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of  Influence","spheres-of-influence","article/spheres-of-influence",{"_uid":557,"date":558,"tags":559,"editor":560,"content":570,"excerpt":1083,"featured":50,"reporter":1084,"_editable":1088,"component":1089,"seo_title":553,"categories":1090,"visibility":1097,"author_company":49,"featured_image":1098,"seo_description":1083,"author_full_name":49,"author_job_title":49,"formattedDate":1104,"formattedArticleDate":1105},"00cad605-73cc-44f0-bc5d-15665e0040dd","2016-07-21 00:00",[],[561],{"slug":562,"name":563,"content":564},"didi-bostock","Didi Bostock",{"job_title":565,"image":566,"bio":568,"linkedin":569},"Editor - Energy Transition & Economics",{"filename":567},"https://a.storyblok.com/f/287943243085208/512x512/2c5ca5c1a3/didi-bostock.jpeg","Didi is the Energy Transition & Economics Editor at Benchmark, covering a broad range of markets across the energy transition. His remit spans from downstream sectors such as BESS and EVs, through to midstream such as new technologies and battery production, to upstream critical minerals mining. He also leads on financial analysis across these supply chains, alongside in-depth policy analysis.\n","https://www.linkedin.com/in/didi-bostock-656342198/",{"type":571,"content":572},"doc",[573,588,593,598,603,608,613,618,625,630,635,638,643,648,653,658,663,668,673,678,683,688,693,698,703,708,713,718,723,726,731,736,741,746,751,756,761,766,771,776,781,786,791,796,801,806,811,816,821,826,831,836,839,844,849,854,859,864,869,874,879,884,887,892,897,902,907,912,917,922,927,932,937,942,945,950,955,960,965,970,973,978,983,988,993,998,1003,1008,1013,1018,1023,1028,1033,1038,1043,1048,1053,1058,1063,1068,1073,1078],{"type":574,"attrs":575,"content":576},"paragraph",{"textAlign":49},[577,580,582,584,586],{"text":578,"type":579}," Graphite versus silicon in a race for the battery anode crown There is more graphite in a lithium ion battery than lithium.","text",{"text":581,"type":579}," Yet while lithium steals the limelight, the importance of graphite’s role in the energy storage revolution is increasing.",{"text":583,"type":579}," The most hotly debated subject in the field of battery materials, outside of whether a new super chemistry will usurp lithium ion, is whether graphite will continue to be the anode material of choice.",{"text":585,"type":579}," If it is to be replaced, silicon is tipped as the next in line to graphite’s throne.",{"text":587,"type":579}," However, as is usually the case with advanced materials, theory often differs from the real world.",{"type":574,"attrs":589,"content":590},{"textAlign":49},[591],{"text":592,"type":579}," George Hawley looks at the fundamentals and argues why graphite may be here for longer than speculators think.",{"type":574,"attrs":594,"content":595},{"textAlign":49},[596],{"text":597,"type":579},"Every few months, another research group announces that graphite is dead. They have a new anode, often based on silicon in some exotic form.",{"type":574,"attrs":599,"content":600},{"textAlign":49},[601],{"text":602,"type":579},"In reality, research into different lithium ion battery anodes is just starting in earnest at a point where the industry and incumbent materials are taking off in a major way.",{"type":574,"attrs":604,"content":605},{"textAlign":49},[606],{"text":607,"type":579},"Lithium ion is the chemistry of choice for the majority of the world’s leading battery producers and electric vehicle (EV) manufacturers as it has a much higher capacity comparative to its weight than lead acid, nickel metal hydride and other mainstream forms of batteries today.",{"type":574,"attrs":609,"content":610},{"textAlign":49},[611],{"text":612,"type":579},"Without lithium ion batteries, EVs are at best impractical.",{"type":574,"attrs":614,"content":615},{"textAlign":49},[616],{"text":617,"type":579},"Therefore, it is important to first understand why graphite is the incumbent advanced material of choice to make a lithium ion battery anode and then to analyse its competitors to see the potential for a new anode material taking its crown.",{"type":619,"attrs":620,"content":622},"heading",{"level":621,"textAlign":49},3,[623],{"text":624,"type":579}," Anatomy of a