SEI/dead Li-turning capacity loss for high-performance anode-free solid-state lithium batteries

Anode-free solid-state lithium metal batteries(AF-SSLBs)have the potential to deliver higher energy density and improved safety beyond lithium-metal batteries.However,the unclear mechanism for the fast capacity decay in AF-SSLBs,either determined by dead Li or solid electrolyte interface(SEI),limits the proposal of effective strategies to prolong cycling life.To clarify the underlying mechanism,herein,the evolution of SEI and dead Li is quantitatively analyzed by a solid-state nuclear magnetic resonance(ss-NMR)technology in a typical LiPF6-based polymer electrolyte.The results show that the initial capacity loss is attributed to the formation of SEI,while the dead Li dominates the following capacity loss and the growth rate is 0.141 mA h cm^(−2)cycle−1.To reduce the active Li loss,the combination of inorganic-rich SEI and self-healing electrostatic shield effect is proposed to improve the reversibility of Li deposition/dissolution behavior,which reduces the capacity loss rate for the initial SEI and following dead Li generation by 2.3 and 20.1 folds,respectively.As a result,the initial Coulombic efficiency(ICE)and stable CE increase by 15.1%and 15.3%in Li-Cu cells,which guides the rational design of high-performance AF-SSLBs.

Tackling application limitations of high-safetyγ-butyrolactone electrolytes:Exploring mechanisms and proposing solutions

Developing wide-temperature and high-safety lithium-ion batteries(LIBs)presents significant challenges attributed to the absence of suitable solvents possessing broad liquid range and non-flammability properties.γ-Butyrolactone(GBL)has emerged as a promising solvent;however,its incompatibility with graphite anode has hindered its application.This limitation necessitates a comprehensive investigation into the underlying mechanisms and potential solutions.In this study,we achieve a molecular-level understanding of the perplexing interphase formation process by employing in-situ spectroelectrochemical techniques and density function calculations.Our findings reveal that,even at high salt concentrations,GBL consistently occupies the primary Li^(+)solvation sheath,leading to extensive GBL decomposition and the formation of a high-impedance and inorganic-poor solid-electrolyte interphase(SEI)layer.Contrary to manipulating solvation structures,our research demonstrates that the utilization of filmforming additives with higher reduction potential facilitates the pre-establishment of a robust SEI film on the graphite anode.This approach effectively inhibits GBL decomposition and significantly enhances the battery's lifespan.This study provides the first reported intrinsic understanding of the unique GBLgraphite incompatibility and offers valuable insights for the development of wide-temperature and high-safety LIBs.

Progress in in-situ electrochemical nuclear magnetic resonance for battery research

A thorough understanding of the fundamental electrochemical and chemical processes in batteries is crucial to advancing energy density and power density.However,the characterizations of such processes are complex.In-situ electrochemical nuclear magnetic resonance(EC-NMR)offers the capability to collect real-time data during battery operation,furnishing insights into the local structures and ionic dynamics of materials by monitoring changes in the chemical environment around the nuclei.EC-NMR also has the advantages of being both quantitative and non-destructive.This paper systematically reviews the design of EC-NMR approach,and delves into the applications and progress of EC-NMR concerning battery reaction mechanisms,failure mechanisms,and overall battery systems.The review culminates in a comprehensive summary of the perspective and challenges associated with EC-NMR.

Deciphering the potassium storage phase conversion mechanism of phosphorus by combined solid-state NMR spectroscopy and density functional theory calculations

