From Intrinsic to Extrinsic Design of Lithium-Ion Battery Layered Oxide Cathode Material Via Doping Strategies

From Intrinsic to Extrinsic Design of Lithium-Ion Battery Layered Oxide Cathode Material Via Doping Strategies
Author: Chul-Ho Jung
Publisher: Springer Nature
Total Pages: 72
Release: 2022-10-20
Genre: Technology & Engineering
ISBN: 9811963983

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This book addresses the comprehensive understanding of Ni-rich layered oxide of lithium-ion batteries cathodes materials, especially focusing on the effect of dopant on the intrinsic and extrinsic effect to its host materials. This book can be divided into three parts, that is, 1. overall understanding of layered oxide system, 2. intrinsic effect of dopant on layered oxides, and 3. extrinsic effect of dopant on layered oxides. To truly understand and discover the fundamental solution (e.g. doping) to improve the Ni-rich layered oxides cathodic performance, understanding the foundation of layered oxide degradation mechanism is the key, thus, the first chapter focuses on discovering the true degradation mechanisms of layered oxides systems. Then, the second and third chapter deals with the effect of dopant on alleviating the fundamental degradation mechanism of Ni-rich layered oxides, which we believe is the first insight ever been provided. The content described in this book will provide research insight to develop high-performance Ni-rich layered oxide cathode materials and serve as a guide for those who study energy storage systems. ​

Advanced High-nickel Layered Oxide Cathodes for Lithium-ion Batteries

Advanced High-nickel Layered Oxide Cathodes for Lithium-ion Batteries
Author: Wangda Li
Publisher:
Total Pages: 322
Release: 2018
Genre:
ISBN:

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The growing demand for rechargeable Li-ion batteries with higher performance metrics has spurred intensive research efforts. In the quest for safe and low-cost cathode materials with desirable energy/power capabilities, high-nickel layered oxides (LiNi [subscript 1- x] M [subscript x] O2; x 0.5, M = Co, Mn, Al) are among the most promising candidates. However, limited cycle/calendar life especially at elevated temperatures and poor thermal-abuse tolerance are serious challenges for their practical applications. This dissertation focuses on the fundamental understanding of electrode-electrolyte incompatibility for high-Ni LiNi [subscript 1-x] M [subscript x] O2 with state-of-the-art nonaqueous electrolytes at deep charge during battery operation, and corresponding strategies for inhibiting the associated unwanted parasitic reactions and enabling excellent cyclability/safety in practical cell configurations. First, we reveal the dynamic behaviors of the CEI on LiNi [subscript 0.7] Co [subscript 0.15] Mn [subscript 0.15] O2 driven by conductive carbon in composite electrodes. Secondary-ion mass spectrometry (SIMS) shows that the CEI, initially formed on carbon black from spontaneous reactions with the electrolyte prior to cell operation, passivates the cathode through a mutual exchange of surface species. By tuning the CEI thickness, we demonstrate its impact on the evolution of the electrode-electrolyte interface during cell operation at high voltages. Next, we study the evolution of the SEI on anodes, where metallic Li deposition causes capacity fade and safety issues. On graphite harvested from pouch cells paired with LiNi [subscript 0.61] Co [subscript 0.12] Mn [subscript 0.27] O2 after 3,000 cycles, SIMS reveals large Li deposition in the SEI, triggered by transition-metal cations dissolved from the cathode and migrated to the anode. With Al doping (~1 mol %) in LiNi [subscript 0.61] Co [subscript 0.12] Mn [subscript 0.27] O2, dissolution is effectively inhibited and superior long-term cyclability is achieved ( 80% after 3,000 cycles). With knowledge on both electrodes, we then conduct a comprehensive assessment on the long-term cyclability of high-Ni LiNi [subscript 0.7] Co [subscript 0.15] Mn [subscript 0.15] O2 and commercially established LiNi [subscript 0.8] Co [subscript 0.15] Al [subscript 0.05] O2 in pouch full cells (1,500 cycles). Various degradation processes leading to performance deterioration are carefully invesitgaeted. Based on the results, we identify key challenges, relative to NCA, for realizing a long service life of high-Ni NCM and corresponding mitigation strategies. Finally, we design tailored nonaqueous electrolytes based on exclusively aprotic acyclic carbonates free of ethylene carbonate (EC) and realize unusual thermal and electrochemical performance of an ultrahigh-nickel cathode (LiNi [subscript 0.94] Co [subscript 0.06] O2), reaching a specific capacity of 235 mA h g−1. By using two model electrolyte systems, we present assembled graphite|LiNi [subscript 0.94] Co [subscript 0.06] O2 pouch full cells with exceptional thermal stability, energy/power capabilities, and long service life

