Unlocking Charge Transfer Limitations for Extreme Fast Charging of Li-Ion Batteries

Extreme fast charging (XFC) of high-energy Li-ion batteries is a key enabler of electrified transportation. While previous studies mainly focused on improving Li ion mass transport in electrodes and electrolytes, the limitations of charge transfer across electrode–electrolyte interfaces remain underexplored. Herein we unravel how charge transfer kinetics dictates the fast rechargeability of Li-ion cells. Li ion transfer across the cathode–electrolyte interface is found to be rate-limiting during XFC, but the charge transfer energy barrier at both the cathode and anode have to be reduced simultaneously to prevent Li plating, which is achieved through electrolyte engineering. By unlocking charge transfer limitations, 184 Wh kg⁻¹ pouch cells demonstrate stable XFC (10-min charge to 80 %) which is otherwise unachievable, and the lifetime of 245 Wh kg⁻¹ 21700 cells is quintupled during fast charging (25-min charge to 80 %).     

固态锂电池中正极/电解质界面的密度泛函计算研究

锂离子电池的广泛应用对储能器件的能量密度、安全性和充放电速度提出了新的要求. 全固态锂电池与传统锂离子电池相比具有更少的副反应和更高的安全性,已成为下一代储能器件的首选. 构建匹配的电极/电解质界面是在全固态锂电池中获得优异综合性能的关键. 本文采用第一性原理计算研究了固态电池中电解质表面及正极/电解质界面的局域结构和锂离子输运性质. 选取β-Li₃PS₄ (010)/LiCoO₂ (104)和 Li₄GeS₄ (010)/LiCoO₂ (104)体系计算了界面处的成键情况及锂离子的迁移势垒. 部分脱锂态的正极/电解质界面上由于Co-S成键的加强削弱了P/Ge-S键的强度,降低了对Li⁺的束缚,从而导致了更低的锂离子迁移势垒. 理解界面局域结构及其对Li+输运性质的影响将有助于我们在固态电池中构建性能优异的电极/电解质界面.     

Equilibrium lithium-ion transport between nanocrystalline lithium-inserted anatase TiO2 and the electrolyte

The power density of lithium-ion batteries requires the fast transfer of ions between the electrode and electrolyte. The achievable power density is directly related to the spontaneous equilibrium exchange of charged lithium ions across the electrolyte/electrode interface. Direct and unique characterization of this charge-transfer process is very difficult if not impossible, and consequently little is known about the solid/liquid ion transfer in lithium-ion-battery materials. Herein we report the direct observation by solid-state NMR spectroscopy of continuous lithium-ion exchange between the promising nanosized anatase TiO(2) electrode material and the electrolyte. Our results reveal that the energy barrier to charge transfer across the electrode/electrolyte interface is equal to or greater than the barrier to lithium-ion diffusion through the solid anatase matrix. The composition of the electrolyte and in turn the solid/electrolyte interface (SEI) has a significant effect on the electrolyte/electrode lithium-ion exchange; this suggests potential improvements in the power of batteries by optimizing the electrolyte composition.     

Monitoring electrode/electrolyte interfaces of Li-ion batteries under working conditions: A surface-enhanced Raman spectroscopic study on LiCoO2 composite cathodes

Lithium-ion batteries are commonly used for electrical energy storage in portable devices and are promising systems for large-scale energy storage. However, their application is still limited due to electrode degradation and stability issues. To enhance the fundamental understanding of electrode degradation, we report on the Raman spectroscopic characterization of LiCoO₂ cathode materials of working Li-ion batteries. To facilitate the spectroscopic analysis of the solid electrolyte interface (SEI), we apply in situ surface-enhanced Raman spectroscopy under battery working conditions by using Au nanoparticles coated with a thin SiO₂ layer (Au@SiO₂). We observe a surface-enhanced Raman signal of Li₂CO₃ at 1090 cm⁻¹ during electrochemical cycling as an intermediate. Its formation/decomposition highlights the role of Li₂CO₃ as a component of the SEI on LiCoO₂ composite cathodes. Our results demonstrate the potential of Raman spectroscopy to monitor electrode/electrolyte interfaces of lithium-ion batteries under working conditions thus allowing relations between electrochemical performance and structural changes to be established.     