Phosphorus is the potential anode material for emerging potassium-ion batteries(PIBs)owing to the highest specific capacity and relatively low operation plateau.However,the reversible delivered capacities of phosphorus-based anodes,in reality,are far from the theoretical capacity corresponding to the formation of K3P alloy.And,their underlying potassium storage mechanisms remain poorly understood.To address this issue,for the first time,we perform high-resolution solid-state31P NMR combined with XRD measurements,and density functional theory calculations to yield a systemic quantitative understanding of(de)potassiation reaction mechanism of phosphorus anode.We explicitly reveal a previously unknown asymmetrical nanocrystalline-to-amorphous transition process via rP←→(K_(3)P_(11),K_(3)P_(7),beta-K_(4)P_(6))←→(alpha-K4P6)←→(K_(1-x)P,KP,K_(4-x)P3,K_(1+x)P)←→(amorphous K4P3,amorphous K3P)that are proceed along with the electrochemical potassiation/depotassiation processes.Additionally,the corresponding KP alloys intermediates,such as the amorphous phases of K_(4)P_(3),K_(3)P,and the nonstoichiometric phases of“K_(1-x)P”,“K_(1+x)P”,“K_(4-x)P_(3)”are experimentally detected,which indicating various complicated K-P alloy species are coexisted and evolved with the sluggish electrochemical reaction kinetics,resulting in lower capacity of phosphorus-based anodes.Our findings offer some insights into the specific multi-phase evolution mechanism of alloying anodes that may be generally involved in conversion-type electrode materials for PIBs.

Revealing the effect of electrolyte coordination structures on the intercalation chemistry of batteries

In-depth understanding of the electrolyte-dependent intercalation chemistry in batteries through direct operando/in situ characterizations is crucial for the development of the high-performance batteries.Herein,taking the Al/graphite battery as a model system,the effect of electrolyte coordination structure on the intercalation processes has been investigated over the batteries with either 1-hexyl-3-methylimidazolium chloride(HMICl)-AlCl_(3) or 1-ethyl-3-methylimidazolium chloride(EMICl)-AlCl_(3) ionic liquid electrolyte using operando X-ray photoelectron spectroscopy(XPS)and X-ray diffraction.With a weaker anion-cation interaction in HMI-based electrolyte,the XPS-derived atomic ratio between cointercalated N and intercalated Al is 0.9,which is lower than 1.6 for EMI-based electrolyte.Attributed to the additional de-solvation process,the batteries with the HMI-based electrolyte show a lower ionic diffusion rate,capacity,and cycling performance,which agree with the operando characterization results.Our findings highlight the critical role of the electrolyte coordination structure on the(co-)intercalation chemistry.

Quasi-Solid-State Ion-Conducting Arrays Composite Electrolytes with Fast Ion Transport Vertical-Aligned Interfaces for All-Weather Practical Lithium-Metal Batteries

The rapid improvement in the gel polymer electrolytes(GPEs)with high ionic conductivity brought it closer to practical applications in solid-state Li-metal batteries.The combination of solvent and polymer enables quasi-liquid fast ion transport in the GPEs.However,different ion transport capacity between solvent and polymer will cause local nonuniform Li+distribution,leading to severe dendrite growth.In addition,the poor thermal stability of the solvent also limits the operating-temperature window of the electrolytes.Optimizing the ion transport environment and enhancing the thermal stability are two major challenges that hinder the application of GPEs.Here,a strategy by introducing ion-conducting arrays(ICA)is created by vertical-aligned montmorillonite into GPE.Rapid ion transport on the ICA was demonstrated by 6Li solid-state nuclear magnetic resonance and synchrotron X-ray diffraction,combined with computer simulations to visualize the transport process.Compared with conventional randomly dispersed fillers,ICA provides continuous interfaces to regulate the ion transport environment and enhances the tolerance of GPEs to extreme temperatures.Therefore,GPE/ICA exhibits high room-temperature ionic conductivity(1.08 mS cm^(−1))and long-term stable Li deposition/stripping cycles(>1000 h).As a final proof,Li||GPE/ICA||LiFePO_(4) cells exhibit excellent cycle performance at wide temperature range(from 0 to 60°C),which shows a promising path toward all-weather practical solid-state batteries.

