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Conformational Regulation of Dielectric Poly(Vinylidene
Fluoride)-Based Solid-State Electrolytes for Efficient Lithium
Salt Dissociation and Lithium-Ion Transportation
Yan-Fei Huang,* Jian-Ping Zeng, Shuang-Feng Li, Chen Dai, Jun-Feng Liu, Chen Liu,*
and Yan-Bing He*
conductivities (≈10−3 S cm−1 at room
Restricted by the poor ability of polymers to dissociate lithium salts and transtemperature).[1,2] Solid-state electrolytes
(SSEs) are developed to replace flammable
port ions, solid-state polymer electrolytes (SPEs) show extremely low ionic
and unstable LEs to improve the safety
conductivities (≈10−7–10−5 S cm−1) and transference number of lithium ions
and stability of lithium metal batteries
(tLi+ ≈0.2–0.4) at 25 °C. Here, a novel polymer matrix of SPEs that simultane(LMBs).[3–6] Among all SSEs, solid-state
ously promotes lithium salt dissociation and ion transportation based on a high
polymer electrolytes (SPEs) have attracted
dielectric poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) (TerP)
extensive attention in recent years due
to their desirable flexibility, low density,
and an all-trans conformational poly(vinylidene fluoride-trifluoroethylene) (CoP),
facile processability, and good interfacial
CH
is developed. The high dielectric constant increases the polarity of
2CF2
contact with electrodes.[7–9] However, most
+
polar groups; then, brings a strong electronegative end that dissociates Li from
SPEs suffer from low ionic conductivities
lithium salts. The all-trans conformation assures all fluorine atoms locate on one
(≈10−7 to 10−5 S cm−1) and low lithium ions
side of the chain, constructing ion hopping highways. As a result, the TerP/CoP
(Li+) transference numbers (tLi+, usually
−4
−1
(TC) SPE exhibits a high ionic conductivity (2.37 × 10 S cm ) and a quite large
≈0.2–0.4) at room temperature.[10–13] This
is mainly because lithium salts cannot be
tLi+ of 0.61 at 25 °C. The Li/TC SPE/Li symmetric cells cycle stably for more than
efficiently dissociated by a polymer matrix
half a year (>4500 h) and the LiNi0.8Co0.1Mn0.1O2/TC SPE/Li cell cycles steadily
with a low εr (usually less than 10) and
for 1000 and 600 cycles at 1 C and 2 C at 25 °C, respectively. This work paves
Li+ is hardly transported through polymer
a new way to prepare high-performance SPEs by simultaneously modulating
chains with disordered hopping sites,
dielectric constants and conformation of polymers.
which consequently result in unsatisfactory cycling stability of LMBs.
To improve the ion conduction ability,
1. Introduction
the most commonly used method is introducing ceramic fillers
such as Li6.5La3Zr1.5Ta0.5O12 and Al2O3 into SPEs to build ion
conducting pathways or reduce the crystallinity of SPEs.[14–17]
Liquid electrolytes (LEs) usually contain cyclic carbonates with
high dielectric constants (εr > 30) to dissociate lithium salts
Nonetheless, inorganic fillers are easy to agglomerate and have
high mass densities,[18,19] which results in inhomogeneous
and linear carbonates to facilitate ions transport for high ionic
Li+ flux distribution and would reduce the energy density of
batteries.[20] It would be highly desirable, yet remains a great
Y.-F. Huang, J.-P. Zeng, S.-F. Li, C. Dai, J.-F. Liu, C. Liu
challenge, to construct an all-polymeric SPE that offers a high
College of Materials Science and Engineering
Shenzhen Key Laboratory of Polymer Science and Technology
ion conduction ability. To achieve this goal, first, the polymer
Guangdong Research Center for Interfacial Engineering of Functional Materials
matrix should have a high ability to dissociate lithium salts,
Shenzhen University
just like cyclic carbonates in LEs. The dissociation of lithium
Shenzhen 518055, P. R. China
salts in SPEs occurs by the coordination interactions between
E-mail: yanfeihuang@szu.edu.cn; liuchen@szu.edu.cn
the Li+ and the polar functional groups in polymer chains.[21–24]
Y.-F. Huang
State Key Laboratory of Polymer Materials Engineering
Increasing the εr intensifies the charge separation in polar
Sichuan University
groups and then promotes Li salts dissociation.[22,24,25] ThereChengdu 610065, P. R. China
fore, a high dielectric polymer is needed as the matrix of
Y.-B. He
SPEs.[26] However, even for poly(vinylidene fluoride) (PVDF)
Shenzhen Gein Graphene Center
that
shows a relatively higher εr (≈10) than the other polymer
Institute of Materials Research
matrix such as poly(ethylene oxide) (PEO) (εr < 5) and
Tsinghua Shenzhen International Graduate School
Tsinghua University
poly(methyl methacrylate) (PMMA) (εr < 4),[27–32] its ability to
Shenzhen 518055, P. R. China
dissociate lithium salts is still far from expectations for high
E-mail: he.yanbing@sz.tsinghua.edu.cn
ionic conductivities. To improve the εr of PVDF, some dielectric
The ORCID identification number(s) for the author(s) of this article
fillers such as BaTiO3 and TiO2 can be incorporated;[33–36] howcan be found under https://doi.org/10.1002/aenm.202203888.
