Bicomponent Blend-electrospun Separator ... · PDF fileBicomponent Blend-electrospun Separator...

Bicomponent Blend-electrospun Separator

for Lithium ion Battery

http://www.tjpu.edu.cn

TJPU

Yanbo Liu*, Dongyue Qi, Wenxiu Yang, Weiya Chen

School of Textiles, Tianjin Polytechnic University, Tianjin 300387, China

1. Introduction

2. Experimental

3. Results and discussion

4. Conclusion

5. Acknowledgement

6. Reference


TJPU1. INTRODUCTION

3

Battery:A container in which chemical energy is

converted into electricity and used as a

source of power, composed of anode,

separator, electrolyte solution, cathode,

shell, etc.

Lithium-ion battery (LIB):An electrochemical system in which

lithium ions move from the negative

electrode to the positive electrode during

discharge and back when charging.Y. Nishi, Chem. Rec. 1(2001) 406-413.

• High energy capacity, high storage energy density

• Long life cycle (charging/discharging: 500-10000 times)

• High nominal voltage, favoring for battery power pack

• High power, low self-discharging rate

• Small volume, light weight

• Green and environmentally friendly tech

• Fast charging/discharging rate

• No memory effect

• Potential to form high capacity battery pack for applications

in electric vehicles

• High cost/price, low safety, easy to explode/get fire


TJPUFeatures of Li Ion Battery


TJPUThe Role of Separator in LIB

Cost: 30%; Profit: 70%

• Provide a barrier between the anode and the cathode while

enabling the exchange of lithium ions from one side to the other in

the battery, to prevent short-circuit.

• Has high porosity (＞45%), high Li ion permeability, low internal

resistance

• Possesses high safety and thermal stability: mechanical; dimensional

• Cut off the electric current when temp of the battery is unreasonably

elevated as a smart safety apparatus: thermal shutdown

• Loose its integrity at high temp: thermal runaway/meltdown

• It is very important to design a battery separator having appropriate

shutdown temp and high meltdown temp.


TJPUThe Role of Separator in LIB

Conventional manufacture methods:

• stretching (dry method); or thermally induced phase separation (wet

method)

• polymers: PP, PE, PP/PE/PP

Most recently developed methods:

• ceramic coating for enhanced performance of high-temp resistance and

dimensional stability, but easy to block the pores

• electrospinning with high melting point polymer such as PVDF, PI, etc.

Shut down temperature and melting point of polyolefin membrane


TJPUExisting Separator Technology

• Monocomponent polymer based separator cannot impart separator

with thermal shutdown property and thermal runaway property at

the same time

• Monocomponent polymer based separator having high melting

point is not safe at elevated temp, because other materials in the

battery may change their properties at high temp due to

unexpected chemical reactions, causing fire or explosion

• Current PP/PE/PP trilayer separator does not have sufficiently high

meltdown temp and sufficiently low shutdown temp

• Proper shutdown temp ranging from 110~125℃; the higher the

better for the meltdown temp


TJPUProblems with Current Separators


TJPUProblems with the LIBs

• The thermal property of separator is a key role in LIB security performance

• Novel bico ES tech could impart the separator with thermal shutdown and thermal

meltdown functions at the same time

Exothermic and decomposed temperature of

cathode materials with electrolyte

Temperature range and enthalpy of various

exothermic reactions in LIBs

The Advantages of ES Separator

Technical features： simple process; easy to control product specification; wide

materials types; high P/C ratio

Product advantages：high electrolyte absorbent rate; high Li ion permeability;

excellent electrochemical performance; long life cycle;

favoring the applications in high power/capacity LIBs, after

the design for enhanced thermal stabilities

Product disadvantages: low mechanical strength

Application fields：separators for medium/high end LIBs, especially for power LIBs

Bico composite electrospun separators

Feature 1: The bico composite electrospun separators contains a lower melting point

thermal plastic polymer compared to the other component

Feature 2: The low melting point component plays as a part of fiber binder, which impart

the bico composite electrospun separator with enhanced mechanical property upon

thermal calender bonding

Feature 3: The low melting point component provides the low temperature shutdown

function, enhancing the security performance of the separator

A schematic for Electrostatic spinning or Electrospinning process

Components of ES setups

（1）DC/AC high voltage power source（2）Spinneret（needle/needleless）（3）Solution feeding system（4）Fiber receiving system

