Initial Discharge Specific Capacity Research Articles

Enhancing the Cycling and Rate Performance of Ni-Rich Cathodes for Lithium-Ion Batteries by Bulk-Phase Engineering and Surface Reconstruction.

The structural and interfacial instability of Ni-rich layered cathodes LiNi0.9Co0.05Mn0.05O2 (NCM9055) severely hinders their commercial application. In this work, straightforward high-temperature solid-state methods are utilized to successfully synthesize Nb-doped and Li3PO4-coated LiNi0.9Co0.05Mn0.05O2 by combining two niobium sources, NbOPO4·3H2O and Nb2O5, for the first time. Studies indicate that Nb doping enhanced the integrity of the layered structure, and the Li3PO4 coating reduced water absorption on the surface and considerably boosted the durability of the interface. The dual-modified cathode Li(Ni0.9Co0.05Mn0.05)0.985Nb0.015O2@Li3PO4 (NCM-2) exhibits remarkable cycling and rate performance. The initial discharge specific capacity of NCM-2 is 203.33 mAh g-1 at 0.1 C and 196.04 mAh g-1 at 1 C, while the capacity retention after 200 cycles is 91.38% at 1 C, which is much higher than that of pristine NCM9055 (49.96%). In addition, it also provides a superior discharge specific capacity of about 175.63 mAh g-1 even at 5 C. This study emphasizes a feasible approach to enhancing the stability of Ni-rich cathodes at the interfaces and bulk structures.

Functionalized polypropylene separator coated with polyether/polyester blend for high-performance lithium metal batteries

Commercial polyolefin separators used in lithium metal batteries (LMBs) have the disadvantages of insufficient thermal stability and poor wettability with electrolytes, which causes bad safety and battery performance. Poly(ε-caprolactone) (PCL)-based electrolytes have drawn widespread attention in the field of polymer electrolytes owing to their electrochemical stability and high lithium-ion transference number. This work proposes a strategy of functionalizing commercial polypropylene (PP) separator coated by blending PCL (M w ~ 50,000) and poly(ethylene oxide) (PEO, M V ~ 600,000). Compared to commercial PP separators, PP-blended PEO60w/PCL5w separators possess better wettability with electrolytes and electrochemical performances. The initial discharge specific capacity of LiFePO4-based LMBs assembled with PP-blended PEO60w/PCL5w separators reaches 144 mAh g-1 (1C) and 103 mAh g-1 (5C) at room temperature, respectively. Notably, Li/PP-blended PEO60w/PCL5w/LiFePO4 shows an improved capacity retention rate of 77% after 800 cycles, confirming that the functionalized separator with coated PEO/PCL blend has great potential for application in the field of LMBs.

Cellulose Fiber based self-supporting paper cathode with multi-scale network structure for high performance lithium-sulfur battery

Lithium-sulfur batteries (LSBs) are gaining attention as a potential energy storage option due to their impressive theoretical specific capacity. However, the main challenges hindering its implementation include the expansion in volume of sulfur and lithium sulfide during the conversion process of charge-discharge, the limited conductivity of the active material, and specifically, the phenomenon known as shuttle effect caused by lithium polysulfides (LiPSs). The development of high-performance LSBs have led to the need for self-supporting cathode materials that can efficiently accommodate volume expansion, build up efficient conductive pathways, and suppress shuttle effects. The poly(3,4-ethylenedioxythiophene) (PEDOT) was synthesized in situ on cellulose nanofibers (CNFs), resulting in the formation of CNF@PEDOT. Subsequently, CNF@PEDOT was combined with plant fibers (PFs) and multi-wall carbon nanotubes (MWCNTs) to fabricate a self-supporting cathode featuring a multi-scale network structure denoted as CNF@PEDOT/MWCNT/PF/S. The PFs serve as the primary backbone network, CNF@PEDOT to form the secondary conductive network, and MWCNTs act as tertiary conducting networks. In fact, the design of multi-level conductive network effectively improves the conductivity of the material, and PEDOT can further adsorb and catalyze LiPSs. The incorporation of PFs significantly enhanced the mechanical robustness of the cathode and augmented its electrolyte permeability. The self-supporting CNF@PEDOT/MWCNT/PF/S cathode exhibits an initial capacity of 1204.6 mA h g−1 when loaded with 2.4 mg cm−2 of sulfur at a rate of 0.2 C. Notably, it maintains an initial discharge specific capacity of 712.9 mA h g−1 even when the sulfur load is increased to 4.3 mg cm−2. This study presents a comprehensive framework for the development of self-supporting cathodes in LSBs.

