Energy Density Lithium-ion Batteries Research Articles

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.

Enhanced cycling performance of SiOx microparticles uniformly coated with graphene sheets

Microsized silicon suboxide (SiOx, 0<x<2) materials promise less interfacial side reactions and higher volumetric capacity than those of nanosized couterpart when used as anode materials for high energy density lithium ion batteries. However, its poorer mechanical stability during charge/discharge process severely frustrates the cycling performance. Here we successfully achieved a conformally graphene-coated microsized SiOx material through surface engineering by a facile PVP-assisted hydrothermal method. PVP connects SiOx and graphene oxide (GO) sheets via hydrogen bonds in hydrothermal process and then in-situ carbonizes to form an amorphous carbon layer between SiOx core and graphene sheets after heat-treatment. The inner amorphous carbon layer and outer graphene sheets together evenly and conformally coat on SiOx particles, forming a double-layer coated SiOx/C@graphene composite. The well-encapsulation of SiOx by the double coating layers guarantees the uniform occurrence of electrode reactions on SiOx surface, which reduces the structural stress and homogenizes the volume variation, thus enabling excellent structural integrity of electrode during lithiation/delithiation process. Owing to the well-engineered structure, the SiOx/C@graphene electrode delivers an excellent cyclic performance (1076 mAh g−1 at 0.5C after 120 cycles with a capacity retention of 88.7%) and superior rate capability (785 mAh g−1 at 3C).

Tin-nitrogen coordination boosted lithium-storage sites and electrochemical properties in covalent-organic framework with layer-assembled hollow structure

Covalent-organic frameworks (COFs) and related composites show an enormous potential in next-generation high energy-density lithium-ion batteries. However, the strategy to design functional covalent organic framework materials with nanoscale structure and controllable morphology faces serious challenges. In this work, a layer-assembled hollow microspherical structure (Sn@COF-hollow) based on the tin-nitrogen (Sn-N) coordination interaction is designed. Such carefully-crafted hollow structure with large exposed surface area and metal center decoration endows the Sn@COF-hollow electrode with more activated lithium-reaction sites, including Sn ions, carbon-nitrogen double bond (CN) groups and carbon-carbon double bond (CC) units from aromatic benzene rings. Besides, the layer-assembled hollow structure of the Sn@COF-hollow electrode can also alleviate the volume expansion of electrode during repeated cycling, and achieve fast electrons/ions transmission and capacitance-dominated lithium-reaction kinetics, further leading to enhanced cycling performance and rate properties. In addition, the effective combination of the inorganic metal and organic framework components in the Sn@COF-hollow electrode can promote its improved conductivity and further enhance lithium-storage properties. Benefited from these merits, the Sn@COF-hollow electrode delivers highly reversible large capacities of 1080 mAh g−1 after 100 cycles at 100 mA g−1 and 685 mAh g−1 after 300 cycles at 1000 mA g−1. This work provides an interesting and effective way to design COF-based anodes of lithium-ion battery with improved electrochemical performances.

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

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

Construction of Macroporous Co2SnO4 with Hollow Skeletons as Anodes for Lithium-Ion Batteries.

Increasing the energy density of lithium-ion batteries (LIBs) can broaden their applications in energy storage but remains a formidable challenge. Herein, with polyacrylic acid (PAA) as phase separation agent, macroporous Co2SnO4 with hollow skeletons was prepared by sol-gel method combined with phase separation. As the anode of LIBs, the macroporous Co2SnO4 demonstrates high capacity retention (115.5% at 200 mA·g−1 after 300 cycles), affording an ultrahigh specific capacity (921.8 mA h·g−1 at 1 A·g−1). The present contribution provides insight into engineering porous tin-based materials for energy storage.