cell",{"type":574,"attrs":626,"content":627},{"textAlign":49},[628],{"text":629,"type":579},"A lithium ion cell is composed of anode, cathode, electrolyte and separator.",{"type":574,"attrs":631,"content":632},{"textAlign":49},[633],{"text":634,"type":579},"The anode material is carbon, either synthetic or natural graphite, that is pasted onto a copper foil. The graphite material can range from 15-25 microns in size and is either synthetic graphite, a man-made material, or natural coated spherical graphite, a mined and processed mineral.",{"type":574,"attrs":636,"content":637},{"textAlign":49},[],{"type":574,"attrs":639,"content":640},{"textAlign":49},[641],{"text":642,"type":579},"The cathode material is where the lithium ion battery gets its name. While there are six different types of mainstream lithium ion batteries, Benchmark Mineral Intelligence has the expectation that the Nickel Manganese Cobalt (NMC) or Nickel Cobalt Aluminium (NCA) formulations will be the dominant chemistries.",{"type":574,"attrs":644,"content":645},{"textAlign":49},[646],{"text":647,"type":579},"The cathode, in a 45-micron oxide form, is coated onto an aluminium foil that is 15 microns thick.",{"type":574,"attrs":649,"content":650},{"textAlign":49},[651],{"text":652,"type":579},"The third and final major component is a separator, a 20-micron thick polymer that plays the simple but important role of preventing short circuiting of the cell.",{"type":574,"attrs":654,"content":655},{"textAlign":49},[656],{"text":657,"type":579},"In total, the thickness of a lithium ion cell is around 100 microns thick and of this total about a quarter is the anode and nearly half is the cathode.",{"type":574,"attrs":659,"content":660},{"textAlign":49},[661],{"text":662,"type":579},"However, 60% of the graphite now used is natural graphite, which has up to 20% greater capacity and is lower in cost.",{"type":574,"attrs":664,"content":665},{"textAlign":49},[666],{"text":667,"type":579},"Battery manufacturers that are planning large scale expansions are aiming to reduce the cost of graphite anodes by more than half, from $7,000-10,000/tonne today to $4,000-5,000/tonne.",{"type":574,"attrs":669,"content":670},{"textAlign":49},[671],{"text":672,"type":579},"However, the price impact of this on the total cost of the cell will be less than 2%, so low that it is hardly worthwhile making any efforts to improve the anode.",{"type":574,"attrs":674,"content":675},{"textAlign":49},[676],{"text":677,"type":579},"In contrast, the electrolyte is 18% of the weight and 37% of the cell cost, and the cathode is 41% of the weight and 78% of the total cost.",{"type":574,"attrs":679,"content":680},{"textAlign":49},[681],{"text":682,"type":579},"Also, the best cathode has less than 50% lower specific capacity than the graphite anode. This is why the cathode is 80% thicker than the graphite anode.",{"type":574,"attrs":684,"content":685},{"textAlign":49},[686],{"text":687,"type":579},"Surely it would be more cost effective to research improvements in the cathode and electrolyte; however, the potential to improve the cathode is more limited as this has been the main focus of intensive research since 2009.",{"type":574,"attrs":689,"content":690},{"textAlign":49},[691],{"text":692,"type":579},"The lower barrier for entry for new research, and the faster route to government grants, is the anode material, which is why activity is increasing in this area, particularly from universities.",{"type":574,"attrs":694,"content":695},{"textAlign":49},[696],{"text":697,"type":579},"The US Department of Energy (DOE) is very generous with grants for research on lithium ion batteries and there has been a trend emerging in recent years with anode research.",{"type":574,"attrs":699,"content":700},{"textAlign":49},[701],{"text":702,"type":579},"This has introduced replacement anode materials into the public domain such as titanium metal and lithium metal.",{"type":574,"attrs":704,"content":705},{"textAlign":49},[706],{"text":707,"type":579},"But the one most talked about is silicon dioxide.",{"type":619,"attrs":709,"content":710},{"level":621,"textAlign":49},[711],{"text":712,"type":579}," Lithium metal",{"type":574,"attrs":714,"content":715},{"textAlign":49},[716],{"text":717,"type":579},"The first