ever, their inert nature for ion conduction may reduce the ion
transport efficiency. Recently, a new family of PVDF that shows
DOI: 10.1002/aenm.202203888
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Research Article
Figure 1. Schematic diagram of Li slat dissociation and ion transportation facilitated by the polymer matrix of SPE with different dielectric constants
and conformations.
a unique relaxor ferroelectric (RFE) behavior is found to show
a high εr (≈30–70).[26,37–39] Therefore, these RFE PVDF would
show high abilities to dissociate Li salt into free ions.
In addition to Li salt dissociation, the ability of PVDF to
transport Li+ is also important for achieving high ionic conductivities and tLi+. As is well known, the residual N, N-dimethylformamide (DMF) would solvate with Li+ to form [Li(DMF)x]+,
which could be transported by the PVDF through interactions
of [Li(DMF)x]+ with PVDF chains.[5,40,41] Such interaction is
through coordination and uncoordination of [Li(DMF)x]+ with
electronegative atoms, that is, the F atoms. In this context,
the spatial arrangement of F atoms on molecular chains (i.e.,
the conformation) would influence the hopping pathways of
[Li(DMF)x]+, then may have a significant effect on ion transport efficiency. For RFE PVDF such as poly(vinylidene fluoride
trifluoroethylene chlorotrifluoroethylene) [P(VDF-TrFE-CTFE)]
terpolymer (TerP) or PVDF prepared by conventional solution
casting, the conformation is mainly trans–gauche–trans–gauche
(TGTG’) and T3GT3G’ in which F atoms distribute on both
sides of the carbon chain (Figure 1a,b).[8,27,28,42,43] When ions
hop from one F site to another, the transmission path would
be twisted and disordered (Figure 1a,b), which is undesired for
[Li(DMF)x]+ transport. Unlike TGTG’ and T3GT3G’, all-trans
(TTTT) conformation assures all F atoms locate on one side of
the carbon chain,[8] which brings a great potential to construct
connected electronegative channels as hopping highways for
[Li(DMF)x]+ (Figure 1c). Unfortunately, due to the limitation of
processing methods, abundant TTTT conformation has never
been achieved in both PVDF and RFE PVDF SPEs as far as
we know.
In this work, a P(VDF-TrFE) random copolymer (CoP) is
innovatively introduced into a RFE TerP to disturb the crystallization of TerP, then induce a conformational change from
Adv. Energy Mater. 2023, 2203888
mixed TGTG’ and T3GT3G’ conformations into TTTT conformation. With well-aligned F atoms, the TTTT conformation
of coupled TerP/CoP (TC) provides ion hopping highways to
motivate ion transportation (Figure 1c). Meanwhile, the
increased real part of relative permittivity (εr′) of TC from ≈10
for PVDF to ≈33 helps to promote the dissociation of lithium
salts. As a result, TC SPE shows an increased ionic conductivity
(2.37 × 10−4 S cm−1) as well as a significantly high tLi+ of 0.61
(vs 0.29 for PVDF SPE and 0.36 for TerP SPE) at 25 °C. Furthermore, the high-voltage LiNi0.8Co0.1Mn0.1O2 (NCM811)/TC
SPE/Li cell cycles stably for 1000 and 600 cycles at 1 and 2 C,
respectively, at 25 °C. The Li/TC SPE/Li symmetric cell shows a
uniform stripping and plating performance for more than half
a year (>4500 h) at 25 °C. This work proposes a new strategy
to prepare high-performance SPEs by manipulating the dielectric constant and conformation of polymers. The prepared SPE
shows great potential to applicate as high-energy-density and
safe solid-state LMBs.