Process parameters

（1）Polymer and solution parameters（2）Equipment：ES type; spinneret specification; receiver type, etc.（3）Process variables：voltage; receiving distance; feeding rate（4）Atmospheric variables：temp; RH; surrounding gas; gas speed


TJPUIntroduction to ES Process

Research objectives and methods

Bico polymer blend ES→ES separator→thermal calender

→ characterization of the ES separator

Bico polymer pair selection：PVdF-HFP)/(PI-TiO2)

For comparison, three samples to be prepared and evaluated:

(1) PI/PVdF-HFP (PI/PH, with no nanoparticles contained in PI),

(2) TiO2@PI/PVdF-HFP (T@PI/PH, with TiO2 mixed in PI)

(3) f-TiO2@PI/PVdF-HFP (f-T@PI/PH, with f-TiO2 blended in PI)

TiO2 is easy to get aggregated when blending with PI in solution,

Modification of TiO2 is required for successful co-electrospinning


TJPU2. EXPERIMENTAL

• PVdF-HFP=Poly(vinylidene fluoride-co-hexafluoropropylene,PH), MW =600,000• PI=Polyimide,MW =180,000• f-TiO2=Functionalized TiO2, synthesized by the atom transfer radical polymerization

process• TiO2=Titanium dioxide powder, average particle sizes of 20-30 nm.• DMF=N,N-Dimethylformamide• NMP=N-methyl-2-Pyrrolidone• APTES=3-aminopropyl triethoxysilane ( 98%),• 2-brom-opropionyl bromide (97%),• PMDETA=N,N,N’,N’’,N’’’-pentamethyldiethylenetriamin (99%),• HEMA=2-hydroxyethyl methacrylate(96%) ,used to modify TiO2

• Other raw materials and reagents: triethylamine, acetone, toluene, methanol andCuBr(cupper bromide)

2.1. Materials and reagents


TJPU2. EXPERIMENTAL

2.2 Synthesis of TiO2-HEMA(f-TiO2)

(a) Agglomerated nanoparticles in the polymer for electrospinning without grafted polymer and

(b) Separation of particles due to the existence of the grafted polymer.

Functionalized TiO2 (f-TiO2) was synthesized by the

atom transfer radical polymerization process


TJPU2. EXPERIMENTAL

2.3. Preparation of separators

The schematic illustration of the preparation of electrospun separator and battery assembling.

Preparation of solutions of polymer solutions: • PI/PVdF-HFP solution (14 wt%) ：using mixture solvent of DMF/acetone(7/3 w/w)

• Nanoparticles@PI/PVdF-HFP solution (23 wt%) : dissolving the polymer and nanoparticles in NMP

with magnetic stirring at the temperature of 70 ℃ for 10 h after 30 min ultrasonic treatment to

achieve dispersion liquid, the ratio of nanoparticles/PI =0, 1, 2, 3% w/w

Co-electrospinning setup:• Four-needle electrospinning apparatus was set up

• Two of which were fed with PVdF-HFP(PH) solution and others with nanoparticles@PI solution

• The two types of polymer solutions were arrayed alternately in a straight line to form a composite

membrane.

Conditions for co-electrospinning:

• Same voltage 20 kV applied for both solutions

• Injected flow rates of 1 ml/h and 1.5 ml/h, respectively.

• Fiber receiving distance: 20 cm(rotational speed of the drum is 2 RPM)

• Needle diameter: OD=0.91 mm; ID=0.61 mm

• Needle spacing: 2cm , moving reciprocally with the amplitude of 30 cm.


TJPU2. EXPERIMENTAL


TJPU2. EXPERIMENTAL

Bico co-electrospinning process Resultant co-electrospun membrane


TJPU3. RESULTS AND DISCUSSION

3.1. Characterization of nanoparticles

The FTIR spectra of TiO2 and

f-TiO2 nanoparticles.

UV-vis absorption spectrum of TiO2 and

f-TiO2 nanoparticles in NMP



3.2. Preparation and characterization of

electrospun composite membrane

SEM images:

(A) PI/PH,

(B) T@PI/PH

(C) f-T@PI/PH

with different nanoparticle concentration: (a)

1%, (b) 2%, (c) 3%

EDX / Energy-dispersive X-ray spectra

(D) 2% T@PI/PH

(E) 2% f-T@PI/PH

Compared with T@PI/PH membrane, the content of

C and O element slightly increased for f-T@PI/PH

membrane demonstrated by higher intensity in EDX

spectrum, which indicated the presence of HEMA.

