Energy Density Lithium-ion Batteries Research Articles

Advancements in Polymer Blend Electrolytes for Lithium-Ion Conduction

Increasing the energy density of lithium-ion batteries requires, among other advances, electrolytes that are compatible with lithium metal and next-generation cathodes. Polymer electrolytes play an important role in this regard, but overcoming slow ion transport is a major challenge. Hybrid electrolytes that combine fast ion transport of ceramic electrolytes and processability of polymer electrolytes are promising. To take advantage of transport in both phases, transference numbers should be comparable. Thus, single-ion conducting polymer electrolytes have received major focus in recent years. In addition to the benefit in hybrid electrolytes, single-ion conduction yields numerous transport and efficiency advantages in neat polymer electrolytes. Due to formulation simplicity and motivated by block copolymer advancements, our team has focused on polymer blend electrolytes. State of the art in these electrolytes will be reviewed including recent advancements from our team using precision polyanions with polyether solvating polymer. This presentation will cover miscibility, conductivity, and transference numbers as a function of composition and temperature. Distinct differences between blends containing the different anionic forms will be explained in the context of ion correlation. Important future directions for the subfield of polymer blend electrolytes will also be discussed.

Mechanism of Improved Lithium-Sulfur Battery Performance by Oxidation Treatment to Microporous Carbon as Sulfur Matrix

1. IntroductionLithium-sulfur (Li-S) batteries are rechargeable devices assembled with a sulfur cathode and a lithium metal anode. Li-S batteries have twice the volumetric energy density and 5 times the gravimetric energy density of lithium-ion batteries (LIB). Hence, Li-S batteries are expected to be applied to stationary power sources and EV vehicles [1]. However, Li-S batteries have the following issues:・Sulfur and the final discharge product (Li2S) are insulators.・In the discharge process, sulfur expands up to 1.8 times, so the structure of batteries is unstable.・Intermediate products (Li2Sx (x = 4 – 8)) dissolve in an electrolyte; Li2Sx (x = 4 – 8) diffused to an anode to provide an insulating layer at the anode surface.・In the charge process, Li2Sx (x = 4 – 8) causes redox shuttling.As a result, Li-S batteries cannot charge and discharge stably. In order to deal with this problem, Nazar et al. reported the method that sulfur is confined in porous carbon [2]. This approach provides a cathode realizing good electronic conductivity, restriction of sulfur expansion, and suppression of Li2Sx (x = 4 – 8) dissolution. Although these improved characteristics allow Li-S batteries to operate, The discharge capacity of Li-S batteries is still not high enough and this needs to be addressed.In our previous study, we reported that oxidation treatment to microporous carbon (MC) with HNO3 improves Li-S batteries' discharge capacity [3]. Moreover, we clarified that the discharge capacity of Li-S batteries has an approximate proportional relation with the amount of oxygen-containing functional groups on the MC surface [4].This work attempts to elucidate the mechanism of improved Li-S battery performance by oxidation treatment to MC. Our report would lead to the proposal of a novel strategy to improve the performance of Li-S batteries.2. Method2.1 Preparation of Oxidized MC-Sulfur composite (Ox MC-S)MC was added into 69 wt.% HNO3 and refluxed at 120ºC for 2 h. By vacuum filtration and washing with deionized water, Ox MC was obtained. Ox MC dried in vacuum at 80ºC overnight was mixed with sulfur at a weight ratio of Ox MC: S = 48: 52. The mixture was thermally annealed at 155ºC for 5 h (Ox MC-S). Untreated MC was also composited with sulfur by the same method (MC-S).2.2 Assembling of CellsEach MC-S cathode was prepared by mixing the MC-S, acetylene black, carboxymethyl cellulose, and styrene butadiene rubber at a respective weight ratio of 89: 5: 3: 3 and coating the resulting aqueous slurry on an Al foil current collector. The cells with the MC-S electrode and Li metal foil as an anode were assembled in a glove box filled with Ar. Lithium bis(trifluorosulfonyl)imide (LiTFSI): tetraglyme (G4): hydrofluoroether (HFE) = 10: 8: 40 (by mol) was used as the electrolyte.2.3 Electrochemical Impedance Spectroscopy (EIS)To elucidate the effect of oxidation treatment on the internal resistance of Li-S batteries, EIS was carried out at various potentials (Discharge 2.0 – 1.0 V and Charge 1.0 – 3.0 V). The obtained Nyquist plots were used for the evaluation of solid electrolyte interphase (SEI) resistance (Rsei), charge-transfer resistance (Rct), and Warburg impedance (Rw). Rw was investigated with the calculation of Warburg coefficient (σ).3. Major results and conclusionSince oxidation treatment to MC significantly increased the discharge capacity of Li-S batteries [3][4], it was expected that oxidation treatment would lower the internal resistance of Li-S batteries. EIS of MC-S and Ox MC-S at various potentials showed that oxidation treatment reduced Rsei by an average of 12.2 Ω. This indicates that the SEI thickness was reduced, or the SEI was composed of highly ion-conductive components by the oxidation treatment. Rct decreased only at lower potentials, and the Warburg coefficient decreased except at the end of charge and discharge potential. These results suggest that the oxidation treatment decreases overall resistance, but especially SEI resistance and Warburg impedance, which may improve the discharge capacity of Li-S batteries.We will also report the activation energy of Rsei and Rct and mechanism analysis of decreasing Rsei by oxidation to MC. This work was supported by “Advanced Low Carbon Technology Research and Development Program, Specially Promoted Research for Innovative Next Generation Batteries (ALCA-SPRING [JPMJAL1301])” from JST.[1] Y. Guo et al., Angew. Chem. Int. Ed., 52 (2013) 13186.[2] X. Ji et al., Nat. Mater., 8 (2009) 500.[3] S. Okabe et al., Electrochemistry, 85 (2017) 671.[4] L. Yoshida et al., ECS 238th PRiME Meeting s (2020).