The manganese oxyborate Mn3(BO3)2 as a high-performance anode for lithium-ion batteries

Borate has aroused great interest as anode materials for lithium-ion batteries (LIBs) due to its high specific capacity and abundant supply of raw materials. To further increase its energy density in LIBs, it is urgent to synthesize a new type of relatively low potential borate material. In this study, Mn3(BO3)2 with a relatively suitable discharge voltage plateau (~0.9 V vs. Li/Li+) was successfully prepared. The synthesized Mn3(BO3)2 has high charge specific capacity (544.4 mAh g−1 at 0.4 A g−1), excellent cycle stability (538.1 mAh g−1 after 400 cycles at 0.4 A g−1) and high rate performance (191.5 mAh g−1 at 3.2 A g−1). The lithium storage behavior of Mn3(BO3)2 was studied by ex-situ XRD and ex-situ XPS.

Surface spinel and interface oxygen vacancies enhanced lithium-rich layered oxides with excellent electrochemical performances

Li-rich layered oxide (LLO) is one of the most promising cathode materials for high energy–density lithium ion battery (LIB) due to its capacity more than 250 mAh g−1. However, the low initial Coulombic efficiency, large voltage decay and poor cycling stability caused by irreversible lattice oxygen releasing hinder its further development. The present work demonstrates that a surface layer of spinel Li4Mn5O12 rich of interface oxygen vacancies in LLO (denote as SLLO) reduces the voltage decay and suppresses the irreversible release of oxygen. When SLLO was used as a cathode in LIBs, the initial Coulombic efficiency is improved from 83% to 97%, a high reversible capacity of 303 mAh g−1 at a rate of 0.1C, as well as a capacity retention of 88% at 0.3C at 200 cycles, and corresponding voltage decay is also mitigated. Characterization and calculation reveal that the enhanced performance is attributed to the rapid Li+ extraction/insertion in the surface spinel; the irreversible release of O2 is reduced through the interfacial oxygen vacancies; the adverse reaction is largely suppressed by spinel coating layer.

Thickness dependence of high volumetric energy density lithium ion battery based on Sn–Zn eutectic alloy foil anode

Thickness dependence of high volumetric energy density lithium ion battery based on Sn–Zn eutectic alloy foil anode

Insight into thermal analysis kinetics of surface protected LiNi0.8Co0.15Al0.05O2 cathode for safe lithium-ion batteries

Surface modification of Ni-rich cathode families has gained the most market interests towards energy-dense lithium-ion batteries (LIBs) due to its ability to strengthen LIBs electrochemical performance. Beyond current understandings, our study of thermal analysis kinetics has first revealed the indispensable role of surface coating against thermal decomposition, which is determinative for LIBs safety and large-scale commercialization. Al2O3 surface protection engages to induce inorganic-rich solid electrolyte interface (SEI) against its decomposition. Furthermore, it limits the formation, propagation and expansion of nanopores and dislocations inside particles, thus restraining transformation-metal ion dissolutions and oxygen releasing, which are the main reason to the stepwise thermal runaway and particle pulverization. Combined with the Arrhenius equation and non-isothermal kinetic equation, the kinetic triplet and decomposition mechanisms are well-defined for the first time, inherently elucidating the reduced decomposition rate and better safety caused by Al2O3-coating. This study has provided kinetic fundamentals and new insights of surface coating towards stable Ni-rich cathode and safe LIBs.

Spinel LiNi0.5Mn1.5O4 shell enables Ni-rich layered oxide cathode with improved cycling stability and rate capability for high-energy lithium-ion batteries

Increasing the charging cut-off voltage is an effective strategy to achieve high energy density Ni-rich layered oxide cathode materials, however the dramatic deterioration of cycling lifespan and thermal stability still remain great challenges in large-scale practical applications. Herein, a rationally designed core-shell structure LiNi0.9Co0.1O2@LiNi0.5Mn1.5O4 composite composed of spinel structure Mn-rich LiNi0.5Mn1.5O4 shell and layered structure Ni-rich LiNi0.9Co0.1O2 core is proposed to enhance the structure stability and thermal stability under high-voltage application scenario. Compared to the pristine LiNi0.9Co0.1O2 cathode, the core-shell structure LiNi0.9Co0.1O2@LiNi0.5Mn1.5O4 composite with optimized LiNi0.5Mn1.5O4 shell exhibits high reversible specific capacity (195.5 mA h g − 1 at 0.5 C), remarkable cycling stability (86% capacity retention after 100 cycles) and superior rate capability (162.5 mA h g − 1 at 5.0 C) within 2.8 V-4.5 V. The comprehensively improved electrochemical performance is mainly attributed to the Mn-rich LiNi0.5Mn1.5O4 shell, which not only effectively prevents the phase transition and microstructural collapse, but also ameliorates the Li+ transport ability, high-voltage charging capability and thermal stability. Such novel core-shell structure LiNi0.9Co0.1O2@LiNi0.5Mn1.5O4 composite as promising cathode is highly expected to greatly promote the practical application of high energy density lithium-ion batteries.