2. Results and Discussion
The polymer and SPE films are prepared by solution casting
following an optimized procedure as reported in our previous
work.[26] First, the TerP and CoP are coupled in different weight
ratios and when it is 5:5, the TC matrix shows a relatively high
εr′ (≈30, Figure S1, Supporting Information), a low glass transition temperature (Tg, Figure S2, Supporting Information), and
the highest ionic conductivity of TC SPE (Figure S3, Supporting
Information). Therefore, 5:5 is the optimized weight ratio and
will be employed hereinafter. From Fourier transform infrared
spectrometer (FTIR), TerP shows mixed TGTG′, T3GT3G′,
and TTTT conformations (Figure 2a, blue curve), and PVDF
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Figure 2. a) FTIR, b) XRD, and c) εr′ as a function of temperature at different frequencies for TC, TerP, CoP, and PVDF films. The SEM images of
d,f) TC SPE and e,g) PVDF SPE. The insets of Figure 2d,e are optical images of TC SPE and PVDF SPE membranes, respectively. h) TGA and i) FTIR
of TC, TerP, and PVDF SPE.
shows mixed TGTG′ and T3GT3G′ conformations (Figure 2a,
green curve). After introducing CoP with pure TTTT conformation (Figure 2a, yellow curve) into TerP, TC shows pure TTTT
conformation with typical peaks at 1285, 842, 505, 472, and
426 cm−1 (Figure 2a, red curve).[27,44–46] This could be further
confirmed by Raman results (Figure S4, Supporting Information) where only the TTTT conformation is observed at typical
peaks at 841, 1443, and 2974 cm−1.[47–49] From X-ray diffraction
(XRD) measurement, PVDF show reflections of (020), (110),
(200), and (002) planes, proving the mixed TGTG′ and T3GT3G′
conformations (Figure 2b). As for the TC film, the (110/200)
crystal plane for RFE phase and (110), (120), and (201) for ferroelectric (FE) phase are observed at the reflections at 12.8, 14.2,
24.7, and 28.5 nm−1, respectively.[8,26] The RFE phase brings TC
with a high εr′ of ≈33 (Figure 2c) compared to ≈10 for PVDF
at 10 Hz and 25 °C.[43] The FE phase that could be further
proved by differential calorimetric scanning (DSC, Figure S5,
Supporting Information) assures a TTTT conformation for TC
at room temperature.[50] The high εr′ and TTTT conformation
Adv. Energy Mater. 2023, 2203888
may endow TC with simultaneously high abilities to dissociate
lithium salts and facilitate ions transport. Then, a high ionic
conductivity and tLi+ can be anticipated for TC SPE.
Scanning electron microscopy (SEM) is employed to observe
the morphologies of TC SPEs. It is shown that granules of
TC (Figure 2d) and TerP (Figure S6a, Supporting Information) are more connected than PVDF SPE (Figure 2e), which
is responsible for the more transparent morphology (insets of
Figure 2d,e) and thinner thickness for TC (Figure 2f) and TerP
SPEs (Figure S6b, Supporting Information) than PVDF SPE
(Figure 2g). The varied morphology between TC and PVDF SPE
is due to the different crystallization driving forces of these two
films (Figure S7, Supporting Information). The denser morphology brings a more continuous path for ion transport and a
better ductility for TC and TerP SPE than PVDF SPE (Figure S8,
Supporting Information), which may contribute to better interfacial compatibility between SPEs with rigid electrodes. Thermo
gravimetric analysis (TGA) is performed to detect the residues
of DMF in SPEs. The minor weight loss before 55 °C (region I)
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Figure 3. a) Ionic conductivities of TC, TerP, and PVDF SPEs at varied temperatures. b) Chronoamperometry profiles of Li/TC SPE/Li symmetrical cells
under a polarization voltage of 10 mV. The insets show EIS curves before and after the polarization. c) tLi+ of TC, TerP, and PVDF SPEs at 25 °C. Raman
peaks of d) TC SPE, e) TerP SPE, and f) PVDF SPE around 741 cm−1. g) Long cycling performance of Li/TC SPE/Li, Li/TerP SPE/Li, and Li/PVDF SPE/
Li symmetrical cells at 25 °C under a current density of 0.05 mA cm−2. h) Long cycling performance of Li/TC SPE/Li symmetrical cell at 25 °C under a
current density of 0.1 mA cm−2.
