High Energy Density Lithium-ion Batteries Research Articles

(Battery Division Technology Award) Understanding Metals' Roles in Layered Structure Oxides for High-Energy Lithium-ion Batteries

The ever-increasing requirements in the high-energy density of lithium-ion batteries (LIBs) and current bottlenecks in cobalt supply place restrictions on the development of the state-of-the-art cathode materials with fine-tuned chemical composition by substituting the cobalt with nickel and manganese. In the layered structure ternary systems (LiNi1-y-zMnyCozO2, NCM), three transition-metal ions play a distinctive role that determines the physicochemical properties. A comprehensive understanding of the basic contribution of each transition metal is critical for further complete replacing expensive cobalt.[1] Here, we demonstrate cobalt and manganese behaviors by comparing various layered oxides with different chemical compositions to reveal their corresponding contributions.[2] Our results affirmed that cobalt plays an undeniable role in fast degradation, and found that cobalt is more destructive than Ni at high voltages. Even the possible instability induced by manganese (III) Jahn-Teller distortion [3], Mn(IV) substitution in the lattice can effectively alleviate this destructive and enables a high potential functionality. By further regulating the chemical composition with a concentration gradient strategy, Co-enriched surface and Mn-enriched core design in Ni-rich particles determines a robust structure, which can effectively suppress the owing to the low stiffness of the surface and stable structure in the core region. With these fundamental discoveries, we provide a guide for developing the promising Co-free cathodes to meet the increasing demand for high-energy density LIBs.

Nano tin encapsulated in copper grooves as an anode for high-performance lithium-ion batteries

With the ever-growing demand for high energy and power density lithium-ion batteries (LIBs), tin (Sn) has been considered a capable anode material because of its high theoretical capacity (993.4 mAh/g). However, the practical application of Sn anodes suffers from low capacity retention due to significant volume expansion (~257 %) and poor ion and electron transportation during cycling. To overcome these problems, a novel architecture is necessary to mitigate volume expansion during cycling without instigating severe electrode fragmentation. In this work, we developed grooves on a copper plate (25 µm thickness) by etching it with SiC sandpaper of different grain sizes (23 µm (#400), 68 µm (#220), and 190 µm (#80)). The Sn (60–70 nm) was inserted in the developed grooves of the copper plate (Sn/Cu) and coated with polyvinylidene fluoride (PVDF) to form a confined structure. The PVDF-coated Sn/Cu plates (#400, #220, and #80) were used as anode materials for LIBs. The prepared electrodes delivered high capacities of 274, 153.7, and 103 mAh/g after 500 cycles at a 0.2 C-rate. The present work opens a novel path for fabricating high-performance LIBs using a simple experimental process.

Self-propagating fabrication of SiO x @rGO film with superior cycling stability and rate performance as anode for lithium-ion batteries

With high theoretical capacity and suitable operating potential, SiO x is regarded as one of the most promising anode materials for high-energy density lithium-ion batteries (LIBs), but it suffers from large volume change during charge/discharge and low electronic conductivity, leading to poor cycling stability and rate capability. To overcome these problems, a SiO x @ reduced graphene oxide (rGO) film with porous structure is prepared through vacuum filtration and self-propagation reduction method, which can be directly used as a free-standing anode for LIBs. The self-propagation process of graphene oxide to graphene can be completed rapidly within 1 s, and endows the film with developed pores due to the instantaneous release of substantial gases. The porous structure is beneficial for exposing massive active sites, facilitating fast ion transport and buffering the volume change of the SiO x during charge/discharge. Moreover, the rGO sheets construct a conductive framework for rapid electron transfer in the film. As a result, the SiO x @rGO film exhibits high lithium storage capacity (1189.7 mAh g−1 at 0.1 A g−1), excellent cycling stability (81.1% capacity retention after 100 cycles) and good rate capability (349.2 mAh g−1 at 3.2 A g−1). This study not only provides a high-performance film anode material for LIBs, but also develops a simple and efficient method for constructing porous film electrodes for various energy storage devices.

Sol/Antisolvent Coating for High Initial Coulombic Efficiency and Ultra-stable Mechanical Integrity of Ni-Rich Cathode Materials.

