Electrochemical Properties of Materials for Electrical Energy Storage Applications Lecture Note 6 November 18, 2013 Kwang Kim Yonsei Univ., KOREA kbkim@yonsei.ac.kr 39 Y 88.91 8 O 16.00 7 N 14.01 34 Se 78.96 53 I 126.9
Galvanic cell vs. Electrolytic cell Galvanic cell Electrolytic cell Discharge Charge Electric load DC power supply Electron flow Current flow Electron flow Electron flow Current flow Electron flow ve +ve ve +ve Zn Zn 2+ + 2e Cu 2+ + 2e Cu Zn 2+ + 2e Zn Cu Cu 2+ + 2e Electron generation Electron consumption Electron consumption Electron generation Anodic oxidation Cathodic reduction Cathodic reduction Anodic oxidation Electrochemical cell determines the polarity of electrodes. DC power supply determines the polarity of electrodes.
Galvanic cell vs. Electrolytic cell I net = i c i a Electrolytic cell Charge Electron flow DC power supply Current flow Electron flow E o Cu2+/Cu potential Cell voltage +ve Anodic polarization ve Cathodic polarization ve +ve E o Zn2+/Zn Current Change in electrode potential with current during galvanostatic discharge Zn 2+ + 2e Zn Electron consumption Cathodic reduction Cu Cu 2+ + 2e Electron generation Anodic oxidation DC power supply determines the polarity of electrodes.
Galvanic cell vs. Electrolytic cell Galvanic cell Discharge I net = i c i a Electric load Electron flow Current flow Electron flow ve Cathodic polarization ve +ve E o Cu2+/Cu potential Cell voltage Zn Zn 2+ + 2e Electron generation Anodic oxidation Cu 2+ + 2e Cu Electron consumption Cathodic reduction Electrochemical cell determines the polarity of electrodes. E o Zn2+/Zn Current Change in electrode potential with current during galvanostatic discharge +ve Anodic polarization
Polarization - Activation Polarization : activation Butler Volmer Equation - Concentration Polarization : concentration Activation Controlled Diffusion or Mass Transfer Controlled
Exchange Current Densities in 1 M H 2 SO 4 Electrode log 10 (A/cm 2 ) Material Palladium 3.0 Platinum 3.1 Rhodium 3.6 Nickel 5.2 Gold 5.4 Tungsten 5.9 Niobium 6.8 Titantium 8.2 Cadmium 10.8 Manganese 10.9 Lead 12 Mercury 12.3 The exchange current density for the hydrogen reduction reaction on metals is useful because it give an indication of the speed of this reaction on various metals.
Concentration Polarization Sometimes the mass transport within the solution may be rate determining in such cases we have concentration polarization Concentration polarization implies either there is a shortage of reactants at the electrode or that an accumulation of reaction product occurs O2 4H 4e 2H2O
Mass Transfer Control - If dissolved O 2 in the O 2 reduction is in short supply, mass transfer of O 2 can become rate limiting. - The cathodic charge-transfer reaction at the metal/solution interface is fast enough to reduce the concentration of the reagent at interface (cathodic sites) to a value less than that in the bulk solution. - This sets up a concentration gradient and the reaction becomes diffusion controlled. dn dt dc D dx 10 3 - Under steady state, mass transfer rate = reaction rate i DnF C B C 10 3 0 - Maximum transport and reaction rate are attained when C 0 approaches zero and the current density approaches the limiting current density: i L CB DnF (1) (3) 10 3 (4)
-Fick s Law: dn dt D dc dx 10 3 (1) - Under steady state, mass transfer rate = reaction rate i DnF C B C 10 3 0 - Maximum transport and reaction rate are attained when C 0 approaches zero and the current density approaches the limiting current density: (3) i L DnF C 10 3 (4)
Overpotential due to concentration polarization When current flows, copper is deposited on the electrode, thereby decreasing surface concentration of copper ions to an activity (Cu 2+ ) s. The potential φ 2 of the electrode becomes: If copper is made cathode in a solution of dilute CuSO 4 in which the activity of cupric ion is represented by (Cu +2 ), then the potential φ 1, in absence of external current, is given by the Nernst equation: 0.337 1 2. 3RT 2 2 0.337 log 0.337 log(cu ) 2 S nf (Cu ) S nf 2. 3RT nf 1 log (Cu 1 2 ) 0.337 2. 3RT 2. 3RT nf log(cu Since (Cu 2+ ) s is less than (Cu 2+ ), the potential of the polarized cathode is less noble, or more active, than in the absence of external current. The difference of potential, φ 2 φ 1, is the concentration polarization, equal to: 2. 3RT nf 2 (Cu log (Cu ) ) S 2 1 2 2 )
Pourbaix diagram Many electron-transfer reactions involve hydrogen ions and hydroxide ions. Because multiple numbers of H + or OH ions are often involved, the potentials given by the Nernst equation can vary greatly with the ph. It is frequently useful to look at the situation in another way by considering what combinations of potential and ph allow the stable existence of a particular species. This information is most usefully expressed by means of a E-vs.-pH diagram, also known as a Pourbaix diagram.
