Energy Density Lithium-ion Batteries Research Articles

Atomic-scale origin of the low grain-boundary resistance in perovskite solid electrolyte Li0.375Sr0.4375Ta0.75Zr0.25O3

Oxide solid electrolytes (OSEs) have the potential to achieve improved safety and energy density for lithium-ion batteries, but their high grain-boundary (GB) resistance generally is a bottleneck. In the well-studied perovskite oxide solid electrolyte, Li3xLa2/3-xTiO3 (LLTO), the ionic conductivity of grain boundaries is about three orders of magnitude lower than that of the bulk. In contrast, the related Li0.375Sr0.4375Ta0.75Zr0.25O3 (LSTZ0.75) perovskite exhibits low grain boundary resistance for reasons yet unknown. Here, we use aberration-corrected scanning transmission electron microscopy and spectroscopy, along with an active learning moment tensor potential, to reveal the atomic scale structure and composition of LSTZ0.75 grain boundaries. Vibrational electron energy loss spectroscopy is applied for the first time to reveal atomically resolved vibrations at grain boundaries of LSTZ0.75 and to characterize the otherwise unmeasurable Li distribution therein. We find that Li depletion, which is a major reason for the low grain boundary ionic conductivity of LLTO, is absent for the grain boundaries of LSTZ0.75. Instead, the low grain boundary resistivity of LSTZ0.75 is attributed to the formation of a nanoscale defective cubic perovskite interfacial structure that contained abundant vacancies. Our study provides new insights into the atomic scale mechanisms of low grain boundary resistivity.

Enhancement of the corrosion resistance of nickel-plated copper used for lithium-ion battery tabs with multilayer electroless coatings

The traditional electrode tabs may not adequately meet the needs of high energy density lithium-ion batteries used in electric vehicles due to their poor corrosion resistance. In this study, multilayer nickel coatings with different phosphor contents and alloying elements were prepared by electroless plating, and then their structure, composition, resistivity and corrosion resistance were characterized by scanning electron microscopy, metalloscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and electrochemical measurements. The obtained multilayer coated sample is resistant to electrochemical corrosion by restricting electrochemical corrosion to the middle layer because of the potential difference, and the outer nickel-chromium-phosphor layer is highly resistant to chemical corrosion due to the high phosphor contents. In conclusion, the multilayer coatings show excellent electrochemical corrosion resistance and conductivity, the corrosion current is 7.674 × 10−6 A/cm2 and the weight loss is only 0.896% after immersion in electrolyte for 168 h. These excellent properties make nickel-plated copper suitable for use as lithium-ion battery tabs.

Optimization of Ni-rich Li[Ni0.92−xCo0.04Mn0.04Alx]O2 cathodes for high energy density lithium-ion batteries

Optimization of Ni-rich Li[Ni0.92−xCo0.04Mn0.04Alx]O2 cathodes for high energy density lithium-ion batteries

Novelty method based on thermal trigger mechanism for high energy density lithium-ion battery safety

Thermal runaway is the most serious issue for high energy density lithium-ion batteries. Adding flame retardants to electrolytes is a general way to improve safety of lithium-ion batteries. However, the addition of flame retardants will give rise to adverse effects on the electrochemical performance of batteries, especially phosphate ester flame retardants decompose on the surface of the negative electrode. This research innovatively outlines a heat-triggered addition method of flame retardants using the polypropylene film (PP film) package. Only under abusive circumstances can the flame retardants be released and have a profound effect. The feasibility of this addition method is verified by the battery thermal safety testing. This ingenious addition method not only avoids the negative effects of flame retardants on battery performance, but also provides a new way to prevent thermal runaway of batteries.