negative electrode (anode) tried in secondary (rechargeable) lithium ion batteries was lithium metal, which is used in primary (non-rechargeable) cells.",{"type":574,"attrs":719,"content":720},{"textAlign":49},[721],{"text":722,"type":579},"It was found that on charging, lithium grows whiskers (dendrites) which eventually reach the positive electrode (cathode) and short out the battery. Since lithium ion batteries hold a lot of energy, the result was a spectacular explosion and fire.",{"type":574,"attrs":724,"content":725},{"textAlign":49},[],{"type":574,"attrs":727,"content":728},{"textAlign":49},[729],{"text":730,"type":579},"Ballore in France has had 25 of the Blue cars that use lithium metal anodes catch fire.",{"type":574,"attrs":732,"content":733},{"textAlign":49},[734],{"text":735,"type":579},"Another problem with lithium metal is that it reacts violently with water, and the oxygen and nitrogen of the air. If damaged or overcharged, batteries made with lithium metal may explode and/or catch fire. In EV, the batteries are located in the chassis, just above the road. Ever had an oil pan busted by a rock?",{"type":574,"attrs":737,"content":738},{"textAlign":49},[739],{"text":740,"type":579},"Also, the battery has to be water cooled. It is no good over 65 deg C. A leak = big bang.",{"type":574,"attrs":742,"content":743},{"textAlign":49},[744],{"text":745,"type":579},"Avestor made lithium metal batteries for U-Verse network equipment cabinets for AT&T.",{"type":574,"attrs":747,"content":748},{"textAlign":49},[749],{"text":750,"type":579},"Four of these exploded. So AT&T had to replace 17,000 of them. Avestor went bankrupt.",{"type":619,"attrs":752,"content":753},{"level":621,"textAlign":49},[754],{"text":755,"type":579}," Lithium ion solution",{"type":574,"attrs":757,"content":758},{"textAlign":49},[759],{"text":760,"type":579},"The solution was to switch to a lithium ion chemistry. In this, the anode is generally graphite as lithium ions do not react with water or air. There are no dendrites to grow.",{"type":574,"attrs":762,"content":763},{"textAlign":49},[764],{"text":765,"type":579},"If overcharged or damaged in a crash in such a way that the electrodes contact each other, the battery shorts out releasing a lot of energy. However, the graphite does not burn.",{"type":574,"attrs":767,"content":768},{"textAlign":49},[769],{"text":770,"type":579},"What catches fire is the organic liquid carrier for the electrolyte, the plastic separator and the plastic battery case.",{"type":574,"attrs":772,"content":773},{"textAlign":49},[774],{"text":775,"type":579},"Graphite is composed of layers of graphene, separated by air so the anode material has 82% porosity. This porosity is only accessible through the exposed edges of the flakes. The graphene planes are impermeable.",{"type":574,"attrs":777,"content":778},{"textAlign":49},[779],{"text":780,"type":579},"The gallery between the planes is 0.275nm thick. So ions like lithium, which has a diameter 0.180nm, and silicon, with a diameter 0.108nm, can easily enter (intercalate). By doing so, they do not force the gallery open.",{"type":574,"attrs":782,"content":783},{"textAlign":49},[784],{"text":785,"type":579},"The problem with graphite is that it has a relatively low specific capacity – less than one-tenth of that of metallic lithium.",{"type":619,"attrs":787,"content":788},{"level":621,"textAlign":49},[789],{"text":790,"type":579}," Enter silicon",{"type":574,"attrs":792,"content":793},{"textAlign":49},[794],{"text":795,"type":579},"Silicon’s competition with graphite is not new. Since 1989, efforts have been made to substitute silicon for graphite.",{"type":574,"attrs":797,"content":798},{"textAlign":49},[799],{"text":800,"type":579},"In theory, a silicon anode is compelling: a different reaction with the lithium ions gives the material a capacity 11 times higher than graphite.",{"type":574,"attrs":802,"content":803},{"textAlign":49},[804],{"text":805,"type":579},"The problem is anode expansion.",{"type":574,"attrs":807,"content":808},{"textAlign":49},[809],{"text":810,"type":579},"For graphite, the lithium ions are taken into the galleries which act as a casing, therefore it does not suffer from extreme expansion in this