in Figure 2h comes from the evaporation of the trapped moisture, and the weight loss between 55 °C and 200 °C is ascribed
to the residual DMF.[5,51] From Figure 2h, PVDF, TerP, and
TC SPEs show comparable amounts (12.8%) of residual DMF,
which are bounded with Li+ to form [Li(DMF)x]+ as evidenced
by FTIR results (Figure 2i), indicating there exist no free DMF
molecules.[5,40]
The ionic conductivity was calculated by electrochemical
impedance spectroscopy (EIS) measurement (Figure S9, Supporting Information). From Figure 3a, ionic conductivities are
much higher for TC SPE in comparison to PVDF SPE at varied
temperatures. Especially, TC SPE shows a high ionic conductivity of 2.37 × 10−4 S cm−1 at 25 °C, which is 2.4 times as much
as PVDF SPE (9.70 × 10−5 S cm−1), and much higher than other
reported all-polymeric SPEs without any inorganic fillers (≈10−7
to 10−5 S cm−1).[5,15,52–55] Moreover, the activation energy Ea
decreases from 0.33 eV for PVDF SPE to 0.27 eV for TC SPE,
Adv. Energy Mater. 2023, 2203888
indicating a lower migration barrier for Li+ in TC SPE. As the
crystallinity (Figure S10, Supporting Information) and DMF
residue (Figure 2h) of TC SPE are comparable to PVDF SPE,
and the segmental motion is more difficult for TC than PVDF
(Tg,TC = −24.0 °C, Tg,PVDF = −35.2 °C, Figure S11, Supporting Information), the much higher ionic conductivities and lower activation energy of TC SPE than PVDF SPE must be attributed to the
high εr′ and abundant TTTT conformation of TC that facilitate
the Li salts dissociation and ions transportation, respectively.
Noting that with an even higher εr′ of TerP (≈45, Figure 2c) than
TC, TerP SPE with minor TTTT conformation (Figure 2a) displays a lower ionic conductivity and a higher Ea (0.29 eV) than TC
SPE (Figure 3a). This indicates the important role of abundant
TTTT conformation in constructing highways for efficient ion
transportation in the TC SPE.
As is well known, the ionic conductivity is contributed by
both Li+ and anions, and for LMBs, only the current carried
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by Li+ matters;[2] so here, the tLi+ that quantifies the proportion of current from Li+ movement is measured according to
a method reported in literature.[56,57] From the chronoamperometry profiles (Figure 3b), the tLi+ of TC SPE is calculated
as 0.61 (Figure 3c), which is not only remarkably higher than
PVDF SPE (0.29) and TerP SPE (0.36, Figure S12, Supporting
Information) but also superior to other reported SPEs (usually
≈0.2–0.4).[5,10,11,26,58] The high tLi+ of TC SPE is highly related
to the mechanism of TC to transport Li+. To be specific, the
[Li(DMF)x]+ first coordinates with the electronegative F atoms
from TC chains, and as the molecular chain segments move,
uncoordination occurs and [Li(DMF)x]+ detaches from the original coordination site and hops to the next F site. The TTTT
conformation with connected electronegative channels of TC
shortens the hopping pathway; then, a high movement of Li+
as well as a high tLi+, can be obtained. The fast Li+ movement
can be further proved by the 350 times higher diffusion coefficients of Li+ (DLi+) for TC SPE than PVDF SPE (Figure S13,
Supporting Information). With such a high tLi+ and DLi+, the
overwhelming movement and accumulation of anions near
electrodes and the resultant concentration polarization can
be greatly hindered,[11,59–61] which benefits the cycling performance of TC SPE when assembled in LMBs. Raman test
is further performed to examine the Li+ coordination state
with FSI anions in TC SPE. The peak around 741 cm−1 can
be fitted into three peaks as shown in Figure 3d–f, where C1
and C2 correspond to cisoid and transoid conformers from
free FSI anions, respectively, and Ccoord comes from the Li+
coordinated FSI anions.[5,62–64] The total amount of C1 and C2
is calculated as 85.3% for TC SPE (Figure 3d), much higher
than 75.5% for TerP SPE (Figure 3e) and 69.0% for PVDF SPE
(Figure 3f ), indicating more amount of movable Li+ exists in
TC SPE. These above results support our speculation that
the high εr′ can facilitate the dissociation of lithium salts
and the TTTT conformation helps to construct ion transport
highways.