High-performance of surface-treated Si-flakes anode via a Schiff-base reaction processed at room-temperature

Silicon (Si) is a promising anode material for high energy density lithium-ion batteries (LIBs). However, it is still a challenge to prepare high-performance Si material in a facile and cost-effective way. In this work, we designed a Schiff-base reaction processed in room temperature to modify the surface of recycled Si-flakes using lowcost p-phthalaldehyde and 3,3′-diaminobenzidine as the monomers and acetic acid as the catalyzer. The formed Schiff-base was well-coated on Si-flakes by forming hydrogen bonds. The resulted Si@Schiff-base exhibited largely enhanced initial coulombic efficiency compared to the bare one at 0.1C. Moreover, it achieved a high capacity of 1589 mAh g−1 at 420 mA g−1 and 975 mAh g−1 at 1000 mA g−1 after 200 cycles and 500 cycles, respectively, representing the outstanding cyclic performance. The greatly improved performance should be attributed to the suppressed volume expansion of Si anode and the reduced side-reactions on Si surface. It is worth noting that the Schiff-base polymer with conjugated structure and abundance of N and O atoms also simultaneouly enhanced the electron transfer and Li+ diffusion of the Si anode. Overall, our work pave the way for the practical application of Si anode in LIBs.

A first-principles study of self-healing binders for next-generation Si-based lithium-ion batteries

Silicon anodes typically suffer from poor intrinsic conductivity and dramatic volume change during charge/discharge cycles, which hinders their commercialization in high energy density lithium-ion batteries (LiBs). This issue can be alleviated by embedding particles of the active material in an adhesive matrix, such as a polymer binder, that can accommodate large volume changes during lithiation and delithiation. Several research efforts have aimed at enhancing the adhesive, elastic, electrical, and ionic properties of binders for use in silicon anodes. Therefore, stable silicon/polymer interfaces are crucial for the performance of high capacity silicon-based LiBs. In this research, we focused on the definition of the mechanisms that determine the adhesion properties of a couple of recently proposed self-healing polymers, on Si-surfaces. The structural and electronic properties as well as the energetics of boronic acid-doped polyaniline and polyvinyl alcohol monomers absorbed on Si (110) and Si (111) surfaces have been investigated through first-principles calculations based on the density functional theory. We showed that the coabsorption of these two monomers increases the absorption energy and in general improves the adhesion properties of both polymers on both Si-surfaces, especially on the Si (111) facet.

Composite electrolytes engineered by anion acceptors for boosted high-voltage solid-state lithium metal batteries

Solid-state batteries (SSBs) are considered as the most promising option to replace commercial lithium-ion batteries due to their ability to address the flammability of liquid organic electrolytes and facilitate the energy density of lithium batteries. Herein, by introducing tris(trimethylsilyl) borate (TMSB) as anion acceptors, we successfully develop the light and thin electrolyte (TMSB-PVDF-HFP-LLZTO-LiTFSI, PLFB) with a wide voltage window to couple the lithium metal anode with the high-voltage cathodes. Consequently, as-prepared PLFB can greatly boost the generation of free Li+ and improve the Li+ transference numbers (tLi+=0.92) at room temperature. Moreover, combined with theoretical calculation and experimental results, the changes in the composition and properties of the composite electrolyte membrane with the addition of anionic receptors are systematically studied, which further implies the intrinsic mechanism of the stability difference. In addition, the PLFB-based SSB assembled by LiNi0.8Co0.1Mn0.1O2 cathode and lithium anode exhibits a high capacity retention of 86% after loop 400 cycles. This investigation on boosted battery performance by immobilized anions not only contributes to the directional construction of dendrite-free and lithium-ion permeable interface, but also brings new opportunities for the screening and design of the next generation of high-energy SSBs.

