Discharge Capacity Retention Research Articles

Bacteria cellulose framework-supported solid composite polymer electrolytes for ambient-temperature lithium metal batteries

Composite polymer electrolyte (CPE) films with high room temperature ionic conductivity are urgently needed for the practical application of high-safety solid-state batteries (SSBs). Here, a flexible polymer-polymer CPE thin film reinforced by a three-dimensional (3D) bacterial cellulose (BC) framework derived from natural BC hydrogel was prepared via the in situ photo-polymerization method. The BC film was utilized as the supporting matrix to ensure high flexibility and mechanical strength. The BC–CPE attained a high room temperature ionic conductivity of 1.3 × 10−4 S cm−1. The Li∣BC–CPE∣Li symmetric cell manifested stable cycles of more than 1200 h. The LCO∣BC–CPE∣Li full cell attained an initial discharge specific capacity of 128.7 mAh g−1 with 82.6% discharge capacity retention after 150 cycles at 0.2 C under room temperature. The proposed polymer-polymer CPE configuration represents a promising route for manufacturing environmental SSBs, especially since cellulose biomaterials are abundant in nature.

Carbon nanoparticle-entrapped macroporous Mn3O4 microsphere anodes with improved cycling stability for Li-ion batteries

Manganese oxide (Mn3O4) has garnered substantial attention as a low-cost, environment-friendly anode material. It undergoes a conversion reaction involving the formation of Li2O and metallic Mn to provide high-energy Li-ion batteries. However, its low electrical conductivity and significant volume change reduce its capacity during the initial lithiation/delithiation, hindering its practical application. To improve the cycle performance, we propose a new composite structure wherein we entrap carbon nanoparticles in macroporous Mn3O4 microspheres with a unique maze-like porous interior. We fabricate the Mn3O4/C composites using a scalable two-step process involving the thermal decomposition of MnCO3 in water vapor and mixing in a carbon-dispersed solution. The fabricated Mn3O4/C composites with varying carbon contents exhibit a high maximum discharge capacity retention of 86% after 50 cycles, compared to the 18% given by bare Mn3O4. The entrapped carbon nanoparticles improve the cycle performance both electrochemically and physically. The microstructure of the composite particles and the fabrication process developed in this study will help improve the performance of other conversion-type anode materials that suffer from cycle degradation, including inexpensive transition metal oxides and sulfides.

Methyl Carbamate‐Lithium Salt Deep Eutectic Electrolyte for Lithium‐Ion Batteries

AbstractDeep eutectic electrolytes (DEEs) represent a burgeoning field in electrolytes for energy storage applications. Compared to the more conventionally studied Li‐ion electrolyte systems, these electrolytes offer numerous advantages, such as high ion concentration, costs, lower temperature operation, and safety. In this work, the formation of a novel eutectic electrolyte based on lithium salts and methyl carbamate was reported. These DEEs were formed via mixing lithium salts and low‐cost methyl carbamate at ratios varying from 1 : 2 to 1 : 5 (mol:mol). The DEE formed from methyl carbamate and lithium hexafluorophosphate (LiPF6) at a 1 : 5 molar ratio generated a 4V stability window and a 25 °C conductivity of up to 3.16E−3 S cm−1. The DEE formed from methyl carbamate and lithium bis(trifluoromethane)sulfonimide (LiTFSI) at a 1 : 5 molar ratio generated a 3.2 V stability window and a 25 °C conductivity of up to 2.87E−3 S cm−1. The LiPF6 DEE also demonstrated a discharge capacity of 128 mAh g−1after 50 cycles with 93 % discharge capacity retention at moderate cycling rates of 0.5C in a lithium titanate (LTO)/lithium iron phosphate (LFP) full cell. These results demonstrate the potential for methyl carbamate to generate eutectics from lithium salts and offer alternative electrolytes for use in low‐temperature Li‐ion battery applications.