Opening and Constructing Stable Lithium‐ion Channels within Polymer Electrolytes

Lithium‐ion batteries play an integral role in various aspects of daily life, yet there is a pressing need to enhance their safety and cycling stability. In this study, we have successfully developed a highly secure and flexible solid‐state polymer electrolyte (SPE) through the in‐situ polymerization of allyl acetoacetate (AAA) monomers. This SPE constructed an efficient Li+ transport channel inside and effectively improved the solid‐solid interface contact of solid‐state batteries to reduce interfacial impedance. Furthermore, it exhibited excellent thermal stability, an ionic conductivity of 3.82×10‐4 S cm‐1 at room temperature (RT), and a Li+ transport number (tLi+) of 0.66. The numerous oxygen vacancies on layered inorganic SiO2 created an excellent environment for TFSI‐ immobilization. Free Li+ migrated rapidly at the C=O equivalence site with the poly(allyl acetoacetate) (PAAA) matrix. Consequently, when cycled at 0.5 C and RT, it displayed an initial discharge specific capacity of 140.6 mAh g‐1 with a discharge specific capacity retention rate of 70% even after 500 cycles. Similarly, when cycled at a higher rate of 5 C, it demonstrated an initial discharge specific capacity of 132.3 mAh g‐1 while maintaining excellent cycling stability.

Enhanced Low-Temperature Resistance of Lithium-metal Rechargeable Batteries Based on Electrolyte Including Ethyl Acetate and LiDFOB Additives.

To meet the demand for higher energy density in lithium-ion batteries and expand their application range, coupling lithium metal anodes with high-voltage cathodes is an ideal solution. However, the compatibility between lithium metal batteries and electrolytes affects their applicability. In this study, proposes a locally concentrated electrolyte based on ethyl acetate (EA) as the solvent, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as the lithium salt, and lithium difluorooxoborate (LiDFOB) as a sacrificial agent to enhance the low-temperature and high-voltage endurance of Li//Lithium cobalt oxide (LCO) batteries. The Li//LCO battery can operate within the voltage range of 3 to 4.5 V, with an initial discharge specific capacity of 174.5 mAh g-1 at 20 oC. At -40 oC, after 200 cycles, the capacity retention rate is 87.7%. It can operate under extreme conditions of -70 oC, with a discharge specific capacity of 112.6 mAh g-1. Additionally, LCO//HC batteries using this electrolyte demonstrate excellent performance. Present work provides a new perspective for the optimization of electrolytes for low-temperature lithium-ion batteries.

Boehmite-PVDF-CTFE/F-PI composite separator irradiated by electron beam for high-rate lithium-ion batteries

As an important part of the fields such as renewable energy and electric vehicles, electrochemical energy storage technology faces significant challenges in improving energy density, extending battery life and improving safety. We successfully prepared a composite battery separator of polyvinylidene fluoride-chlorotrifluorinylene (PVDF-CTFE) and fluorinated polyimide (F-PI) -based materials, mixed it with different contents of boehmite nanoparticles, and then modified it by different doses of electron beam irradiation to improve the performance, especially to overcome the problem of maintaining capacity decline in high-speed charging environment. The results showed that the prepared battery separators exhibited outstanding thermal stability, electrochemical properties and ionic conductivity with 12 % boehmite nanoparticles. After 1000 high-speed charge and discharge cycles in current density of 10C, the battery based on the modified separator still maintained a capacity retention rate of 84.4 %, with the initial discharge specific capacity of 111.9 mAhg−1. This means that irradiated separators not only maintain a high energy density in a high-speed charging environment, but also overcome the problem of maintaining capacity decline. Electron beam irradiation further improved the comprehensive performance of the separator. After 1000 and 1500 cycles at the current density of 10C and 15C, the specific discharge capacity of the battery can still retain more than 90 % and 80 % of the initial specific discharge capacity, which provides a longer life in practical applications.