Modification of NASICON Electrolyte and Its Application in Real Na-Ion Cells

The low ionic conductivity of solid-state electrolytes(SSEs)and the inferior interfacial reliability between SSEs and solid-state electrodes are two urgent challenges hindering the application of solid-state sodium batteries(SSSBs).Herein,sodium(Na)super ionic conductor(NASICON)-type SSEs with a nominal composition of Na_(3+2x)Zr_(2-x)MgxSi_(2)PO_(12) were synthesized using a facile two-step solid-state method,among which Na_(3.3)Zr_(1.85)Mg_(0.15)Si_(2)PO_(12)(x=0.15,NZSP-Mg_(0.15))showed the highest ionic conductivity of 3.54mS∙cm^(-1) at 25℃.By means of a thorough investigation,it was verified that the composition of the grain boundary plays a crucial role in determining the total ionic conductivity of NASICON.Furthermore,due to a lack of examination in the literature regarding whether NASICON can provide enough anodic electrochemical stability to enable high-voltage SSSBs,we first adopted a high-voltage Na_(3)(VOPO_(4))2F(NVOPF)cathode to verify its compatibility with the optimized NZSP-Mg_(0.15) SSE.By comparing the electrochemical performance of cells with different configurations(low-voltage cathode vs high-voltage cathode,liquid electrolytes vs SSEs),along with an X-ray photoelectron spectroscopy evaluation of the after-cycled NZSP-Mg_(0.15),it was demonstrated that the NASICON SSEs are not stable enough under high voltage,suggesting the importance of investigating the interface between the NASICON SSEs and high-voltage cathodes.Furthermore,by coating NZSP-Mg_(0.15) NASICON powder onto a polyethylene(PE)separator(PE@NASICON),a 2.42 A∙h non-aqueous Na-ion cell of carbon|PE@NASICON|NaNi_(2/9)Cu_(1/9)Fe_(1/3)Mn_(1/3)O_(2) was found to deliver an excellent cycling performance with an 88%capacity retention after 2000 cycles,thereby demonstrating the high reliability of SSEs with NASICON-coated separator.

Revealing the correlation between structure evolution and electrochemical performance of high-voltage lithium cobalt oxide

Lithium cobalt oxide(LCO)is the dominating cathode materials for lithium-ion batteries(LIBs)deployed in consumer electronic devices for its superior volumetric energy density and electrochemical performances.The constantly increasing demands of higher energy density urge to develop high-voltage LCO via a variety of strategies.However,the corresponding modification mechanism,especially the influence of the long-and short-range structural transitions at high-voltage on electrochemical performance,is still not well understood and needs further exploration.Based on ss-NMR,in-situ X-ray diffraction,and electrochemical performance results,it is revealed that the H3 to H1-3 phase transition dictates the structural reversibility and stability of LCO,thereby determining the electrochemical performance.The introduction of La and Al ions could postpone the appearance of H1-3 phase and induce various types of local environments to alleviate the volume variation at the atomic level,leading to better reversibility of the H1-3 phase and smaller lattice strain,and significantly improved cycle performance.Such a comprehensive long-range,local,and electronic structure characterization enables an in-depth understanding of the structural evolution of LCO,providing a guiding principle for developing high-voltage LCO for high energy density LIBs.

Reversible potassium storage in ultrafine CF_(x): A superior cathode material for potassium batteries and its mechanism

Current studies of cathodes for potassium batteries(PBs) mainly focus on the intercalation-type materials.The conversion-type materials that possess much higher theoretical capacities are rarely discussed in previous literatures.In this work,carbon fluoride(CF_x) is reported as a high capacity conversion-type cathode for PBs for the first time.The material delivers a remarkable discharge capacity of>250 mAh g^(-1) with mid-voltage of 2.6 V at 20 mA g^(-1).Moreover,a highly reversible capacity of around 95 mAh g^(-1) is achieved at 125 mA g^(-1) and maintained for 900 cycles,demonstrating its excellent cycling stability.The mechanism of this highly reversible conversion reaction is further investigated by nuclear magnetic resonance spectra,X-ray diffraction,and transmission electron microscopy studies.According to the analyses,the C-F bond in the cycled material is different from that in the pristine state,which presents relatively higher reversibility.This finding offers important insights for further improving the performance of the CF_x.This work not only demonstrates the CF_x as a high performance cathode for PBs,but also paves a new avenue of exploring conversion-type cathodes for high energy density PBs.