Application of 1-butyl-3-menthylimidazolium-hexafluorophosphate as flame retardant in electrolyte of lithium ion battery

Carbonate-based organic electrolytes with lower flash points are widely used in commercial lithium-ion batteries, boosting the development of energy storage system. Safety problems, arising from the combustion and explosion caused by carbonate-based organic electrolytes, have become one of the bottlenecks restricting large-scale application of lithium-ion batteries. In this work, flame-retardant or non-combustible electrolyte systems were investigated. Because of the excellent flame retardancy, low flammability, and high conductivity, thermal, and electrochemical stability, 1-butyl-3-menthylimidazolium-hexafluorophosphate ([Bmim]PF6) was used to generate imidazolium ionic liquids based electrolytes. The flame retardant and electrochemical performances of [Bmim]PF6-based binary electrolytes with different ionic liquid ratios, and the comparison with commercial carbonate electrolytes (CEs) were characterized. Results show that compared with commercial carbonate solvent electrolytes, battery performances, such as thermal safety and electrochemical stability of the proposed [Bmim]PF6 binary electrolyte, are superior to that of CEs when they are used in LiFePO4 electrode batteries. The binary electrolyte with 5% of [Bmim]PF6 ionic liquid possesses the best comprehensive performance. Explicitly speaking, the ionic conductivity and combustibility of the binary electrolyte are higher and significantly lower than that of CEs, respectively, thus the significantly improving the conductivity and thermal stability. Furthermore, since the battery's discharge capacity and capacity retention rate using the binary electrolyte after 100 cycles of charge and discharge at 1 C charge-discharge rate are higher than those using CEs, the [Bmim]PF6 binary electrolyte also shows good electrochemical stability.

Introducing a Bio-Degradable Binder for Aqueous Production of NMC111 Cathodes

The LiNixMn1-x-yCoyO2 (NMC) is a widely used cathode material in lithium-ion batteries (LIBs) due to its high capacity. By enabling water-based cathode processing, the cost and environmental impact of LIBs will be reduced substantially. However, the water compatibility of Ni-containing materials has been problematic due to lithium (Li)-leaching, corrosion of the aluminium (Al) current collector, and lack of aqueous dissoluble binders. For the first time, we demonstrated that NMC111 cathodes with comparable specific capacities to the standard polyvinylidene fluoride/N-methyl-2-pyrrolidone (PVDF/NMP)-processed cathodes can be formulated in water using lignin as binder material. Rheology measurements revealed that less solvent is needed to obtain the same slurry viscosity when replacing the NMP solvent with water. Cycling voltammetry and differential scanning calorimetry revealed that lignin is electrochemically inactive between 2.5-4.5 V and thermally stable up to 152 oC, respectively. Drying the cathode coatings at 50 oC allowed for a controlled evaporation rate as surface cracks and binder migration detected using scanning electron microscopy diminished. The lignin binder provided strong cohesion forces to the carbon black (CB) and the NMC111 particles, and the use of carbon(C)-coated Al-foil (C-Al) further increased the coating's mechanical strength. Scratch tests revealed that calendaring magnified the nature of the initial mechanical strength, intensifying a poor adhesion of the coating to the Al-foil and strong cohesion between the particles. While calendering and pore removal improved the rate performance for PVDF-cathodes (85:10:5 wt % NMC:CB:binder), the rate capability of lignin-cathodes (80:11:9 wt %) decreased with lower porosity (from 53 to 0 %) and higher mass loading (9.7 mg/cm2). Particle deformation and extensive pore-blocking at high carbon contents created a Li+-transfer barrier across the cathode/electrolyte surface, decreasing the rate performance. Cathodes using a CMC/lignin-binder mix (2:7 wt% ratio) and C-Al foil (75 % capacity retention) electrochemically outperformed those with the commercial CMC/SBR mix and plain Al-foil (35 % capacity retention) at a high C-rate (5 C). Of all the aqueous produced cathodes, the uncalendered with pure lignin-binder, C-Al foil, dried at 50 oC, and a mass loading of 7.4 mg/cm2 showed the highest capacity retention at 5 C (60 %). Additionally, the lignin-cathodes have poor electrolyte wetting abilities and need longer exposure time before cycling and additional formation cycles compared to the PVDF-cathodes. Lignin-cathodes with the smallest lignin/CB matrix (90:5:5 wt% NMC:CB:binder) wetted for 35 days with 5 formation cycles at C/10 showed similar initial discharge capacity and capacity retention (154 mAh/g and 89 %) as 85:10:5 PVDF-based cathodes (153 mAh/g and 93 %) after 100 cycles at C/2.