High-voltage Oxide Cathodes for High-energy-density Lithium-ion Batteries

High-voltage Oxide Cathodes for High-energy-density Lithium-ion Batteries
Author: Zehao Cui
Publisher:
Total Pages: 0
Release: 2023
Genre:
ISBN:

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The worldwide electrification of the automobile industry has been strongly pushing the advancement of lithium-ion batteries (LIBs) with high energy density and long service life. Since the cathode is currently the limiting electrode for energy density, safety, and cost of commercial LIBs, extensive efforts have been devoted into investigating next-generation high-performance cathode materials with high capacity and operating voltage. Among the pool of cathodes, high-nickel layered oxide cathodes, LiNixM1−xO2 (M = Co, Mn, Al, etc.; x > 0.7), are regarded as one of the most promising candidates. However, the practical viability of high-Ni cathodes is compromised by their air instability, fast structural and interfacial deteriorations during operation, poor thermal stability, and high cost. On the other hand, another promising cathode, high-voltage spinel LiNi0.5Mn1.5O4, exhibits better thermal and structural stabilities, but suffers from rapid performance degradations due to its high operating voltage of > 4.7 V vs. Li+/Li. This dissertation focuses on stabilizing the operation of high-Ni and high-voltage spinel cathodes with diverse modification strategies and advancing the understanding of the degradation mechanisms of cells with high-voltage cathodes assisted by state-of-the-art characterizations. First, the function of atomic scale zinc-doping in a high-Ni cathode LiNi0.94Co0.04Zn0.02O1.99 is investigated. The incorporation of Zn greatly mitigates the average voltage and capacity fade by ameliorating the anisotropic lattice distortion, enhancing the structural integrity, and reducing cathode-electrolyte side reactions. Moreover, Zn-doping is proved beneficial to improve the thermal stability. Second, a cobalt- and manganese-free LiNi0.93Al0.05Ti0.01Mg0.01O2 cathode is rationally designed, synthesized, and comprehensively investigated. Collectively, the use of Al, Ti, and Mg in the cathode enables a stable operation of practical full cells over 800 cycles by alleviating electrolyte decomposition reactions, transition-metal crossover, and active lithium loss. Third, single-element doped cathodes, viz., LiNi0.95Co0.05O2, LiNi0.95Mn0.05O2, and LiNi0.95Al0.05O2, along with undoped LiNiO2, are compared through a control of cutoff energy density to elucidate the role of dopants in high-Ni cathodes. Via a group of advanced analytical techniques, it is unveiled that one critical role of dopant is regulating the state-of-charge and the occurrence of H2–H3 phase transition of high-Ni cathodes, which essentially dictates the cycle stability. Finally, electrochemical modifications on the graphite anode and high-voltage spinel cathode are performed and characterized. The results suggest that the graphite anode interphase degradations caused by acidic and transition-metal crossover species generated from the cathode predominately contribute to the cell performance deterioration. Based on in-depth analyses, pathways towards long-life high-voltage full cells are pictured

High-nickel Layered Oxide Cathodes for High-performance Lithium-ion Batteries

High-nickel Layered Oxide Cathodes for High-performance Lithium-ion Batteries
Author: Qiang Xie (Ph. D.)
Publisher:
Total Pages: 0
Release: 2020
Genre:
ISBN:

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The ever-growing market of consumer electronics has been driving surging demand for higher-energy-density lithium-ion batteries (LIBs). Since cathode materials primarily dictate the energy density and cost, extensive investigations have been devoted to exploring advanced cathodes for high-performance LIBs. High-nickel layered oxides LiNi [subscript x] M [subscript 1-x] O2 (x ≥ 0.6, M = Co, Mn, etc.) are one of the most promising candidates and are being extensively pursued. Unfortunately, the practical applicability of high-Ni cathodes is seriously hampered by their poor cyclability, alarming susceptibility to thermal abuse, and decreased air-stability. This dissertation focuses on enhancing the stability of high-Ni cathodes with diverse strategies and advancing the scientific comprehension of high-Ni cathode materials. First, the effect of pillaring Mg-ion doping in the high-Ni cathode LiNi0.94Co0.06O2 is investigated. The incorporation of Mg greatly suppresses the anisotropic lattice collapse and maintains the integrity of cathode particles upon high-voltage cycling, significantly enhancing the cyclability. More importantly, the thermal stability of high-Ni cathodes is notably improved by Mg doping. Second, boron-based polyanion is employed to tune high-Ni cathodes. The introduction of boron-based polyanion enables a well-passivated boron/phosphorus-rich cathode-electrolyte interphase, which alleviates electrolyte corrosion on high-Ni cathodes and thus improves the cyclability. Meanwhile, the boron-based polyanion improves the air stability of high-Ni cathodes as well. Third, a well-designed phosphoric acid treatment approach is presented to modify the high-Ni cathode LiNi0.94Co0.06O2. The implemented treatment not only reduces the detrimental surface residual lithium, but also remarkably improves the electrochemical performance and long-term air-storage stability. Via a range of advanced analytical techniques, the underlying mechanisms involved on the improved performance are disclosed from interphasial and structural perspectives at the nanoscale. Finally, a comparative study is performed to unveil the stabilities of LiNi [subscript 1-x-y] Mn [subscript x] Co [subscript y] O2 (NMC) cathodes with different Ni contents at identical degrees of delithiation. The overall stabilities of two representative cathodes, LiNi0.8Mn0.1Co0.1O2 and LiNiO2, are evaluated with a rigorous control of an identical 70 mol % delithiation. The results suggest that NMC cathodes with higher-Ni contents may have better overall stability than low-Ni NMC cathodes at a given degree of delithiation, disparate from the prevailing belief that high-Ni cathodes with higher-Ni content have inherently reduced stabilities

High-nickel Layered Oxide Cathodes for High-energy-density Lithium-ion Batteries

High-nickel Layered Oxide Cathodes for High-energy-density Lithium-ion Batteries
Author: Jianyu Li (Ph. D. in chemical engineering)
Publisher:
Total Pages: 334
Release: 2019
Genre:
ISBN:

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The thriving energy-storage market has been motivating enormous efforts to advance the state-of-art lithium-ion batteries. The development of cathode materials, in particular, holds the key to realizing the high-energy-density and low-cost promise. Among the insertion-reaction cathodes currently in play, the layered oxides, especially the LiNiO2-based high-Ni type, are being intensively pursued as one of the most promising candidates. However, the high-Ni layered oxides inherently encounter a trade-off between capacity and stability – the higher the capacity contributed by the higher Ni content, the worse the electrochemical cyclability. This dissertation focuses on improving the stability of high-Ni layered oxide cathodes through multiple effective approaches. First, a practical doping method is presented by incorporating a small dose of Al into the layered structure, which significantly improves the electrochemical performance of the cathode. It reveals that Al-incorporation greatly enhances the stability of cathode-electrolyte-interphase (CEI) due to the modified cathode electronic structure. Furthermore, in-situ X-ray diffraction provides an operando evidence for the reduced lattice distortions during cycling with Al-incorporation. Second, lithium bis(oxalate) is employed as an effective electrolyte additive to improve the electrode-electrolyte-interphase stability. The well-tuned electrode-electrolyte interphase is featured with excellent robustness against electrochemical abuse. Moreover, the correlation between cathode-surface chemistry and anode-electrolyte interphase is revealed by studying the interphases at atomic level. Third, by constructing a dual-functional binder framework with a conductive polymer polyaniline, the high-Ni layered oxide cathodes exhibit significantly improved cyclability. This new binder framework not only promotes the rate performance even at low temperatures, but also effectively scavenges the acidic species in the electrolyte through a protonation process. Hence the cathode-surface reactivity is greatly suppressed and the rock-salt phase propagation into the bulk structure is considerably alleviated. Finally, in comparing with the state-of-art cathode (LiNi [subscript 0.8] Co [subscript 0.1] Mn [subscript 0.1] O2), the interphasial and structural evolution processes of high-Ni layered oxides (LiNi [subscript 0.94] Co [subscript 0.06] O2) are systematically investigated over the course of their service life (1,500 cycles). By applying advanced analytical techniques (e.g., Li-isotope labeling and region-of-interest method), the dynamic chemical evolution on the cathode surface is revealed with spatial resolution, and the correlation between lattice distortion and cathode-surface reactivity is established for the first time