Electrocatalytic properties of La0.9Sr0.1MnO3-based electrodes for oxygen reduction

Electrochemical reduction of oxygen at the interface between a La_0.9Sr_0.1MnO₃ (LSM)-based electrode and an electrolyte, either yttria-stabilized-zirconia (YSZ) or La_0.8Sr_0.2Ga_0.9Mg_0.1O₃ (LSGM), has been investigated using DC polarization, impedance spectroscopy, and potential step methods at temperatures from 1053 to 1173 K. Results show that the mechanism of oxygen reduction at an LSM/electrolyte interface changes with the type of electrolyte. At an LSM/YSZ interface, the apparent cathodic charge transfer coefficient is about 1 at high temperatures, implying that the rate-determining step (r.d.s.) is the diffusion of partially reduced oxygen species, while at an LSM/LSGM interface the cathodic charge transfer coefficient is about 0.5, implying that the r.d.s. is the donation of electrons to atomic oxygen. The relaxation behavior of the LSM/electrolyte interfaces displays an even more dramatic dependence on the type of electrolyte. Under cathodic polarization, the current passing through an LSM/YSZ interface increases with time whereas that through an LSM/LSGM interface decreases with time, further confirming that it is the triple phase boundaries (TPBs), rather than the surface of the LSM or the LSM/gas interface, that dominate the electrode kinetics when LSM is used as an electrode. Electronic Publication     

锂离子电池低温性能改善研究进展

锂离子电池因其能量密度高,循环寿命长等优点已成为新型动力电池领域的研究热点,但其温度特性尤其是低温性能较差制约着锂离子电池的进一步使用. 本文综述了锂离子电池低温性能的研究进展,系统地分析了锂离子电池低温性能的主要限制因素. 从正极、电解液、负极三个方面讨论了近年来研究者们提高电池低温性能的改性方法. 并对提高锂离子电池低温性能的发展方向进行了展望.     

Stabilizing the Electrochemistry of Lithium-Selenium Battery via In situ Gelated Polymer Electrolyte: A Look from Anode

Li metal possesses a high theoretical specific capacity,high electronic conductivity,and a low electrochemical potential,making it a promising anode material for building next-generation rechargeable metal batteries.In case conventional liquid electrolytes were used,and the anode using Li metal has been hindered by unstable(electro)chemistry at Li/electrolyte interface and the accompanied dendrite issue.Specifically,for the Li-Se batteries,the dissolution and shuttle of polyselenide intermediates lead to the deposition of poorly-conductive species on the anode,which further aggravates the chemical environment at the anode.In this work,we proposed to stabilize the Li-Se electrochemistry by constructing a gel polymer electrolyte via in situ gelations of conventional ether-based electrolytes at room temperature.The results demonstrate that the in situ gelated electrolyte helps to build electrochemically stable electrode/electrolyte interfaces and promote the efficient transfer of charge carriers across the interface.Compared with the liquid electrolytes,the gelated electrolyte shows improved chemical compatibility with the Li metal anode,which effectively alleviates the unfavorable side reactions and dendrite formation at the anode/electrolyte interface,and the polyselenide shuttle from the cathode to the anode.As a result,the Li-Se battery shows a higher Coulombic efficiency and improved cycling performance.     

Probing non-polarizable liquid/liquid interfaces using scanning ion conductance microscopy

The study of microscopic structure of a liquid/liquid interface is of fundamental importance due to its close relation to the thermodynamics and kinetics of interfacial charge transfer reactions.In this article,the microscopic structure of a non-polarizable water/nitrobenzene(W/NB) interface was evaluated by scanning ion conductance microscope(SICM).Using SICM with a nanometer-sized quartz pipette filled with an electrolyte solution as the probe,the thickness of this type of W/NB interface could be measured at sub-nanometer scale,based on the continuous change of ionic current from one phase to another one.The effects for thicknesses of the non-polarizable W/NB interfaces with different electrolyte concentrations,the Galvani potentials at the interface and the applied potentials on the probe were measured and systematically analyzed.Both experimental setups,that is an organic phase up and an aqueous down,and a reverse version,were employed to acquire the approach curves.These data were compared with those of an ideal polarizable interface under the similar experimental conditions,and several characteristics of non-polarizable interfaces were found.The thickness of a non-polarizable interface increases with the decrease of electrolyte concentration and the increase of applied potential,which is similar to the situation of a polarizable liquid/liquid interface.We also find that the Galvani potential across a non-polarizable interface can also influence the interfacial thickness,this phenomenon is difficult to observe when using polarizable interface.Most importantly,by the comparison of two kinds of liquid/liquid interfaces,we experimentally proved that much more excess ions are gathered in the space charge layer of non-polarizable interfaces than in that of polarizable interfaces.These results are consistent with the predictions of molecular dynamic simulations and X-ray reflectivity measurements.     