process.",{"type":574,"attrs":812,"content":813},{"textAlign":49},[814],{"text":815,"type":579},"There is on average a 10% expansion, caused by the lithium ions reacting with the electrolyte and dragging these larger products into the galleries, jacking them open. This is a problem caused by the electrolyte and can be overcome by changing the electrolyte.",{"type":574,"attrs":817,"content":818},{"textAlign":49},[819],{"text":820,"type":579},"Silicon, however, has no galleries, so it reacts with the lithium to form an alloy. This alloy has a volume 375% larger than the original silicon.",{"type":574,"attrs":822,"content":823},{"textAlign":49},[824],{"text":825,"type":579},"The result: the silicon anode balloons up on charging and deflates during discharge.",{"type":574,"attrs":827,"content":828},{"textAlign":49},[829],{"text":830,"type":579},"The first major challenge for battery manufacturers is to design a casing to constrain this expansion, in a way mimicking what graphite’s galleries or layers of graphene do naturally.",{"type":574,"attrs":832,"content":833},{"textAlign":49},[834],{"text":835,"type":579},"The second and perhaps most important challenge is to stop the surface of the silicon anode cracking and flaking off during the expansion.",{"type":574,"attrs":837,"content":838},{"textAlign":49},[],{"type":574,"attrs":840,"content":841},{"textAlign":49},[842],{"text":843,"type":579},"The lithium ions contact the silicon surface first and make it expand with the silicon surface below. As a result, the surface alone expands by almost four times and it has nowhere to go, so it flakes off. This breaks the electrical contact so the capacity drops sharply after only a few cycles.",{"type":574,"attrs":845,"content":846},{"textAlign":49},[847],{"text":848,"type":579},"An apt analogy is how potholes are formed in an asphalt pavement due to the freeze-thaw action of ice in the springtime and, interestingly, the ice-to-water expansion is only 10%.",{"type":619,"attrs":850,"content":851},{"level":621,"textAlign":49},[852],{"text":853,"type":579}," Silicon’s nano fix?",{"type":574,"attrs":855,"content":856},{"textAlign":49},[857],{"text":858,"type":579},"An area where silicon could have hope for a future in batteries is in nano technology.",{"type":574,"attrs":860,"content":861},{"textAlign":49},[862],{"text":863,"type":579},"Silicon’s Achilles heel is its structural weak spots at its crystal boundaries where it tends to crack. A partial fix for this is to reduce the silicon in size down to nano particle scale, which has less micro-cracks.",{"type":574,"attrs":865,"content":866},{"textAlign":49},[867],{"text":868,"type":579},"The second part of the solution is to encapsulate these nano silicon particles, effectively creating a cage in which the silicon can freely expand but not drop off and break electrical contact.",{"type":574,"attrs":870,"content":871},{"textAlign":49},[872],{"text":873,"type":579},"To date, this has been the approach of researchers whereby nano silicon particles have been encapsulated or coated onto the surface of carbon nanotubes, bucky balls, graphene and in the form of foam or whiskers.",{"type":574,"attrs":875,"content":876},{"textAlign":49},[877],{"text":878,"type":579},"Through this approach the Pacific Northwest National Laboratory together with the DOE has reduced the expansion of the silicon anode in a foam form to 30% and has achieved 750 mAh/g – 18% of theoretical capacity.",{"type":574,"attrs":880,"content":881},{"textAlign":49},[882],{"text":883,"type":579},"But there is still a need to allow for the 375% expansion.",{"type":574,"attrs":885,"content":886},{"textAlign":49},[],{"type":574,"attrs":888,"content":889},{"textAlign":49},[890],{"text":891,"type":579},"The capacity per unit volume will be lower than with graphite and a much larger battery would be needed, and one would like to have room to carry children and luggage in an EV.",{"type":574,"attrs":893,"content":894},{"textAlign":49},[895],{"text":896,"type":579},"There are several problems with this nanofix for silicon; these are:",{"type":574,"attrs":898,"content":899},{"textAlign":49},[900],{"text":901,"type":579},"1.Manufacture",{"type":574,"attrs":903,"content":904},{"textAlign":49},[905],{"text":906,"type":579},"The major