Mn(II) deposition on anodes and its effects on capacity fade in spinel lithium manganate–carbon systems

Transition metal (TM) ions dissolution from positive electrodes, migration to and deposition on negative electrodes, followed by Mn-catalyzed reactions of solvents and anions, with loss of Li + ions, is a major degradation (DMDCR) mechanism in Li-ion batteries (LIBs) with spinel positive electrode materials. While the details of the DMDCR mechanism are still under debate, it is clear that HF and other acid species' attack is the main cause in solutions with LiPF 6 electrolyte. We first review the work on various mitigation measures for the DMDCR mechanism, now spanning more than two decades. We then discuss recent progress on our understanding of Mn species in electrolyte solutions and the extension of a mitigation measure first proposed by Tarascon and coworkers in 1999, namely chelation of TM cations, to Mn cation trapping, HF scavenging, and alkali metal ions dispensing multi-functional materials. We focus on practicable, drop-in technical solutions, based on placing such materials in the inter-electrode space, with significant benefits for LIBs performance: increased capacity retention during operation at room and above-ambient temperatures as well as robust (both maximally ionically conducting and electronically insulating) solid-electrolyte interfaces, having reduced charge transfer and film resistances at both negative and positive electrodes. We illustrate the multifunctional materials approach with both new and previously published data. We also discuss and offer our evaluation regarding the merits and drawbacks of the various mitigation measures, with an eye for practically relevant technical solutions capable to meet both the performance requirements and cost constraints for commercial LIBs, and end with recommendations for future work. Li-ion batteries (LIBs) dominate the global market for energystorage devices nowadays and are used in a variety of applications, ranging from portable consumer electronics, to electrical grid storage, to load-levelling and electrified vehicles.1 Electrified vehicles are the most demanding among all LIBs applications in terms of both duty cycle and durability, since the batteries are subjected to a wide range of temperatures and charging/discharging rates, while customers expect a 10 years lifetime. Incessant research on various positive and negative active materials resulted in several promising electrode materials with various crystal structures and chemistries being developed over the past decades, such as layered (LiCoO 2 , LiNi 1-x-y Co x Al y O 2 , Ni 1-x-y Co x Mn y O 2 ), spinel (LiMn 2 O 4 , a.k.a. LMO; LNi 0.5 Mn 1.5 O 2 , a.k.a. LNMO), and olivine (LiFePO 4, LiVPO 4 ) for positive, as well as graphite, silicon, silicon-oxide, and lithium titanate for negative electrodes.2 New developments in electrode materials notwithstanding, LIBs for automotive transportation still need considerable improvements in terms of both performance and durability. Among transition metal (TM) oxide cathodes, LiMn 2 O 4 spinel would be most suited for automotive power cells due to i...

Section: A6316mentioning

confidence: 99%

Review—Multifunctional Materials for Enhanced Li-Ion Batteries Durability: A Brief Review of Practical Options

Banerjee

Shilina

Ziv

et al. 2017

“…27-29 for a review). The released Mn can be directly observed in the SEI on delithiated graphite electrodes harvested from cycled cells using fluorescence, 30 X-ray absorption, 28,29,31 and magnetic resonance spectroscopies. 29 In the SEI the Mn II ion is coordinated by six oxygen atoms, and has several Li + ions nearby; further away from the ion, fluorine atoms and protons are observed.…”

mentioning

confidence: 99%

Transition Metal Dissolution, Ion Migration, Electrocatalytic Reduction and Capacity Loss in Lithium-Ion Full Cells

