Atomic layer deposition of solid-state electrolyte coated cathode materials with superior high-voltage cycling behavior for lithium ion battery application

227

135

Despite the extensive commercial use of Li 1-x Ni 1-y-z Mn z Co y O 2 (NMC) as the positive electrode in Li-ion batteries, and its long research history, its fundamental transport properties are poorly understood. These properties are crucial for designing high energy density and high power Li-ion batteries. Here, the transport properties of NMC 333 and NMC 523 are investigated using impedance spectroscopy and DC polarization and depolarization techniques. The electronic conductivity is found to increase with decreasing Li-content (increasing state-of-charge) from ∼10 −7 Scm −1 to ∼10 −2 Scm −1 over Li concentrations x = 0.00 to 0.75, corresponding to an upper charge voltage of 4.8 V with respect to Li/Li + . The lithium ion diffusivity is at least one order of magnitude lower, and decreases with increasing x to at x = ∼0.5. The ionic conductivity and diffusivity obtained from the two measurements techniques (EIS and DC) Cathodes having high energy and power density, adequate safety, excellent cycle life, and low cost are a critical need for Li-ion batteries to enable the commercialization of electric transportation and stationary storage.1 Towards this end, much previous research focused on the development of LiNi 1-x Co x O 2 (NC) 2-10 cathode due to its high capacity (∼275 mAh/g) and favorable operating cell voltage (4.3 V vs. Li/Li + ), which is within the voltage stability window of current liquid electrolytes, and lower cost than LiCoO 2 . Despite extensive optimization, e.g., with respect to the Ni/Co ratio, 2-10 NC suffers from poor structural stability during electrochemical cycling. 11Significant efforts were subsequently focused on improving structural stability and electrochemical performance by partial substitution Mn 12-17 (electrochemically inactive in this compound over the operating cell voltage window). Thus our objective in this work is to systematically characterize and interpret the transport properties of NMC 333 and NMC 523 . We use additive-free, single phase sintered samples in which the extrinsic effects due to binders, conductive additives, and particle microstructures that may be present in composite electrodes are avoided. Using electron blocking and ionic blocking cell configurations, respectively, and electrochemical impedance spectroscopy and DC polarization and depolarization techniques (see Table I), we deconvolute the electronic and ionic conductivities of NMC 333 and NMC 523 as a function of temperature and Li content, up to a lithium deficiency of x = 0.75, which corresponds to high charge voltages of 4.7 V and 4.8 V for NMC 333 and NMC 523 respectively. Our sample configuration permits measurement of single-phase properties up to delithiation levels (state-of-charge) where electrochemically-induced microfracture intrudes. Electronic conductivity was not apparently affected by these effects, whereas ionic transport shows an apparent increase beyond x = 0.50 which we attribute to fast transport paths created by microfracture. • C for 12 h in ambient atmosphere, preceded by h...

mentioning

confidence: 99%

mentioning

confidence: 99%

Characterization of Electronic and Ionic Transport in Li_1-_xNi_0.33Mn_0.33Co_0.33O₂(NMC₃₃₃) and Li_1-_xNi_0.50Mn_0.20Co_0.30O₂(NMC₅₂₃) as a Function of Li Content

Amin

Chiang

2016

227

135

“…Determining Entropic Heat Flow.-In order to differentiate between the parasitic heat flow during charge and discharge, it is necessary to know the entropic heat flow during both charge and discharge given bẏ q entropy ± =q total ± −q over potential ± −q parasitic ± [5] where + denotes charge and -discharge. However,q parasitic± was the original quantity of interest, and it is therefore not possible to calculatė q entropy ± exactly.…”

Section: Electrochemical and Calorimetrymentioning

confidence: 99%

“…Metal oxide surface coatings such as Al 2 O 3 have been found to improve the stability of this interface, mitigate electrolyte oxidation, improve cycling performance and scavenge HF. [4][5][6][7][8] Selected ratios of transition metals in Li(Ni 1-x-y Mn x Co y )O 2 (NMC) positive electrodes can also lower the reactivity of the electrode surface with electrolyte at high potentials. 9,10 Isothermal microcalorimetry is a very useful tool to probe reactions in electrochemical cells in-situ in a non-destructive manner.…”

mentioning

confidence: 99%

The Effect of Different Li(Ni_1-x-yMn_xCo_y)O₂Positive Electrode Materials and Coatings on Parasitic Heat Flow as Measured by Isothermal Microcalorimetry, Ultra-High Precision Coulometry and Long Term Cycling