Copper/cobalt metal-organic framework composites for advanced anode material of lithium-ion battery

In this paper, two new types of metal-organic frameworks (MOFs) materials, namely Cu-IM and Co-MOF, have been successfully applied to the anode of lithium-ion batteries with LiPF6 (EC: DMC = 1:1, volume) electrolyte additive. Cu-IM and Co-MOF employed imidazole (IM) and 2-methylimidazole (2-MeIM) as organic ligands, respectively. The results revealed the synthesized MOFs exhibited high initial discharge specific capacities (Cu-IM: 1964.5 mAh g−1, Co-MOF: 1423.3 mAh g−1) as well as low internal resistances (Cu-IM: 146 Ω; Co-MOF: 236 Ω). To alleviate the issue of capacity decay in single MOFs, we attempted the dual-MOFs materials through the rational design of interfacial/surface properties and microstructure. Compared to Cu-IM, the prepared Cu-IM/Co-MOF composites have a higher specific surface area and pore volume. Furthermore, the charge transfer resistance of Cu-IM/Co-MOF composites (141 Ω) was lower than that of Cu-IM and Co-MOF respectively. After a heat treatment to Cu-IM/Co-MOF composites, the electrochemical performance of obtained Cu-IM/Co-MOF 250 dual-MOFs composites have been significantly improved. The Cu-IM/Co-MOF 250 dual-MOFs composites demonstrated excellent cycling stability and high discharge specific capacities at various current densities. The composites displayed stable discharge specific capacity retention of 834 mAh g−1 (50 mA g−1, 75 cycles), 710.5 mAh g−1 (200 mA g−1, 50 cycles), and 392.5 mAh g−1 (500 mA g−1, 50 cycles), highlighting their promising performance for energy storage applications. The synthesized Cu-IM/Co-MOF 250 dual-MOFs composites demonstrates exceptional cycling performance and rate capability, implying that it has the promising prospects as anode material for lithium-ion batteries.

Development and understanding of the lithiation/de-lithiation mechanism of a low cobalt and nickel-rich cathode material for lithium‐ion batteries

Nickel-rich LiNixMnyCo1−x−yO2 (NMC, with x ≥ 0.6) layered oxides are regarded as cathode candidates for high-energy density lithium-ion batteries (LIBs). However, this technology faces several challenges due to the scarcity of crucial raw materials such as cobalt precursors and the negative environmental impact of their extraction process. It is therefore, it becomes imperative to develop low cobalt content cathode compositions that offer alternative options with comparable electrochemical performance. Herein, we have used a systematic approach to modify the composition while keeping all other properties (particle size and morphology) constant to synthesise low-Co-cathode materials, namely LiNi0·8Mn0·1Co0·1O2 (NMC-10 %) and LiNi0·8Mn0·15Co0·05O2 (NMC-5%). A co-precipitation route using a continuous stirred thank reactor was used for synthesis. The physico-chemical properties, electrochemical performances, cycling stability, and rate capabilities of NMC-5% materials are comparable to those of NCM-10 % materials. NMC-10 % and NMC-5% half cells show initial specific discharge capacities of 191 mAh.g−1, and 185 mAh.g−1, respectively, in a voltage range of 2.8–4.3 V (vs. Li+/Li). The NMC-5% exhibits excellent thermal stability, characterized by a predominant exothermic peak at 432 °C and significantly lower total heat energy when compared to NMC-10 % counterpart, which displayed its main exothermic peak at 339 °C. The structural and electronic changes of both materials were evaluated through in operando synchrotron-based X-ray techniques. Regardless of the cobalt content, both materials show comparable structural and electronic evolution upon the de-intercalation/intercalation of Li+ ions. An irreversible phase transition at the first delithiation was observed as emphasized by diffraction of synchrotron radiations.