Boosting Cyclability and Rate Capability of SiOx via Dopamine Polymerization-Assisted Hybrid Graphene Coating for Advanced Lithium-Ion Batteries.

SiOx suffers from the 200% volume change during cycling and low electronic conductivity, resulting in poor cyclability and rate capability as a lithium-ion battery anode. Herein, we demonstrate a dopamine polymerization-guided carbon coating for SiOx anodes (SiOx@PDA@GNH). SiOx@PDA@GNH delivers charge capacities of 1269 and 1140 mA h·g-1 at charge rates of 0.05 and 3 C, respectively, and a capacity retention of 79.60% after 150 cycles at 1 C. A full cell with LiNi0.8Co0.1Mn0.1O2 or cathode demonstrates a capacity retention of >80% after 100 cycles at the rate of 0.33 C with an area capacity over 3.2 mA h·cm-2. Suppressed crack and overgrowth of the SEI layer are the key contributions for the improved performance. These results enlighten a practical pathway for the designing and modifications of SiOx anodes for high energy density lithium-ion batteries.

Lithium-Rich O2-Type Li0.66[Li0.22Ru0.78]O2 Positive Electrode Material

Increasing the energy density of lithium-ion batteries is an important step towards flexible electricity supply, which can be achieved by developing large-capacity positive electrodes. Lithium-rich oxides have been a longstanding research target because of their large capacity involving extra oxygen-redox reactions. In this work, we report the synthesis, electrochemical properties, electronic structure, and structural evolution of O2-type lithium-rich layered oxide Li1.22‒x Ru0.78O2. A robust Ru‒O layered framework without Ru migration allows for unveiling the solid-state electrochemistry of O2-type lithium-rich layered oxides with possibility of a large yet stable extra capacity for oxygen-redox reaction. Using a combination of X-ray photoelectron spectroscopy, X-ray absorption/emission spectroscopy, and in situ/ex situ X-ray diffraction, we clarified that O2-Li1.22‒x Ru0.78O2 delivers a large capacity of 200 mAh g‒1 in association with Ru5+/Ru4+ and Ru4+/Ru3+ two-electron redox reactions under a solid-solution process, but with no contribution from the extra oxygen-redox reaction.

The new-type batteries with ultimate energy density

In recent years, many countries have made plans for the development of electric vehicles. In 2021, the EU announced a plan to completely stop the sale of fuel cars by 2035 and replace all fuel cars with pure electric vehicles, reducing the carbon emissions to 100%. This is the most radical emissions reduction plan in history, and it means that the era of pure electric cars has officially arrived. The limited energy density of lithium-ion batteries currently used in cars has hampered the development of electric vehicle mileage. To meet the demand for electric vehicles, the development and research of high energy density batteries are urgent. Based on a review of the current literature, this paper summarizes the development history, working principles, current challenges and solutions of the solid-state battery, lithium-air batteries and nuclear batteries. The current dilemma for solid-state batteries is the lack of a suitable solid electrolyte, which is needed to possess high ionic conductivity of above 10 (mS/cm) at room temperature and negligible electronic conductivity with a high ionic transference number wide electrochemical stability windows. Lithium-air batteries have low power density, battery energy attenuation, and high safety performance. The research and application of nuclear batteries are more difficult, including low energy conversion rate and health problem. The result provides some guidance to researchers initially involved in the high energy density battery industry.

