MOF/Poly (eteeni oksidi) komposiitti polymeeri elektrolyytti for solid-state litium akku
LIANG Fengqing% 2c WEN Zhaoyin
1. CAS avain laboratorio materiaalit energia muuntaminen % 2c Shanghai instituutti keramiikka % 2c kiina akatemia tieteet % 2c Shanghai 200050% 2c Kiina
2. Center materiaalit tiede ja optoelektroniikka tekniikka % 2c yliopisto kiina akatemia tieteet % 2c Peking 100049, Kiina
Abstrakti
Solid polymer electrolytes (SPEs) with high flexibility and processability enable the fabrication of leak-free solid-state batteries with varied geometries. However, SPEs usually suffer from low ionic conductivity and poor stability with lithium metal anodes. Here, we propose nano-sized metal-organic framework (MOF) material(UiO-66) as filler for poly(ethylene oxide) (PEO) polymer electrolyte. The coordination of UiO-66 with oxygen in PEO chain and the interaction between UiO-66 and lithium salt significantly improve the ionic conductivity (3.0×10 -5 S/cm at 25 degree , 5.8×10 -4 S/cm at 60 degree ) and transference number of Li plus (0.36), widen the electrochemical window to 4.9 V (vs Li plus /Li), enhance the stability with lithium metal anode. As a result, the as-prepared Li symmetrical cells can continuously operate for 1000 h at 0.15 mA∙cm -2, 60 degree . The results show that UiO-66 filler is effective to improve the electrochemical performance of polymer electrolyte.
Avainsanat: komposiitti elektrolyytti % 3b poly (eteeni oksidi) % 3b metalli-orgaaninen kehys materiaali % 3b litium metalli akku
Lithium-batteries technology can be enhanced by replacing the liquid electrolytes currently in use with solid polymer electrolytes (SPEs), enabling the fabrication of flexible, compact, laminated solid-state structures free from leaks and available in varied geometries. The SPEs explored for these purposes are ionically conducting polymer membranes formed by complexes between lithium salt (LiX) and high molecular weight polymer containing Li plus coordinating groups, such as poly(ethylene oxide) (PEO). In PEO polymer electrolytes, with the polymer in amorphous state, Li plus is fast transported along with local relaxation and segmental motion of polymer chain, but the PEO tends to crystallize below 6{{10}} degree . So the conductivity of PEO polymer electrolytes reaches practically useful values (of the order of 10-4 S/cm) only at the temperature above 6{{20}} degree . Numerous attempts for diminishing the polymer crystallinity were made to improve the conductivity of the polymer electrolytes, including mixing with other co-polymers, adding plasticizers and doping inorganic particles. Incorporating inorganic materials into polymer matrix is the most successful approach, which improves ionic conductivity as well as electrochemical stability and mechanical properties. These inorganic materials mainly include nonconductive materials, such as SSZ-13, Al2O3, SiO2, and conductive materials, such as Li0.33La0.57TiO3, Li6.75La3Zr1.75Ta0.25O12, and Li1.5Al0.5Ge1.5(PO4)3. Investigations showed that nanoparticles with Lewis acidic surface properties can more efficiently boost the dissociation of lithium salt and reduce the crystallinity of PEO, thus improving the ionic conductivity. However, the poor contact between inorganic nanoparticle and PEO for the surface energy gap usually leads to inhomogeneous dispersion. Ceramic fillers grafted with molecular brushes and modified with dopamine are endowed with inorganic-organic properties. They are expected to enhance the miscibility with PEO, future improving the ionic conductivity and stability of polymer electrolytes.
Metalli-orgaaniset kehykset (MOF: t) koostuvat metallista ioni klustereista ja orgaanisista linkkereistä ovat tyypillisiä nanohuokoisia materiaaleja% 2c jotka omistavat epäorgaaninen-orgaaninen hybridi ominaisuus ja korkea spesifinen pinta-ala % 2c siten oleminen ihanteellinen täyteaineet täyteaineet polymeeri elektrolyytit sisään 2013% 2c yuan et ai. käytetty Zn4O (1% 2c% 7b % 7b % 7b5% 7 d% 7 d) kuten täyteaine PEO elektrolyytti hankkiminen korkea ioninen johtavuus of 3. 16×10-5 S∙cm-1} (25 aste ) erääntynyt to the tasaisesti dispersio. mutta heikko metalli-orgaaninen koordinaatio sidokset of MOF-5 are helppo olla hyökätty, johtava to kristalli siirtymä tai rakenne romahdus ja huono vakaus litium akku.