The Ni-rich cathode holds great promise for high energy density lithium-ion batteries because of its high capacity and operating voltage. However, crucial problems such as cation disorder, structural degradation, side reactions, and microcracks become serious with increasing nickel content. Herein, a novel and facile sol/antisolvent coating modification of Ni-rich layered oxide LiNi0.85Co0.1Mn0.05O2 (NCM) is developed where we use ethanol to disperse the nanosized LiBO2 to form the sol and adopt tetrahydrofuran (THF) as antisolvent to prepare the cluster of nanoparticles to be coated on the surface of NCM. The coating thickness can be tuned through the THF addition amount. The LiBO2 nanorod deposition is formed as well over the crack of the NCM cathode, likely acting as a patch to repair the original defect of the intrinsic crack. The uniform LiBO2 nanospherical particle coating together with LiBO2 nanorod wrapping provides a double protection against electrolytes. Compared with the raw material, LiBO2-coated LiNi0.85Co0.1Mn0.05O2 (LiBO2-coated NCM) exhibits a high initial Coulombic efficiency of 90.3% at 0.2 C between 2.8 and 4.3 V vs Li+/Li, a superior rate capability, enhanced fast charge property at 3 C, and restricted microcrack formation. This simple in-site modification and repairing technology guarantees a good mechanical integrity of the polycrystalline Ni-rich cathode.

Solvent-Free Fabrication of Thick Electrodes in Thermoplastic Binders for High Energy Density Lithium-Ion Batteries.

The rapid development of electric vehicles has generated a recent demand for high energy density lithium-ion batteries (LIBs). One simple, effective way to enhance energy density of LIBs is to increase the thickness of electrodes. However, the conventional wet process used to fabricate thick electrodes involves the evaporation of large amounts of organic solvents, which causes an inhomogeneous distribution of conductive additives and binders. This weakens the mechanical and electrochemical network between active materials, resulting in poor electrochemical performance and structural degradation. Herein, we introduce a new strategy to produce homogeneous thick electrodes by using a dry, solvent-free process. Instead of using a conventional PVDF (polyvinylidene fluoride) binder, we employed a phenoxy resin as the binder in dry process for the first time. This thermoplastic binder exhibits better ductile properties than PVDF in the way that it generates a uniform network structure that connects the active materials during the hot press process. This enables the production electrochemically stable electrodes without using organic solvents, which record capacity retention rates of 73.5% over 50 cycles at a 40 mg/cm2 of thick electrodes. By contrast, thick electrodes produced with a PVDF binder via wet processing only have a capacity retention rate of 21.8% due to rapid structural degradation.

Porous silicon particles embedded in N-doped graphene and carbon nanotube framework for high-performance lithium-ion batteries

Silicon holds great promise as an anode material for high energy density lithium-ion batteries (LIBs). Despite its extremely high theoretical capacity, challenge with severe capacity fading remains to be overcome. In this study, a rational strategy for trapping porous silicon (PSi) within a highly stable 3D framework constructed with interconnected N-doped graphene (NG) and carbon nanotubes (CNTs) to form a novel composite of PSi@NG/CNT via a modified magnesiothermic reduction method is developed for alleviating the large volume expansion and particle fracture and improve electronic conductivity. More importantly, for the first time, the vacancy defects in the trapped PSi within the 3D framework are analyzed. When explored as an anode, the as-developed PSi@NG/CNT exhibits excellent lithium storage properties with high specific capacity, remarkable rate capability (850 mAh g−1 at 5 A g−1), good cycling retention of 79.7% over 200 cycles, and consistently high columbic efficiency at a current density of 0.2 A g−1. This work provides new insights into the rational design of electroactive materials with ultrahigh stability and paves the way toward practical applications of silicon-based anodes for high energy density lithium-ion batteries.

A dual force cross-linked γ-PGA-PAA binder enhancing the cycle stability of silicon-based anodes for lithium-ion batteries

