−1 to 108 mA h g−1 with a retention of 90.8%.

Three-dimensional porous radical polymer/reduced graphene oxide composite with two-electron redox reactions as high-performance cathode for lithium-ion batteries

Organic cathode materials, especially stable radical polymers, have been considered as ideal substitutes to inorganic cathode for rechargeable lithium batteries (LIBs) due to their fast electron transfer kinetics, tunable electrochemical properties, facile solution processing and environmental sustainability. Unfortunately, unsatisfied electronic conductivity of polymers leads to poor practical capacity, low utilization efficiency, and hinder their application for LIBs. In this work, a three-dimensional porous electrode composed by poly(2,2,6,6-tetramethylpiperidinyloxy-4-yl methacrylate) and reduced graphene oxide (PTMA/rGO) is prepared via a simple dissolution-assembly-depositing method. Since the 3D porous structure effectively promotes the electrolytes penetration and facilitates electron conduction pathways, satisfactorily, the PTMA/rGO electrode shows an obvious two-electron redox reactions and delivers the highest reversible capacity of 153 mA h g−1 at 20 mA g−1 with an ultrahigh utilization efficiency of 98.8%, which is much higher than that of PTMA/CB electrode prepared by the traditional physical mixing method (104 mA h g−1, utilization efficiency of 66.1%). Meanwhile, the PTMA/rGO electrode also exhibits excellent rate performance and cycle stability. This kind of high performance PTMA/rGO electrode with simple preparation method provides a broad application prospect of the next generation of high performance LIBs based on organic electrode.

Raspberry-like hierarchical structure FeS2 decorated by dual-carbon framework as high-performance cathode for rechargeable lithium batteries

To address the large volume variation and low lithium-ions/electronic conductivity of FeS2 cathode for rechargeable lithium batteries, we elaborately design a raspberry-like hierarchical structure FeS2 cathode decorated by dual-carbon framework. The in-situ formed disordered carbon matrix functions as a buffer to accommodate the volume change as well as an isolated layer to prevent the FeS2 nano-grains/clusters from aggregation during (de)lithiation. Meanwhile, the out shell graphene (rGO) sheets intimately wrapped on the FeS2@C microspheres surface further help to maintain the electrode structure integrity upon cycling. Moreover, the rGO sheets can effectively construct the conductive bridges for electrons transfer between each individual FeS2@C microsphere. Combining with the carbon matrix that provides the electrons conductive channels inside the hierarchical structure, a continuous three-dimensional conductive network is built, leading to accelerated charge transfer inside the electrode. In addition, the tiny FeS2 nano-grains/clusters are uniformly dispersed in the carbon matrix with interfacial chemical coupling, further favoring the structural stability and electron transportation. As a result, the FeS2@C/rGO electrode displays a high specific capacity (0.1 C: 566 mAh g−1), a remarkable cycling stability (capacity decay rate of 0.014% per cycle at 1 C), and an excellent rate capability, demonstrating a promising cathode for rechargeable lithium batteries.

Dense and high loading sulfurized pyrolyzed poly (acrylonitrile)(S@pPAN) cathode for rechargeable lithium batteries

High energy density lithium-sulfur (Li-S) batteries have been extensively investigated in recent years due to the urgent demands for advanced energy storage systems. Among various sulfur cathodes reported in past decades, sulfurized pyrolyzed poly (acrylonitrile) (S@pPAN) cathode displayed several superiorities on electrochemical behaviors. However, further scale-up practical application of Li-S battery with S@pPAN cathode has been plagued by high-loading sulfur electrode preparation. Herein, a network binder system (i.e., guar gum and poly(acrylic acid)) is constructed through binding effect between substantial functional groups. The network binder ensures a simple blade-cast method for high-loading S@pPAN cathode up to 17.5 ​mg ​cm-2 on planar aluminum-based current collector. The optimization of dense sulfur electrode after rolling pressure reached a compacted density close to 1.15 ​g ​cm-3 and demonstrated a high areal capacity of 6 ​mAh cm-2 after 120 cycles. Benefiting from the simple method to prepare dense and high-loading S@pPAN cathode, the correlation between areal specific capacity with rolling pressure applied on electrodes was carefully analyzed. This study sheds light on the key issues of sulfur electrode preparation for high energy density lithium sulfur batteries.