Sisään tämä työ % 2c nanokokoinen UiO% 7b % 7 b1 % 7d % 7 d % 2c yksi laaja tutkittu MOF% 2c otettiin käyttöön täyteaineena osaksi PEO elektrolyytti. The UiO% 7b% 7b% 7b% 7d% kanssa erinomainen hydroterminen ja kemiallinen stabiilisuus ei sisällä siirtymä metallit jotka tarjoavat redox-aktiiviset keskukset % 2c so elektroninen johtavuus voi olla välttää kun kosketa metallin kanssa Li.
1 Kokeellinen
1.1 synteesi nanokokoinen UiO% 7b% 7b3% 7d% 7d
Nanokokoinen UiO% 7b% 7b1% 7d% 7d syntetisoitu sen mukaan raportoitu kaksivaiheinen synteesi. (1) 2% 7b % 7b % 7 b 14 % 7 d7 mg ZrCl4 (98 % 2c Aladdin) oli liuennut sisään 40 ml N% 2cN-dimetyyliformamidi (DMF) (99,9 % % 2c Aladdin) ali sekoittaen % 2c ja liuos kuumennettiin noin 120 aste for 2 h h. 7b20}}bentseenidikarboksyyli happo (H2BDC) (99 prosenttia , Aladdin) lisättiin liuokseen. ja tulos seos lisättiin lisättiin into a 50 ml teflonvuorattu ruostumaton teräs autoklaavi ja sijoitettu an uuni at 120 aste for 24 h. Jälki jäähdytys huone lämpötila, the tuloksena saatavat saostuvat sentrifugoidut, pesty kanssa DMF, puhdistettu sisään metanoli ja sitten kuivattu at 60 aste alipaine tyhjiö for 24 h.
1.2 Valmistelu UiO% 7b% 7b2% 7d% 7d% 2fPEO komposiitti polymeeri elektrolyytit (CPE: t)
PEO (Mw {{0}} ~600,000, 99.9 percent , Aladdin) was dried at 50 degree , and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) (99 percent , Aladdin) was dried at 100 degree for 24 h under vacuum and stored in an Ar-filled glove box. Firstly, LiTFSI was dissolved in anhydrous acetonitrile, and UiO-66 and PEO were added under magnetic stirring to afford homogeneous solution, in which the molar ratio of EO : Li plus was kept 16 : 1, and the content of nano-sized UiO-66 fillers was designed to be 0, 5 percent , 10 percent , 15 percent , 20 percent , 25 percent , naming the corresponding electrolytes as SPE, CPE-(5 percent , 10 percent , 15 percent , 20 percent , 25 percent ). Afterwards, the solution was cast on polytetrafluoroethylene template to volatilize the solvent at ambient temperature. Finally, the membranes were dried at 60 degree for 12 h under vacuum to volatilize the residual solvent.
1.3 Näyte karakterisointi
The kiteinen rakenteet ainesosat kerättiin röntgen diffraktio (XRD) kanssa Cu-K säteily (λ=0.1542 nm) at huone lämpötila (2θ=5 aste -50 aste ) with the step of 0}.1 ( degree )/s. The structure morphologies of UiO{-66 and CPE paljastettiin by the scanning elektroni mikroskopia (SEM, Hitachi, S-3400N).
1.4 Sähkökemiallinen mittaus ja kennot kokoonpano
The ionic conductivity was measured at temperature from 25 to 80 degree in symmetric cell with stainless steel (SS) electrodes by the AC impedance analysis (Autolab, Model PGSTAT302N) in the frequency range from 1 Hz to 1 MHz and at an amplitude of 50 mV. Linear sweep voltammetry (LSV) was employed to examine the electrochemical window in SS/electrolyte/Li cells, conducting from 3 to 5.5 V at a scan rate of 10 mV/s. The transference number of Li plus (t plus ) was tested in Li/electrolyte/Li cells and calculated according to t plus {{10}} I∞( Δ V−I0R0)I0( Δ V−I∞R∞), where ΔV is the applied DC polarization voltage (10 mV), I0 and I∞ are the initial and steady current values during polarization, respectively. R0 and R∞ are the resistance values before and after polarization, respectively. For inhibition ability of lithium dendrites growth test, a symmetric cell with solid electrolyte sandwiched between two lithium metal electrode was assembled, and the test was carried out at 60 degree .