What Is Important? Effect of Primary and Secondary Particle Size

High nickel layered oxides are attractive cathode materials that can achieve high energy density in lithium-ion batteries (LIBs). Many researchers have strived to improve the cycling stability and energy density of LiNiO2 (LNO) through another metal mixing, dopping, or coating method. However, the particle size effect of pure LNO during the charging/discharging system has not been fully understood yet. Many computing research results revealed that smaller-particle materials with highly connective interfaces and reduced diffusion paths exhibit higher rate performance and good cycling stability than bulk counterparts. However, our study revealed that the different particle size of LNO has a very different trend in contrast to the computation results because they overlooked the influence of primary particles. In this study, we focus on the impact of the particle size distribution of spherical cathode material on positive electrodes in LIBs. We designed four different particle sizes of Ni(OH)2 by controlling pH, time, and agitation speed. When the other conditions were the same except for the particle size, we were able to explore how the grain size, Li off-stoichiometry (Li1-zNi1+zO2), and activation energy affect the battery performance. Through size comparison, a better understanding of the influence of particle size distribution was obtained, which would be an important basis to engineer electrodes for higher C-rate capability, higher performance, and better stability during battery cycling.

High-Energy and Long-Lasting Lithium Metal Batteries Employing Garnet-Type Solid Electrolytes with Tailored Lithium Metal Compatibility

One of the viable options to significantly augment the energy density of lithium-ion batteries (LIBs) is to adopt lithium metal anode in the cell, which offers the highest theoretical capacity (3,860 mAh g-1) among anode materials.1 However, the practical obstacles such as dendrite growth, low Coulombic efficiency, and safety issues still remain unresolved, despite the extensive efforts to employ the lithium metal anode in LIBs.2 Recent progress in solid-state electrolyte development has granted a new promising opportunity for the utilization of lithium metal anodes, whose mechanical rigidity and non-flammable nature are supposed to effectively suppress lithium dendrite short-circuiting, thereby securing battery safety. Nevertheless, there has been no report thus far that demonstrates acceptable levels of electrochemical performance of solid-state lithium metal batteries for real-world applications.3,4 In our research, a lithium-metal-battery employing tailored garnet-type Li7-xLa3-aZr2-bO12 (LLZO) solid-electrolytes that can meet the lifespan requirements of both electric vehicles and stationary applications has been achieved, affording remarkable stability and energy density over 2,000 cycles. It is demonstrated that the compatibility between LLZO and lithium metal is crucial for the long-term stability, which can be accomplished by regulating bulk dopants and the corresponding dopant-specific interfacial treatment using protonation/etching. The appropriate selection of dopant and dopant-specific protonation/etching agent for LLZO leads to (i) the formation of a stable passivation layer at the interface with lithium metal, (ii) effective release of residual stress in LLZO, and (iii) intact contact at the interface.The lithium-metal cell with 2 mAh cm-2 cathode (12 mg cm-2) delivers a cumulative capacity of over 4,000 mAh cm-2 at 3 mA cm-2, which to the best of our knowledge, is the highest long-term cycle value reported for lithium metal batteries with LLZO electrolytes. Moreover, even with the thin 110-µm-LLZO electrolyte and 20-µm lithium metal, a high-loading-capacity cell (3.2 mAh cm-2) exhibits a superior cycle life (>600 cycles) at 2 mA cm-2 without short-circuiting, affording a basis for the high-energy-cell design with ultra-thin electrolyte. In addition, an all-solid-state-battery, excluding the ionic liquid electrolyte, was successfully demonstrated using the composite cathode, which could cycle over 1,000 times at a high current density of 3 mA cm-2 without short-circuiting. To the best of our knowledge, this is the first all-solid-state battery that can operate over 1,000 cycles, enabled by the garnet-type electrolytes and cathode with a commercially acceptable capacity.These findings are expected to open a new avenue for developing long-lasting solid-state lithium metal batteries by highlighting the efficacy of the coupled bulk and interface doping of solid electrolytes.