problem is making nano silicon.",{"type":574,"attrs":908,"content":909},{"textAlign":49},[910],{"text":911,"type":579},"One method is that they are manufactured by extracting silicon from a bulk sample by laser, plasma, or electron beams.",{"type":574,"attrs":913,"content":914},{"textAlign":49},[915],{"text":916,"type":579},"Alternatively, they can be made by high speed ball milling, precipitation and reduction, and by vapour deposition from silane or silicon tetrachloride.",{"type":574,"attrs":918,"content":919},{"textAlign":49},[920],{"text":921,"type":579},"The latter is a low cost solution at only $3,000/tonne – until one calculates the cost of the contained silicon at $18,180/ All of these production methods are expensive and of low capacity and very high capital cost.",{"type":574,"attrs":923,"content":924},{"textAlign":49},[925],{"text":926,"type":579},"2. Cost of silicon feedstock",{"type":574,"attrs":928,"content":929},{"textAlign":49},[930],{"text":931,"type":579},"There is cheap silicon available but it is too impure for batteries, which require a high purity material in excess of 99%.",{"type":574,"attrs":933,"content":934},{"textAlign":49},[935],{"text":936,"type":579},"Other industries that use ultra-pure silicon include the solar energy sector, which uses silicon as its main material to form photovoltaic (PV) which trades at $20-23,000/tonne but peaked at $80,000/ tonne in 2011.",{"type":574,"attrs":938,"content":939},{"textAlign":49},[940],{"text":941,"type":579},"High purity silicon is also used in electronics with a semi-conductor grade selling for the equivalent of $35,000/tonne to $50,000/tonne.",{"type":574,"attrs":943,"content":944},{"textAlign":49},[],{"type":574,"attrs":946,"content":947},{"textAlign":49},[948],{"text":949,"type":579},"3. Cost of expansion",{"type":574,"attrs":951,"content":952},{"textAlign":49},[953],{"text":954,"type":579},"Space must be allowed for the 375% expansion.",{"type":574,"attrs":956,"content":957},{"textAlign":49},[958],{"text":959,"type":579},"This extra space is not filled with air but electrolyte, one of the most expensive components of a lithium ion cell at $60,000/tonne, 23.4% of the total cost, according to Argonne National Laboratory.",{"type":574,"attrs":961,"content":962},{"textAlign":49},[963],{"text":964,"type":579},"Resistivity Silicon is a semiconductor. Its resistivity is 85,000 ohm.cm. This makes it an insulator in battery anodes.",{"type":574,"attrs":966,"content":967},{"textAlign":49},[968],{"text":969,"type":579},"Graphite is semi-metallic. It is a conductor of electricity with resistivity of 1,400 ohm. cm.",{"type":574,"attrs":971,"content":972},{"textAlign":49},[],{"type":574,"attrs":974,"content":975},{"textAlign":49},[976],{"text":977,"type":579},"Even graphite needs the addition of highly conductive expensive carbon black or graphene to make it work, but silicon needs far more.",{"type":574,"attrs":979,"content":980},{"textAlign":49},[981],{"text":982,"type":579},"4. Reactivity",{"type":574,"attrs":984,"content":985},{"textAlign":49},[986],{"text":987,"type":579},"Nano particles have a very high surface area, so are very reactive.",{"type":574,"attrs":989,"content":990},{"textAlign":49},[991],{"text":992,"type":579},"Silicon reacts with oxygen to form a silica coating, which has to be removed with hydrofluoric acid, a very corrosive and toxic chemical. Nano silicon reacts with water to form explosive hydrogen.",{"type":574,"attrs":994,"content":995},{"textAlign":49},[996],{"text":997,"type":579},"Thus making batteries with nano silicon requires making them in a vacuum or in argon.",{"type":574,"attrs":999,"content":1000},{"textAlign":49},[1001],{"text":1002,"type":579},"Graphite anodes are made in the open air.",{"type":619,"attrs":1004,"content":1005},{"level":621,"textAlign":49},[1006],{"text":1007,"type":579}," Perfect harmony?",{"type":574,"attrs":1009,"content":1010},{"textAlign":49},[1011],{"text":1012,"type":579},"While silicon and graphite have gone head to head for the last 30 years, the future anode may actually lie in a combination of both advanced materials.",{"type":574,"attrs":1014,"content":1015},{"textAlign":49},[1016],{"text":1017,"type":579},"Some cell makers are already adding modest amounts of