Glazier

Nelson

Allen

et al. 2017

Isothermal microcalorimetry is used to investigate the effect of different Li(Ni 1-x-y Mn x Co y )O 2 materials (NMC442, NMC532, NMC622) and coatings (Al 2 O 3 and a proprietary high voltage coating) on parasitic reactions that occur in Li-ion pouch type cells. NMC/graphite pouch cells were prepared with a typical organic carbonate-based electrolyte containing a well-known additive blend and were tested up to 4.4 V at 40 • C. A new method of extracting the parasitic heat flow during both charge and discharge is introduced. Differences between charge and discharge parasitic heat flow yielded more insight into the behavior of high voltage parasitic reactions. Ultra-high precision coulometry, long-term charge discharge cycling, in-situ gas measurements, and electrochemical impedance spectroscopy were also used to compare the observed heat flow to well-known performance metrics. All coated cell types performed significantly better than uncoated NMC442/graphite cells. It was found that the magnitude of the parasitic heat flows did not correlate as expected to the precision coulometry results nor to the long term cycling results. In particular, cells with Al 2 O 3 -coated NMC622 had the highest parasitic heat flow among the cells with coated electrodes but competed for best performance in the cycling tests. High voltage lithium ion batteries have become a focus of academic and industrial research in order to meet the increasing demand for high energy density, low cost and long lifetime energy storage applications. In order to increase the operational voltage of lithium ion cells, all components must be as electrochemically stable as possible in order to prevent unwanted parasitic reactions within the cell, especially at high potentials. Arguably one of the most effective solutions to minimizing parasitic reactions and improving cell lifetime has been the addition of small amounts of additives to typical electrolytes already used in research and industry.1-3 These additives typically: are incorporated at a few percent by weight, introduce little to no change in the manufacturing process, and form protective passivating films known as the solid-electrolyte interphases (SEI) on both the positive and negative electrodes during cell operation. Although extensively studied, the mechanisms and chemical pathways responsible for the SEI films and the observed changes in performance caused by electrolyte additives are relatively poorly understood.Another common technique to reduce parasitic reactions is to alter the electrode materials in order to create a more electrochemically stable interface between the electrolyte and the highly delithiated positive electrode during high voltage operation. Metal oxide surface coatings such as Al 2 O 3 have been found to improve the stability of this interface, mitigate electrolyte oxidation, improve cycling performance and scavenge HF.4-8 Selected ratios of transition metals in Li(Ni 1-x-y Mn x Co y )O 2 (NMC) positive electrodes can also lower the reactivity of the electrode surface with ...

“…[16][17][18][19] Another approach to improve cell stability is the application of an inorganic coating onto the NMC surface. [23][24][25][26][27][28][29] For example, Arumugam et al reported that a surface coating of Al 2 O 3 greatly improves NMC622/graphite cell performance. 24 Whereas both of these approaches have proven to be quite valuable, further improvements to the lifetime of NMC-containing cells at high voltages are still desired.…”

mentioning

confidence: 99%

Measuring Oxygen Release from Delithiated LiNi_xMn_yCo_1-x-yO₂and Its Effects on the Performance of High Voltage Li-Ion Cells

Xiong

Ellis

et al. 2017

There can be a trade-off between the lifetime and energy density of LiNi x Mn y Co 1-x-y O 2 (NMC)-containing cells that depends on their upper cutoff voltage. This work applies thermogravimetric analysis coupled with mass spectrometry (TGA-MS) to measure the release of oxygen from delithiated NMC electrode materials at high electrode potentials, i.e., low lithium content. This release is observed at relatively mild temperatures as low as 40 • C. The amount of oxygen released is greatly limited using single crystal NMC particles. Electrochemical measurements demonstrate a correlation between TGA-MS results and the cycling performance of NMC/graphite cells. X-ray photoelectron spectroscopy complements the TGA-MS results and provides evidence of the solid electrolyte interphase decomposition. The results in this work offer strong support that the release of oxygen from NMC can cause oxidative decomposition of the electrolyte and is a major reason why high voltage cells can generate gas and can have poor capacity retention. There is a need for longer-lasting and higher energy density lithium-ion cells for electrified vehicles and grid energy storage applications.1-3 Layered LiNi x Mn y Co 1-x-y O 2 (NMC) materials make good positive electrodes on account of their well-balanced properties of high specific capacity, moderate cost, and good safety.4-9 As a result, NMC/graphite cells have become a ubiquitous part of our society. However, to avoid electrolyte and material degradation, commercially available NMC-containing cells normally operate at a much lower voltage (typically ≤ 4.2 V) than their theoretical limit. This is because trade-offs exist between the lifetime and the energy density of a NMC cell that depends on its upper cutoff voltage. 10,11 One method to improve existing NMC technology is the development of new electrolyte solution chemistries. The use of new solvent blends and the introduction of electrolyte additives are two practical ways to improve the lifetime of high voltage NMC Li-ion cells. 12-22Ma et al. and Nelson et al. found that a ternary additive combination can greatly improve NMC442/graphite cell performance at high voltage.11-13 Xia et al. reported that fluorinated electrolyte and ECfree electrolyte also enhance NMC/graphite cell performance. [16][17][18][19] Another approach to improve cell stability is the application of an inorganic coating onto the NMC surface. [23][24][25][26][27][28][29] For example, Arumugam et al. reported that a surface coating of Al 2 O 3 greatly improves NMC622/graphite cell performance. 24 Whereas both of these approaches have proven to be quite valuable, further improvements to the lifetime of NMC-containing cells at high voltages are still desired.Great effort has been put forward to understand the chemical mechanisms behind the degradation of high voltage NMC cells. Analytical approaches have included monitoring impedance growth, 12,13,30-38 the volume and composition of gases produced, 39-43 the heat flow [44][45][46][47][48] and the leakage current 49,50 du...