Mixed valence Mo2C-MoC/C catalyst enhances polysulfides conversion kinetics in lithium–sulfur batteries

Lithium-sulfur batteries have received extensive attention in the field of electrochemical energy storage systems due to their extremely high theoretical energy density (2600 Wh·kg−1) and low cost. However, poor electrical conductivity, shuttle effect, and volume expansion effect still need to be addressed. Here, we controllably synthesized hollow spherical Mo2C-MoC/C structure as the cathode material for lithium-sulfur batteries. Through high-temperature calcination, the synthesis of graphitized reticular carbon matrix and the loading of Mo2C and MoC nanoparticles with mixed valence of Mo2+ and Mo3+ were simultaneously achieved. The two synergistically improved the electronic conductivity and ensured excellent battery performance. From the experimental results, Mo2C-MoC/C structure strongly adsorbed polysulfides and promoted the conversion of polysulfides to lithium sulfide, accelerating the reaction kinetics and enhancing the battery performance. The initial discharge specific capacity of Mo2C-MoC/C electrode with 57.12 wt% sulfur content was 870.4 mAh·g−1 at 0.2 C, and remained at 770.7 mAh·g−1 at 0.5 C, which was significantly better than that of Mo2C/C/S. The rational design of the Mo2C-MoC/C structure in this study can be generalized to the advanced electrode materials of other Mo-based nanomaterials.

Al-doped flower-like VO2(B) microspheres as high-performance cathode materials for lithium-ion batteries

VO2(B), as a potential cathode material for lithium-ion batteries (LIBs), is attracting extensive attention from researchers because of its great superiority in terms of theoretical specific capacity, energy density, and cost. Nevertheless, VO2(B), leads to irreversible decay of specific capacity during cycling for reasons including structural stability and inferior electrical conductivity. In this work, the electrochemical performance of VO2(B) electrode materials are further enhanced via Al ion doping. The results reveal that the prepared Al-doped 3D flower-like VO2(B) microspheres exhibit a high initial discharge specific capacity (as high as 314.8 mAh/g at 0.1 A/g current density) at an Al doping amount of n(Al3+)/n(V5+) = 6.0 %. Moreover, it displays a first discharge specific capacity of up to 229.2 mAh/g at a current density of 1 A/g with the capacity retention rate of 90.0 % after 120 cycles. As a result, Al-doped 3D flower-like VO2(B) microspheres provide enormous commercialization potential as cathode materials for LIBs.

Enhancing the Electrochemical Performances of Disordered Li1.23Ni0.3Nb0.3Fe0.16O0.85F0.15 Cathode Material for Lithium-Ion Batteries by LiNbOx Coating.

For the next generation of lithium-ion batteries (LIBs), it is primary to seek high capacity and long-lifetime electrode materials. Li-excess disordered rock-salt structure (DRS) cathodes have gained much attention due to their high specific capacity. However, Li-excess can lead to a decrease in the structural stability of an electrode material. A new Li-rich DRS oxyfluorides, Li1.23Ni0.3Nb0.3Fe0.16O0.85F0.15 (F0.15) with a series amounts of LiNbOx (LN) coating (0, 5, 10, and 15 wt % denoted as F0.15-LN0, F0.15-LN5, F0.15-LN10, and F0.15-LN15, respectively), are successfully synthesized and evaluated as cathode materials in LIBs. Among them, F0.15-LN10 exhibits the highest initial discharge specific capacity of 296.1 mAh g-1 (at a current density of 20 mA g-1) with the capacity retention rate of 14% higher than that of the uncoated F0.15 after 80 cycles. Even at 300 mA g-1, F0.15-LN10 still delivers the highest discharge specific capacity of 130 mAh g-1. After 20 cycles, the charge-transfer impedance of F0.15-LN10 remained the smallest. The characterizations indicate that LN coating reduces the surface polarization of the cathode materials, slows the interfacial side reactions between the electrolyte and the electrode, and speeds up the Li+ diffusion. These results demonstrate that LN coating is an effective strategy to improve the electrochemical performance.