Understanding the Unreliability Issues of Performance and Safety Diagnostics of Lithium-Ion Batteries Under Extreme Conditions

The research and development (R&D) community is continually pushing for high energy density Lithium-ion batteries (LiBs) by innovating materials, designs, and operating conditions.1 We expect these batteries to operate under a range of conditions (e.g., fast charging, fast discharging, low temperatures, etc.).1,2 Advanced diagnostics could play a key role in ensuring an extended life of these energy-dense LiBs while ensuring their safety. Therefore, a parallel effort is enabling advanced diagnostics and prognostics to ensure the safe operation of these batteries under the stated conditions throughout their service lives.Many researchers have proposed different performance and safety diagnostics of LiB in their early stages, often using small or specially designed cells through controlled tests.1 Extending these diagnostics to automotive grade cells in real life environments has not been performed extensively to understand their uncertainties. This gap in development between the early R&D stage to near the deployment stage is impeding their maturity; hence, delaying their adoption in their expected applications.In this presentation, we will discuss the unreliability issues of different electrochemical and electromechanical diagnostics related to LiBs under different safety critical conditions when cell size, age, and operating conditions changes. We will discuss the underlying issues of unreliability in different diagnostics with experimental data, followed by a discussion of several emerging safety diagnostics. Finally, the need for independent evaluation of LiB safety diagnostics along with some logistical pathways to do so will be discussed. References T.R. Tanim, E. J. Dufek, and S. V. Sazhin, MRS Bulletin, 46, 420-428 (2021)S. Ahmed et al., J. Power Sources, 367, 250–262 (2017).