MXene‐Ti3C2 Armored Layer for Aluminum Current Collector Enable Stable High‐Voltage Lithium‐Ion Battery

AbstractElevating operating voltage (above 4.5 V) is a consequential approach to increasing the energy density of lithium‐ion batteries (LIBs). Unfortunately, the corrosion of cathode aluminum (Al) current collector at high voltage limits the application of high‐voltage LIBs. In this report, for the first time, MXene‐Ti3C2Tx nanosheets are proposed as an armored layer for Al current collector to conquer the corrosion under high operating voltage over 4.5 V versus Li+/Li. The MXene armored layer is fabricated via a self‐assembly procedure, which exhibits ultra‐thinness less than 100 nm, attaches to Al substrate homogeneously, and ensures the electron conduction of current collector by virtue of outstanding conductivity. More importantly, the obtained MXene‐Al can be stabilized under a broad electrochemical window of 2–5.5 V versus Li/Li+ in commercial LiPF6‐carbonates electrolyte. As a consequence, the execution of MXene‐Al current collector to ternary cathode LiCo1/3Ni1/3Mn1/3O2 (NCM333) can significantly enhance electrochemical performance. Under a high cut‐off voltage of 4.5 V, the discharge capacity retention is increased from 21% to 81.4% after 300 cycles at 0.5 C with the protection of MXene armored layer. This work proposes an effective strategy for developing stable high‐voltage LIBs and contributes to the MXene application in energy‐related field.

Novel ether-free membranes based on poly(p-terphenylene methylimidazole) for vanadium redox flow battery applications

The fabrication of low-cost and high-performance membranes is one of the most critical issues for vanadium redox flow batteries (VRFBs). Herein, a novel ether-free poly(p-terphenylene methylimidazole) (PTMIm) is synthesized by a facile one-pot Friedel-Crafts polyhydroxyalkylation of p-terphenyl and 1-methyl-2-imidazolecarboxaldehyde. The PTMIm has excellent organic solubility and good chemical stability towards high valence vanadium ions. Meanwhile, due to the present pendant imidazole groups, the PTMIm membrane exhibits a high sulfonic acid absorption capability, achieving a suitable area resistance (AR). In order to further enhance the performance of the PTMIm membrane, side-chain quaternization is carried out by using 1-bromopropane, 3-bromo-N,N,N-trimethylpropan-1-aminium bromide and 3-chloro-2-hydroxypropyltrimethyl ammonium chloride as quaternized reagents. Comparing with pure PTMIm membrane and propyl group grafted membrane (i.e. PTMIm-C3), terminal quaternary ammonium side chain grafted membranes of PTM-C3-QA and PTMIm-C3-OH-QA possess lower AR and better vanadium ion resistance simultaneously. Consequently, the ion selectivity value of the PTMIm-C3-QA membrane is 8.7 × 105 S min cm−3, which is approximately 130 times higher than that of Nafion 115 (6.6 × 103 S min cm−3), mainly resulting from its low AR (0.68 Ω cm2) and ultralow vanadium ion permeability (9.5 × 10−9 cm2 min−1). Meanwhile, both PTMIm and its grafted membranes exhibit excellent chemical stabilities within 400 h chemical stability test. Owing to the superior restriction on vanadium migration, the single cell with PTMIm-C3-QA displays an excellent self-discharge duration of 500 h, which is greatly longer than that of Nafion 115 (58 h). In the range of 40–160 mA cm−2, the PTMIm-C3-QA based cell expresses higher coulombic efficiencies (>99.5%) and larger energy efficiencies than the cell with Nafion 115. For the cycling test of VRFB during 500 cycles, the PTMIm-C3-QA based cell displays excellent cycle stability and good discharge capacity retention, indicating a great application potentiality of the PTMIm-C3-QA membrane for VRFBs.