Benefiting from the high ionic conductivity and tLi+, the Li/
TC SPE/Li symmetric cell shows a quite stable cycling performance for more than 4500 h (>half a year) with a small polarization voltage of only 22 mV at 25 °C under a current density
of 0.05 mA cm−2 (Figure 3g). In clear contrast, Li/TerP SPE/
Li and Li/PVDF SPE/Li symmetric cells display short circuits
only after 1300 and 500 h, with polarization voltage of 29 and
52 mV, respectively. At the current density of 0.1 mA cm−2,
the Li/TC SPE/Li symmetric cell still displays a stable cycling
performance for 1500 h (Figure 3h). Further increasing the
current density to 0.2 and 0.3 mA cm−2, Li/TC SPE/Li symmetric cell still shows better stability than the Li/PVDF SPE/
Li symmetric cell (Figure S14a,b, Supporting Information)
although they have comparable critical current densities
(≈0.6 mA cm−2; Figure S14c, Supporting Information). These
results demonstrate that the TC SPE has a superior ability to
suppress the Li dendrite growth. This will be proved later by
SEM observation.
The electrochemical stability window (ESW) is measured by
linear sweep voltammetry (LSV), and it is 4.5 V for TC SPE
(Figure 4a) and TerP SPE (Figure S15a, Supporting Information), and 4.7 V for PVDF SPE (Figure S15b, Supporting Information). The higher ESW of PVDF SPE than TC SPE may
Adv. Energy Mater. 2023, 2203888
be related to the higher nonbonding orbital energy of F than
Cl, which gives PVDF a lower valence band minimum then
a higher oxidation potential to widen the ESW.[65] However,
although the ESW of TC SPE is slightly lower than PVDF SPE,
it is high enough to match well with high voltage NCM811
cathodes. To prove this, the rate performance of NCM811/TC
SPE/Li batteries is detected. As shown in Figure 4b; Figure S16,
Supporting Information, the NCM811/TC SPE/Li cell shows
a specific capacity of 160.4, 143.2, 132.9, and 111.3 mAh g−1 at
0.5, 1.5, 2.5, and 5 C, respectively. When the rate goes back
to 0.5 C, the specific capacity returns to 160.0 mAh g−1 and
retains ≈98% after 100 cycles (Figure 4c). This suggests a
good compatibility between TC SPE and NCM811 cathodes.
Increasing the rate to 1 C, the NCM811/TC SPE/Li cell presents a rather stable cycling performance with capacity retention of 97.8% and 65.1% after 500 and 1000 cycles at 25 °C,
respectively (Figure 4d,e). In clear contrast, the NCM811/PVDF
SPE/Li cell exhibits a dramatical capacity decay (Figure 4d;
Figure S17a, Supporting Information), and the NCM811/TerP
SPE/Li cell only cycles steadily for the initial 50 cycles then
short circuits after 120 cycles at 1 C and 25 °C (Figure 4d;
Figure S17b, Supporting Information). The much better cycling
performance of NCM811/TC SPE/Li cells than NCM811/PVDF
SPE/Li cells is attributed to the remarkably better stability of
TC SPE against Li anodes (Figure 3g), the much higher tLi+
(Figure 3c) that could reduce the concentration polarization
near NCM811 cathodes, the better compatibility between TC
SPE and NCM811 (Figure S18, Supporting Information), and
the more stable interfacial impedance of NCM811/TC SPE/
Li cells during cycling (Figure S19, Supporting Information).
Further increasing the rate to 2 C, a quite high rate for SPE,
the NCM811/TC SPE/Li cell still shows good cycling performance with capacity retention of 82.6% after 600 cycles at
25 °C (Figure 4f,g). These above results demonstrate that the
promoted Li salts dissociation by high εr′ and the highly efficient ion transport provided by TTTT conformation endows
the TC SPE with high electrochemical properties, especially the
high tLi+, good cycling stability of both Li//Li and NCM811//Li
batteries in comparison to other reported SPEs (Table S1, Supporting Information).