Surface state engineering of molecule-molecule interactions

Engineering the electronic structure of organics through interface manipulation, particularly the interface dipole and the barriers to charge carrier injection, is of essential importance to improve organic devices. This requires the meticulous fabrication of desired organic structures by precisely controlling the interactions between molecules. The well-known principles of organic coordination chemistry cannot be applied without proper consideration of extra molecular hybridization, charge transfer and dipole formation at the interfaces. Here we identify the interplay between energy level alignment, charge transfer, surface dipole and charge pillow effect and show how these effects collectively determine the net force between adsorbed porphyrin 2H-TPP on Cu(111). We show that the forces between supported porphyrins can be altered by controlling the amount of charge transferred across the interface accurately through the relative alignment of molecular electronic levels with respect to the Shockley surface state of the metal substrate, and hence govern the self-assembly of the molecules.     

Enhancing Capacity Performance by Utilizing the Redox Chemistry of the Electrolyte in a Dual‐Electrolyte Sodium‐Ion Battery

A strategy is described to increase charge storage in a dual electrolyte Na‐ion battery (DESIB) by combining the redox chemistry of the electrolyte with a Na⁺ ion de‐insertion/insertion cathode. Conventional electrolytes do not contribute to charge storage in battery systems, but redox‐active electrolytes augment this property via charge transfer reactions at the electrode–electrolyte interface. The capacity of the cathode combined with that provided by the electrolyte redox reaction thus increases overall charge storage. An aqueous sodium hexacyanoferrate (Na₄Fe(CN)₆) solution is employed as the redox‐active electrolyte (Na‐FC) and sodium nickel Prussian blue (Na_x‐NiBP) as the Na⁺ ion insertion/de‐insertion cathode. The capacity of DESIB with Na‐FC electrolyte is twice that of a battery using a conventional (Na₂SO₄) electrolyte. The use of redox‐active electrolytes in batteries of any kind is an efficient and scalable approach to develop advanced high‐energy‐density storage systems.     

The positive limit of photoemission of electrons into electrolytic solutions

The photoemission of electrons into electrolytic solutions was studied from metals bearing positive charge, when the metal is polarized in the potential range positive of the p.z.c. The dependence on potential of the energy of the red limit of photoemission is given by a curve which increases due to increasing positive charge of the electrode up to a limit at about +0.35 V vs. SCE, where the photoemission ceases.     

Interfacial compatibility issues in rechargeable solid-state lithium metal batteries: a review

Solid-state lithium metal batteries(SSLBs) contain various kinds of interfaces, among which the solid electrode|solid electrolyte(ED|SE) interface plays a decisive role in the battery's power density and cycling stability. However, it is still lack of comprehensive knowledge and understanding about various interfacial physical/chemical processes so far. Although tremendous efforts have been dedicated to investigate the origin of large interfacial resistance and sluggish charge(electron/ion) transfer process, many scientific and technological challenges still remain to be clarified. In this review, we detach and discuss the critical individual challenge, including charge transfer process, chemical and electrochemical instability, space charge layers, physical contact and mechanical instability. The fundamental concepts, individual effects on the charge transfer and potential solutions are summarized based on material's thermodynamics, electrode kinetics and mechanical effects. It is anticipated that future research should focus on quantitative analysis, modeling analysis and in-situ microstructure characterizations in order to obtain an efficient manipulation about the complex interfacial behaviors in all solid-state Li batteries.     

Electrolytic molybdenum sulfides for thin-layer lithium power sources

The active molybdenum sulfide compound Mo₂S₃, which should be considered as a cathode material for thin-layer rechargeable power source, has been produced by electrolysis. Using impedance spectroscopy and potential relaxation method after current interruption, the kinetic parameters of lithium intercalation in electrolytic Mo₂S₃ have been obtained. Activation energy of Li⁺ migration in electrolyte (13.76 kJ/mol), charge transfer through the Mo₂S₃ electrode/electrolyte interface (38.8 kJ/mol), and Li⁺ diffusion in a solid phase (57.3 kJ/mol) have also been established. Taking into account the coefficient data of charge mass transfer in a solid phase and the reaction rate coefficient of charge transfer through the interface electrode/electrolyte within the temperature range 20–50 °C, the stage of Li⁺ transfer in a solid phase has been determined as a limiting stage for lithium intercalation in electrolytic molybdenum sulfide Mo₂S₃.     

Mechanism and kinetics of electrode processes in systems comprising solid polyaluminate electrolyte

Cathodic reduction of organic semiconductors (charge-transfer complexes and radical-ion salts) at interfaces in Na(Hg)/β-Al₂O₃/organic semiconductor systems is studied by inversion voltammetry and chronopotentiometry. Formation of transition layer at the organic semiconductor/solid electrolyte interface is revealed. The mechanism of the charge transfer complex and radical-ion salt cathodic reduction depends on the potential scan rate; the cathodic process at nonmetal electrodes occurs under the conditions of double injection of electronic and ionic charge carriers to electrode bulk.     