One Stone for Multiple Birds: A Versatile Cross-Linked Poly(dimethyl siloxane) Binder Boosts Cycling Life and Rate Capability of an NCM 523 Cathode at 4.6 V.

Increasing working voltage is a promising way to increase the energy density of lithium-ion batteries. Cycling and rate performance deteriorated due to excessive electrolyte decomposition and uncontrolled formation of a cathode-electrolyte interface (CEI) layer at a high voltage. A new concept is proposed to construct a high-voltage-stable electrode-electrolyte interface. An elastomeric poly(dimethyl siloxane) (PDMS) binder is incorporated into the electrode to modify the LiNi0.5Co0.2Mn0.3O2 (NCM 523) particle surface via an in situ cross-linking reaction between hydroxy-terminated PDMS and methyl trimethoxy silane promoted by moisture at ambient conditions (MPDMS). Improved electrochemical performance is achieved with the MPDMS binder in terms of reversible capacity (201 vs 185 mAh·g-1 at 0.2C), capacity retention (80 vs 68%, after 300 cycles at 1C), and rate performance (55.6% increase at 5C), as demonstrated by the NCM 523||Li half-cell. The NCM 523||graphite full-cell also shows improved performance at 4.6 V (147 vs 128 mAh·g-1, 82 vs 76%, after 200 cycles at 1C). The mechanism studies indicate that MPDMS exerts multiple effects, including cathode surface passivation, solvation structure tuning, electrolyte uptake enhancement, and mechanical stress relief. This work provides an inspiring route to realize high-voltage application of lithium-ion battery technology.

Boosting high voltage cycling of LiCoO2 cathode via triisopropanolamine cyclic borate electrolyte additive

Energy density of lithium-ion batteries (LIBs) can be promoted by raising the charge cutoff voltage, which faces the challenges of accelerated structural and interfacial degradation. Introducing a functional electrolyte additive is considered as an effective approach by forming a robust and protective cathode electrolyte interphase (CEI). Herein, triisopropanolamine cyclic borate (TPCB) additive is probed for the first time as an electrolyte additive to significantly enhance the interfacial stability of LiCoO2 (LCO) cathode at high charge cutoff voltages (≥4.6 V). With optimized 0.5% TPCB in electrolyte, a thin (about 8 nm) and dense CEI layer, containing C–N, B–O/B–F species and less LiF, is generated to suppress the decomposition of electrolyte at high voltages and alleviate structure damage of LCO during long-term cycling. As a result, the LCO cathode in the TPCB-modified electrolyte displays remarkably enhanced capacity retention of 82.2% after 200 cycles at 1C at high charge cut-off 4.6 V, exceeding that of 63.2% in the Base electrolyte.

Promoting Mechanistic Understanding of Lithium Deposition and Solid‐Electrolyte Interphase (SEI) Formation Using Advanced Characterization and Simulation Methods: Recent Progress, Limitations, and Future Perspectives

AbstractIn recent years, due to its great promise in boosting the energy density of lithium batteries for future energy storage, research on the Li metal anode, as an alternative to the graphite anode in Li‐ion batteries, has gained significant momentum. However, the practical use of Li metal anodes has been plagued by unstable Li (re)deposition and poor cyclability. Although tremendous efforts have been devoted to the stabilization of Li metal anodes, the mechanisms of electrochemical (re‐)deposition/dissolution of Li and solid‐electrolyte‐interphase (SEI) formation remain elusive. This article highlights the recent mechanistic understandings and observations of Li deposition/dissolution and SEI formation achieved from advanced characterization techniques and simulation methods, and discusses major limitations and open questions in these processes. In particular, the authors provide their perspectives on advanced and emerging/potential methods for obtaining new insights into these questions. In addition, they give an outlook into cutting‐edge interdisciplinary research topics for Li metal anodes. It pushes beyond the current knowledge and is expected to accelerate development toward a more in‐depth and comprehensive understanding, in order to guide future research on Li metal anodes toward practical application.