Rational Design of Composite Cathodes and Functional Electrolytes for High-Energy Lithium-Metal Batteries

Rational Design of Composite Cathodes and Functional Electrolytes for High-Energy Lithium-Metal Batteries
Author: Panpan Dong
Publisher:
Total Pages: 188
Release: 2020
Genre: Cathodes
ISBN:

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Metallic lithium has been considered one of the most attractive anode materials for high-energy batteries because it has a low density (0.53 g cm8́23), the lowest reduction potential (8́23.04 V vs. the standard hydrogen electrode), and a high theoretical specific capacity (3,860 mAh g8́21). Chalcogen elements, such as sulfur and selenium, have been widely reported as promising cathode candidates for next-generation lithium-metal batteries (LMBs) that demonstrate much higher energy density than current lithium-ion batteries. However, lithium0́3chalcogen batteries still suffer from the loss of cathode active materials and the degradation of lithium metal anode owing to the shuttle effects of intermediate products (e.g., polysulfides and polyselenides), leading to fast capacity fading and poor cyclability. Moreover, for lithium metal anodes, the cracking of solid electrolyte interphase (SEI) layer during long cycling results in dead lithium formation and lithium dendrite growth, leading to poor Coulombic efficiency and potential safety issues. The abovementioned challenges hinder the commercialization of LMBs. To address these problems, various strategies have been developed to mitigate the dissolution/diffusion of redox intermediates and stabilize metallic lithium anodes. In this dissertation, sulfur- and selenium-based nanocomposites were synthesized and employed as advanced cathode materials for high-energy LMBs. The correlations between syntheses, properties, and performances of such chalcogen cathode materials were established by various characterization methods such as microstructural analyses, solid-state nuclear magnetic resonance, X-ray photoelectron spectroscopy, and nanoscale X-ray computed tomography. Additionally, the interfacial electrochemistry of lithium metal anodes and ionic liquid0́3based electrolytes is comprehensively investigated, revealing the effective stabilization and protection of lithium anode via the formation of an in situ SEI layer with specific compositions. Moreover, strategies for achieving novel solid polymer electrolytes with improved lithium-ion transference number were demonstrated, paving the way toward safe LMBs by mitigating lithium dendrite growth. This dissertation provides a combined strategy of advanced cathode design, electrolyte engineering, and lithium anode stabilization to develop high-energy LMBs for practical applications.

Gas-solid Interfacial Modification of Oxygen Activity in Layered Oxide Cathodes for Lithium-ion Batteries

Gas-solid Interfacial Modification of Oxygen Activity in Layered Oxide Cathodes for Lithium-ion Batteries
Author:
Publisher:
Total Pages:
Release: 2016
Genre:
ISBN:

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Lattice oxygen can play an intriguing role in electrochemical processes, not only maintaining structural stability, but also influencing electron and ion transport properties in high-capacity oxide cathode materials for Li-ion batteries. We report the design of a gas-solid interface reaction to achieve delicate control of oxygen activity through uniformly creating oxygen vacancies without affecting structural integrity of Li-rich layered oxides. Furthermore, theoretical calculations and experimental characterizations demonstrate that oxygen vacancies provide a favourable ionic diffusion environment in the bulk and significantly suppress gas release from the surface. The target material is achievable in delivering a discharge capacity as high as 301 mAh g-1 with initial Coulombic efficiency of 93.2%. After 100 cycles, a reversible capacity of 300 mAh g-1 still remains without any obvious decay in voltage. Our study sheds light on the comprehensive design and control of oxygen activity in transition-metal-oxide systems for next-generation Li-ion batteries.

Optimization of Spray Pyrolysis for the Synthesis of Cathode Materials for Lithium- and Sodium-ion Batteries

Optimization of Spray Pyrolysis for the Synthesis of Cathode Materials for Lithium- and Sodium-ion Batteries
Author: Kuan-Yu Shen
Publisher:
Total Pages: 146
Release: 2017
Genre: Electronic dissertations
ISBN:

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Energy storage in the 21st century has become one of the most critical requirements to maintain sustainable development and a growing global economy. Today, the advancement of lithium-ion batteries is being taken to the next level with targeted applications being electric vehicles (EVs) and grid storage. Current widespread application of EVs is primarily limited by their short range and high price, which are significantly driven by the cost of the battery pack. The cost of the battery pack is driven by the cost of the cathode material that empowers it.The most common conventional synthesis method of cathode materials is co-precipitation, which includes long processing time and complex steps. Moreover, poor batch-to-batch uniformity due to differences in solubility and diffusivity of precursors further hinders large-scale implementation. To reduce energy consumption during production, and improve homogeneity of the product, we use spray pyrolysis for synthesizing multi-component metal oxide cathode materials. Spray pyrolysis, a promising development for larger scale synthesis in industry, requires shorter residence time in the reactor, eliminates washing and purification steps, and achieves excellent batch-to-batch reproducibility.Lithium, manganese-rich layered cathode material (LMR-NMC) has been studied intensively in the past decades and is one of the most attractive cathode materials under development. Its ability to reach discharge capacity above 200 mAh g-1 and low cobalt content make it a promising candidate for cathode material of electric vehicles. 0.5Li2MnO3·0.5LiMn1/3Ni1/3Co1/3O2 (Li1.2Mn0.54Ni0.13Co0.13O2) is currently the most widely studied chemistry. Yet, as recently demonstrated, the materials suffer from an inherent layered-spinel phase change. This leads to capacity and voltage fade over extended cycling, and this shortcoming needs to be addressed before commercial implementation is feasible.In the first part of the dissertation, voltage fade was addressed by trace elemental doping. Results demonstrated for the first time that by selectively doping the LMR-NMC materials, voltage fade can be reduced. The aluminum doped Li1.2Mn0.54Ni0.13Co0.13O2 demonstrated improved capacity retention of 99.4 % comparing to 91.5 % of the undoped material after 100 cycles. Furthermore, Atomic Layer Deposition (ALD) was used to modify the surface of Li1.2Mn0.54Ni0.13Co0.13O2 with thin layer CeO2, aiming to decrease voltage and capacity fade by increasing the substrate conductivity and setting a barrier for metal dissolution. The optimal CeO2 film thickness was 2.5 nm deposited by 50 cycles of CeO2 ALD. The cyclic stability improved to 60 % capacity retention after 400 cycles at C/1 and 55 °C. The CeO2 coating also reduced voltage fade.In addition, with the rising interest in sodium-ion battery research, tunnel structure sodium manganese oxide cathode materials were synthesized via spray pyrolysis. The materials demonstrate rod-like morphology after annealing. Optimal electrochemical performance was obtained from the sample produced with a Na/Mn precursor ratio of 0.50, which yielded phase pure Na4Mn9O18 structure. A discharge capacity of 115 mAh g-1 is reached for this material in the first cycle and the material demonstrates good cycleability and rate performance. This demonstrates the versatility of spray pyrolysis and its ability to synthesize a wide range of material with different structure and morphology.In later part of the work, a low temperature flame spray pyrolysis (LT-FSP) process is developed for the synthesis of Li1.2Mn0.54Ni0.13Co0.13O2. High water content ethanol was used as a fuel and a swirl-stabilized burner was used to achieve stable operation at the low reactor temperature, which is lower than can be attained via traditional FSP. The effects of reactor temperature, which is controlled via altering ethanol concentration, on the physical properties and the electrochemical performances of the synthesized materials were characterized. Li1.2Mn0.54Ni0.13Co0.13O2 synthesized with 25 wt% ethanol showed the best results and delivered a discharge capacity of 203 mAh g-1 after 100 cycles under C/3. It also achieved good rate capability showing 201 mAh g-1 and 169 mAh g-1 under C/2 and C/1, which are comparable to state-of-the-art performances. The production rate of LT-FSP also reaches 90 g h-1.In addition, LT-FSP was used to investigate the seed loading density of slurry spray pyrolysis. Slurry spray pyrolysis is the only known solution to the hollow sphere issue that has challenged spray pyrolysis synthesis for decades, namely producing particles greater than 2 om size with a solid (non-hollow) but porous interior morphology. Tap densities achieved 1.1 g cc-1 with 32 wt% of seed loading, which is half the amount of what was previously demonstrated. Li1.2Mn0.54Ni0.13Co0.13O2 produced by slurry spray pyrolysis reproduces the electrochemical performance of the conventional spray pyrolysis, meeting or exceeding the performance of materials produced by co-precipitation.