Effects of chain length and anions on ion transport in PEO-lithium salt systems

ABSTRACT Understanding the transport mechanism of Li+ in solid polymer electrolytes is beneficial for improving the safety and energy density of lithium-ion batteries. In this work, we investigate the effects of chain length of poly (ethylene oxide) (PEO) and anions (TfO-, TFSI-, PFSI-) on ion transport properties in PEO-lithium salt systems using all-atom molecular dynamics simulations. We found that the Li+ and PEO monomers are co-diffusion, regardless of the PEO chain length and the type of anion. The diffusion of Li+ becomes slower with PEO chain length and reaches an asymptotic value. In addition, the motion of the Li+ is the slowest in PEO/LiTfO systems. We conclude that the free volume of the systems plays a decisive role in the transport properties of Li+.

Impacts of Mg doping on the structural properties and degradation mechanisms of a Li and Mn rich layered oxide cathode for lithium-ion batteries

The Li- and Mn-rich layered oxide cathode material class is a promising cathode material type for high energy density lithium-ion batteries. However, this cathode material type suffers from layer to spinel structural transition during electrochemical cycling, resulting in energy density losses during repeated cycling. Thus, improving structural stability is an essential key for developing this cathode material family. Elemental doping is a useful strategy to improve the structural properties of cathode materials. This work examines the influences of Mg doping on the structural characteristics and degradation mechanisms of a Li1.2Mn0.4Co0.4O2 cathode material. The results reveal that the prepared cathode materials are a composite, exhibiting phase separation of the Li2MnO3 and LiCoO2 components. Li2MnO3 and LiCoO2 domain sizes decreased as Mg content increased, altering the electrochemical mechanisms of the cathode materials. Moreover, Mg doping can retard phase transition, resulting in reduced structural degradation. Li1.2Mn0.36Mg0.04Co0.4O2 with optimal Mg doping demonstrated improved electrochemical performance. The current work provides deeper understanding about the roles of Mg doping on the structural characteristics and degradation mechanisms of Li-and Mn-rich layered oxide cathode materials, which is an insightful guideline for the future development of high energy density cathode materials for lithium-ion batteries.

A smart polymer electrolyte coordinates the trade-off between thermal safety and energy density of lithium batteries

In this article, we develop a smart polymer electrolyte through in-situ radical random polymerization of the cyclic carbonate urethane methacrylate monomer and the 2-isocyanatoethyl methacrylate monomer, which coordinates the trade-off between thermal safety and energy density of lithium batteries. It is demonstrated that the as-developed polymer electrolyte can incur the battery thermal shutdown before reaching the thermal runaway temperature. This originates from the highly crosslinking network caused by the nucleophilic addition of carbamate to isocyanate in the polymer matrix under the elevated temperature exceeding 170 °C. Besides, superior cycle performance of 4.5 V-class LiNi0.6Co0.2Mn0.2O2/Li batteries can be achieved, with a capacity retention of 80% after 200 cycles at 0.5 C and 30 °C, owing to enhanced interface compatibility of this polymer electrolyte. Noting that this polymer electrolyte possesses a superior water-scavenging ability, which helps improve the moisture resistance and battery cycle performance. Impressively, this polymer electrolyte can achieve improved energy density and superior safety characteristic of lithium batteries under high cut-off voltage.

Surface coating engineering of Li-excess cathode additive of lithium-ion batteries for initial charge compensation

Silicon based anodes are known to have a high specific capacity and low operating voltage (less than 0.5 V vs. Li/Li+). Even so, the solid electrolyte interphase (SEI) formation induces the severe capacity loss at the first cycle, known as a critical factor in reducing the energy density of lithium-ion batteries (LIBs). To improve the energy density by compensating the initial Li+ loss, the utilization of Li-excess cathode additives has been considered as the most practical strategy for supplying surplus Li+ during the initial charge. Li2NiO2 is an ideal cathode additive thanks to its large charge capacity (≥320 mAh g−1) and low Coulombic efficiency (∼35%) at the first cycle. Surface protection of Li2NiO2 is still required, however, due to its vulnerability to moisture (H2O) and carbon dioxide (CO2) in the ambient atmosphere. In addition, Li2NiO2 becomes more structurally unstable due to oxygen (O2) gas evolution, leading to the formation of microcracks. Herein, we introduce a functional LiTaO3 coating layer onto the surface of Li2NiO2 for structural stabilization. The LiTaO3 coating layer can effectively suppress the formation of impurities (i.e., LiOH and Li2CO3) after air exposure. Furthermore, the gas evolution and mechanical cracking can be minimized by enhancing the structural integrity of Li2NiO2 during cycling.