Sulfurized Electrolyte Additives for Stable Lithium Metal Anodes

Researchers around the world are striving to develop new materials for energy-efficient and high energy density lithium-ion batteries [1]. Lithium metal with a theoretical specific capacity of 3860 mAh/g, low density (0.534 g/cm3), and the lowest potential (−3.040 V vs. standard hydrogen electrode) is consider the ultimate anode material for high specific energy batteries [2]. However, various issues remain to be address that hinder its use in commercial batteries, namely, cycling stability, Coulombic efficiency, and safety aspects associated with dendritic growth [3]. Inactive lithium, also known as “dead lithium,” originating from the dendrites that become separated from the surface over prolonged cycling contribute to anode capacity loss and require high negative to positive electrode capacity ratio (N/P). In addition, due to the extremely low standard redox potential of lithium, electrolytes readily react with the lithium metal surface even without any potential polarization. These reactions lead to the formation of mostly insoluble species in a layer often referred to as solid electrolyte interface, SEI. Ideally, the SEI layer is self-terminating; however, as fresh lithium gets exposed via dendritic growth, SEI formation continues. The steady and uncontrollable growth of SEI throughout the functional life of the battery leads to gradual resistant growth responsible for the capacity fade and eventual “death” of the battery.In previous art, alternative electrolytes, electrolyte additives, and artificial SEIs were studied [4] [5]. For example, the electrolyte additive lithium fluoride (LiF) was used in carbonate electrolytes and provided a strong protective layer that reduced side reactions and improved the life capacity of the battery [6]. Recently, 3-dimensional design of the anode’s current collector was shown to accommodate Li deposition resulting in suppressed SEI growth and volume expansion during cycling [7].In the present work, we use sulfur-containing compounds as additives at a very low concentration (1 – 50 mM) in standard 1M LiPF6 EC:DMC (v:v = 1:1). Coin cells (2032) were assembled using lithium foil (100 mm thick), separator (Celgard), and NMC811 cathode (> 10 mg/cm2). Cells were first rested and activated at a slow rate then cycled at C/3 and 1C for charge and discharge respectively in prescribed voltage cutoff window. As shown in Figure 1, the sulfur-containing cell had more than 300 cycles before 90% capacity retention relative to the beginning of life (BOL) capacity. The sulfur-free control cell lasted less than 150 cycles above the 90% retention line. Electrochemical impedance spectroscopy (EIS) measurements for cycled cells showed lower interfacial resistance for cells with sulfur-containing additives compared to control cells. The reason for the improved cycle stability can be attributed to the stability afforded by the additives to the SEI layer. Figure 1: A comparison of cell performance between control (black) and sulfur-containing additive (green). The Red line indicates the 90% retention of the battery. References Yoshio, Masaki, Ralph J. Brodd, and Akiya Kozawa. Lithium-ion batteries. Vol. 1. New York: Springer, 2009.Liu, Bin, Ji-Guang Zhang, and Wu Xu. "Advancing lithium metal batteries." Joule2, no. 5 (2018): 833-845.Xiao, Jie, Qiuyan Li, Yujing Bi, Mei Cai, Bruce Dunn, Tobias Glossmann, Jun Liu et al. "Understanding and applying coulombic efficiency in lithium metal batteries." Nature Energy5, no. 8 (2020): 561-568.Tikekar, Mukul D., Snehashis Choudhury, Zhengyuan Tu, and Lynden A. Archer. "Design principles for electrolytes and interfaces for stable lithium-metal batteries." Nature Energy1, no. 9 (2016): 1-7.Wang, Qian, Chengkai Yang, Jijin Yang, Kai Wu, Cejun Hu, Jing Lu, Wen Liu, Xiaoming Sun, Jingyi Qiu, and Henghui Zhou. "Dendrite‐free lithium deposition via a superfilling mechanism for high‐performance Li‐metal batteries." Advanced Materials31, no. 41 (2019): 1903248.Choudhury, Snehashis. "Lithium fluoride additives for stable cycling of lithium batteries at high current densities." In Rational Design of Nanostructured Polymer Electrolytes and Solid–Liquid Interphases for Lithium Batteries, pp. 81-94. Springer, Cham, 2019.Yun, Qinbai, Yan‐Bing He, Wei Lv, Yan Zhao, Baohua Li, Feiyu Kang, and Quan‐Hong Yang. "Chemical dealloying derived 3D porous current collector for Li metal anodes." Advanced Materials28, no. 32 (2016): 6932-6939. Figure 1

Moisture Sensitive Ni Rich Cathode Towards Large Scale Electrode Processing

High-capacity Ni-rich cathode is great candidate to enable higher energy density lithium-ion batteries (LIBs) for long-range electrical vehicles. However, the utilization of Ni rich cathode in large-scale application is still challenging. Fundamental research on Ni rich develops the understanding on material design and failure mechanism, but the moisture sensitivity of Ni-rich and its implications in storage and large-scale electrode coating are not well explored. Many challenges are existed on the way to large-scale processing for industry application. To overcome these challenges, we studied the key parameters impacting the rheological properties of NMC811 slurries and the corresponding properties of dried electrodes. Effective solutions are proposed to address the gelation issue of NMC811 slurry during large-scale coating to hopefully inspire more effective and practical approaches to tackle the grand challenges in electrochemical energy storage.

Numerical Models of the Electrolyte Filling Process of Lithium-Ion Batteries to Accelerate and Improve the Process and Cell Design

In order to meet consumer demands for electric transportation, the energy density of lithium-ion batteries (LIB) must be improved. Therefore, a trend to increase the overall size of the individual cell and to decrease the share of inactive materials is needed. The process of electrolyte filling involves the injection of electrolyte liquid into the cell, as well as the absorption of the electrolyte into the pores of the electrodes and the separator, which is known as wetting. The trend towards larger-format LIB challenges the electrolyte filling due to an increase in wetting distance for the electrolyte as well as a decrease in the void volume of the cell. The optimization of the process via numerical simulation promises to reduce costs and ensure quality during battery production. The two models developed in this study are based on a commercial computational fluid dynamics (CFD) program to study the effect of process parameters, such as pressure and temperature, on the filling process. The results were verified with neutron radiography images of the dosing process and a feasibility study for a wetting simulation is shown. For all simulations, specific recommendations are provided to set up the electrolyte filling process, based on which factors generate the greatest improvement.