2 Tulokset ja keskustelu
UiO{{{0}} ([Zr6O4(OH)4(BDC)6], missä BDC2- is 1,4- bentseenidikarboksyyli happo radikaali) kanssa a kasvokeskeinen kuutio (fcc) hila rakenne (kuva 1(a)) koostuu of Zr6O4(VAI NIIN)4 klusterit ja BDC linkittimet omistaa 1,2 nm oktaedrinen ja 0,75 nm tetraedral häkit. Kuva 1(b) is SEM kuva of valmis UiO-66 missä kiteet are pallomainen muoto kanssa 80-150} nm in koko. The UiO-66 was incorporated into PEO-LiTFSI polymeeri elektrolyytti to fabricate komposiitti elektrolyytti by simple solution-cast method. A sileä pinta of komposiitti elektrolyytti on havaittu in kuva kuva 1(c), inindication that the nano-sized UiO-66 täyteaineet ovat tasaisesti jakautuneet in PEO matriisi johtuva to the epäorgaaninen-orgaaninen hybridi ominaisuus of UiO-66}.
Kuva 1% c2% a0 % c2% a0 (a) kide rakenne UiO% 7b % 7 b 1 % 7 d % 7 d % 2c ja SEM kuvat (b) nanokokoinen UiO% 7b % 7 d ja (c) Uio % 7b % 7b4% 7d % 7 d % 2 fPEO komposiitti polymeeri elektrolyytti
The vaihe puhtaus of valmisteltu UiO-66 kiteet vahvistettiin by XRD kuvio joka vastaa hyvin kanssa simuloitu yksi perustuu on raportoitu hila parametrit, as näytetty in kuva 2(a), osoittava onnistunut synteesi nanorakenne of UiO-66}. The content of UiO{{{-66 in polymeeri elektrolyytti oli optimoitu saavuttaa korkea ioni johtavuus. Arrhenius tontit for PEO elektrolyytit kanssa erilainen UiO-66 contents are shown in Fig. 2(b).
Viikuna. 2 (a) XRD kuviot of simuloitu UiO-66, syntetisoitu nanokokoinen UiO{-66, PEO, ja CPE-10 prosenttia ; (b) Arrhenius tontit for the ioni johtavuus of PEO elektrolyytit kanssa erilainen sisältö of UiO-66; (c) Nyqiust plots within taajuus of 1 Hz-1 MHz for the CPE-10 prosenttia at lämpötila aste % 3b (d) LSV käyrät SPE CPE in SS% 2felektrolyytti % 2fLi solut at 60 aste % 3b (e) DC polarisaatio profiili symmetrinen Li% 2fSPE /Li kenno at an an sovellettu jännite jännite 10 mV at at at 60 60 aste aste ; 3a AC impedanssi spektrit vastaava symmetriset solut ennen ja jälkeen DC polarisaatio
It is clear that higher ionic conductivity is obtained with the addition of the nano-sized UiO-66 into PEO electrolyte. As the coordination of [Zr6O4(OH)4]12 plus with oxygen in PEO reduces the crystallinity of PEO chain to promote the segmental motion of polymer chain, which is proved by the XRD pattern of CPE-10 percent compared with PEO (Fig. 2(a)). Moreover, the interaction between [Zr6O4(OH)4]12 plus and TFSI- promotes the dissociation of lithium salt. The increase of UiO-66 fillers content below a certain value is accompanied by the promotion of ionic conductivity. However, the further increase of fillers reduces ionic conductivity owing to dilution and block effects. The CPE-10 percent shows the highest ionic conductivity (3.0×10-5 S/cm at 25 degree , 5.8×10-4 S/cm at 60 degree ), while the ionic conductivity of SPE is only 5.0×10-6 S/cm at 25 degree and 1.7×10-4 S/cm at 60 degree . The conducting properties of CPE-10 percent at the temperature from 25 to 80 degree were also investigated by AC impedance spectroscopy, and the Nyqiust plots are presented in Fig. 2(c). It shows that the impedance value decreases with the temperature increasing.