A pomegranate-like porous carbon nanomaterial as selenium host for stable lithium-selenium batteries

Selenium has received increasing attention as a potential alternative to sulfur cathode for rechargeable lithium batteries because of its high electronic conductivity and better electrochemical performance. However, the shuttle effect of polyselenides in lithium-selenium batteries, similar to that of polysulfides in lithium-sulfur batteries, is still one of the main drawbacks. Here, we designed and synthesized a new pomegranate-like porous carbon/Se (PPC/Se) cathode that could effectively improve the shuttle effect of polyselenides. The pomegranate-like carbon nanoparticles used as the host materials for Se were prepared via carbonization of well-assembled ketjen black nanosubunits. The batteries assembled with such new-synthesized PPC/Se cathodes exhibit relatively high specific capacity of 380 mA h g−1 at 1 C and high Coulombic efficiency of ∼ 98% due to the restrained dissolution of polyselenides.

Staging Phenomena in Lithium-Intercalated Boron-Carbon.

Hole-doped LiBC has become of great interest as a candidate for high-temperature superconductivity with its structural similarity to MgB2 and as a possible cathode for rechargeable lithium batteries with the large graphenelike BC hexagons. The limitation on synthesis studies has detracted from the structural and electronic properties and application studies of Li xBC. Here, we present the successful synthesis of hole-doped Li0.5BC and its structural and electronic characterization using detailed structural modeling based on a unique stage-2 Daumas-Hérold-type domain structure consistent with X-ray diffraction data. The strong intralayer motion of the guest Li island induces extraordinary structural properties, such as staging and staging disorder, which are confirmed by the compressibility results obtained from Li0.85BC (anisotropic cell compressibility with B0 ∼ 134 GPa) and Li0.48BC (isotropic cell compressibility with B0 ∼ 190 GPa). Li deficiency increases the conductivity; however, the temperature-dependent conductivity is dominated by the thermal excitation of carriers in a strongly disordered regime with well-defined localized states.

Performance Improvements of Cobalt Oxide Cathodes for Rechargeable Lithium Batteries

AbstractLithium‐ion batteries are essential mobile power sources for portable devices and energy supplies. Among the various cathode materials, cobalt oxides are the most important materials used in lithium‐ion batteries. But the intrinsic drawbacks of cobalt oxides restrict their wide application. In this paper, we present an overview of current approaches to improve the electrochemical performance of the cathode materials, as well as the capacity and cycling capability of the lithium‐ion batteries.

A phenyl disulfide@CNT composite cathode for rechargeable lithium batteries

A phase extraction technique is used to prepare a core–sheath structured composite consisting of carbon nanotubes (CNTs) coated with a layer of phenyl disulfide (PDS, C6H5SSC6H5). The PDS@CNT paper cathode delivers a discharge capacity of 218 mA h g−1 at 1C while retaining 70% of the capacity after 150 cycles. High rate performance (180 mA h g−1 at 3C) and scalable synthesis prove its capability for energy storage applications.

Combining electrospinning and sputtering to improve rechargeable lithium battery cathodes: coating carbon fibre felt with nickel sulfide

Various nickel sulfide nanostructures have been developed for the fabrication of high surface area electrodes for rechargeable lithium batteries. In this study, we fabricated a nickel sulfide covered carbon fibre felt with high uniformity, high density, and large area for cathode materials for use in rechargeable lithium batteries, by using a combined electrospinning and sputtering deposition technique. In particular, the nickel sulfide/carbon fibre felt is a multi-functional material that can act as a conducting electrode itself without the use of binders and conductive materials owing to the high conductivity of the interlinked carbon fibre structures. A Li/nickel sulfide cell with current density of 100 mA g−1 exhibits good cycle performance and high first discharge capacity (970.46 mAh g−1) and good coulombic efficiency of 99% at 20 cycles. This electrode has good structural and electrochemical properties and has a potential to be commercialized when the properties are matured.