Single-crystalline particle Ni-based cathode materials for lithium-ion batteries: Strategies, status, and challenges to improve energy density and cyclability

• This review covers single-crystalline Ni-based cathode material for lithium-ion batteries. • Single-crystalline particles improve tap density. • Such mechanical properties improve volumetric energy density of lithium-ion batteries. • However, intragranular cracking of single-crystalline particles is inevitable in Li cells. • Doping or surface modification of single particles can resolve these difficulties. Ni-based cathode materials for lithium-ion batteries (LIBs) have long been in the spotlight because of their high energy density. However, conventional Ni-based cathode materials are generally composed of polycrystalline ceramic powders, the secondary particle morphology of which can lead to several issues requiring mitigation to further improve the cell performance. Namely, electrode compression should be limited to prevent particle rupture and capacity loss caused by inter/intragranular cracking-induced particle pulverization that leads to isolation of the diffusion path among primary particles. A recently proposed successful approach has been the use of single-crystalline particles, which results in improved mechanical properties such as high tap density and high specific surface area, thereby increasing the volumetric energy density of Ni-based cathode cells to levels similar or higher than those of LiCoO 2 cathode cells. Despite these efforts, intragranular cracking and cation disordering of single-crystalline particles is inevitable during electrochemical cycling. These difficulties can be resolved through advanced synthetic methods and understanding of the corresponding improvement mechanisms via doping or surface modification. Herein, we discuss technical challenges regarding the synthesis, morphology control, physical and electrochemical stabilities, reaction mechanism, and surface modification of high-energy-density single-crystalline particle Ni-based cathode materials for LIBs. The single-crystalline particle method, which improves the technical limitation of polycrystalline Ni-based cathode material, can further improve its performance by doping with heterogeneous elements and surface coating.

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.

Camphene-Assisted Fabrication of Free-Standing Lithium-Ion Battery Electrode Composites.

Free-standing electrode (FSE) architectures hold the potential to dramatically increase the gravimetric and volumetric energy density of lithium-ion batteries (LIBs) by eliminating the parasitic dead weight and volume associated with traditional metal foil current collectors. However, current FSE fabrication methods suffer from insufficient mechanical stability, electrochemical performance, or industrial adoptability. Here, we demonstrate a scalable camphene-assisted fabrication method that allows simultaneous casting and templating of FSEs comprising common LIB materials with a performance superior to their foil-cast counterparts. These porous, lightweight, and robust electrodes simultaneously enable enhanced rate performance by improving the mass and ion transport within the percolating conductive carbon pore network and eliminating current collectors for efficient and stable Li+ storage (>1000 cycles in half-cells) at increased gravimetric and areal energy densities. Compared to conventional foil-cast counterparts, the camphene-derived electrodes exhibit ∼1.5× enhanced gravimetric energy density, increased rate capability, and improved capacity retention in coin-cell configurations. A full cell containing both a free-standing anode and cathode was cycled for over 250 cycles with greater than 80% capacity retention at an areal capacity of 0.73 mA h/cm2. This active-material-agnostic electrode fabrication method holds potential to tailor the morphology of flexible, current-collector-free electrodes, thus enabling LIBs to be optimized for high power or high energy density Li+ storage. Furthermore, this platform provides an electrode fabrication method that is applicable to other electrochemical technologies and advanced manufacturing methods.

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.

External-to-internal synergistic strategy to enable multi-scale stabilization of LiCoO2 at high-voltage

High-voltage LiCoO2 (LCO) offers a prelude to breaking the bottleneck of the energy density of lithium-ion batteries, however, LiCoO2 is subject to serious structural and interfacial degradation above voltages >4.55 V (vs. Li/Li+). Herein, an in-situ Li6.25La3Zr2Al0.25O12 (LLZAO) layer is constructed on the LCO surface to achieve operating voltage at 4.6 V. The detailed characterizations (ex-situ XRD, ex-situ Raman, DFT, etc.) reveal that the LLZAO layer greatly enhances Li+ conductivity attributed to the ion-conducting layer on the surface/interface, and closely combines with LiCoO2 particle to ensure stable cathode/electrolyte interface, thus suppressing the highly reactive Co4+ and O- triggered surface side reactions at high-voltage. Moreover, the introduction of La3+/Zr4+/Al3+ with a larger ionic radius (La3+/Zr4+ are larger than Co3+) and weaker electronegativity (La/Zr/Al are weaker than Co) into Co3+ sites readjusts the electron cloud density between Co–O–Li, which reinforces the Co–O bond and widens the band-center gap of Co 3d and O 2p, thus restraining the detrimental phase transition (from H3 to H1-3 phase) and the formation of Co3O4 spinel phase (attributed to lattice oxygen release), subsequently alleviating the particle cracking and structural collapse during repeated Li+ de/intercalation. Therefore, after 100 cycles at 3.0–4.6 V, LCO@1.0LLZAO exhibits a superior discharge capacity of 188.5 mA h g−1, with a capacity retention of 85.1%. The above research has brought about meaningful guidance for the evolution of cathode materials with high voltage.