高电压镍锰酸锂正极/电解液界面本征性质的研究

高电压正极材料的应用是提高锂离子电池能量密度的有效手段,然而高电压下正极/电解液界面稳定性成为决定锂离子电池在高电压工作条件下循环性能和安全性能的关键因素,因此高电压下正极/电解液界面具有重要的研究价值. 但是,目前报道的正极/电解液界面的研究中通常使用传统的极片制备方法,这需要引入导电剂和粘结剂,会对后期正极活性物质表面钝化膜的形貌和组分表征带来干扰,甚至造成固体电解质界面(SEI)膜存在的假象,难以获得正极材料与电解液之间界面的本征信息. 这里,我们采用溶胶凝胶旋涂法制备了不含导电剂和粘结剂的镍锰酸锂(LNMO)正极,以其为研究对象,通过扫描电镜(SEM)、原子力显微镜(AFM)和X射线光电子能谱(XPS)技术,结合电化学阻抗谱(EIS)研究了LNMO正极/电解液界面在充放电过程中的结构演变过程以及本征性质. 研究结果显示在充放电过程中,电解液中溶剂和电解质都会参与反应,其中LiPF₆的降解主要发生在高电压下,其降解产物在放电过程中又会被反应消耗掉. 它们的降解产物沉积到LNMO正极形成表面膜,该表面膜的主要成分随着电压的不同组分有所不同.     

Using atomic layer deposition to hinder solvent decomposition in lithium ion batteries: first-principles modeling and experimental studies

Passivating lithium ion (Li) battery electrode surfaces to prevent electrolyte decomposition is critical for battery operations. Recent work on conformal atomic layer deposition (ALD) coating of anodes and cathodes has shown significant technological promise. ALD further provides well-characterized model platforms for understanding electrolyte decomposition initiated by electron tunneling through a passivating layer. First-principles calculations reveal two regimes of electron transfer to adsorbed ethylene carbonate molecules (EC, a main component of commercial electrolyte), depending on whether the electrode is alumina coated. On bare Li metal electrode surfaces, EC accepts electrons and decomposes within picoseconds. In contrast, constrained density functional theory calculations in an ultrahigh vacuum setting show that, with the oxide coating, e(-) tunneling to the adsorbed EC falls within the nonadiabatic regime. Here the molecular reorganization energy, computed in the harmonic approximation, plays a key role in slowing down electron transfer. Ab initio molecular dynamics simulations conducted at liquid EC electrode interfaces are consistent with the view that reactions and electron transfer occur right at the interface. Microgravimetric measurements demonstrate that the ALD coating decreases electrolyte decomposition and corroborates the theoretical predictions.     

高能量密度的锂离子混合型电容器

锂离子混合型电容器兼有锂离子电池和超级电容器的优点,在电化学储能领域具有广泛的应用前景. 但其产业化仍存在一系列的基础及工艺方面的问题,具体包括器件结构设计、电极材料筛选、预嵌锂工艺和电解液与电极的界面等. 本文结合作者课题组的研究工作介绍了近年来高能量密度的锂离子混合型电容器的研究进展,内容涉及锂离子电容器正/负极材料的筛选、预嵌锂工艺的优化、内并联结构的锂离子电池型超级电容器复合正极组成材料的调控、隔膜的选择、电解液的组成、以及器件的高/低温性能,分析了锂离子电容器的容量衰减机制,探讨了锂离子电池型超级电容器的储能机制,提出了未来对高能量密度的锂离子混合型电容器研究的展望.     

Discrete Helmholtz model: a single layer of correlated counter-ions. Metal oxides and silica interfaces,ion-exchange and biological membranes

The mechanism by which interfaces in solution can be polarised depends on the nature of the charge carriers. In the case of a conductor, the charge carriers are electrons and the polarisation is homogeneous in the plane of the electrode. In the case of an insulator covered by ionic moieties, the polarisation is inhomogeneous and discrete in the plane of the interface. Despite these fundamental differences, these systems are usually treated in the same theoretical framework that relies on the Poisson–Boltzmann equation for the solution side. In this perspective, we show that interfaces polarised by discrete charge distributions are rather ubiquitous and that their associated potential drop significantly differs from those of conductor–electrolyte interfaces. We show that these configurations, spanning liquid–liquid interfaces, charged silica–water interfaces, metal oxide interfaces, supercapacitors, ion-exchange membranes and even biological membranes can be uniformly treated under a common “Discrete Helmholtz” model where the discrete charges are compensated by a single layer of correlated counter-ions, thereby generating a sharp potential drop at the interface.

Electrolytes in solution are strongly correlated with discrete charges at insulating interfaces inducing a behavior significantly different from that of conducting interfaces.