Unique electrochemical behavior of heterocyclic selenium–sulfur cathode materials in ether-based electrolytes for rechargeable lithium batteries

Mixed chalcogenide systems represent a new class of promising cathode materials for high performance rechargeable lithium batteries. Among them, heterocyclic selenium–sulfur (SexSy) cathodes, coupling the good conductivity of Se and high capacity of S, have attracted great attention in recent years. However, further research is still needed to better understand the lithiation/delithiation process of SexSy cathodes in ether-based electrolytes. Herein, SexSy-based composites with covalent Se–S bonds were prepared by infiltrating various proportions of S and Se powders into the mesoporous carbon microsphere (MCM) host at 500°C in vacuum. As cathodes for rechargeable lithium batteries, SexSy/MCM composites exhibit unique electrochemical behavior rather than a simple hybrid of Li–S and Li–Se batteries in ether-based electrolytes. The Se–S bonds in SexSy/MCM could anchor S during cycling, and effectively reduce the formation of long-chain polysulfides. As a result, the SexSy/MCM cathodes demonstrate superior overall electrochemical performance than Se/MCM or S/MCM. Moreover, Se/S ratio could also affect the electrochemical behavior of SexSy/MCM composites. The optimal Se2S5/MCM cathode delivers the best performance with a high reversible capacity of 796.4mAhg−1 at 0.5C over 100 cycles, and good rate capability of 688.8mAhg−1 at 5C. Especially, a superior coulombic efficiency of ~100% is achieved without addition of LiNO3. This work could help us to better understand the inherent synergistic mechanism behind SexSy cathodes for high performance rechargeable lithium batteries in ether-based electrolytes.

Cu-Based Ternary Fluorides As High-Energy Cathodes for Rechargeable Lithium Batteries

Transition metal fluorides are promising for use as high-capacity cathodes in rechargeable lithium batteries for large-scale applications, such as electric vehicles and grid-scale storage, but energy-efficiency and kinetics related issues remain a major hurdle to their commercial use. Cu based fluorides are particularly attractive due to the intrinsic high redox potential and extraordinarily high specific energy density. Here we report on the synthesis, structural and electrochemical properties of new nanostructured ternary metal fluorides, which may overcome some of these issues. By substituting Cu into the Fe lattice, forming the solid solution CuyFe1-yF2, reversible Cu and Fe redox reactions were achieved with surprisingly small hysteresis (<150 mV). This finding indicates that cation substitution may provide a new pathway for tailoring electrochemical properties of conversion electrodes [1]. The Li storage/release mechanisms and limits to cycling stability of CuyFe1-yF2 were also investigated by combining electrochemical measurement with comprehensive structural and chemical analysis using in-situ X-ray absorption spectroscopy, X-ray diffraction, and transmission electron microscopy-electron energy loss spectroscopy (TEM-EELS). Detailed lithium reaction mechanisms, Cu-loss related issues along with possible remedy solutions in the CuyFe1-yF2 system, will be discussed. The work was supported as part of the NorthEastern Center for Chemical Energy Storage, an EFRC Center funded by the U.S. DOE-BES, under Award Number DESC0001294, and by DOE-EERE under the Advanced Battery Materials Research program, under Contract No. DE-SC0012704. [1] Wang et al., “Ternary Metal Fluorides as High-Energy Cathodes with Low Cycling Hysteresis”, Nat. Commun. 6: 6668 (2015). Figure 1

Structure Integrity Endowed by a Ti-Containing Surface Layer towards Ultrastable LiNi0.8Co0.15Al0.05O2 for All-Solid-State Lithium Batteries

LiNi0.8Co0.15Al0.05O2 (NCA) is regarded as a promising high capacity cathode for rechargeable lithium batteries used in electric vehicles and energy storage devices. However, NCA is structurally unstable under the high voltage operation (>4.3 V) as cracks may develop on the surface and finally lead to capacity fading. To address this problem, we succeed in achieving a nanoscale solid solution surface layer containing Ti on the NCA second particles based on a one step pre-coating method. NCA with a novel functional surface layer shows an obvious enhancement of electrochemical performances in all-solid-state lithium batteries. In particular, NCA-Ti2 exhibits an ultrastable reversible capacity of 115 mAh g−1 with capacity retentions 94% after 100 cycles for all-solid-state lithium batteries. The cracks are directly observed on the surface of the pristine sample while the surface of the Ti-doped sample is intact under high cutoff voltage. These results clearly indicate that the cracks during cycles play an important role in the capacity fading for the NCA cathode materials and Ti-containg solid solution surface layer could effectively improve capacity retention.