silicon to boost the capacity of the graphite anode.",{"type":574,"attrs":1019,"content":1020},{"textAlign":49},[1021],{"text":1022,"type":579},"Tesla Motors’ CEO, Elon Musk, is the highest profile person to publicly speak on this trend.",{"type":574,"attrs":1024,"content":1025},{"textAlign":49},[1026],{"text":1027,"type":579},"“It’s a baby step in the direction of using silicon in the anode, but we will be increasing the use of silicon in the anode,” Musk explained in an investor conference call in July 2015.",{"type":574,"attrs":1029,"content":1030},{"textAlign":49},[1031],{"text":1032,"type":579},"The point was never elaborated on, with many believing Musk had spoken too soon on any battery material developments that Tesla may have in the pipeline for its Gigafactory towards the end of the decade.",{"type":574,"attrs":1034,"content":1035},{"textAlign":49},[1036],{"text":1037,"type":579},"However, it was an interesting development and one many industry participants had expected: using silicon as an additive in a graphite anode.",{"type":574,"attrs":1039,"content":1040},{"textAlign":49},[1041],{"text":1042,"type":579},"Amprius, a spin-off of Silicon Valley-based Stanford University, has also made progress on small-scale silicon anode production.",{"type":574,"attrs":1044,"content":1045},{"textAlign":49},[1046],{"text":1047,"type":579},"Although the cost has never been divulged,Amprius found very good anode performance with nano silicon wires. This focus, however, has now been switched to using 10-50% silicon additive in a graphite anode.",{"type":574,"attrs":1049,"content":1050},{"textAlign":49},[1051],{"text":1052,"type":579},"The company has achieved 650 Whr/litre compared to 400-620 Whr/litre with graphite alone, and 280 Whr/kg compared to 200-240 for graphite alone.",{"type":574,"attrs":1054,"content":1055},{"textAlign":49},[1056],{"text":1057,"type":579},"Argonne National Laboratories and the DOE have developed an anode with 7.9% silicon in graphite, with reversible capacity of 604 mAh/g versus 369 for a good graphite product. These results are seen as a small improvement, but they do allow more energy to be packed into a smaller volume.",{"type":574,"attrs":1059,"content":1060},{"textAlign":49},[1061],{"text":1062,"type":579},"The results claim 6.8% weight saving over the graphite standard, representing 2.45g saving in a cell phone, about 1.5% of the total weight.",{"type":574,"attrs":1064,"content":1065},{"textAlign":49},[1066],{"text":1067,"type":579},"The question is whether this benefit is worth the additional cost.",{"type":574,"attrs":1069,"content":1070},{"textAlign":49},[1071],{"text":1072,"type":579},"The field of battery raw materials is one of the most rapidly advancing in the world today. In Silicon Valley, the most sought after jobs are now in the field of energy storage and advanced materials.",{"type":574,"attrs":1074,"content":1075},{"textAlign":49},[1076],{"text":1077,"type":579},"The balance is developing a real world anode that can be reliably, safely and cost effectively adopted by the mainstream battery industry. It is a much greater challenge than many materials scientists will even realise.",{"type":574,"attrs":1079,"content":1080},{"textAlign":49},[1081],{"text":1082,"type":579},"The six concluding points below offer a summary of where we stand today:","Graphite versus silicon in a race for the battery anode crown There is more graphite in a lithium ion battery than lithium.",[1085],{"slug":562,"name":563,"content":1086},{"job_title":565,"image":1087,"bio":568,"linkedin":569},{"filename":567},"\u003C!--#storyblok#{\"name\": \"article\", \"space\": \"\", \"uid\": \"00cad605-73cc-44f0-bc5d-15665e0040dd\", \"id\": \"\"}-->","article",[1091,1094],{"slug":1092,"name":1093},"batteries","Batteries",{"slug":1095,"name":1096},"critical-minerals","Critical Minerals","private",{"id":49,"alt":1099,"name":1100,"focus":1100,"title":1099,"source":1100,"filename":1101,"copyright":1100,"fieldtype":1102,"meta_data":1103,"is_external_url":51},"Spherical graphite","","https://a.storyblok.com/f/287943243085208/ac0aae2b18/bm-screen-shot-2016-07-21-at-143424.png","asset",{"alt":1099,"title":1099,"source":1100,"copyright":1100},"Jul 21, 2016","21st July 2016",[],[],1792773947215]