Silicon (Si) is considered to be one of the most suitable anode materials for high energy density lithium-ion batteries due to its high theoretical specific capacity. However, the practical application of Si anode is limited by its huge volume change, leading to the rupture of electrode during cycling. In this study, a natural polymer of poly-glutamic acid ( γ -PGA) is derived from nattomycin gum and poly-acrylic acid (PAA) through thermal cross-linking method and served as a dual force cross-linked binder. The two polymers are firmly bonded by dehydration to form the cross-linked γ -PGA-PAA binder with stable ester bonds, which readily creates hydrogen bonding forces with the hydroxyl groups on Si surface. The γ -PGA-PAA exhibits robust mechanical properties to achieve excellent electrochemical performance of Si-based electrode. When the γ -PGA-PAA is used as binder of Si nanoparticle anodes, the capacity retention of Si/ γ -PGA-PAA electrode can reach 63.1% after 300 cycles at charge/discharge current density of 420 mA g −1 with a mass loading of about 0.7 mg cm −2 . As a comparison, the capacity retentions of the Si/PAA and Si/ γ -PGA electrodes are respectively 8.7 and 17.9% under the same conditions. At higher current density of 2940 mA g −1 , the capacity retention of Si/PAA electrode has dropped dramatically to 23.3%, and the Si/ γ -PGA-PAA electrode keeps still high-capacity retention of 72.5% after 400 cycles, while the Si/ γ -PGA electrode can only last 40 cycles. When the three binders are applied to SiO electrode with 1 mg cm −2 loading, the γ-PGA-PAA binder yields also the highest capacity retention of 87.3% after 100 cycles at 160 mA g −1 , while those corresponding to PAA and γ-PGA binders are 81.3% and 74.9%, respectively. XPS characterization results indicate that the γ -PGA-PAA binder has a strong adhesion to Si particles. This cross-linked binder network of γ -PGA-PAA effectively enhances the cycling performance and maintains the structural integrity of Si and SiO electrodes.

Fluorinated co-solvent electrolytes for high-voltage Ni-rich LiNi0.8Co0.1Mn0.1O2 (NCM811) positive electrodes

Nickel-rich LiNi0.8Co0.1Mn0.1O2 (NCM811) is one of the most promising positive electrodes for utilization in the next-generation of lithium-ion batteries. Charging the NCM cells above 4.3 V is proposed to be beneficial for its reversible capacity. However, the high reactivity of the NCM811 usually results in parasitic electrolyte degradation, which is accelerated with the increase of the Ni content in the NCM positive electrodes, leading to the thickening of the positive electrode-electrolyte interphase during cycling. Herein, to counter this issue, we select partially fluorinated solvents, such as methyl 3,3,3-trifluoropropanoate (MTFP) and 1,1,1,2,2,3,3,4,4-nonafluoro-4-methoxybutane (NFMB), as a co-solvent for fluoroethylene carbonate (FEC)-based electrolytes, and detailed investigate theirs physical, chemical, and electrochemical properties for applications in NCM811 materials. Compared to the carbonate-based electrolyte without a fluorinated solvent, the electrolytes with a fluorinated co-solvent display an obviously enhanced cycling performance of the Li/NCM811 cells charged to above 4.5 V. This work suggests that fluorinated co-solvent electrolytes provide an alternative way to the high-concentration electrolyte for the design of new electrolyte systems for high energy density lithium-ion batteries.

Fastly PECVD-Grown vertical carbon nanosheets for a composite SiOx-C anode material

SiOx has been regarded as the most promising anode material for high energy density lithium-ion batteries (LIBs). However, SiOx materials suffer from intrinsic defects such as poor electrical conductivity, large volume expansion effects, and low initial Coulomb efficiency. In order to solve these problems, vertically arrayed carbon nanosheet encapsulated disproportionated-SiOx (d-SiOx@CNs) composites was fabricated by using a fast plasma-enhanced chemical vapor deposition (PECVD) processing. The PECVD produced vertically arrayed carbon nanosheets provided good interfacial contacts and significantly improved the electronic conductivity and Li+ diffusivity of the SiOx material. As LIBs anode, the d-SiOx@CNs composite displays a high reversible capacity (first charge/discharge capacity of 1456.7 and 1794.4 mAhg−1, respectively) and excellent cycling stability (capacity retention of 87.2 % after 200 cycles at a current density of 0.4 Ag−1). The full cell (d-SiOx@CNs15/G‖NCM811) assembled with the commercial NCM811cathode material also showed an excellent electrochemical performance (capacity retention rate of 76.3 % after 200 cycles at 1C current density) and provided a high energy density of 424.2 Wh kg−1. The fast-growth mechanism of the vertically oriented carbon nanosheet by PECVD was also analyzed in terms of the plasma characteristic.

Single-Layer-Particle Electrode Design for Practical Fast-Charging Lithium-Ion Batteries.