Gilbert

Shkrob

Abraham

2017

385

501

Continuous operation of full cells with layered transition metal (TM) oxide positive electrodes (NCM523) leads to dissolution of TM ions and their migration and incorporation into the solid electrolyte interphase (SEI) of the graphite-based negative electrode. These processes correlate with cell capacity fade and accelerate markedly as the upper cutoff voltage (UCV) exceeds 4.30 V. At voltages ≥4.4 V there is enhanced fracture of the oxide during cycling that creates new surfaces and causes increased solvent oxidation and TM dissolution. Despite this deterioration, cell capacity fade still mainly results from lithium loss in the negative electrode SEI. Among TMs, Mn content in the SEI shows a better correlation with cell capacity loss than Co and Ni contents. As Mn ions become incorporated into the SEI, the kinetics of lithium trapping change from power to linear at the higher UCVs, indicating a large effect of these ions on SEI growth and implicating (electro)catalytic reactions. We estimate that each Mn II ion deposited in the SEI causes trapping of ∼10 2 additional Li + ions thereby hastening the depletion of cyclable lithium ions. Using these results, we sketch a mechanism for cell capacity fade, emphasizing the conceptual picture over the chemical detail. Increasing the energy and power density of Li-ion batteries (LIBs) for transportation applications is desirable for extending driving range and for providing the burst of power required for vehicle acceleration.1-3 Layered transition metal (TM) oxides containing Co, Mn, and Ni are promising high-energy electrode materials, as they exhibit theoretical oxide-specific capacities >200 mAh/g and can be cycled to potentials exceeding 4.50 V vs. Li/Li + . 4,5 However, the performance deterioration of full cells, in which these oxides are paired with a graphite (Gr) negative electrode, increases markedly at potentials exceeding 4.30 V, limiting their wider use as high-energy cathode materials.6,7 Therefore, it is imperative to examine the causes for their performance loss at high voltages. In this study we aim at understanding both the phenomenology and mechanism of capacity loss; mitigation of this loss will be the focus of future articles.Several possible causes for cell performance degradation have been identified over the years. These causes include, but are not limited to (i) TM oxide structure changes leading to voltage fade, 8 (ii) buildup of electrode surface films, especially the solid-electrolyte interphases (SEIs) 9,10 at the negative electrode, leading to Li + inventory depletion and/or impedance rise, 11-13 (iii) decomposition of the electrolyte, [14][15][16] (iv) pitting corrosion of aluminum current collectors, 17-19 (v) binder destabilization leading to delamination of electrode coatings, and (vi) dissolution of electrode-active materials. [20][21][22][23] This last source, especially the dissolution of Mn and its deposition in the negative electrode SEI, has been shown to be particularly detrimental to cell performance. [24][25][26] All steps o...

“…This "dialog" between both electrodes was proposed as creating a "shuttle" which could damage cell performance. 6 Li et al recently found that oxidized species from LiNi 0.5 Mn 1.5 O 4 caused severe parasitic reactions on the Li 4 Ti 5 O 12 electrode using an innovative "pseudo-full cell" configuration. 7 When NMC/graphite Li-ion cells are operated at a cutoff potential higher than 4.2 V, severe impedance increase can be the main contributor to cell failure instead of conventional mechanisms, like loss of Li inventory, that dominate in low voltage cells.…”

mentioning

confidence: 99%

“…This interaction has been shown to be detrimental to cell performance. [2][3][4][5] Another proposed example is CO 2 generation at the positive electrode followed by reduction at the negative electrode. This "dialog" between both electrodes was proposed as creating a "shuttle" which could damage cell performance.…”

mentioning

confidence: 99%

Interactions between Positive and Negative Electrodes in Li-Ion Cells Operated at High Temperature and High Voltage

Xiong

Petibon

Nie

et al. 2016

121

125

When NMC/graphite Li-ion cells are operated at elevated temperature or at a cutoff potential above 4.2 V, electrolyte oxidation becomes increasingly severe leading to gaseous products and other oxidized species. These generated gas products and oxidized species can migrate to, and then interact with, the negative electrode. A variety of cell formats (pouch cells, symmetric cells and coin cells) as well as pouch bags, containing only a delithiated positive electrode or a lithiated negative electrode, were used to investigate electrode/electrode interactions. Open circuit potential measurements during high temperature storage, ex-situ measurements of gas volume produced versus time, gas chromatography-mass spectrometry (GC-MS) of the gases produced and electrochemical impedance spectroscopy (EIS) of the electrodes versus time were performed. During storage at 60 • C, pouch bags containing only a lithiated negative electrode and electrolyte produced no gas while charged full pouch cells produced some gas and pouch bags containing only a delithiated positive electrode and electrolyte produced a significant amount of gas. The predominant gas produced in the positive electrode pouch bags was CO 2 while virtually no CO 2 was detected in the gases evolved in the charged full cell, suggesting that the negative electrode in the full cell consumes CO 2 generated at the charged positive electrode. In addition, the impedance of the surface film on the charged positive electrodes in the pouch bags increased at least three times more than the positive electrodes in the charged pouch cells, even though they were both in contact with electrolyte for the same period of time. These impedance results suggest that oxidized species created at the positive electrode in the pouch bag remain in the vicinity of the positive electrode and create a high impedance film possibly a rock salt surface layer, while the same species migrate to the negative and are "consumed" in the pouch cell where the impedance of the positive electrode remains small. These interactions are apparently essential for the health of a NMC/graphite Li-ion pouch cell when operated at an elevated temperature or at a cutoff voltage above 4. Increasing evidence show that interactions between positive and negative electrodes exist in full Li-ion cells.1 A well-known example is Mn dissolution from the positive electrode and its subsequent deposition at the negative electrode. This interaction has been shown to be detrimental to cell performance.2-5 Another proposed example is CO 2 generation at the positive electrode followed by reduction at the negative electrode. This "dialog" between both electrodes was proposed as creating a "shuttle" which could damage cell performance. When NMC/graphite Li-ion cells are operated at a cutoff potential higher than 4.2 V, severe impedance increase can be the main contributor to cell failure instead of conventional mechanisms, like loss of Li inventory, that dominate in low voltage cells. [8][9][10][11][12] It is our opinion that the pr...