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Highly Conducting Carbon-Coated Current Collector "SDX®" for Large Li-Ion Batteries

Advanced Battery Materials DivisionSHOWA DENKO K.K.

AABC Europe 2017

Tuesday, 31 January

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Agenda

■ Introduction of SDX®

■ Today’s presentation

1. Evaluation of Area-densification with SDX®

2. Evaluation of Cell performance with SDX® in several distribution

states of conducting additives

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SDX® is carbon coated current collectorSDX® which is surface coated Al foil (AL) with carbon black (CB) and organic binder, makes a cell resistance lower and adhesion between active materials and collector stronger, so as to improve battery performances dramatically.1)～3)

SDX®Collector

Cu Foil

Active material

：Graphite, etc.

Anode Cathode

Separator

< 1μm

Active material

：LFP, NMC, NCA, LCO

Conducting additives

：CB, VGCF®

Binder：PVdF

（ Carbon coated layer＋AL ）

【 Surface appearance 】

【 Secondary electron image 】

1) M. Ohmori et al., Electrochemistry, 78, 308, (2011)2) The AABC Europe (2011)3) M. Ohmori et al., Electrochemistry, 79, 165, (2012)AL is conventional current collector, and will be used as ref. and compared to SDX.

What’s Cell internal resistance ?

Electronic resistance

Discharge

+= Material

resistance

e-

e-

e-

CathodeAnodee-

Li+

e-

e-

e-

Separator

Cu foil AL

FePO4 ＋ Li+ ＋ e- → LiFePO4C6Li → 6C ＋ Li+ ＋ 6e-

Ion resistance

Cell internal resistance

= +Interface

resistance

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The interface resistance between LFP and AL was higher thanthe material resistance of LFP by almost one order of magnitude.4)

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The material resistance and the interface resistance of LFP

Cathode : LFPCathode density : 150g/m2

Electrode density : 2.0g/cc

Measured by Electrode Resistance Meter (HIOKI E.E. CORPORATION).

AL_Interface resistance

AL_Material resistance

4) H. Tomozawa et al., Electrochemistry, 2C25, (2015)

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The material resistance and the interface resistance of LFP

Cathode : LFPCathode density : 150g/m2

Electrode density : 2.0g/cc

Measured by Electrode Resistance Meter (HIOKI E.E. CORPORATION).

AL_Interface resistance

AL_Material resistance

4) H. Tomozawa et al., Electrochemistry, 2C25, (2015)

SDX®_Material resistance

SDX®_ Interface resistance

The interface resistance of LFP with SDX® was lower than with AL by almost one order of magnitude.4)

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Adhesive performance of cathode

Pe

elin

g st

ren

gth（

N/m

）

Peeling distance（mm）

【 180°peeling test 】

Cathode：LFPCathode density：150g/m2

Electrode density：2.0g/cc

Peeling speed：300mm/minSample width：30mm

Higher adhesive strength than AL based electrode.

Current Collector / CB / PVdF

SDX® / 3% / 3%

SDX® / 12% / 7%

AL / 12% / 7%

Relations of Cell DCR with AL or SDX®

The Cell DCR with SDX® was maintained at a lower resistance level than with AL even if a smaller amount of conducting additives was added.4)

【 Cell DCR 】

Anode：Artificial Graphite_SCMG®Electrolyte：EC / EMC, LiPF6

Discharge capacity：100mAh

AL

SDX®

Conducting additives（%）

84) H. Tomozawa et al., Electrochemistry, 2C25, (2015)

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SDX®_Charge／Discharge Performance

SDX® has excellent charge/discharge performance for high rate.

【 Discharge Performance 】 【 Charge Performance 】

AL

SDX®

SDX®

AL

Cap

acit

yre

ten

tio

n v

s 0

.5C（

%）

rate （C） Cathode：LFP / CB / PVdF = 84 / 6 / 10Anode：SCMG® / CB / PVdF = 94 / 1 / 5

rate （C）

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■Improve cell performance

・ Reduction of conducting additives and binder. ⇒ For Higher Capacity

・ Improvement of the charge and discharge performance by decreasing of resistance.⇒ For Higher Power

・ Decrease of resistance and enhancement of adhesive strength. ⇒ For longer life

■lower cost of cell

・ Reduction of total material cost by area-densification.→ Today’s presentation 1.

・ Improvement of productivity by speed-up of coating.

→ Today’s presentation 2.

Advantage of SDX® application

By applying SDX®, the interface resistance of cathode could be decreased largely and be maintained at a lower resistance level

even if a smaller amount of conducting additives was added.

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Today’s presentation 1.Evaluation of area-densification with SDX® 4)

4) H. Tomozawa et al., Electrochemistry, 2C25, (2015)

Area-densification⇒ Reduction number of laminating layers

⇒ Reduction of materials consumption – Cu foil, separator and AL

⇒ Cost reduction and higher energy density

Anode

Separator

Cathode

It can reduce materials consumption – Cu foil, separator and AL etc.