The interface modification with polyethyleneimine enhances both ionic conductivity and interfacial compatibility of composite solid electrolyte

The composite solid electrolyte (CSE), polyethylene oxide (PEO)-Li6.4La3Zr1.4Ta0.6O12 (LLZTO), is deemed a promising candidate for all-solid-state batteries. Nevertheless, due to the poor interfacial compatibility between LLZTO nanoparticles and PEO, achieving a homogeneous dispersion of LLZTO nanoparticles within PEO is not readily attainable. The aggregation of LLZTO within PEO leads to a decline in the ionic conductivity of the CSE and poor interface stability with the electrode, ultimately resulting in deteriorated battery cyclic performance. In this work, the interface between LLZTO and PEO is designed and comprehensively investigated. Initially, dopamine self-polymerization is employed to form a uniform coating layer on the surface of LLZTO nanoparticles. Subsequently, by utilizing the amino groups present in polyethyleneimine (PEI), which can react with the phenolic hydroxyl groups of dopamine and the ether linkages in PEO, PEI serves as a bridging agent, enhancing the interfacial compatibility between LLZTO and PEO. Here it is shown that, the ionic conductivity of the LLZTO-PEO CSE containing 40 wt% modified LLZTO increases from 6.14✕10−5 S cm−1 to 1.89✕10−4 S cm−1. Furthermore, this CSE exhibits improved thermal stability, an enlarged electrochemical window of 4.8 V, a lithium-ion transference number of 0.45, and excellent interface stability with the lithium anode. The assembled LiFePO4 | 40 wt% LLZTO@PDA@PEI-PEO CSE | Li all-solid-state battery demonstrates an initial discharge specific capacity of 151.8 mA h g−1 at 0.2 C, with a capacity retention of 85.8% after 200 cycles. This work provides a novel strategy for interface-modified polymer- inorganic composite solid electrolytes, which will advance the development of high-energy-density all-solid-state lithium batteries.

UV Curved PESF-LLZTO Composite Solid Electrolyte to In Situ Construct Ultrastable Interface for All Solid-State Lithium Battery

Optimizing interfacial contact between electrolyte and electrode is one of key factors to achieve stable all solid-state lithium batteries (ASSLBs). In this work, UV curving technique is reported to produce ASSLBs by in situ constructing integrated interface between PESF-LLZTO composite solid electrolytes (CSEs) and LiFePO4 (LFP) cathode. Benefiting from the integral structure and ultrastable properties of the as-prepared CSE/LFP interface, the obtained ASSLBs delivers an initial discharge specific capacities of 162.8 mAh g−1 at 0.1 C and 30 °C, and successfully runs over 520 cycles at 0.5 C with a discharge capacity retention ratio of 96.3%.

High specific capacity of Li3V2(PO4)3/C glass-ceramic with ultralow carbon content

Li3V2(PO4)3 glass-ceramic, as an intrinsic insulator, necessitates compositing with conductive carbon to function as a cathode for energy storage in lithium-ion batteries, inevitably reducing the specific energy of the final devices. This study synthesized Li3V2(PO4)3/C composite with an ultralow carbon content (1.39 wt%) using a sol-gel method with glucomannan as a soft template. The Li3V2(PO4)3/C composite cathode achieved an initial discharge specific capacity of 128.22 mA h g−1 at 0.1 C, which is 97.14% of the theoretical specific capacity. Additionally, it demonstrated excellent rate capabilities, with 106.20 mA h g−1 at 5 C and 78.91 mA h g−1 at 10 C, as well as long-term cycling stability, with 114.94 mA h g−1 at 2 C and retaining 92.09% capacity after 500 cycles. The ultralow carbon content feature will contribute to the commercialization of cathodes. This work provides a novel direction for the design and fabrication of new electrode materials.

Boosting the capacity and stability of Na3V2(PO4)2F3-2xO2x microspheres, using atomic layer deposition of artificial CEI

Phosphate-based materials [e.g. Na3V2(PO4)2F3-2xO2x; (NVPFO2x;0 < x < 1)] are regarded as a promising intercalation cathodes for Sodium-ion batteries (SIBs) due to their high reversible specific capacity and stability. However, so far only 2 Na ion were demonstrated to be active in these polyanionic cathodes, which limit their capacity. Herein we provide a strategic approach towards electrochemical activation of a 3rd Na ion, which leads to higher capacity, and preserves structural integrity. We synthesize and study a series of NVPFO2x (0 < x < 1) with well-controlled surface morphology and vanadium oxidation state, and study the dependence of the electrochemical behavior on the various composition and morphology. The optimized NVPFO cathode exhibited highest initial specific discharge capacity (131 mA h g−1) indicating the activation of 3rd Na ion. Nevertheless, the material suffers rapid capacity fading within ~50 cycles. We demonstrate how this instability is suppressed profoundly through the formation of a thin artificial cathode electrolyte interface (CEI) layer of TiO2 (ca. 2 nm) on the surface of NVPFO by atomic layer deposition (ALD). This TiO2 coating enabled even further extraction of sodium through higher voltage domain, but more importantly, it facilitated excellent long-term stability over 200 cycles. The structural stability of the cathode material was revealed by post cycling HRSEM, XPS, and XRD study. All these studies demonstrate that the thin TiO2 layer effectively contributes to formation of a robust CEI layer, diminishes the parasitic reaction on the electrode surface, reduces carbonate formation, and restricts the electrolyte decomposition.