Phosphazene based LATP precursor for a CEI coating layer on high voltage LiNi0.5Mn1.5O4 cathode with improved cycling durability

Extensive research has been conducted on NASICON type Li1+xAlxTi2-x(PO4)3 (LATP) with high Li+ ion conductivity as an artificial cathode electrolyte interphase (CEI) layer on the electrode surface to improve the cycling stability of rechargeable Li-ion batteries. Although highly soluble LATP precursor is crucial for facile and scalable coating of the CEI layer on the Li-ion battery electrode, the conventional LATP precursor suffers from poor solubility of the phosphorus source and poor Li+ ion conductivity. In this study, we present the highly soluble hexachlorophosphazene (HCP) as a novel phosphorus source of the soluble LATP precursor. Furthermore, we demonstrate that the LATP film can be optimized through the simultaneous control of the Al source and Li:Ti ratio. The optimized LATP film with an Li:Ti molar ratio of 1.5:0.8 presents the highest Li+ ion conductivity of 1.15 x 10−5 S cm−1 and the lowest activation energy of 0.26 eV. The HCP-based LATP precursor is implemented for artificial CEI layer formation. Consequently, the LATP 1 wt% coated LNMO half-cell exhibits a superior discharge capacity retention of 84.92% over the 70.97% retention of a bare LNMO half-cell at 1 C after 300 cycles. The LATP-based CEI layer presents a more effective pathway for Li+ diffusion, while preventing Mn2+ elution and side reactions during the charging/discharging process.

Triggering Zn2+ Unsaturated Hydration Structure via Hydrated Salt Electrolyte for High Voltage and Cycling Stable Rechargeable Aqueous Zn Battery

AbstractOcean‐like free water in conventional aqueous electrolytes limits operating voltage and induces parasitic reactions in rechargeable Zn metal batteries (AZMBs). Herein, a hydrated salt electrolyte (HSE), which suppresses the presence of free water and triggers an unsaturated hydration structure (Zn(H2O)n2+, n < 6), is proposed to circumvent the parasitic reactions occurring on the zinc anode and cathode and elevate the decomposition voltage (to ≈2.55 V vs Zn2+/Zn). In a full cell with a transition metal oxide cathode, the parasitic reactions of dissolution and diffusion of discharge products are inhibited, and high discharge capacity retention above 80% at 500 mA g‐1 and super‐stable Coulombic efficiency (average value ≈99.97%) are delivered. Moreover, when applied in a high‐voltage AZMB with zinc hexacyanoferrate cathode, the full cell yields an average output voltage above 1.8 V together with a 132.3 Wh kg‐1 energy density at 10 mA g‐1 and 1.78 V output voltage combining high energy density and power density (88.5 Wh kg‐1/106.2 W kg‐1). The exceptional electrochemical performance of HSE indicates rosy prospects for the prevention of parasitic reactions in AZMBs, a key step on the road to further commercialization of AZMBs.

Enhanced electrochemical properties of NCM811 cathode material due to synergistic modification with Sm as doping and coating agent

Ni-rich LiNi0.8Co0.1Mn0.1O2 (NCM811) has been considered as the most attractive cathode material for lithium-ion batteries (LIBs). However, the fast capacity decay and poor rate performance limit its practical applications. Bulk doping and surface coating have been demonstrated as the most important and effective technologies for enhancing its electrochemical performance; nevertheless, overall performance still remains unsatisfactory. In this study, simple dual-modification strategy was proposed in which samarium (Sm) was both doped into and coated on NCM811 to provide inside and outside synergistic modification. This can comprehensively improve electrochemical performance of NCM811. X-ray diffraction, transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and electrochemical tests were used to discuss improvement mechanism. Results indicated that parts of Sm successfully enter crystal lattice, which increases interlayer spacing, stabilizes structure, and reduces Li+/Ni2+ mixing. Simultaneously, another part of Sm coated on surfaces in the form of oxide, prevents electrolyte corrosion and inhibits side reactions. With the optimum Sm content (0.5%), obtained NCM811 displayed the highest discharge specific capacity (184.2 mA h g−1 at 1 C), capacity retention (94.19% after 100 cycles at 1 C), and rate performance (152.2 mA h g−1 at 5 C). This study provides efficient approach to improve electrochemical performance of NCM811 as cathode material.