【 Design of area-densification 】

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Trial of area-densification for cathode

Anode：Artificial Graphite_SCMG®Electrolyte：EC / EMC, LiPF6

Cathode collector AL SDX®

Cathode：LFP 90.5% 92.5% 93.5% 94%

Conducting additives：CB 4.5% 2.5% 1.5% 2.5%

Binder：PVdF 5% 3.5%

Cathode density（g/m2） 160 ～ 220 g/m2

Solid content of cathode slurry（%）@5Pa・s

47% 50% 55% 53%

※ Key point : Reduction of CB and PVdF with SDX®

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CB:1.5% / PVdF:5%

CB:2.5% / PVdF:5%▲

CB:2.5% / PVdF:3.5%

CB:4.5% / PVdF:5%AL

CB:4.5% / PVdF:5%

◇：1319mΩ◇：721mΩ

Cathode density（g/m2）

Solid line：SDX®Dotted line：AL

Cell DCR_After initial discharge @SOC50%

The Cell DCR with SDX® was maintained at a lower resistance level than with AL in the area-densification.

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Sample width ： 30mmPeeling rate： 300mm/min

CB:2.5% / PVdF:5%

CB:2.5% / PVdF:3.5%

AL_160g/m2

SDX®_205g/m2

SDX®_205g/m2

Peeling distance（mm）

Pe

elin

g st

ren

gth（

N）

Adhesive performance of cathode【 180°peeling test 】

CB:4.5% / PVdF:5%

The peeling strength of electrode with SDX®_205g/m2

was higher than with AL_160g/m2.

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AL160g/m2_CB:4.5% / PVdF:5%

SDX®160g/m2_CB:4.5% / PVdF:5%205g/m2_CB:2.5% / PVdF:5%205g/m2_CB:2.5% / PVdF:3.5%205g/m2_CB:1.5% / PVdF:5%

AL205g/m2_CB:4.5% / PVdF:5%

Cycle performance @50℃,1C/1CC

apac

ity

Ret

en

tio

n（

%）

The cycle performances with SDX® in the area-densification was better than AL.

・ Solid content of cathode slurry・ Adhesive performance of cathode

・ Cell DCR・ Cycle performance

Reduction of CB and PVdF with SDX® was evaluated.As a result, the following performance was improved.

Electrode performance

Cell performance

→ Area-densification is recommended from results above.

Summary 1.

By applying SDX®,

➢ Cost reduction and higher energy density by reduction of materials consumption is expected.

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Today’s presentation 2. Evaluation of Cell performancewith SDX® in several distribution state of conducting additives5)

When the coating speed is fast, most of solvents aren’t dried mildly during pre-drying and are dried rapidly during main-drying. At this moment a solvent, binder and conducting additives are moved to the upper portion because slurry viscosity at an early stage of drying is low, and diffusion speed is high. On the other hand, when the coating speed is slow, most of solvents are dried mildly during pre-drying.6)

5) H. Tomozawa et al., PRiME 2016, A06-0898

6) H. Fukumitsu et al.,Sumika Chemical Analysis Service, Ltd.,The 53rd Battery Symposium in Japan, 3C05

Coating speed 300mm/min 400mm/min 500mm/min

Electrode image drawing

Distribution states of conducting additives and binder

AL

Conducting additive

Binder

moved to the upper portionEvenly

distributedUnevenly

distributed

Mild drying Rapid drying

➢ It’s presumed the above result is caused by the decreaseof conducting additives in the bottom portion. 18

The material resistance and the interface resistance of LFP

The interface resistance of LFP increased as coating speed increased.

AL

_Interface resistance

AL_Material resistance

Measured by Electrode Resistance Meter (HIOKI E.E. CORPORATION).

➢ It was stable irrespective of the decrease ofconducting additives in the bottom portion.

The material resistance and the interface resistance of LFP

AL

_Interface resistance

AL_Material resistance

Measured by Electrode Resistance Meter (HIOKI E.E. CORPORATION).

The interface resistance of LFP with SDX® was constant.

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SDX®_Interface resistance

SDX®_Material resistance

The cell DCR showed similar behavior to the interface resistance.➢ The cell DCR with SDX® was constant irrespective of

the distribution state of conducting additives. 20

【 Cell DCR 】

AL

SDX®

【 Electrode resistance (previous report) 】

Electrode resistance, Cell DCR of LFP with AL or SDX®

AL

_Interface resistance

SDX®_Interface resistance

Result：Distribution states of conducting additives and binder, behavior of the interface resistance in LFP

Coating speed 300mm/min 400mm/min 500mm/min

Electrode image drawing

Distribution states of conducting additives and binder

AL_Interface resistance

SDX®_Interface resistance

AL, SDX®_Peeling strength

AL

Conducting additive

Binder

moved to the upper portionEvenly

distributedUnevenly

distributed Increase

conducting additives in the bottom portion decrease

Maintained at a lower resistance level

decreaseBinder in the bottom portion decrease

Mild drying

Rapid drying

The capacity retention with AL decreased as the coating speed increased.

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From the left, the coating speed is 300, 400, 500mm/min

AL_Discharge Performance

Cap

acit

yre

ten

tio

n v

s 0

.5C

300400

500

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From the left, the coating speed is 300, 400, 500mm/min

Cap

acit

yre

ten

tio

n v

s 0

.5C

AL, SDX®_Discharge Performance

■：AL■：SDX®

300400

500

・The discharge performance with SDX® was higher than with AL.

・The capacity retention with SDX® was constant irrespective of the coating speed.

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Summary 2.

・ Interface resistance of LFP could be decreased largely irrespective of the distribution state of conducting additives.

・ As a result, Cell DCR and discharge capacity retention of LFP was constant irrespective of the coating speed.

・ In LIB manufacturing process, even if each cell has a different distribution state of the conducting additives in electrode,

➢ Uniformity of performance of LIB can be obtained. ➢ Productivity is improved. ➢ Cost reduction by speed-up of coating is expected.

By applying SDX®,

Thank you for your attention

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