Cracking causing cyclic instability of LiFePO4 cathode material

Wang, Deyu; Wu, Xiaodong; Wang, Zhaoxiang; Chen, Liquan

doi:10.1016/j.jpowsour.2004.06.059

Cited by 306 publications

(218 citation statements)

References 12 publications

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“…ARTICLE represents the classic 'domino-cascade' mode. In contrast, large-sized particles are not so robust that the large mismatch in micron scale particles generally result in energy relaxation 38 , contributing to the emergence of cracks or structural dislocations, as some cracks were often found in many different reports 39,40 .…”

Section: Discussionmentioning

confidence: 99%

In operando tracking phase transformation evolution of lithium iron phosphate with hard X-ray microscopy

2014

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The delithiation reaction in lithium ion batteries is often accompanied by an electrochemically driven phase transformation process. Tracking the phase transformation process at nanoscale resolution during battery operation provides invaluable information for tailoring the kinetic barrier to optimize the physical and electrochemical properties of battery materials. Here, using hard X-ray microscopy-which offers nanoscale resolution and deep penetration of the material, and takes advantage of the elemental and chemical sensitivity-we develop an in operando approach to track the dynamic phase transformation process in olivine-type lithium iron phosphate at two size scales: a multiple-particle scale to reveal a rate-dependent intercalation pathway through the entire electrode and a single-particle scale to disclose the intraparticle two-phase coexistence mechanism. These findings uncover the underlying twophase mechanism on the intraparticle scale and the inhomogeneous charge distribution on the multiple-particle scale. This in operando approach opens up unique opportunities for advancing high-performance energy materials.

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Section: Discussionmentioning

confidence: 99%

In operando tracking phase transformation evolution of lithium iron phosphate with hard X-ray microscopy

2014

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“…In fact, fracturing has been observed in ex situ studies. 20,43 . After fracturing, a fresh surface of LiFePO 4 is exposed, enabling further delithiation.…”

Section: Inhomogeneity and Lithiation Mechanismsmentioning

confidence: 99%

Nanoscale Imaging of Lithium Ion Distribution During In Situ Operation of Battery Electrode and Electrolyte

et al. 2014

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The integration of renewable, and often intermittent, energy sources such as solar and wind into the energy landscape, as well as the electrification of transportation, requires dramatic advances in electrical energy conversion and storage technologies including fuel cells, batteries and supercapacitors. TEM detection of lithium through a liquid is difficult, because lithium is a weak elastic scatterer and multiple scattering from the liquid overwhelms the inelastic core-loss signal in electron energy-loss spectroscopy (EELS). In this work, we successfully observed the lithiation state by valence energy-filtered TEM (EFTEM), which probes the low-energy regime (~1-10 eV), and allows us to work in thicker liquid layers than core-level A Baseline for Electrochemistry in the TEMWe use a liquid cell holder developed by Protochips using chips we designed to mimic a typical electrochemical cell (Figure 1a-b). The tip of the holder is a microfluidic flow cell with silicon nitride viewing membranes that confine a liquid, shown in cross section in Figure 1a. Figure 1b illustrates the top chip, with three patterned electrodes optimized for electrochemical cycling and imaging. Traditional silicon-processing methods use a chromium adhesion layer and gold electrodes. However, chromium diffuses rapidly 6 through gold (especially at grain boundaries) and can affect and even dominate the electrochemical signal. In addition, high-atomic-number electrodes such as Pt and Au obscure imaging. Instead, we used a carbon working electrode which only weakly scatters electrons and is commonly used in bulk electrochemistry, and titanium adhesion layers under platinum reference and counter electrodes. This allows us to image through the electrode with little loss in spatial resolution and contrast, which is dominated by scattering in the liquid instead. As a practical matter, and discussed below, spatial resolution is often limited by the low doses needed to control radiation damage than by beam spreading in the cell.To demonstrate that in situ electrochemistry reproduces well-established criteria, we performed cyclic voltammetry of a film of platinum, shown in Figure 1c-d, in the TEM.This control experiment represents a test case for quantitative electrochemistry, since the features are surface effects -including hydrogen adsorption and desorption and oxide formation and reduction -which are sensitive to contaminants at the sub-monolayer level.The in situ electrochemistry reproduced the characteristic voltametric profile of a polycrystalline platinum electrode at an appropriate current scale, regardless of the electron beam. In thin liquid layers, the ohmic drop in the solution becomes significant, as evidenced by the slanted curve in Figure 1d. This implies an inherent compromise between the highest spatial resolution imaging and quantitative electrochemistry.Accounting for ohmic drops in solution, this setup replicates results of a conventional electrochemical cell while obtaining nanometer resolution. 7Having established the electroch...

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“…The volume change of crystalline lattice between LFP and fully delithiated FP is 6.5% 1 . Microcracks are often formed because of the stress inside the LFP cathodes during the repeated charge/discharge cycle, which is widely accepted as the major degradation mechanism of the LFP cathode 11 . The degradation could therefore be retarded by reducing the volume change of the crystalline lattice during the charge/discharge cycle.…”

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confidence: 99%

Accelerated discovery of cathode materials with prolonged cycle life for lithium-ion battery

Nishijima¹,

Ootani²,

Kamimura³

et al. 2014

Nat Commun

114

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Large-scale battery systems are essential for efficiently utilizing renewable energy power sources from solar and wind, which can generate electricity only intermittently. The use of lithium-ion batteries to store the generated energy is one solution. A long cycle life is critical for lithium-ion battery when used in these applications; this is different from portable devices which require 1,000 cycles at most. Here we demonstrate a novel co-substituted lithium iron phosphate cathode with estimated 70%-capacity retention of 25,000 cycles. This is found by exploring a wide chemical compositional space using density functional theory calculations. Relative volume change of a compound between fully lithiated and delithiated conditions is used as the descriptor for the cycle life. On the basis of the results of the screening, synthesis of selected materials is targeted. Single-phase samples with the required chemical composition are successfully made by an epoxide-mediated sol-gel method. The optimized materials show excellent cycle-life performance as lithium-ion battery cathodes.

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Cracking causing cyclic instability of LiFePO4 cathode material

Cited by 306 publications

References 12 publications

In operando tracking phase transformation evolution of lithium iron phosphate with hard X-ray microscopy

In operando tracking phase transformation evolution of lithium iron phosphate with hard X-ray microscopy

Nanoscale Imaging of Lithium Ion Distribution During In Situ Operation of Battery Electrode and Electrolyte

Accelerated discovery of cathode materials with prolonged cycle life for lithium-ion battery

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