Stability of water As was noted in connection with the shaded region, water is subject to decomposition by strong oxidizing agents such as Cl 2 and by reducing agents stronger than H 2. The reduction reaction can be written either as 2 H + + 2 e H 2 (g) or, in neutral or alkaline solutions as H 2 O + 2 e H 2 (g) + 2 OH These two reactions are equivalent and follow the same Nernst equation. E + H /H2 = E o H + /H 2 + (RT / 2F) ln {[H + ] 2 / P H2 } at 25 C and unit H 2 partial pressure reduces to E = E 0.059 ph = 0.059 ph
Stability of water Similarly, the oxidation of water H 2 O O 2 (g) + 4 H + + 2 e is governed by the Nernst equation. E O2 /H 2 O = E o O 2 /H 2 O + (RT/4F) ln {P O2 [H + ] 4 } at 25 C and unit H 2 partial pressure reduces to E = 1.23 0.059 ph
1 gram equivalent weight : 96485C or 26.8 Ah [Coulomb] = [Ampere] x [second] = [Ampere] x [h/3600] Zn(s) Zn 2+ (aq) + 2e Cu 2+ (aq) + 2e Cu(s) Atomic weight : 65.4 g g equi. weight : 65.4 / 2 = 32.7g Capacity : 26.8Ah/32.7g = 0.82Ah/g 1.22 g/ah Atomic weight : 63.5 g g equi. weight : 63.5 / 2 = 31.75g Capacity : 26.8Ah/31.75g = 0.84Ah/g 1.19 g/ah
Theoretical Capacity (Ah/g or mah/g) of LiCoO 2 1 gram equivalent weight : 96485C or 26.8 Ah [Coulomb] = [Ampere] x [second] = [Ampere] x [h/3600] CoO 2 + Li + + e LiCoO 2 ; discharge Molecular weight of LiCoO 2 : 97.871 g g equi. weight : 97.871 / 1 = 97.871 g Capacity : 26.8 Ah / 97.871 g = 0.274 Ah/g = 274 mah/g
1950 년 1970 년 1990 년 2000 년 2005 년 2013 년 납축전지생산 (1944, 한국전지 ) 건전지생산 (1946, 로켓트전지 ) 니켈카드뮴전지생산 (1986, 로켓트전지 ) 니켈수소전지생산 (1996, 로켓트전지 ) 리튬이차전지생산 (1999, LG 화학, 삼성 SDI) 전기차용리튬폴리머전지생산 (2005 LG 화학 ) 전기차용리튬이차전지생산 (2011, 삼성 SDI) 납축전지 (40Wh/kg) 니켈카드뮴 (60Wh/kg) 니켈수소 (80Wh/kg) 리튬이온 (150Wh/kg) 나트륨황 (120Wh/kg) 레독스흐름 (35Wh/kg) 슈퍼커패시터 (40Wh/kg) 공기아연 (300Wh/kg) 04 년처음으로수출이수입량추월 11 년리튬이차전지세계시장점유율 1 위
전지산업의파급효과로본융 복합산업 후방산업의원천기술개발과전방산업의미래시장선점등산업장벽을뛰어넘는시너지효과발생 1 녹색성장의핵심산업 2 핵심소재의중요성 3 전 후방산업에대한연쇄효과가큰산업 [ 후방산업 ] [ 전방산업 ] 소재산업 소재 양극음극분리막전해질 전지산업 IT 산업 스마트폰 (Communication) Tablet PC / 노트북 (Computer) MP3/ 디카 (Consumer) 전기자동차 원료 수송기계산업 / 전기자전거 원료산업 리튬망간흑연황 코발트니켈수은아연 지능형로봇 신재생에너지에너지산업 ( 효율향상 ) ESS ( 저장 활용 )
EV ESS
이차전지시장전망 이차전지시장은 12 년 601 억불에서 20 년 1,149 억불로연평균 8% 성장 리튬이차전지는 12 년 157 억원에서 20 년 659 억불로연평균 19.6% 고성장전망전체이차전지중리튬이차전지의비중이큰폭으로증가할전망 전체이차전지중리튬의비중의변화전망은 12 년 26% 20 년 57% ( 억불 ) 연평균성장률 1,149 1,200 이차전지 ( 전체 ) : 8% 1,000 800 600 리튬이차전지 : 19.6% 601 26.1% 157 762 301 39.5% 659 57.4% 리튬이차전지 납축전지 전체 400 200 73.9% 60.5% 444 461 490 42.6% - 2012 년 2015 년 2020 년 ( 출처 : B3, 후지경제 )