(a) Porosity, liquid electrolyte uptake and (b) liquid electrolyte contact angle of electrospun

composite membranes with different nanoparticle concentration (0%, 1%, 2% and 3%) after

thermal calendering process.



Thermal calendering:135 ℃, 0.8 for 5 min



3.3. Mechanical and thermal properties of electrospun composite membrane

3.3.1. Mechanical property

The morphologies:

(a) PI/PH

(b) 2% T@PI/PH

(c) 2% f-T@PI/PH membranes

after thermal calendering process

(d) the stress-strain curves before and after

thermal calendering process of membranes.



3.3. Mechanical and thermal properties of electrospun composite membrane

3.3.2 Thermal property of electrospun composite membrane

(a) DSC curves of PI/PH, 2% T@PI/PH and 2% f-T@PI/PH after thermal calendering

(b) Photos of composite electrospun membranes before and after thermal treatment.

SEM photos of co-ES membrane before and after thermal calendering process: tortuous pores



Mono directional stretched PP and PE

Celgard (dry method)Asahi Hipore-2 (wet method)



SEM of commercial separators: through holes

Co-electrospun separator after

drying for 30min at 150℃

SEM photos before and after drying for 30min at 150℃

Co-electrospun separator before

drying for 30min at 150℃

Thermal stabilityshutdown & meltdown

Asahi stretched film Asahi stretched film

Before and after heating at 150℃,for 30min





3.4 Electrochemical performances of composite separator

Nyquist plots of SS/electrolyte-soaked

separator/SS cells at room temperature.

Linear sweep voltammograms of different

electrospun separators.



3.5. Battery performances

The AC impedance spectra of the half-cell

with different electrospun separators.

First-cycle charge-discharge curves of Li/LiCoO2

cells containing PI/PH, 2% T@PI/PH and 2%

f-@PI/PH fibrous separator at 0.5C.



3.5. Battery performances

Cycling performance of Li/LiCoO2 cells containing PI/PH,

2%T@PI/PH and 2%f-T@PI/PH fibrous separator at 0.5C.


TJPU4. CONCLUSION

• The TiO2 nanoparticles@PI/PH bico composite separators could be successfully

prepared by co-electrospinning process.

• 2% f-TiO2 nanoparticle with better dispersibility produced by ATRP method:

• reduced the PI fiber diameter

• improved the physical property of co-ES membrane: porosity, liquid electrolyte

uptake and wettability.

• excellent mechanical property: due to the existence of fiber binder with low

melting point

• superior ionic conductivity, interfacial and electrochemical stability

• excellent cycling performance

• thermal dimensional stability: due to the existence of PI blended with f-TiO2

• higher safety performance: low temp shutdown & high temp meltdown

• suitable for lithium ion battery separator, particularly power battery separator.

5. Acknowledgement

This study is supported by NSFC（Approval No. 51373121）

Thanks for the efforts and contributions from my graduate students

6. REFERENCE

1. Liu Ling, Zhang Naiqing, Sun Kening, et al. Rare Metal Materials and

Engineering, 2010, 39(5): 936-940

2. Yi Tingfeng，Hu Xingguo，Gao Kun. Battery, 2005, 35(6): 468

3. Huang Haijiang. Shanghai: Shanghai Institute of Microsystem and

Information Technology, 2005:103

4. Kominato A. Journal of Power Sources, 1997, 68: 471

5. Gerardine Botte G. Journal of Power Sources, 2001, 97-98: 570

6. WeiyaChen, Yanbo Liu, Ying Ma, et al. Materials Letters, 2014, 133:

67–70

7. Weiya Chen, Yanbo Liu, Ying Ma, Wenxiu Yang. Journal of Power

Sources 2015, 273: 1127-1135

8. QI Dong-yue;LIU Yan-bo;MA Ying;XIAO You-hua;SONG Guo-wen.

9. Wu Kai, Zhang Yao, Zeng Yuquan, Yang Jun. Progress in Chemistry.

2011，23 (2 /3) : 401-409

TJPU

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