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.

Onset Potential for Electrolyte Oxidation and Ni-Rich Cathode Degradation in Lithium-Ion Batteries.

High-capacity Ni-rich layered metal oxide cathodes are highly desirable to increase the energy density of lithium-ion batteries. However, these materials suffer from poor cycling performance, which is exacerbated by increased cell voltage. We demonstrate here the detrimental effect of ethylene carbonate (EC), a core component in conventional electrolytes, when NMC811 (LiNi0.8Mn0.1Co0.1O2) is charged above 4.4 V vs Li/Li+—the onset potential for lattice oxygen release. Oxygen loss is enhanced by EC-containing electrolytes—compared to EC-free—and correlates with more electrolyte oxidation/breakdown and cathode surface degradation, which increase concurrently above 4.4 V. In contrast, NMC111 (LiNi0.33Mn0.33Co0.33O2), which does not release oxygen up to 4.6 V, shows a similar extent of degradation irrespective of the electrolyte. This work highlights the incompatibility between conventional EC-based electrolytes and Ni-rich cathodes (more generally, cathodes that release lattice oxygen such as Li-/Mn-rich and disordered rocksalt cathodes) and motivates further work on wider classes of electrolytes and additives.

Enabling structural and interfacial stability of 5 V spinel LiNi0.5Mn1.5O4 cathode by a coherent interface

Spinel LiNi0.5Mn1.5O4 (LNMO), a 5 V class high voltage cathode, has been regarded as an attractive candidate to further improve the energy density of lithium-ion battery. The issue simultaneously enabling side stability and maintaining high interfacial kinetics, however, has not yet been resolved. Herein, we design a coherent Li1.3Al0.3Ti1.7(PO)4 (LATP) layer that is crystally connected to the spinel LNMO host lattices, which offers fast lithium ions transportation as well as enhances the mechanical stability that prevents the particle fracture. Furthermore, the inactive Li3BO3 (LBO) coating layer inhibits the corrosion of transition metals and continuous side reactions. Consequently, the coherent-engineered LNMO-LATP-LBO cathode material exhibits superior electrochemical cycling stability in a window of 3.0–5.0 V, for example a high-capacity retention that is 89.7% after 500 cycles at 200 mA g−1 obtained and enhanced rate performance (85.1 mA h g−1 at 800 mA g−1) when tested with a LiPF6-based carbonate electrolyte. Our work presents a new approach of engineering 5 V class spinel oxide cathode that combines interfacial coherent crystal lattice design and surface coating.

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.

Review of spinel LiMn2O4 cathode materials under high cut-off voltage in lithium-ion batteries: Challenges and strategies

• We explore the limitations of LiMn 2 O 4 cathode material at high cut-off voltage. • Presents the key strategies to improve the performance under high cut-off voltage. • The developments of electrolyte for high voltage are also particularly reviewed. The growing demand for high energy and power density in lithium-ion batteries mandates the utilization of cathode material with improved capacity and output voltage. Among various cathode materials, spinel structured lithium manganese oxide stands out for its acceptable energy density, high working voltage, excellent safety, and cost-effectiveness. Extending the upper cut-off voltage of cathode materials is realized to be a convenient way of increasing the energy density of lithium-ion batteries. Nevertheless, as charging to a higher voltage (>4.3 V vs Li/Li + ), several derogatory issues such as surface distortions, the interfacial reaction between cathode and electrolyte, and stress-induced cracking could emerge, leading to a rapid decline in capacity and cycle life. This review summarizes the failure mechanism of LiMn 2 O 4 , focusing on high voltage stability. Additionally, various modification strategies, such as doping and surface coating, are proposed to acquire high-voltage LiMn 2 O 4 . We also discuss prominent modification approaches for structural or electrolytes, such as concentration-gradient design, electrolyte additives, and solid-state electrolytes.

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.