리튬이차전지시장전망 향후리튬이차전지시장은중대형중심으로연 40% 이상급속히성장 향후자원고갈, 환경규제에따라 xev, ESS 등중대형시장중심으로재편될전망 소형전지는완만한성장이예상되며, 당분간세계 1 위는지속전망 2003 년 ~2010 년까지는소형전지가시장주도 ( 연평균 20.2% 성장 ) 연평균성장률 659 ( 억불 ) 소형 IT : 0.9% 700 600 전기차 : 46.7% E S S : 40.9% 264 40.1% ESS 용 LIB 500 xev 용 LIB 400 300 200 100 17 12 157 10.8% 7.6% 81.5% 257 128 138 39.0% 20.9% 소형 LIB 전체 - `12 년 `20 년 ( 출처 : B3, 후지경제 )
주요국별산업현황
생 ( 억불 ) 250 200 150 100 50 0 산 : 12년약 87억불수준수출 : 12년약 58억불수준 160 224 40 48 67 16 20 20 22 24 10 년 11 년 12 년 15 년 20 년 리튬전지 납축전지 ( 억불 ) 60 50 40 30 20 10 0 24 33 35 10 8 11 13 12 `08 년 `09 년 `10 년 `11 년 `12 년 40 46 리튬전지 납축전지 점유율 ( 전지 ) ( 출처 : 업계조사자료 ) 점유율 ( 소재 ) ( 출처 : 무역협회 & 업계조사자료 ) 국산화율 2012 43% 30% 21% 5% 한국 2011 40% 35% 20% 5% 일본 2010 35% 41% 20% 4% 중국 2009 31% 43% 20% 3% 기타 2008 22% 51% 23% 2% 0% 50% 100% 출처 : B3 Report 2012 24% 41% 27% 8% 한국 2011 21% 47% 24% 9% 일본 2010 16% 52% 22% 10% 중국 2009 13% 55% 20% 12% 기타 2008 12% 63% 14% 12% 0% 50% 100% 출처 : Yano 구분 (%) `09 `10 `11 `12 양극재 41 46 62 69 음극재 0 0 0 1 분리막 15 12 15 21 전해액 54 66 70 80 ( 출처 : 녹색기술선도형이차전지기술개발, 한국전지산업협회재구성 ) * 양극 : 한국유미코아 ( 벨기에 ) 의국산화율 37% 포함 * 전해액 : 첨가제전량수입의존
기업현황 국내 10 대그룹중 7 대그룹이이차전지산업에투자 제조 양극 L&F 신소재, 삼성코닝정밀소재, 에코프로 한국유미코아, 삼성정밀화학, 코스모신소재 한화케미칼, 포스코 ESM, 대정이엠 음극 부품 소재 GS 에너지, 포스코켐텍, 일진전기 애경유화, 모간코리아, 세진이노테크 분리막 SK 이노베이션, SKC, 씨에스텍 장비 전해액 후성, 에코프로, 파낙스이텍, 솔브레인
이차전지의응용분야
모바일디바이스의전원의발전 Trend( 삼성전자 )
Energy Storage Systems (ESS) Smart grids provide enhanced, real-time data on demand patterns, which although useful to utilities and customers, cannot be efficiently managed without integrated energy storage. More efficient use of generated electricity reduces dependency on fuel imports and cuts CO₂ emissions. With $32bn spent on smart grids worldwide, many governments are finally investing in the benefits of smart grid management.
Batteries
Battery Electrode Reactions
Battery Electrode Reactions The Li electrode in Figure B is discharged by oxidation. The formed Li+ cation is going into solution. The reaction is reversible by redeposition of the lithium. However, like many other metals in batteries, the redeposition of the Li is not smooth, but rough, mossy, and dendritic, which may result in serious safety problems. Here, the formed Pb2+ cation is only slightly soluble in sulfuric acid solution, and PbSO4 precipitates at the reaction site on the electrode surface. This solution precipitation mechanism is also working during the charge reaction, when PbSO4 dissolves and is retransformed into metallic Pb.