The origins of kinetics hysteresis and irreversibility of monoclinic Li_(3)V_(2)(PO_(4))_(3)

Monoclinic Li_(2)V_(2)(PO_(4))_(3);is a promising cathode material with complex charge–discharge behavior.Previous structural investigation of this compound mainly focuses on local environments;while the reaction kinetics and the driving force of irreversibility of this material remain unclear.To fully understand the above issues,both the equilibrium and the non-equilibrium reaction routes have been systematically investigated in this study.Multiple characterization techniques including X-ray diffraction,variable temperature(spinning rate)and ex/in situ ^(7)Li,^(31)P solid state NMR have been employed to provide comprehensive insights into kinetics,dynamics,framework structure evolution and charge ordering,which is essential to better design and application of lithium transition metal phosphate cathodes.Our results suggest that the kinetics process between the non-equilibrium and the quasi-equilibrium delithiation pathways from Li_(2)V_(2)(PO_(4))_(3);to V_(2)(PO_(4))_(3);is related with a slow relaxation from two-site to one-site delithiation.More importantly,it has been demonstrated that the irreversibility in this system is not solely affected by cation and/or charge ordering/disordering,but mainly driven by framework structure distortion.

铌酸锂调控固态电解质电场结构促进锂离子高效传输

聚合物基固态电解质得益于其易加工性,最有希望应用于下一代固态锂金属电池.目前,聚合物基态电解质的离子电导率提升策略多为加入导锂陶瓷以构建离子传输通道,其提升程度有限.电场在锂离子输运过程中存在重要影响,目前研究中有关电场对锂离子传输的影响机制尚不明确.本文将兼具高离子电导率和高介电常数的铌酸锂嵌入聚偏氟乙烯基体中,设计了一种新型复合固态电解质.铌酸锂颗粒有效调节电解质内部电场结构,增强了离子输运方向电场强度,实现了离子电导率的大幅提升(7.39×10^(-4)S cm^(-1),25℃).该电解质匹配高镍正极和锂金属负极的固态电池可稳定循环1000次以上,容量保持率为72%.该研究为设计下一代固态锂电池用高离子电导复合固态电解质提供了新的策略.

Lithium-ion spontaneous exchange and synergistic transport in ceramic-liquid hybrid electrolytes for highly efficient lithium-ion transfer

Ceramic electrolytes are important in ceramic-liquid hybrid electrolytes(CLHEs),which can effectively solve the interfacial issues between the electrolyte and electrodes in solid-state batteries and provide a highly efficient Li-ion transfer for solid–liquid Li metal batteries.Understanding the ionic transport mechanisms in CLHEs and the corresponding role of ceramic electrolytes is crucial for a rational design strategy.Herein,the Li-ion transfer in the ceramic electrolytes of CLHEs was confirmed by tracking the 6Li and 7Li substitution behavior through solid-state nuclear magnetic resonance spectroscopy.The ceramic and liquid electrolytes simultaneously participate in Li-ion transport to achieve highly efficient Li-ion transfer in CLHEs.A spontaneous Li-ion exchange was also observed between ceramic and liquid electrolytes,which serves as a bridge that connects the ceramic and liquid electrolytes,thereby greatly strengthening the continuity of Li-ion pathways in CLHEs and improving the kinetics of Li-ion transfer.The importance of an abundant solid–liquid interface for CLHEs was further verified by the enhanced electrochemical performance in LiFePO4/Li and LiNi0.8Co0.1Mn0.1O2/Li batteries from the generated interface.This work provides a clear understanding of the Li-ion transport pathway in CLHEs that serves as a basis to build a universal Li-ion transport model of CLHEs.