Nonflammable perfluoropolyether-based electrolytes for lithium batteries

Wong, Dominica H. C.; Thelen, Jacob L.; Fu, Yanbao; Devaux, Didier; Pandya, Ashish; Battaglia, Vincent; Balsara, Nitash P.; DeSimone, Joseph M.

doi:10.1073/pnas.1314615111

Cited by 204 publications

(242 citation statements)

References 37 publications

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“…It is based on the measurement of conductivity by ac impedance, salt diffusion coefficient by restricted diffusion, steady-state current under dc polarization, and the thermodynamic factor using concentration cells. Our approach, based on concentrated solution theory, is very similar to that proposed by Ma et al 33 A majority of t + values reported in the literature [41][42][43][44][45][47][48][49]58,59,61 are based on the steady-state current method pioneered by Bruce and Vincent. 42,57 In a few cases [34][35][36][37] where the approach of Ma et al is used to determine t + , there is no attempt to relate t + values thus obtained with those that might be obtained using the steady-state current method.…”

Section: Discussionmentioning

confidence: 98%

Negative Transference Numbers in Poly(ethylene oxide)-Based Electrolytes

Pesko

Timachova

Bhattacharya

et al. 2017

J. Electrochem. Soc.

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191

367

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The performance of battery electrolytes depends on three independent transport properties: ionic conductivity, diffusion coefficient, and transference number. While rigorous experimental techniques for measuring conductivity and diffusion coefficients are well-established, popular techniques for measuring the transference number rely on the assumption of ideal solutions. We employ three independent techniques for measuring transference number, t + , in mixtures of polyethylene oxide (PEO) and lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) salt. Transference numbers obtained using the steady-state current method pioneered by Bruce and Vincent, t +,SS , and those obtained by pulsed-field gradient NMR, t +,NMR , are compared against a new approach detailed by Newman and coworkers, t +,Ne , for a range of salt concentrations. The latter approach is rigorous and based on concentrated solution theory, while the other two approaches only yield the true transference number in ideal solutions. Not surprisingly, we find that t +,SS and t +,NMR are positive throughout the entire salt concentration range, and decrease monotonically with increasing salt concentration. In contrast, t +,Ne has a non-monotonic dependence on salt concentration and is negative in the highly-concentrated regime. Our work implies that ion transport in PEO/LiTFSI electrolytes at high salt concentrations is dominated by the transport of ionic clusters. Energy density and safety of conventional lithium-ion batteries is limited by the use of liquid electrolytes comprising mixtures of flammable organic solvents and lithium salts. Polymer electrolytes have the potential to address both limitations. However, the power and lifetime of batteries containing solvent-free polymer electrolytes remain inadequate for most applications. The performance of electrolytes in batteries depends on three independent transport properties: ionic conductivity, σ, salt diffusion coefficient, D, and cation transference number, t + .1 The poor performance of batteries with polymer electrolytes is generally attributed to low conductivity, which is on the order of 10 −3 S/cm at 90• C for mixtures of polyethylene oxide (PEO) and lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) salt, 2,3 compared to that of liquid electrolytes which is 10 −2 S/cm at ambient temperatures. 4 Much of the literature in this field has been devoted to increasing the ionic conductivity of these materials.5-32 The purpose of our work is to shed light on another transport property of polymer electrolytes, the transference number.In a pioneering study, Ma and coworkers showed that the transference number of a mixture of PEO and a sodium salt is negative. 33Following this approach, others have obtained t + <0 in polymers containing lithium or sodium salts. [34][35][36] Nevertheless, the majority of reports for t + in polymer electrolytes fall between zero and one. [37][38][39][40][41][42][43][44][45][46][47][48][49][50][51] In contrast, all reports of t + in non-aqueous liquid electrolytes containi...

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Section: Discussionmentioning

confidence: 98%

Negative Transference Numbers in Poly(ethylene oxide)-Based Electrolytes

Pesko

Timachova

Bhattacharya

et al. 2017

J. Electrochem. Soc.

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191

367

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“…The exclusion of Li 2 S 8 from hybrid electrolyte may, at first, seem counterintuitive because of the presence of PFPE. Note, however, that solubility of lithium-containing salts in PFPE is driven by the fluorinated anions that are absent in lithium polysulfides (11). According to the data in Fig.…”

mentioning

confidence: 90%

“…In addition, we also studied a liquid electrolyte comprising a mixture of PFPE-diol and LiTFSI with r = 0.04 prepared using the method described in ref. 11. The compositions of all three electrolytes are given in Fig.…”

Section: Significancementioning

confidence: 99%

Compliant glass–polymer hybrid single ion-conducting electrolytes for lithium batteries