TiO2(B) nanosheets modified Li4Ti5O12 microsphere anode for high-rate lithium-ion batteries

With the increasing applications of Lithium-ion batteries in heavy equipment and engineering machinery, the requirements of rate capability are continuously growing. The high-rate performance of Li4Ti5O12 (LTO) needs to be further improved. In this paper, we synthesized LTO microsphere-TiO2(B) nanosheets (LTO-TOB) composite by using a solvothermal method and subsequent calcination. LTO-TOB composite combines the merits of TiO2(B) and LTO, resulting in excellent high-rate capability (144.8, 139.3 and 124.4 mAh g−1 at 20 C, 30 C and 50 C) and superior cycling stability (98.9% capability retention after 500 cycles at 5 C). Its excellent electrochemical properties root in the large surface area, high grain-boundary density and pseudocapacitive effect of LTO-TOB. This work reveals that LTO-TOB composite can be a potential anode for high power and energy density lithium-ion batteries.

Dictating the interfacial stability of nickel-rich LiNi0.90Co0.05Mn0.05O2 via a diazacyclo electrolyte additive – 2-Fluoropyrazine

Nickel-rich (Ni-rich) cathode materials, LiNixCoyMnzO2 (NCM, x ≥ 0.9, x + y + z = 1) hold great promise for developing high energy density lithium ion batteries especially for vehicle electrification. However, the practical application of Ni-rich cathode materials is still suffered from fast structural and interfacial degradation, and the resulted capacity decay. In this study, a diazacyclo type electrolyte additive, 2-fluoropyrazine (2-FP), was explored for the first time to boost the interfacial stabilization of single crystal LiNi0.90Co0.05Mn0.05O2 (NCM90) cathode. The capacity retention of the NCM90 is evidently promoted from 72.3% to 82.1% after 200 cycles at 1C (180 mA g−1) when adding 0.2% 2-FP into the electrolyte. The improvement of the electrochemical performance is ascribed to the generation of a compact and homogeneous cathode electrolyte interphase (CEI) film through ring-opening electrochemical polymerization of 2-FP upon the NCM90 electrode particles. This enhanced CEI layer benefits the suppression of the decomposition of LiPF6 electrolyte and the dissolution of the transition metals (Co and Mn), thus preventing the detrimental side reactions between the NCM90 electrode and the electrolyte.

Design Strategies of Flame-Retardant Additives for Lithium Ion Electrolyte

Abstract As the energy density of lithium-ion batteries continues to increase, battery safety issues characterized by thermal runaway have become increasingly severe. Battery safety issues have severely restricted the large-scale application of power batteries. Among them, the flammable liquid organic electrolyte is one of the main reasons for the safety hazards of battery thermal runaway. This article reviews the flame-retardant mechanism and research progress of phosphorus-based flame-retardant additives, nitrogen-based flame-retardant additives, and halogen-based flame-retardant additives. The design strategies of conventional flame-retardant additives and intelligent flame-retardant additives in lithium-ion batteries are summarized. Finally, a development direction and research prospects of flame-retardant additives in lithium-ion battery electrolytes are prospected.

Systematic study and effective improvement of voltammetry for accurate electrochemical window measurement of solid electrolytes

The availability of solid electrolytes promisingly boosts the energy density of lithium-ion batteries (LIBs), yet the accurate voltammetry measurement of their electrochemical windows (EWs) poses a longstanding and critical concern. In this work, the mechanism of EW measurement of electrolytes is explained using the electrical double layer theory. The influence of crucial variables in voltammetry, including the scan mode, the working electrode, and the selection of two- or three-electrode test systems is investigated. Furthermore, the step voltammetry method is proposed and applied to EW testing of the inorganic solid electrolyte Li10GeP2S12 for the first time. Finally, suggestions for EW measurement of electrolytes are presented. The results of this work promote a comprehensive understanding and more accurate EW measurement of electrolytes, facilitating the selection of suitable solid electrolytes to match different cathodes, thus advancing the development of safer high-energy density LIBs.