Guar gum as a novel binder for sulfur composite cathodes in rechargeable lithium batteries

Due to their high theoretical energy densities, lithium sulfur (Li-S) batteries are currently some of the most extensively investigated electrochemical power sources. As a sustainable and environmentally friendly biopolymer, guar gum (GG) is chosen as a binder for use in Li-S batteries for the first time. The results show that GG is a promising binder for sulfur composite cathode materials, and exhibits excellent cycling performance and a favorable high rate capability.

Electrospun FeS2@Carbon Fiber Electrode as a High Energy Density Cathode for Rechargeable Lithium Batteries.

In this study, an FeS2@carbon fiber electrode is developed with FeS2 nanoparticles either embedded in or attached to carbon fibers by using an electrospinning method. By applying this binder-free, metal-current-collector-free FeS2@carbon fiber electrode, both the redox reaction and capacity decay mechanisms for the Li-FeS2 system are revealed by changing the electrolyte (conventional carbonate electrolyte and a "solvent-in-salt"-type Li-S battery electrolyte) and working voltage ranges (1.0-3.0 V and 1.5-3.0 V vs Li/Li(+)). The FeS2@carbon fiber electrode shows stable cycling performance in both the conventional carbonate electrolyte and the solvent-in-salt-type Li-S battery electrolyte in the voltage range of 1.5-3.0 V. Electrochemical tests in the solvent-in-salt-type Li-S battery electrolyte indicate that the Li-FeS2 system becomes a hybrid of the Li-S cell and Li-iron sulfide cell after the initial cycle. Based on the understanding on the capacity decay mechanisms, the cycling stability of the Li-FeS2 system in the voltage range of 1.0-3.0 V is then significantly enhanced by coating the FeS2@carbon fiber electrode with a thin layer of Al2O3. The Al2O3-coated electrode demonstrates excellent cycling performance with high discharge energy densities at both the material level (∼1300 Wh/kg-FeS2) and the electrode level (∼1000 Wh/kg-FeS2 electrode).

Ternary Metal Fluorides As High-Energy Cathodes with Low Cycling Hysteresis

Transition metal fluorides (MFx) are promising for use as high-capacity cathodes in rechargeable lithium batteries for large-scale applications, such as electric vehicles and grid-scale storage, but energy-efficiency and kinetics related issues remain a major hurdle to their commercial use. Cu based fluorides are particularly attractive due to the 3.55 V redox potential and extraordinarily high specific energy (1874 Wh/kg). Here we report on the synthesis, structural and electrochemical properties of new ternary metal fluorides (M1yM21-yFx: M1, M2 = Fe, Cu), which may overcome these issues. By substituting Cu into the Fe lattice, forming the solid solution CuyFe1-yF2, reversible Cu and Fe redox reactions were achieved with surprisingly small hysteresis (<150 mV; Figure 1). This finding indicates that cation substitution may provide a new pathway for tailoring electrochemical properties of conversion electrodes. The Li storage/release mechanisms and limits to cycling stability of CuyFe1-yF2 were investigated by combining electrochemical measurement with comprehensive structural and chemical analysis using in-situ X-ray absorption spectroscopy, X-ray diffraction, and transmission electron microscopy-electron energy loss spectroscopy (TEM-EELS). The lithium reaction process is much more complicated in CuyFe1-yF2 than the binary metal counterparts (i.e. FeF2, CuF2) [2-4]. Some of the recent results on synthesis, structural and electrochemical characterization of the ternary metal fluorides will be presented. Detailed lithium reaction mechanisms, and Cu-loss related issues along with possible remedy solutions in the CuyFe1-yF2system, will be discussed. [1] Wang et al., “Ternary Metal Fluorides as High-Energy Cathodes with Low Cycling Hysteresis”, Nat. Commun.6:6668 (2015). [2] Wang et al., “Conversion Reaction Mechanisms in Lithium Ion Batteries: Study of the Binary Metal Fluoride Electrodes”, J. Am. Chem. Soc., 133, 18828 (2011). [3] Wang et al., “Tracking Li Transport and Electrochemical Reaction in Nanoparticles”, Nat. Commun., 3, 1201(2012). [4] Hua et al., “Comprehensive Study of the CuF2 Conversion Reaction Mechanism in a Lithium Ion Battery”, J. Phys. Chem. C 118, 15169 (2014). Figure 1