The effect of UiO{{0}} on the electrochemical window of PEO electrolyte was investigated by LSV at 60 degree . As shown in Fig. 2(d), the steady platform of CPE-10 percent at about 4.9 V is higher than that of SPE, owing to the coordination of UiO-66 with oxygen which promotes the oxidation voltage of PEO and the fact that Zr(IV) in UiO-66 is difficult to be reduced. Thus, it is expected that the CPE is suitable for a lithium battery matching with high-voltage positive cathode. The transference number of Li plus is an important parameter providing information about the rate capability contribution of Li plus in solid state electrolyte. Time-current curves following 10 mV of DC polarization for SPE and CPE-10 percent are presented in Fig. 2(e-f). The t plus of CPE-10 percent is 0.36 and higher than that of SPE (0.25). It is due to the fact that the coordination of [Zr6O4(OH)4]12 plus with the oxygen of PEO in CPEs weakens the coordination of oxygen with Li plus deriving the transfer of Li plus , and a fraction of anions are immobilized by [Zr6O4(OH)4]12 plus .
The long-term electrochemical stability against lithium anode is one important feature of solid-state electrolyte, which could be measured by galvanostatic lithium plating and striping in symmetric Li/electrolyte/Li cells. Fig. 3(a) shows a voltage window with a constant current density of 0.15 mA∙cm-2 for 1 h each cycle at 60 degree . In Fig. 3(b), the symmetric Li/CPE-10 percent /Li cell shows a charge-discharge voltage range between -0.058 and 0.06 V in the first cycle and then slightly decreases to -0.048-0.053 V after 900 cycles, indicating the good electrochemical stability between CPE and lithium metal and the excellent CPE ability to block lithium dendrite growth. This ability can be ascribed to the following factors: (1) the improved mechanical strength; (2) a fraction of anions immobilized by [Zr6O4(OH)4]12 plus boosting the uniform Li plating and striping. In contrast, the charge-discharge voltage of symmetric Li/SPE/Li cell ranges from -0.25 to 0.37 V in the first cycle (Fig. 3(b)), and the battery shows short circuit after 104 h. Such poor cycle performance could be blamed for uneven Li plating and striping, which results from the low t plus of SPE possessing plenty of free anions.
Kuva 3% c2% a0 % c2% a0 (a) galvanostaattinen syklit kanssa a vakio virta tiheys % 7b % 7 b 1 % 7 d % 7 d .15 mA% e2% 88% 99cm % 7b % 7 b symmetrinen Li 2fCPE % 7b % 7 b4 % 7 d% 7d prosentti % 2fLi ja Li Li 2fSPE % 2fLi solut at 60 aste % 2c (b) suurennus of galvanostaattiset syklit of Li % 2fCPE % 7 d prosenttiaof galvanostaattinen syklit of Li/CPE-10 prosentti /Li solu at 895-900 sykli
3 Johtopäätös
In summary, the PEO-based electrolyte with UiO-66 as filler was fabricated via solution-casting technique. The as-obtained CPE-10 percent shows high ionic conductivities of 3.0×10-5 S/cm at 25 degree and 5.8×10-4 S/cm at 60 degree , which are attributed to the following factors: (1) the low crystallinity of PEO owing to the coordination of [Zr6O4(OH)4]12 plus with oxygen in PEO chain; (2) the interaction between TFSI- and [Zr6O4(OH)4]12 plus promoting the dissociation of lithium salt. The higher transference number of Li plus (0.36) is due to the immobility of a fraction of anion which also benefits the ability to suppress lithium dendrite growth of the CPE. The improved mechanical strength and excellent electrochemical stability of CPE against lithium metal endow the effective suppression of lithium dendrite growth, enabling a long cycle life for lithium metal batteries (over 1000 h cycling at 0.15 mA∙cm-2, 60 degree ).
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