Tin Metal Improves the Lithiation Kinetics of High-Capacity Silicon Anodes

Si-based anodes present a great promise for high energy density lithium-ion batteries. However, its commercialization is largely hindered by a grand challenge of a rapid capacity fade. Here, we demonstrate excellent cycling stability on a Si–Sn thin film electrode that outperforms pure Si or Sn counterpart under the similar conditions. Combined with the first-principles calculations, in situ transmission electron microscopy studies reveal a reduced volume expansion, increased conductivity, as well as dynamic rearrangement upon lithiation of the Si–Sn film. We attribute the improved lithiation kinetics to the formation of a conductive matrix that comprises a mosaic of nanostructured Sn, LiySn (specifically, Li7Sn2 develops around the lithiation potential of Si), and LixSi. This work provides an important advance in understanding the lithiation mechanism of Si-based anodes for next-generation lithium-ion batteries.

Towards extreme fast charging of 4.6 V LiCoO2 via mitigating high-voltage kinetic hindrance

High-voltage LiCoO2 (LCO) is an attractive cathode for ultra-high energy density lithium-ion batteries (LIBs) in the 3 C markets. However, the sluggish lithium-ion diffusion at high voltage significantly hampers its rate capability. Herein, combining experiments with density functional theory (DFT) calculations, we demonstrate that the kinetic limitations can be mitigated by a facial Mg2++Gd3+ co-doping method. The as-prepared LCO shows significantly enhanced Li-ion diffusion mobility at high voltage, making more homogenous Li-ion de/intercalation at a high-rate charge/discharge process. The homogeneity enables the structural stability of LCO at a high-rate current density, inhibiting stress accumulation and irreversible phase transition. When used in combination with a Li metal anode, the doped LCO shows an extreme fast charging (XFC) capability, with a superior high capacity of 193.1 mA h g−1 even at the current density of 20 C and high-rate capacity retention of 91.3% after 100 cycles at 5 C. This work provides a new insight to prepare XFC high-voltage LCO cathode materials.

Mitigation of cation mixing of LiNiO2-based cathode materials by Li-doping for high-performing lithium-ion battery

Element doping of transition metal (TM) ions is commonly employed in the enhancement of structural and interfacial stability of layered nickel-rich cathode materials to construct high energy density lithium-ion batteries. However, one of the main factors for structural evolution and poor electrochemical stability of the layered nickel-rich cathode materials is the inherent Li+/Ni2+ disorder caused by dopants. To regulate the cation mixing, herein, the Li-doping is introduced into the TM slabs of the LiNiO2-based materials. Benefited from the charge compensation of the TM layers, the doped Li+ ions lead to the alleviation of the Li+/Ni2+ disorder generated during the synthesis stage and electrochemical charge/discharge cycles. It is demonstrated that proper amount of the doped Li+ ions would enhance the stability of the crystal lattice, improve the Li+ diffusion between electrode and electrolyte, and suppress the microcrack formation in the secondary grains of the materials. This is verified by the synergistic effect of Li/Mn co-doping, in particular, the LiNiO2-based layered material with 11 mol% Li and 1 mol% Mn exhibits great improvement in long-term cycling stability with capacity retention 71.11% after 200 cycles at 0.5C. The Li-doping strategy might provide a new perspective to the enhancement of structural stability of the layered nickel-rich materials for lithium-ion batteries in the future.