Thermostable and nonflammable polyimide/zirconia compound separator for lithium-ion batteries with superior electrochemical and safe properties

Separators are applied to segregate cathode and anode, and provide ion transport channels in lithium-ion batteries (LIBs). Nevertheless, present commercial polyolefin separators represent high thermal shrinkage and inferior electrolyte wettability, seriously limiting wider development of LIBs. In this work, we prepared zirconia (ZrO2) nanolayer encapsulated polyimide (PI) nanofiber compound separator through in-situ polar adsorption and hydrolysis strategy. The obtained PI/ZrO2 compound separator has superior thermal stability, electrolyte wettability and flame retardance in comparison with polypropylene (PP) separator. The shrinkage ratio of prepared PI/ZrO2 compound separator is 0 even at 300 °C, while the PP separator significantly shrank at 160 °C. Furthermore, the ionic conductivity of PI/ZrO2 separator reaches up to 1.32 mS cm−1, far higher than 0.34 mS cm−1 of PP separator. Besides, the coin batteries of LiNi0.8Co0.1Mn0.1O2 (NCM811)/electrolyte-separator/lithium (Li) assembled with PI/ZrO2 compound separator exhibit enhanced rate performance, high discharge capacity retention rate of 88.3% after 100 cycles at 1C and excellent battery safety performance even at 140 °C. Thus, combined with its advantages, such as preparation, thermostability, electrolyte wettability, electrochemical property and safety, the PI/ZrO2 compound separator exhibits promising prospect in the application of commercial LIBs.

Expanding the active charge carriers of polymer electrolytes in lithium-based batteries using an anion-hosting cathode

Ionic-conductive polymers are appealing electrolyte materials for solid-state lithium-based batteries. However, these polymers are detrimentally affected by the electrochemically-inactive anion migration that limits the ionic conductivity and accelerates cell failure. To circumvent this issue, we propose the use of polyvinyl ferrocene (PVF) as positive electrode active material. The PVF acts as an anion-acceptor during redox processes, thus simultaneously setting anions and lithium ions as effective charge carriers. We report the testing of various Li||PVF lab-scale cells using polyethylene oxide (PEO) matrix and Li-containing salts with different anions. Interestingly, the cells using the PEO-lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) solid electrolyte deliver an initial capacity of 108 mAh g−1 at 100 μA cm−2 and 60 °C, and a discharge capacity retention of 70% (i.e., 70 mAh g−1) after 2800 cycles at 300 μA cm−2 and 60 °C. The Li|PEO-LiTFSI|PVF cells tested at 50 μA cm−2 and 30 °C can also deliver an initial discharge capacity of around 98 mAh g−1 with an electrolyte ionic conductivity in the order of 10−5 S cm−1.

Large‐Scale Manufacturing of Pattern‐Integrated Paper Li‐Ion Microbatteries through Roll‐to‐Roll Flexographic Printing

AbstractElectrode architectures significantly influence the electrochemical performance, flexibility, and applications of lithium‐ion batteries (LiBs). However, the conventional bar coating for fabricating electrodes limits the addition of customized architecture or patterns. In this study, as a novel approach, patterns are integrated into electrodes through large‐scale roll‐to‐roll (R2R) flexographic printing. Additionally, flexible, recyclable, and biodegradable paper are innovatively used as a printing substrate during printing LiBs manufacturing, which exhibited superior printability. Moreover, the paper is modified with a thin‐layer Al2O3 to function as the separator in the printed LiB. The Al2O3‐coated paper enables an admirable wettability for printing, excellent mechanical properties for high‐speed R2R manufacturing, and outstanding thermal stability for the safe and stable operation of LiBs. The assembled paper cells exhibit nearly 100% discharge capacity retention after 1000 cycles at 3 C and outstanding rate performance. This work inspires future large‐scale microbatteries manufacturing integrated with high‐resolution architecture designs.