Efforts to enable fast charging and high energy density lithium-ion batteries (LIBs) are hampered by the trade-off nature of the traditional electrode design: increasing the areal capacity usually comes with sacrificing the fast charge transfer. Here a single-layer chunky particle electrode design is reported, where red-phosphorus active material is embedded in nanochannels of vertically aligned graphene (red-P/VAG) assemblies. Such an electrode design addresses the sluggish charge transfer stemming from the high tortuosity and inner particle/electrode resistance of traditional electrode architectures consisting of randomly stacked active particles. The vertical ion-transport nanochannels and electron-transfer conductive nanowalls of graphene confine the direction of charge transfer to minimize the transfer distance, and the incomplete filling of nanochannels in the red-P/VAG composite buffers volume change locally, thus avoiding the variation of electrodes thickness during cycling. The single-layer chunky particle electrode displays a high areal capacity (5.6 mAh cm-2 ), which is the highest among the reported fast-charging battery chemistries. Paired with a high-loading LiNi0.6 Co0.2 Mn0.2 O2 (NCM622) cathode, a pouch cell shows stable cycling with high energy and power densities. Such a single-layer chunky particle electrode design can be extended to other advanced battery systems and boost the development of LIBs with fast-charging capability and high energy density.

Surface modification enabling 4.7 V Nickel-rich layered cathode with superior long-term cyclability via novel functional polyimide binders

High voltage operation of LiNi0.8Co0.1Mn0.1O2 (NCM) for high energy density lithium-ion batteries has poor cycling performance, due to the unstable cathode-electrolyte interface. Herein, two functional polyimides (PIs), one polyimide with hydroxyl group is abbreviated as PI-OH and the other polyimide with carboxyl group is abbreviated as PI-COOH, are designed to contain hydroxyl, carboxyl, trifluoromethyl and ether groups and used as cathode binder, which allows a strong hydrogen bond interaction, abundant chemical bonding sites, superior electrochemical oxidation resistance, and excellent flexibility. Experimental results reveal that both PI-OH and PI-COOH binders show the impressive efficiency on improving the cathode-electrolyte interface stability and long-term cyclability. Especially, the NCM cathode using PI-COOH binder exhibits the highest cyclability (205 mAh g−1 at 40 mA g−1 with 73% capacity retention after 100 cycles at 4.7 V), contrasting to NCM cathode with commonly-used polyvinylidene fluoride (PVDF) binder (208 mAh g−1 with 34% capacity retention). Furthermore, the fully-charged NCM cathode with PI-COOH binder releases the less heat than the NCM/PVDF cathode during high-temp treatment to 300 °C, demonstrating the superiority of polyimide binders in improving the safety of the cathode materials.

Strengthening the Interfacial Stability of the Silicon-Based Electrode via an Electrolyte Additive─Allyl Phenyl Sulfone.

Silicon-based anodes have received widespread attention because of their high theoretical capacity, which, however, still faces challenges for practical applications due to the large volume changes during repeated charge/discharge processes, despite being developed for many years. Herein, we explore an electrolyte additive, allyl phenyl sulfone (APS), to enhance the interfacial stability and long-term durability of the SiOx/C electrode. It is revealed that additive APS contributes to forming a dense and robust solid electrolyte interphase film with high mechanical strength and favorable lithium-ion diffusion kinetics, which effectively suppresses the parasitic side reactions at the electrode-electrolyte interface. Meanwhile, the strong interaction between APS and trace water/acid in the electrolyte is further beneficial for enhancing the interfacial stability. By incorporating 0.5 wt% APS, the cycling stability of the silicon-based electrode is significantly improved, reserving a capacity of 777 mAh g-1 after 200 cycles at 0.5C and 30 °C (79.3% capacity retention), which well exceeds that of the baseline electrolyte (57.8% capacity retention). More importantly, additive APS effectively promotes the cycling performance of the corresponding SiOx/C||NCM90 (LiNi0.9Co0.05Mn0.05O2) full battery. This work provides valuable understanding in developing new electrolyte additives to enable the commercial application of high-energy density lithium-ion batteries using silicon-based anodes.