Optimized multi-hidden layer long short-term memory modeling and suboptimal fading extended Kalman filtering strategies for the synthetic state of charge estimation of lithium-ion batteries

With the demand for high-endurance lithium-ion batteries in new energy vehicles, communication and portable devices, high energy density lithium-ion batteries have become the main research direction of the battery industry. State of Charge (SoC), as a state parameter that must be accurately evaluated by the battery management system, enables online safety monitoring of the battery operation, and prolongs its service life. In this paper, an improved algorithm based on multi-hidden layer long short-term memory (MHLSTM) neural network and suboptimal fading extended Kalman filtering (SFEKF) is proposed for synthetic SoC estimation. First, the battery external measurable information is captured. The battery real data properties are matched with the network topology without additional battery model construction, and the battery SoC is roughly evaluated using an MHLSTM network. Then, a suboptimal fading factor is inserted into the extended Kalman filter (EKF) algorithm for iterative recursion and adaptive handling to smooth the prediction results of the MHLSTM network and enhance the accuracy of state estimation, system stability, and generality. Three customized electric vehicle (EV) driving conditions datasets are categorized into training and testing sets to fulfill the efficient estimation of synthetic SoC by the fusion algorithm and solve the time series problem. Using the maximum error (ME), mean absolute error (MAE), root mean squared error (RMSE), and mean absolute percentage error (MAPE), the results show that the maximum bias of the fusion algorithm to estimate the synthetic SoC is limited to within 1.2%, even under the abrupt change of the system. It can converge to the real value quickly and maintains an excellent tracking capability for data changes, reflecting the high accuracy estimation capability and the robustness possessed by the system.

Recent Progress in Silicon-Based Materials for Performance-Enhanced Lithium-Ion Batteries.

Silicon (Si) has been considered to be one of the most promising anode materials for high energy density lithium-ion batteries (LIBs) due to its high theoretical capacity, low discharge platform, abundant raw materials and environmental friendliness. However, the large volume changes, unstable solid electrolyte interphase (SEI) formation during cycling and intrinsic low conductivity of Si hinder its practical applications. Various modification strategies have been widely developed to enhance the lithium storage properties of Si-based anodes, including cycling stability and rate capabilities. In this review, recent modification methods to suppress structural collapse and electric conductivity are summarized in terms of structural design, oxide complexing and Si alloys, etc. Moreover, other performance enhancement factors, such as pre-lithiation, surface engineering and binders are briefly discussed. The mechanisms behind the performance enhancement of various Si-based composites characterized by in/ex situ techniques are also reviewed. Finally, we briefly highlight the existing challenges and future development prospects of Si-based anode materials.

Spontaneous local redox reaction to passivate CNTs as lightweight current collector for high energy density lithium ion batteries

Extensive usage of highly conductive carbon materials with large specific surface area (e.g., carbon nanotubes, CNTs) in lithium ion batteries (LIBs), especially as current collector of anodes, suffers from low initial coulombic efficiency (ICE), large interfacial resistance, and severe embrittlement, as the large specific surface area often results in severe interfacial decomposition of the electrolyte and the formation of thick and fluffy solid electrolyte interphase (SEI) during cycling of LIBs. Herein, we demonstrate that when the CNT-based current collector and Na foil (which are being stacked intimately upon each other) are being placed in Na+-based organic electrolyte, local redox reaction between the Na foil and the electrolyte would occur spontaneously, generating a thin and homogeneous NaF-based passivating layer on the CNTs. More importantly, we found that owing to the weak solvation behaviors of Na+ in the organic electrolyte, the resulting passivation layer, which is rich in NaF, is thin and dense; when used as the anode current collector in LIBs, the pre-existing passivating layer can function effectively in isolating the anode from the solvated Li+, thus suppressing the formation of bulky SEI and the destructive intercalation of solvated Li+. The relevant half-cell (graphite as anode) exhibits a high ICE of 92.1%; the relevant pouch cell with thus passivated CNT film as current collectors for both electrodes (LiCoO2 as cathode, graphite as anode) displays a high energy density of 255 Wh kg−1, spelling an increase of 50% compared with that using the conventional metal current collectors.