Preparation of poly(ionic liquid) composite quasi-solid electrolyte by incorporating metal − organic framework filler decorated with ionic liquid for lithium batteries

Poly(ionic liquids) (PILs) electrolytes combine the advantages of ionic liquids and polymers and have been widely studied to boost the performance of lithium batteries. However, one main problem that most of PILs electrolytes encounter is the tradeoff between mechanical integrity and high ionic conductivity. Therefore, elevating ionic conductivity is still a problem to be solved urgently. In this work, ether group-functionalized PIL is synthesized and an ionic liquid (IL) decorated metal−organic framework (MOF) filler IL@UIO-66 is prepared. Subsequently, one composite polymer electrolytes (MCPEs) involving IL@UIO-66 and PIL are built via solution-casting approach. The as-prepared optimal MCPE membranes with 10% IL@UIO-66 (MCPE-10%) express higher ionic conductivity as high as 2.06 × 10−4 S cm−1 and larger lithium ion transference number of 0.49 at 30 °C than the electrolytes without filler (CPE). Comparing with CPE, the thermal stability of MCPE-10% is significantly improved to 300 °C by IL@UIO-66 and the electrochemical stability of MCPE-10% with an oxidation potential of 5.10 V vs. Li+/Li is almost unaffected. Besides, the interfacial stability between MCPE-10% and lithium electrode is improved. The assembled LiFePO4/MCPE-10%/Li cells show a promising rate and cycle performance at 25 °C. They show an initial discharge capacity of 123 mAh g−1 at current density of 0.5C, and their discharge capacity retention is up to 95% after 100 cycles with coulombic efficiency higher than 99%.

Eu2O3-doped Li4SiO4 coating layer with a high ionic conductivity improving performance of LiNi0.8Co0.1Mn0.1O2 cathode materials

Ni-rich layered cathode materials are being paid much attention to because their high capacity can handily improve energy density of lithium-ion batteries. However, Ni-rich cathode materials still suffer from the deficiencies such as poor cycle stability, weak structural and thermal stability. In this work, Eu2O3-doped Li4SiO4 with an enhanced ionic conductivity is proposed as surface coating layer for LiNi0.8Co0.1Mn0.1O2 (NCM) cathode material to improve the capacity retention and structural stability during cycling. The doping of Eu2O3 in Li4SiO4 makes the coating layer have higher ion conductivity and better stability than pure Li4SiO4 layer. When the doping amount is 10 mol% of Li4SiO4, the corresponding cathode material NCM-LS3-0.10Eu2O3 exhibits the optimal cycle and rate performance. The discharge specific capacity and capacity retention after 400 cycles at 1 C rate are 150.1 mAh g−1 and 80.48%, respectively. In particular, the NCM-LS3-0.10Eu2O3 secondary particles avoid the appearance of serious cracks and maintain excellent structural stability even after long cycling. It is proved finally that the Eu2O3-doped Li4SiO4 coating layer can not only inhibit the side reactions caused by the contact between electrode surface and electrolyte, but also reduce the resistance of lithium ion migration and suppress the microstructure changes caused by local stress.

Fast Charge and High Stability of Solid‐State Graphite Organic Ionic Plastic Crystal Composite Anodes

AbstractAll‐solid‐state batteries (ASSBs) using organic ionic plastic crystals (OIPCs) are promising candidates to overcome the inherent safety issues of lithium‐ion batteries (LIBs). Although OIPCs have excellent process applicability in the roll‐to‐roll electrode fabrication process, their application as solid electrolytes incorporated in composite electrodes has yet to be demonstrated in detail. Herein, we denote the positive effect of the N‐ethyl‐N‐methylpyrrolidinium bis(fluorosulfonyl)imide ([C2mpyr][FSI]) incorporated within a composite graphite anode on the charge rate capability and cycle life. The highest charge capacity ratio (the charge capacity at 2C vs. that measured at 0.1C) was measured for the composite anode with an OIPC composite ratio of 50 wt % (89.5 %, 295.7 mAh/g at 2C charge), almost the same as that of the graphite anode with a liquid electrolyte (85.7 %, 295.9 mAh/g at 2C charge). More favorable lithium‐ion conduction pathways were resolved for the anode with a higher OIPC composite ratio, whereas an excessive amount of OIPC reduced the long‐term cyclability. The most stable discharge capacity retention was obtained for 30 wt % OIPC composite (257.4 mAh/g at the 100th discharge), which showed no signs of discharge capacity fading within 100 cycles. The lithiation/delithiation process of the solid‐state graphite‐[C2mpyr][FSI] composite anode was evaluated to be stable and reversible. In addition, the incorporated OIPC composite enhanced the electrolyte/electrode and electrode/current collector contacts. This work highlights multiple advantageous functions of the OIPC in a composite graphite anode, which will broaden our horizons for the use of OIPC composites in ASSBs.