Synergistic Pyridinic N/Pyrrolic N configurations in rGO/CNT composite sulfur hosts for high-performance lithium-sulfur batteries

Significant progress has been made in the field of nitrogen-doped carbon sulfur host materials to address the shuttle effect, expansion effect, and conductivity issues of lithium-sulfur (Li-S) battery cathode materials. However, there has been limited study on the synergistic effects of different nitrogen configurations. In this work, ammonia and hydrazine hydrate were used as nitrogen source precursors to prepare three kinds of rGO and CNT composite sulfur hosts with different nitrogen configurations. Ammonia is conducive to the formation of Pyrrolic N, while hydrazine hydrate is conducive to the formation of Pyridinic N. Lithium-sulfur batteries assembled with 3NG/CNT/S which has similar Pyridinic N and Pyrrolic N contents, have a specific initial discharge capacity of 1345 mAh/g at 0.2 C. The initial discharge specific capacity at 2 C was 819 mAh/g, and after 400 cycles, the remaining capacity is 667 mAh/g. The synergistic impact mechanism of Pyridinic N/Pyrrolic N configurations was further revealed by first principles calculations. The results indicate that Pyridinic N/Pyrrolic N configurations enhance electronic non-locality, significantly improve the reactivity of carbon materials, reduce the Gibbs free energy during polysulfide reactions, and accelerate the reaction rate.

Electrochemical properties of spinel LiMn1.92-xCu0.08NixO4 cathode material prepared by a solution combustion method

A series of Ni-Cu co-doped spinel LiMn1.92-xCu0.08NixO4 cathode materials were successfully synthesized by a solution combustion method. X-ray diffraction (XRD) spectra showed that all the as-prepared LiMn1.92-xCu0.08NixO4 samples belong to spinel LiMn2O4 structure without any impurity phase. Scanning electron microscopy (SEM) showed that the particle size of the samples decreased with the increase of Ni-doping amount, and the crystallinity increased gradually. The galvanostatic charge/discharge tests results showed that the LiMn1.86Cu0.08Ni0.06O4 sample shows excellent rate performance and cyclic stability. At room temperature and 1 C, the initial discharge specific capacity of LiMn1.86Cu0.08Ni0.06O4 was 103.4 mAh g-1, and the capacity retention rate of 67.80% was obtained after 1000 cycles, which was higher than 49.60% of LiMn2O4. Even at high current densities of 5 C and 10 C, the good capacity retention rates of 73.55% and 67.29% for LiMn1.86Cu0.08Ni0.06O4 sample were obtained after 1000 cycles, respectively.

Efficient and Homogenous Precipitation of Sulfur Within a 3D Electrospun Heterocatalytic Rutile/Anatase TiO2-x Framework in Lithium–Sulfur Batteries