Naturally-derived thermal barrier based on fiber-reinforced hydrogel for the prevention of thermal runaway propagation in high-energetic lithium-ion battery packs

Due to the constant increase in energy density of lithium-ion batteries (LIBs), safety concerns in case of a thermal runaway event become more critical. Thermal runaway propagation (TP) can destroy an entire LIB pack, rapidly releasing energy and material through heat and fire. A solution for TP that minimally affects the LIB pack remains one of the main unsolved safety-related issues in battery systems. This paper presents an eco-friendly thermal barrier made of a high water-content hydrogel derived from natural polymers reinforced by a flame-retardant fiber material. The 2-mm-thick barrier, when placed between 50 Ah LIB cells, was able to prevent thermal propagation in 2-cell modules. Once the barrier temperature reaches around 100 °C, it can absorb a large amount of energy due to water vaporization. Afterward, the remaining low thermally conductive fiber material provides thermal insulation between cells. In addition, the mechanical properties of the barrier, such as compressive strength and flexibility, make it a suitable material to be placed between LIB cells. Furthermore, its ease of manufacturing and biodegradability enable the barrier to provide higher safety for LIB packs while maintaining the cost and environmental impact to a minimum.

Pathway for high-energy density LiMnFePO4 cathodes

Polyanion cathodes are credited for its thermal stability and better safety, no matter in lithium ion batteries or sodium ion batteries. Polyanion oxides with phosphate groups came to the public's attention in 1997, and the representative material is LiFePO4, which has been widely applied and plays a huge role in the field of powder batteries and energy storage system. However, owing to the low lithiation potentials and storage sites, the energy densities of polyanion cathodes have been restricted, resulting of low-endurance and limited application scenarios. Accordingly, here, we use cheap and environmental friendly raw materials as precursors to synthesis high energy density LiMn0.6Fe0.4PO4@C cathode by a simple spray-drying and high temperature calcination process. The self-designed liquid polyacrylonitrile (LPAN) is added for the intention of nanoparticle coating, conductive network construction and particle granulation. The low-cost and carbon-coated LiMn0.6Fe0.4PO4 cathode exhibits excellent reversible capacity, low electrochemical polarization and excellent rate capacity, which maintains 93.5% capacity retention after cycling 1000 times at 5C. The work introduces a new avenue to fabricate olivine structure cathodes with outstanding electrochemical performance for the high energy density lithium ion batteries.

A simple and green self-conversion method to construct silicon hollow spheres for high-performance Li-ion battery anodes

Silicon (Si) anode has garnered attention as a potential replacement for high energy density lithium-ion battery anodes. Its commercial application, however, is still hindered by the issues of rapid capacity attenuation due to large volume change during (de)lithiation process, complex preparation process, and high cost. In this work, a simple and green strategy was proposed to fabricate carbon-coated hollow porous silicon spheres (Hp-Si@C) by a self-conversion method and subsequent magnesiothermic reduction. The synthesis of Hp-Si@C by this method used inexpensive tetraethyl orthosilicate precursors and did not involve the use of additional sacrificial template, complicated CVD and toxic hydrofluoric acid, which was simple, inexpensive, green and scalable. NaCl was introduced as a heat scavenger to avoid the formation of SiC and maintain the hollow morphology of the precursor. The electrochemical behaviors of Hp-Si@C were investigated by in situ electrochemical characterization. The structure of Hp-Si@C defined fast ion transport routes and provided expansion space during lithiation process, endowing it with stable cycling performance and fast electrochemical reaction kinetics. Hp-Si@C had a delithiation capacity of 1228 mAh g−1 with a capacity retention of 69% at 2 A g−1, and a rate capacity of 865 mAh g−1 at 10 A g−1.