To verify the superior ability of TC SPE to inhibit lithium
dendrite growth, the cycled Li surfaces are observed by SEM.
From Figure 5a, the Li surface from cycled NCM811/TC SPE/
Li cell is dense, uniform, and smooth, while for NCM811/PVDF
SPE/Li cell, the cycled Li shows a coarse and roughened appearance (Figure 5b). This reveals that TC SPE has a much stronger
ability than PVDF to impede the growth of lithium dendrites.
It is probably because there are more amount of free ions with
high mobility in TC SPE, which brings a more continuous
and uniform Li deposition then gets rid of lithium dendrite
growth.[66] Furthermore, owing to the much better ductility of
TC SPE than PVDF SPE (Figure S8, Supporting Information),
TC SPE shows a very tight interface with NCM811 cathodes
(Figure 5c,e,f), in clear contrast to the loose contact between
PVDF SPE and NCM811 (Figure 5d). Such a good interfacial compatibility between TC SPE and NCM811 reduces the
interface impedance (Figure S13, Supporting Information)
and favors ions transport, consequently bringing a quite long
lifespan for high-voltage LMBs (Figure 4d).
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Figure 4. a) The LSV curve of TC SPE. b) Rate capacities of the NCM811/TC SPE/Li cell. c) Long-term cycling performance of NCM811/TC SPE/Li cells
at 0.5 C and 25 °C after the rate cycling in (b). Long-term cycling performance of d) NCM811/TC SPE/Li, NCM811/TerP SPE/Li, and NCM811/PVDF
SPE/Li cells at 1 C and 25 °C and f) NCM811/TC SPE/Li cell at 2 C and 25 °C. Charge–discharge voltage profiles of NCM811/TC SPE/Li cells e) at 1 C
and 25 °C from (d), and g) at 2 C and 25 °C from (f).
3. Conclusion
We developed a novel polymer matrix of SPE with simultaneously high abilities to dissociate Li salts and transport ions
through coupling a high dielectric P(VDF-TrFE-CTFE) with
an all-trans conformational P(VDF-TrFE). The dielectric constant of the coupled matrix, TC, increased from ≈10 for PVDF
to ≈33, which intensified the charge separation in polar functional groups and brought a highly electronegative end that
absorbed Li+ to realize high-efficient Li salts dissociation.
The TTTT conformation made all electronegative F atoms
locate on one side of the carbon chain, which provided ion
transport highways for rapid hopping motion of [Li(DMF)x]+.
As a result, TC SPE showed a high ionic conductivity of
2.37 × 10−4 S cm−1 at 25 °C and a quite high tLi+ of 0.61 (vs
0.2–0.4 for other SPEs). With more amount of free Li+ with
desirable mobility, Li stripping and plating are more uniform.
Adv. Energy Mater. 2023, 2203888
Therefore, the Li/TC SPE/Li symmetric cell shows a stable
cycling for more than half a year (>4500 h) at 25 °C, in clear
contrast to Li/PVDF SPE/Li symmetric cell that is short circuit only after 500 h. Furthermore, TC SPE exhibits a denser
morphology and better ductility than PVDF SPE, which
contributes to a continuous path for ions transport, a better
affinity with electrodes, and a lower interfacial impedance of
LMBs. In consequence, the high-voltage NCM811/TC SPE/
Li cell performs stably for 1000 and 600 cycles at 1 and 2 C
at 25 °C, respectively. In particular, the capacity retention of
NCM811/TC SPE/Li cell is 97.8% after 500 cycles at 1 C, which
is significantly higher than 16.7% for NCM811/PVDF SPE/Li
cells after 200 cycles at 1 C. This work, for the first time, demonstrates that the dielectric and conformational modulation
can enable polymers to show high abilities to dissociate Li
salts and transport ions. The prepared TC SPE shows great
application potential as high-energy-density LMBs.
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using a VMP3 multichannel electrochemical station. The Li/SPEs/Li
symmetric cells were assembled to explore the Li plating/stripping
performance on a battery test system (LAND CT2001A) at 25 °C. The
NCM811/SPEs/Li cells were cycled at 25 °C with a voltage range from
2.8 to 4.3 V.