Investigation of Cathodes for Next Generation High Energy

Investigation of Cathodes for Next Generation High Energy
Author: Minghao Zhang
Publisher:
Total Pages: 156
Release: 2017
Genre:
ISBN:

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Recently, anionic activity, oxygen redox reaction, has been discovered in the electrochemical processes, providing extra reversible capacity for lithium-rich layered oxide cathode. However, the huge irreversible capacity loss in the first charge-discharge cycle and voltage degradation during cycling process prevent their utilization in LIBs. Herein, modified carbonate co-precipitation synthesis without addition of chelating agent is introduced to obtain meso-structure controlled Li-rich layered oxides. This unique design not only decreases surface area compared with the sample with dispersive particles, but also increases overall structure mechanical stability compared with the sample with larger secondary particles as observed by TXM. As a result, the voltage decay and capacity loss during long term cycling have been minimized to a large extent. Gas-solid interface reaction is designed to achieve delicate control of oxygen activity through uniformly creating oxygen vacancies without affecting structural integrity of Li-rich layered oxides. Theoretical calculations and experimental characterizations demonstrate that oxygen vacancies provide a favorable ionic diffusion environment in the bulk and significantly suppress gas release from the surface. The target material is achievable in delivering a discharge capacity as high as 301 mAh g-1 with initial Coulombic efficiency of 93.2%. After 100 cycles, a reversible capacity of 300 mAh g-1 still remains without any obvious decay in voltage. We further design a path to remove the defects in the structure of Li-rich layered oxides by high temperature annealing. This treatment recovers the superstructure and average discharge voltage. The novel understanding of the structure metastability and reversibility phenomenon will provide clues for identifying more realistic pathway to fully address voltage decay issue of high-capacity Li-rich layered oxide electrodes. On the other hand, Magnesium-ion batteries (MIBs) have twofold volumetric energy density than that of lithium without the dendritic deposition morphology associated with Li, which makes MIBs attractive options. We investigate the feasibility of using anatase-phase TiO2 as an electrode material for MIBs. Electrochemical, microscopic, and spectroscopic analyses are performed in order to probe Mg-ion insertion as well as determine the limitation of TiO2 as a viable electrode material.

Enhancing Electrochemical Performance of Electrode Materials for Li-ion Batteries and Na-ion Batteries Via Thermodynamic Surface/Interface Contro

Enhancing Electrochemical Performance of Electrode Materials for Li-ion Batteries and Na-ion Batteries Via Thermodynamic Surface/Interface Contro
Author: Jiajia Huang
Publisher:
Total Pages: 215
Release: 2017
Genre:
ISBN:

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A facile and low-cost route based on thermodynamic principles of surface amorphous films (SAFs), intergrainular films (IGFs), and cation surface segregation benefits electrochemical performances of electrode materials for lithium-ion batteries and sodium-ion batteries. SAFs as a facile and generic surface modification method is utilized to significantly improve the rate performance and cycling stability of cathode materials for lithium-ion batteries. A thermodynamic framework of SAFs is proposed. These nanoscale SAFs form spontaneously and uniformly upon mixing and annealing at a thermodynamic equilibrium, and they exhibit a self-regulating or "equilibrium" thickness due to a balance of attractive and repulsive interfacial interactions acting on the films. Specially, spontaneous formation of nanoscale Li3PO4-based SAFs has been demonstrated in two proof-of-concept systems LiCoO2 and LiNi0.5Mn1.5O4. Furthermore, SAFs introduced by nitridation can also benefit the performance of TiO2 anode material for sodium-ion batteries. The amorphous intergrainular films (IGFs) are found in the system of Sn doped Si anode for lithium-ion batteries. The coexistence of IGFs and porous secondary structure (characterized by FIB/SEM on the cross section) results in an enhanced performance. SAFs and IGFs can be used to guide future experiments of other material systems. Utilizing anisotropic surface segregation to thermodynamically control the particle morphology and the surface composition is another economic, facile, and effective method to significantly improve the electrochemical performance of battery electrodes. WO3 doping and anisotropic surface segregation can change the facet relative surface energy to tailor the particle Wulff shape of LiMn1.5Ni0.5O4 spinel materials and the surface Mn/Ni ratio and benefits performances. The WO3 surface segregation can also improve Co-free Li-rich layered oxide Li1.13Ni0.3Mn0.57O2 cathode material performance. X-ray photoelectron spectroscopy in conjunction with ion sputtering has shown that W segregates to the particle surfaces and decreases the surface Ni/Mn atomic ratio; high-resolution transmission electron microscopy has further suggested that the segregation of W increases the structural disorder at the particle surfaces, which may also benefit the rate performance.