Investigation and Characterization of in-Situ Polymer Brush SEI Core Shell Layer Effects on Si Anode Material and Its Battery Performance

Silicon is a promising material for lithium-ion batteries due to its super high capacity.1 However, the volume expansion and the pulverization of Si limit its perforamce.2 This study investigates the effect of a polymer brush core-shell structure of Si as an anode material. The polymer brush is designed through Si-C covalent bond of vinyl monomers by thermal hydrosilylation reaction. According to the results, the PBCS structure provides three significant functions on Si particles because of the intramolecular effect of hydrogen bonding with PBCS and binder delivers a good dispersion in the slurry, a mechanical protection during cycling, and excellent ionic conductivity for high-rate tests. Compared with the unmodified electrode (SiNP), the modified electrodes (SiNP-M1 and SiNP-M2) incorporating the PBCS provides better initial columbic efficiency of 87.1% with the first discharge capacity of 1988.9 mAh g-1. The TEM and operando TXM results display that the PBCS structure significantly protects the nano Si from cracking owing to the high elastic function and intramolecular hydrogen bonding effect of the PBCS. Operando X-ray diffraction is also used to provide the phase information of the Si electrodes. With this novel PBCS-Si material, a high energy density lithium-ion battery contains pure Si can be expected. Reference Li, C.; Shi, T.; Li, D.; Yoshitake, H.; Wang, H., Effect of surface modification on electrochemical performance of nano-sized Si as an anode material for Li-ion batteries. RSC Advances 2016, 6 (41), 34715-34723.Gao, Y.; Yi, R.; Li, Y. C.; Song, J.; Chen, S.; Huang, Q.; Mallouk, T. E.; Wang, D., General Method of Manipulating Formation, Composition, and Morphology of Solid-Electrolyte Interphases for Stable Li-Alloy Anodes. J Am Chem Soc 2017, 139 (48), 17359-17367. Figure 1

Effect of Post-Grinding and Heat Treatment on the Electrochemical Performance of NMC622 Li-Ion Battery Cathode Materials

Given the increasing demands for high energy density lithium-ion batteries (LIBs), all cell components, particularly cathode materials, will need significant improvement in the future. Among the possible cathode materials for LIBs, NMC-based materials (LiNixMnyCozO2) have been receiving more attention due to their high energy density and low price. However, NMC-based cathode materials still suffer from degradation and capacity fading due to polarization and structural change over charge-discharge cycling which may be associated with, for example, cation mixing and particle morphology. Among these, the particle size of NMC-base cathodes plays an important role in degradation mechanism during long-term electrochemical cycling [1,2].The present study comprehensively highlights the effect of post-grinding methods and re-heating on electrochemical performance of Li-NMC622 cathode materials. For this purpose, NMC622 samples were synthesized using commercial precursors and different grinding methods were employed to break up the agglomerated secondary particles into smaller sizes. Accordingly, the microstructural, morphological, and electrochemical evolution of unground and ground samples were studied. Microscopy observations, along with electrochemical data, suggest that marked performance improvements can be achieved by controlling the particle size of NMC622 through post-grinding and heat treatment. References B. Huang et al., Solid State Ionics, 345, 115200 (2020).A. Liu et al., J. Electrochem. Soc., 168, 050506 (2021).

Application of Tetraethylsulfamide (TES) As a Cathode Additive in Cylindrical Cells