Supporting Information
Supporting Information is available from the Wiley Online Library or
from the author.
Acknowledgements
Figure 5. SEM images of the cycled Li surface from a) NCM811/TC SPE/
Li and b) NCM811/PVDF SPE/Li. The cross-section of the c) NCM811/TC
SPE interface and d) NCM811/PVDF SPE interface after cycling. e,f) The
energy dispersive spectroscopy (EDS) maps of (c).
4. Experimental Section
Conflict of Interest
Preparation of SPEs: P(VDF-TrFE-CTFE) 65.4/26.2/8.8 mol% (TerP,
Mw = 5.8 × 105 g mol−1, Arkema), P(VDF-TrFE) 80/20 mol% (CoP,
Mw = 4.5 × 105 g mol−1, Arkema), and LiFSI (Canrd, China) were
dissolved in DMF at a weight ratio of 1:1:2 under magnetically stirring
for 8 h at 25 °C. Then, the polymer solution was transferred into a glass
dish and dried at 55 °C to obtain the TC SPE. The preparation of PVDF
SPE and TerP SPE followed a similar procedure with a polymer to LiFSI
weight ratio of 1:1. To make sure the amount of residue DMF was similar,
different preparation time ranging from 19 to 50 h was used to prepare
TC, TerP, and PVDF SPEs.
Characterizations: FTIR measurement was conducted using a
Nicole 6700 FTIR spectrometer (Thermo Fisher Scientific, USA) in an
attenuated total reflection (ATR) mode. XRD curves were collected using
a Rigaku Smartlab with Cu-Kα radiation. The equation q = (4π sinθ)/λ
was used to calculate the scattering vector q, where θ and λ are the
half-scattering angle and the wavelength (1.5418 Å), respectively. BDS
(Novocontrol Concept 40) was performed under an applied voltage of
1.0 Vrms (i.e., room-mean-square voltage), and before test, the polymer
films were evaporated with Au electrodes on both sides. SEM (Hitachi
SU-70, Japan) was conducted under an operation voltage of 5 kV. TGA
curves were collected by a TGA 55 analyzer (TA Instrument, USA) from
room temperature to 800 °C under a N2 atmosphere, and the ramping
rate was 10 °C min−1. Raman test was conducted on a RENISHAW invia
Raman microscope (UK).
Assembling of Cells and Electrochemical Measurements: NCM811,
super P, PVDF, and LiFSI were dissolved into N-methyl-2-pyrrolidone
(NMP) with weight ratio of 8:1:1:1 to obtain a slurry. After casting the
slurry on an Al foil and drying at 80 °C for 8 h, the NCM811 cathode
was prepared with mass loading of ≈1 mg cm−2. The CR2032 solid-state
cells were assembled in an Ar-filled glove box. The ionic conductivities
of SPEs were calculated from the EIS data obtained from a VMP3
multichannel electrochemical station (Bio-Logic Science Instruments,
France) with frequency from 7 MHz to 1 Hz and a 10 mV AC oscillation
voltage. The tLi+ was obtained from the chronoamperometry profiles
under a polarization voltage of 10 mV and EIS data before and after the
polarization. LSV was examined by assembling Li/SPEs/stainless steel
(SS) cells from 0 to 6 V versus Li/Li+ at a scanning rate of 1 mV s−1
Adv. Energy Mater. 2023, 2203888
Y.-F.H. acknowledges the financial support from the National Natural
Science Foundation of China (52103037), the Natural Science Foundation
of Guangdong Province (2023A1515030247; 2021A1515011976),
Shenzhen Science and Technology Research and Development Fund
(JCYJ20220531102013031; 20200807113743001), and the Opening Project
of State Key Laboratory of Polymer Materials Engineering (Sichuan
University) (Grant No. sklpme2022-4-07). Y.-B.H. acknowledges the
financial support from the Shenzhen All-Solid-State Lithium Battery
Electrolyte Engineering Research Center (XMHT20200203006) and the
Shenzhen Technical Plan Project (RCJC20200714114436091).
The authors declare no conflict of interest.
Data Availability Statement
The data that support the findings of this study are available from the
corresponding author upon reasonable request.
Keywords
all-trans conformation, dielectric constant, ionic conductivity, lithium
ions, solid-state polymer electrolytes
Received: November 15, 2022
Revised: January 29, 2023
Published online:
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