Villaluenga

Wujcik

Tong

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

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108

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Despite high ionic conductivities, current inorganic solid electrolytes cannot be used in lithium batteries because of a lack of compliance and adhesion to active particles in battery electrodes as they are discharged and charged. We have successfully developed a compliant, nonflammable, hybrid single ion-conducting electrolyte comprising inorganic sulfide glass particles covalently bonded to a perfluoropolyether polymer. The hybrid with 23 wt% perfluoropolyether exhibits low shear modulus relative to neat glass electrolytes, ionic conductivity of 10 −4 S/cm at room temperature, a cation transference number close to unity, and an electrochemical stability window up to 5 V relative to Li + /Li. X-ray absorption spectroscopy indicates that the hybrid electrolyte limits lithium polysulfide dissolution and is, thus, ideally suited for Li-S cells. Our work opens a previously unidentified route for developing compliant solid electrolytes that will address the challenges of lithium batteries.hybrid electrolytes | inorganic sulfide glasses | fluorinated polymers | lithium batteries | lithium-sulfur batteries E lectrolytes used in lithium ion batteries that power personal electronic devices and electric vehicles comprise lithium salts dissolved in flammable organic liquids. Catastrophic battery failure often begins with the electrolyte decomposition and combustion. In addition, side reactions between the electrolyte and anode particles result in steady capacity fade. Some of the byproducts of side reactions can dissolve in the electrolyte and migrate from one electrode to the other. This effect is minimized in the case of solid electrolytes because of limited solubility and slow diffusion (1). Mixtures of liquids and salts have additional limitations. The passage of current results in an accumulation of salt in the vicinity of one electrode and depletion close to the other electrode, because only the cation participates in the electrochemical reactions. Both overconcentrated and depleted electrolytes have lower conductivity, which accentuates cell polarization and reduces power capability. Concentration polarization is absent in single-ion conductors, wherein the anions are immobilized (2). Nonflammable, single ionconducting solid electrolytes have the potential to dramatically improve safety and performance of lithium batteries (3-6).Solid electrolytes, such as inorganic sulfide glasses (Li 2 S-P 2 S 5 ), are single-ion conductors with high shear moduli (18-25 GPa) and high ionic conductivity (over 10 −4 S/cm) at room temperature (7,8). However, these materials, on their own, cannot serve as efficient electrolytes, because they cannot adhere to moving boundaries of the active particles in the battery electrode as they are charged and discharged. Hayashi et al. (9) prepared hybrid electrolytes by mixing sulfide glasses and poly(ethylene oxide) (PEO) polymers. Although the addition of PEO improves mechanical flexibility, there is a dramatic decrease in ionic conductivity because of the insulative nature of PEO. For exampl...

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“…z E-mail: nbalsara@berkeley.edu transference number which has not yet been rigorously measured and is estimated to be between 0.1 and 0.2 based on preliminary data. 37 The numerical values reported in the previous sentence apply to high M n SEO copolymers. The electrochemical stability window of the electrolyte determine the potential of the battery.…”

mentioning

confidence: 99%

Failure Mode of Lithium Metal Batteries with a Block Copolymer Electrolyte Analyzed by X-Ray Microtomography

Devaux

Harry

Parkinson

et al. 2015

J. Electrochem. Soc.

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Solid block polymer electrolytes are promising candidates for the development of high energy density rechargeable lithium metal based batteries. All solid-state batteries comprising lithium metal negative electrode and lithium iron phosphate (LiFePO 4 ) composite positive electrode were assembled. A polystyrene-b-poly(ethylene oxide) (SEO) copolymer doped with a lithium salt was used as the electrolyte. After cycling the batteries, the reason for capacity fade and failure was determined by imaging the batteries using synchrotron hard X-ray microtomography. These experiments revealed partial delamination of the lithium foil and the block copolymer electrolyte layer. The void volume between the foil and electrolyte layer obtained after 40 to 90 cycles is comparable to volume change in the battery during one cycle. A simple model to account for the effect of delamination on current density in the battery is presented. Capacity fade and battery failures observed in our experiments are consistent with this model. No evidence of lithium dendrite formation was found. In contrast, cycled lithium-lithium symmetric cells with the same polymer electrolyte at the same current density failed due to dendrite formation. No evidence of delamination was found in these cells. Solid polymer electrolytes are promising candidates for the development of high performance rechargeable batteries comprising a lithium (Li) metal electrode due to their chemical stability toward lithium and their mechanical resistance to dendrite growth.1-3 After the pioneering work by Fenton et al., 4 where poly(ethylene oxide) (PEO) laden with alkali metal salts was shown to possess good ionic conductivity, its application as a polymer electrolyte in a full cell was demonstrated by Armand et al. [5][6][7] PEO is a semi-crystalline polymer at room temperature. Ionic transport in PEO electrolytes is linked to segmental motion of the polymer chains, 8,9 and occurs predominantly in the amorphous phase.10 Thus solid polymer electrolyte based batteries must be operated at temperatures (T) above the PEO melting temperature. However, amorphous PEO is too soft to avoid short circuit due to lithium dendrite growth. 11,12 One approach for resolving this problem is the use of a block copolymer electrolyte. [13][14][15][16][17][18][19][20][21][22] Immiscibility between the blocks induces microphase separation, producing hard insulating phases interspersed with soft, ionically conductive phases. [23][24][25] In studies utilizing block copolymers as solid polymer electrolytes, the mechanical phase is usually made of a high glass transition temperature polymer such as polystyrene. [26][27][28][29] Extensive work on the thermodynamics of polystyrene-b-poly(ethylene oxide) (SEO) diblock copolymers [30][31][32][33] indicate that the tendency for microphase separation is enhanced by the presence of ions. 34,35 For symmetric SEO electrolytes, i.e. copolymers wherein the volume fraction of the conducting phase is above 50%, the ionic conductivity has been shown to increase wit...

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Nonflammable perfluoropolyether-based electrolytes for lithium batteries

Cited by 204 publications

References 37 publications

Negative Transference Numbers in Poly(ethylene oxide)-Based Electrolytes

Negative Transference Numbers in Poly(ethylene oxide)-Based Electrolytes

Compliant glass–polymer hybrid single ion-conducting electrolytes for lithium batteries

Failure Mode of Lithium Metal Batteries with a Block Copolymer Electrolyte Analyzed by X-Ray Microtomography

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