Recently, sulfonamides have been shown to be promising electrolyte components due to their high chemical and electrochemical stability in lithium batteries [1, 2]. The electrolyte stability becomes critical when applying high voltage and/or utilizing Ni-rich layered oxides in high energy density lithium-ion batteries. Another approach to successful Ni-rich cathode performance is to develop a stable and effective cathode electrolyte interphase (CEI). Given the success of sultones and sulfates in this regard [3, 4], it is hypothesized that nitrogen analogs, like sulfonamides, could be tailored to provide a similar benefit. Indeed, Yim et al. [5, 6] have shown that N,N,N’,N’-tetraethylsulfamide (TES) forms a CEI on NMC811 that imparts high voltage cycling stability and less cathode corrosion. Our earlier studies of TES with Ni-rich NCA also formed a favorable CEI and these results are the topic of this presentation.Herein, we examine the performance of 0 - 4 wt.% TES in our commercially available, high power INR18650-P28A. These cells contain a composite SiO/graphite anode in addition to a Ni-rich cathode. As shown in Fig 1, TES significantly decreased the impedance of the cathode interface after conditioning compared to the control electrolyte. Thereafter, cells containing up to 2%TES show improved capacity retention during long-term high-rate cycling (+1C/-80W). Part of this success was due to a suppression of resistance growth during cycling by TES. Fast charge cycling (+3C/-2C), however, was moderately impaired with increased TES. Considering the largely reduced impedance of the cathode, fast-charge performance may have suffered due to anode rate limitations. These results will be discussed as well as gas generation, storage performance, and additional rate and cycling tests.[1] Shuting Feng, Mingjun Huang, Jessica R. Lamb, Wenxu Zhang, Ryoichi Tatara, Yirui Zhang, Yun Guang Zhu, Collin F. Perkinson, Jeremiah A. Johnson, Yang Shao-Horn. Chem, 5, 2630-2641 (2019)[2] Weijiang Xue, Mingjun Huang, Yutao Li, Yun Guang Zhu, Rui Gao, Xianghui Xiao, Wenxu Zhang, Sipei Li, Guiyin Xu, Yang Yu, Peng Li, Jeffrey Lopez, Daiwei Yu, Yanhao Dong, Weiwei Fan, Zhe Shi, Rui Xiong, Cheng-Jun Sun, Inhui Hwang, Wah-Keat Lee, Yang Shao-Horn, Jeremiah A. Johnson, Ju Li. Nature Energy, 6, 495-505 (2021)[3] Koji Abe, Manuel Colera, Kei Shimamoto, Masahide Kondo, Kazuhiro Miyoshi. Journal of Electrochemical Society, 161 (6) A863-A870 (2014)[4] Jian Xia, N. N. Sinha, L. P. Chen, J. R. Dahn. Journal of Electrochemical Society, 161 (3) A264-A274 (2014)[5] Kwangeun Jung, Taeeun Yim. Journal of Alloys and Compounds, 834,155155 (2020)[6] Ji Won Kim, Kwangeun Jung, Taeeun Yim. Journal of Mater. Sci & Tech. 86, 70-76 (2021) Figure 1

Three-Dimensional Modeling of Electrochemical Behavior in SiO/Graphite Composite Anode for High Energy Density Lithium-Ion Battery

Abstract SiO/Graphite (Gr) composite has been regarded as one of the most promising anode materials for the next generation of high-energy-density lithium-ion batteries (LIBs). The heterogeneous composition of such an anode system brings in highly nonlinear and complex electrochemical behaviors compared to the single-material anode. The computational modeling provides an efficient and accurate way to explore the electrochemical behaviors of SiO/Gr composite anode. Herein, we propose a 3D model at the electrode level containing particle geometries based on a representative volume element (RVE) and study the electrochemical process of the half-cell charging. The effects of SiO proportion, charging rate, SiO distribution, and SiO particle size on the electrochemical performance are discussed. The results reveal that an anode with higher SiO proportions performs a better rate capability. We also discover that moving SiO particles towards the separator and shrinking the SiO particle can improve the cell performance. Results provide an in-depth understanding of the electrochemical behaviors of the composite anode and guide the design for SiO/Gr anode materials in maximizing the theoretical capacity while maintaining better rate performance.

Biocarbon-directed vertical δ-MnO2 nanoflakes for boosting lithium-ion diffusion kinetics

Manganese dioxide (MnO2) with high theoretical capacity (1230 mAh/g) and low cost is considered as a promising anode material for next generation high energy density lithium-ion (Li+) batteries. However, the intrinsic low electric conductivity and volume change during cycling process limit its applications. In this work, a unique δ-MnO2/C composite has been synthesized through the directed growth of 2D δ-MnO2 nanosheets on the cabbage-leaf-derived biocarbon. The biocarbon acts as both structure buffer to accommodate the volume expansion and conductive agent to promote electron and ion transport. Moreover, oriented δ-MnO2 nanosheets are beneficial for increasing contact area between electrode and electrolyte, thus providing more active sites and shortening the Li+ transmission routes. Electrochemical performances show that δ-MnO2/C displays large reversible capacity (754 mAh/g after 250 cycles at current density of 0.1 A/g), excellent rate capability as well as low charge transfer resistance (17.3 Ω), and high Li+ diffusion rate (DLi+ = 2.91 × 10-14 cm2/s) during the cycles. Furthermore, the density functional theory calculations reveal the lower Li+ migration barrier energies and improved Li+ diffusion kinetics in δ-MnO2/C hetero-layer. This study provides a novel strategy to design advanced nanocomposites, using natural plant-leaf derivatives as structure-directing agents, for the next generation energy storage and conversion systems.