Effects of Fe doping on the electrochemical performance of LiV1−xFexPO4F/C (x = 0, 0.01, 0.02, 0.04) cathode materials for lithium‐ion batteries

AbstractThe Fe‐doped LiVPO4F/C cathode material was synthesized by a one‐step solid‐state reaction method. The effects of Fe doping content on the structure and electrochemical performance of LiVPO4F/C were investigated. X‐ray diffraction (XRD) analyses demonstrated that the appropriate addition of Fe3+ did not destroy the lattice structure of LiVPO4F/C. Scanning electron microscopy (SEM) showed that the surface of LiVPO4F/C is covered by a carbon film. The decreased grain size of the Fe‐doped LiVPO4F/C could shorten the ion transport path and thus improve the migration rate of lithium ions. X‐ray photoelectron spectroscopy (XPS) showed that the Fe ion exists in the Fe‐doped LiVPO4F/C as Fe3+ ion. At the discharge rate of 1 C, the initial discharge capacity and capacity retention rate of the LiV0.98Fe0.02PO4F/C after 500 cycles were 123.5 mAh/g and 88.6%, respectively.

In Situ Directional Polymerization of Poly(1,3‐dioxolane) Solid Electrolyte Induced by Cellulose Paper‐Based Composite Separator for Lithium Metal Batteries

In traditional in situ polymerization preparation for solid‐state electrolytes, initiators are directly added to the liquid precursor. In this article, a novel cellulose paper‐based composite separator is fabricated, which employs alumina as the inorganic reinforcing material and is loaded with polymerization initiator aluminum trifluoromethanesulfonate. Based upon this, a separator‐induced in situ directional polymerization technique is demonstrated, and the extra addition of initiators into liquid precursors is no longer required. The polymerization starts from the surface and interior of the separator and extends outward with the gradually dissolving of initiators into the precursor. Compared with its traditional counterpart, the separator‐induced poly(1,3‐dioxolane) electrolyte shows improved interfacial contact as well as appropriately mitigated polymerization rate, which are conducive to practical applications. Electrochemical measurement results show that the prepared poly(1,3‐dioxolane) solid electrolyte possesses an oxidation potential up to 4.4 V and a high Li+ transference number of 0.72. After 1000 cycles at 2 C rate (340 mA g−1), the assembled Li||LiFePO4 solid battery possesses a 106.8 mAh g−1 discharge capacity retention and 83.5% capacity retention ratio, with high average Coulombic efficiency of 99.5% achieved. Our work may provide new ideas for the design and application of in situ polymerization technique for solid electrolytes and solid batteries.

Influence of synthesis route on the structure and electrochemical performance of biphasic (O'3/O3) NaNi0.815Co0.15Al0.035O2 cathode for sodium-ion batteries

Sodium-ion batteries have gained widespread attention for energy storage devices because of low cost and high abundance of sodium sources. In this paper, Biphasic O'3/O3 layered NaNi0.815Co0.15Al0.035O2 cathode materials (Na-NCA) are synthesized by using three different chemical routes viz. coprecipitation, hydrothermal and sol-gel methods. X-ray diffraction pattern and Raman analysis show the clear evidence of layered structure of all three samples. The kinetics of sodium ion [Na+] is deduced from cyclic voltammetry techniques and the values of Na+ ion diffusion coefficient is found to be 1.62×10−12, 1.11×10−13 and 1.71×10−12cm2s−1 for Na-NCA synthesized by coprecipitation, sol-gel and hydrothermal methods, respectively implying the better kinetics of Na+- ions in hydrothermal prepared Na-NCA cathode. Furthermore, the Cyclic voltammetry and differential capacity versus voltage (dQ/dV vs.V) studies reveal the good reversibility of phase transition in cathode prepared using hydrothermal route. Electrochemical testing indicates the better performance of hydrothermally prepared Na-NCA in terms of discharge capacity, capacity retention and energy density. This improved electrochemical performance is attributed to decease in solid electrolyte interface, reversible phase transition and high surface area as well as better diffusion coefficient. Additionally, evolution of phase after cycling process are also investigated and only single O'3 phase is observed for hydrothermal prepared Na-NCA cathode which is highly stable at room temperature.

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.