AbstractLithium–sulfur (Li–S) batteries can potentially outperform state-of-the-art lithium-ion batteries, but their further development is hindered by challenges, such as poor electrical conductivity of sulfur and lithium sulfide, shuttle phenomena of lithium polysulfides, and uneven distribution of solid reaction products. Herein, free-standing carbon nanofibers embedded with oxygen-deficient titanium dioxide nanoparticles (TiO2-x/CNFs) has been fabricated by a facile electrospinning method, which can support active electrode materials without the need for conductive carbon and binders. By carefully controlling the calcination temperature, a mixed phase of rutile and anatase was achieved in the TiO2-x nanoparticles. The hybridization of anatase/rutile TiO2-x and the oxygen vacancy in TiO2-x play a crucial role in enhancing the conversion kinetics of lithium polysulfides (LiPSs), mitigating the shuttle effect of LiPSs, and enhancing the overall efficiency of the Li–S battery system. Additionally, the free-standing TiO2-x/CNFs facilitate uniform deposition of reaction products during cycling, as confirmed by synchrotron X-ray imaging. As a result of these advantageous features, the TiO2-x/CNFs-based cathode demonstrates an initial specific discharge capacity of 787.4 mAh g−1 at 0.5 C in the Li–S coin cells, and a final specific discharge capacity of 584.0 mAh g−1 after 300 cycles. Furthermore, soft-packaged Li–S pouch cells were constructed using the TiO2-x/CNFs-based cathode, exhibiting excellent mechanical properties at different bending states. This study presents an innovative approach to developing free-standing sulfur host materials that are well suited for flexible Li–S batteries as well as for various other energy applications. Graphical Abstract

Win-Win on both ion-conducting and mechanical properties achieved in PEO-based solid electrolytes through microstructure regulation

Solid state electrolytes are of great importance in the design of all-solid-state lithium metal batteries (ASLMBs) that with excellent properties and glorious working stability. And solid polymer electrolytes (SPEs) are the attention-getting candidate, because of its flexibility lightweight and suitable ionic transportation ability. However, current SPEs always need balance between ionic conductivity (σ) and the mechanical strength. To this end, organic-inorganic composite solid-state electrolytes (CSEs) are designed by introduction of BN nanosheets into the polymer matrix, coupled with using the electrospinning technique. It is proved show that the PEO crystallinity in the fibrous electrolyte is significantly suppressed, with only 1 wt% BN adding. And the σ of the designed sample is raised to 1.93×10−4 S∙cm−1 at 40 ℃, on account of that the BN layered structure and three-dimensional fibrous framework help to provide dual channels for Li+ transport. Also better interfacial miscibility with Li metal is realized in the obtained fibrous CPEs and the Galvanostatic cycling of the symmetric Li//Li cell sustains as long as 850 h with 0.1 mA·cm−2 current density. Compared with the solution-casted sample with the same composition, the tensile strength (0.88 MPa) and electrochemical stability of the electrospun membrane (5.1 V) are both significantly enhanced. In addition, the obtained LiFePO4|PEO/LiClO4/BN CSE|Li all solid state coin cells exhibit excellent cycling and rate performances. The initial discharge specific capacity reaches to 144.1 mAhg−1. And coin cells cycled at 1 C current and at 80℃ give a capacity retention ratio of 81.1% after 200 cycles. It demonstrates that thin and flexible CSEs with excellent electrochemical performance can be accomplished through electrospining technique.

Research on Sodium Storage Performance of Cu and Mg Doped P2 Type Layered Oxide Cathode Materials

The P2-type Ni–Mn-based oxide cathode materials have drawbacks such as the Jahn-Teller effect and crystal phase transition under high pressure. In this study, Cu and Mg modifications were introduced to inhibit the P2–O2 phase transition and increase the lattice spacing, thereby reducing the resistance of sodium ion de-embedding and intercalation to improve the overall electrochemical performance of the battery. A series of P2-type Na0.67Ni0.33−xMn0.67CuxO2 and Na0.67Ni0.33−xMn0.67MgxO2 cathode materials were synthesized through solid-state reaction. Cu substitution significantly alters the structural stability and electrochemical properties. In the voltage range from 1.5 V to 4.2 V and at 0.1 C, the initial discharge specific capacity of Na0.67Ni0.18Mn0.67Cu0.15O2 was 167 mAh·g−1, with 86 mAh·g−1 remaining after 100 cycles at 1 C. Additionally, a high discharge specific capacity of 207 mAh·g−1 was achieved with 0.075 Mg doping, suggesting that part of O2− participated in the internal electrochemical reaction. Furthermore, the rate performance of Na0.67Ni0.28Mn0.67Mg0.05O2 was found to be the best. This phenomenon was attributed to the inactive Mg2+ retaining more Na+ in the interlayer, inhibiting crystal structure transformation and Jahn-Teller distortion. The larger radius of Mg2+ increased the layer spacing, widened the Na+ de-embedding channels, and increased the diffusion coefficient.