Li8MnO6: A Novel Cathode Material with Only Anionic Redox.

In Li-excess transition metal-oxide cathode materials, anionic oxygen redox can offer high capacity and high voltages, although peroxo and superoxo species may cause oxygen loss, poor cycling performance, and capacity fading. Previous work showed that undesirable formation of peroxide and superoxide bonds was controlled to some extent by Mn substitution, and the present work uses density functional calculations to examine the reasons for this by studying the anionic redox mechanism in Li8MnO6. This material is obtained by substituting Mn for Sn in Li8SnO6 or for Zr in Li8ZrO6, and we also compare this to previous work on those materials. The calculations predict that Li8MnO6 is stable at room temperature (with a band gap of 3.19 eV as calculated by HSE06 and 1.82 eV as calculated with the less reliable PBE+U), and they elucidate the chemical and structural effects involved in the inhibition of oxygen release in this cathode. Throughout the whole delithiation process, only O2- ions are oxidized. The directional Mn-O bonds formed from unfilled 3d orbitals effectively inhibit the formation of O-O bonds, and the layered structure is maintained even after removing 3 Li per Li8MnO6 formula unit. The calculated average voltage for removal of 3 Li is 3.69 V by HSE06, and the corresponding capacity is 389 mAh/g. The high voltage of oxygen anionic redox and the high capacity result in a high energy density of 1436 Wh/kg. The Li-ion diffusion barrier for the dominant interlayer diffusion path along the c axis is 0.57 eV by PBE+U. These results help us to understand the oxygen redox mechanism in a new lithium-rich Li8MnO6 cathode material and contribute to the design of high-energy density lithium-ion battery cathode materials with favorable electrochemical properties based on anionic oxygen redox.

Modeling and simulation of high energy density lithium-ion battery for multiple fault detection

Lithium-ion battery, a high energy density storage device has extensive applications in electrical and electronic gadgets, computers, hybrid electric vehicles, and electric vehicles. This paper presents multiple fault detection of lithium-ion battery using two non-linear Kalman filters. A discrete non-linear mathematical model of lithium ion battery has been developed and Unscented Kalman filter (UKF) is employed to estimate the model parameter. Occurrences of multiple faults such as over-charge, over-discharge and short circuit faults between inter cell power batteries, affects the parameter variation of system model. Parallel combinations of some UKF (bank of filters) compare the model parameter variation between the normal and faulty situation and generates residual signal indicating different fault. Simulation results of multiple numbers of statistical tests have been performed for residual based fault diagnosis and threshold calculation. The performance of UKF is then compared with Extended Kalman filter (EKF) with same battery model and fault scenario. The simulation result proves that UKF model responses better and quicker than that of EKF for fault diagnosis.

In situ co-doping strategy for achieving long-term cycle stability of single-crystal Ni-rich cathodes at high voltage

Single-crystal Ni-rich layered cathode (SC-NCM) is economically appealing for high-energy–density lithium-ion battery but its life span in practical application, especially under high-voltage operation, is significantly hindered by its poor structural instability, irreversible phase transitions, and sluggish electrochemical reaction kinetic. Herein, in-situ zirconium and titanium co-doped single-crystal LiNi0.6Co0.1Mn0.3O2 (Z/T@SC-NCM) material is rationally designed as the structurally and electrochemically stable cathodes for high-energy density batteries. Both the experimental analyses and theoretical calculations reveal that the synergistic effect of Zr/Ti co-doping at transition metal (TM) sites of SC-NCM materials. can not only effectively enhance the Li+ diffusion mobility but also release the internal stress concentration as well as reducing the cationic disordering. As a result, the material-level specific energy of 715 Wh kg−1 is achieved for the single-crystal LiNi0.598Co0.08Mn0.3Zr0.002Ti0.002O2 (Z/T@SC-NCM-0.2) cathode at 2.75–4.6 V with a satisfying capacity retention of 88.5 % after 150 cycles. Impressively, the pouch-type full cell of Zr/Ti@SC-NCM||graphite with a practical area capacity of 4.96 mAh cm−2 delivers an superior capacity retention of 80.6 % after 4000 cycles, which could be expected to extend the battery life-span to more than a decade for electric vehicles. It suggests that engineering the dual-doping in SC-NCM cathodes may provide an effective path toward the low-cost, excellent long-term cycling stability, and high energy density of lithium-ion batteries.