Battery Electrode Reactions Figure D shows a typical electrochemical insertion reaction. The term electrochemical insertion refers to a solid state redox reaction involving electrochemical charge transfer, coupled with insertion of mobile guest ions (in this case Li+ cations) from an electrolyte into the structure of a solid host, which is a mixed, that is, electronic and ionic, conductor (in this case graphite). The insertion electrodes (Figure D) have the capability for high reversibility, due to a beneficial combination of structure and shape stability. Many secondary batteries rely on insertion electrodes for the anode and cathode. A prerequisite for a good insertion electrode is electronic and ionic conductivity. However, in those materials with poor electronic conductivity, such as MnO2, good battery operation is possible. In this case, highly conductive additives such as carbon are incorporated in the electrode matrix, as in Figure E. The utilization of the MnO2 starts at the surface, which is in contact with the conductive additive and continues from this site throughout the bulk of the MnO2 particle.
Lead-Acid Battery PbSO 4 Pb
Lead - Acid Battery
Lead-acid batteries Positive electrode: Lead dioxide (PbO 2 ) Negative electrode: Lead (Pb) Electrolyte: Solution of sulfuric acid (H 2 SO 4 ) and water (H 2 O) PbO 2 H 2 O H 2 O Pb H 2 O H 2 O H 2 O
Lead-acid batteries Chemical reaction (discharge) PbO 2 2e - O 2-2 Pb 2+ 2H 2 O 2H + 2H + SO 4 2- PbSO 4 H 2 SO 4 SO 4 2- H 2 SO 4 PbSO 4 Pb 2+ 2e - Pb H 2 O H 2 O H 2 O H 2 O H 2 O
Lead-acid batteries Chemical reaction (discharge) Negative electrode Pb Pb 2+ + 2e- Pb 2+ + SO 4 2- PbSO 4 Electrolyte 2H 2 SO 4 4H + + 2SO 4 2- Positive electrode PbO 2 + 4H + + 2e - Pb 2+ + 2H 2 O Pb 2+ + SO 4 2- PbSO 4 Overall Pb + PbO 2 + H 2 SO 4 2PbSO 4 + 2H 2 O The nominal voltage produced by this reaction is about 2 V/cell. Cells are usually connected in series to achieve higher voltages, usually 6V, 12 V, 24 V and 48V.
GRIDS Each positive and negative plate in a battery is constructed on a framework, or grid, made primarily of lead. The positive plates have lead dioxide placed onto the grid framework. The negative plates are pasted with a pure porous lead, called sponge lead, and are gray in color. The positive and the negative plates must be installed alternately next to each other without touching. Many batteries use envelope-type separators that encase the entire plate and help prevent any material that may shed from the plates from causing a short circuit between plates at the bottom of the battery. FIGURE 16-2 The grid provides support for the plate active material.
Lead-acid batteries Cells are constructed of positive and negative plates with insulating separators between each plate. Most batteries use one more negative plate than positive plate in each cell. FIGURE 16-5 Two groups are interlaced to form a battery element.
Lead-acid batteries Each cell is separated from the other cells by partitions,which are made of the same material as that used for the outside case of the battery. FIGURE 16-6 A cutaway battery showing the connection of the cells to each other through the partition.
+ - + - + - - + All 6 cells are connected inside the box to make a 12 volt battery (+) and (-) plates are connected to make a 2 volt cell. The case is filled with electrolyte (sulfuric acid & water) Electrolyte must always cover the battery plates (but don t fill to top).
Figure Depiction of the components of a lead acid battery showing the differences between theoretical and practical energy density of a lead acid battery and source of the differences. Both the Pb and PbO2 electrode reaction mechanisms follow the solution precipitation mechanism and the cell reaction shown in this Figure. In addition to the lead and lead oxide electrodes, sufficient amounts of sulfuric acid and water have to be provided for the cell reaction and formation of the battery electrolyte. For ionic conductivity in the charged and discharged states, an excess of acid is necessary. Considering the limited mass utilization and the necessity of inactive components such as grids, separators, cell containers, etc., the practical value of specific energy (Wh/kg) is only 25% of the theoretical one for rechargeable batteries. Due to the heavy electrode and electrolyte components used, the specific energy is low.
Battery Basics-Cell Chemistry Additional Reactions of Significance Oxygen Reaction Cycle:: ½O 2 + Pb PbO C PbO + H 2 SO 4 C PbSO 4 + H 2 O Note: Oxygen reaction cycle is a benchmark characteristic of VRLA batteries. It is more pronounced with AGM than with gel constructions. Severe Overcharge Reaction: 2H 2 O O 2 + 4H + + 4e - C Note: This results in water loss due to venting of O 2 and can be life limiting. Positive Grid Corrosion: Pb + 2H 2 O PbO 2 + 4H + + 2e - Note: This results in water loss and can be life limiting. C