A tour of Apple's iPhone 6 battery helps nail down the one variable that determines manufacturing cost.
Li-polymer batteries are ubiquitous. They are everywhere: cellphones, tablets, laptops and hybrid or electric cars. We rarely think about them except when the discussion turns to the rather short battery life seen in some consumer electronics. Smartwatches, like some laptops, come to mind where battery life is measured at less than a day. This has me thinking about batteries, and are there commonalities between the batteries seen in smartwatches, cellphones and tablets.
And this has our curiosity piqued at TechInsights as to whether a single variable can be used to predict their manufacturing cost (bill of materials or BoM)? Simple proxies would include the battery mass or its charge capacity as both are easily measured.
Figure 1 shows a typical lithium-polymer pouch-type battery taken from a smartphone, in this case the Apple iPhone 6 Plus. The copper anode and aluminum cathode current collector tabs are seen extending out of the right end of the battery package. A flex ribbon containing control electronics has been removed from this battery but is shown on another iPhone 6 Plus battery in Figure 2 (on next page). We note the use of two Ricoh battery protection IC’s and a Texas Instruments Li-ion fuel gauge.
Figure 1: Apple iPhone 6 Plus Li-polymer Battery. (Source: TechInsights)
Figure 2: iPhone 6 battery electronics. (Source: Deep Dive Teardown of the Apple iPhone 6 Plus A1524, TechInsights)
Our first question: is this battery special? And to answer this we examine the energy density (Wh/g) for a number of batteries used in smartphones, cellphones and tablets that have passed through TechInsights labs over the last year or so.
The graph shown in Figure 3 includes smartwatch batteries that tend to be less than 25 g in weight, cellphones of various kinds, and tablets weighing in at more than 70 g. The slope of the straight line through the data is about 220 Wh/kg and it is a pretty good fit to most of the data points. The small scatter in the data points about the fitted line indicates that these batteries are using the same or at least fairly similar cell technologies. A significantly improved battery should lie well above the trend line, and a poor battery technology would be below the trend line. A few batteries are measurably below the trend line, though this underperformance might be due to excess packaging that would increase the weight of the battery without adding capacity.
Figure 3: Li-Polymer battery capacity. (Source: TechInsights)
The iPhone 6 Plus battery, weighing in at 43 g, is not standing out from the trend line and does not seem to be special. But being Apple it is nonetheless interesting.
Our next item of interest is the BoM cost for the battery and to do this we need to know more about the battery’s structure. Our teardown begins with Figure 4 where we peel away the outer foil casing to expose a polymer film that envelopes the battery cells. This polymer film has been peeled away to expose the outer aluminum cathode collector layer shown in Figure 5.
Figure 4: Cutting away outer casing.(Source: Deep Dive Teardown of the Apple iPhone 6 Plus A1524, TechInsights)
Figure 5: Outer aluminum cathode collector layer. (Source: Deep Dive Teardown of the Apple iPhone 6 Plus A1524, TechInsights)
Figure 6 is a cross section taken through the iPhone 6 Plus battery showing its layered structure. The battery contains eleven cathode (positive battery terminal) and 10 aluminum anode (negative battery terminal) current collector layers that are connected in parallel. The anode and cathode collector electrodes are coated with their electrode respective active layers and then stacked one on top of the other. Separator layers are inserted between the anode and cathodes to prevent short circuits but at the same time allows for the transfer of lithium ions between the anode and cathodes.
Figure 6: iPhone 6 Plus battery in cross section. (Source: Detailed Structural Analysis of the Apple iPhone 6 Plus Li-ion Polymer Battery, TechInsights)
Figure 7 shows the edge of the battery where the cathode current collector layers are brought and welded together to form the battery’s anode battery terminal. The anode current collectors are brought out of the package in a similar fashion.
Figure 7: Cathode battery terminal. (Source: TechInsights)
From TechInsights’ Detailed Structural Analysis report, we know that the iPhone 6 Plus battery uses lithium cobalt oxide (LiCoO2) for the cathode and graphite for the anode as shown in Figure 8.
Figure 8: SEM cross section iPhone 6 battery. (Source: Detailed Structural Analysis of the Apple iPhone 6 Plus Li-ion Polymer Battery, TechInsights)
LiCoO2 (LCO) is a mature battery technology commonly used for mobile battery applications such as cell phones, tablets and laptops, and this likely explains why all of the batteries shown in Figure 3 fall on the same energy density curve.
Table 1 lists as few other cathode materials. The last three are used in electric vehicles such as the Chevy Volt and Nissan Leaf. TechInsights has previously analysed the Chevy Volt battery fabricated by LG Chemical where we observed a mixture of lithium manganese oxide (LMO) and lithium nickel manganese oxide (NMC) being used for the cathode.
|Lithium cobalt oxide (LiCoO2)
||cell phones, tablets, laptops, cameras
|Lithium nickel manganese cobalt oxide (LiMnCoO2)
|Lithium iron phosphate (LiFePO4)
|Lithium nickel cobalt aluminum oxide (LiNiCoAlO2)
Table 1: Common lithium ion battery compositions and applications
The graphite anode and CoO2 cathode have lattice structures in which lithium ions are reversibly inserted (intercalation) into the interstitial spaces between the atomic layers. Figure 9 is a high resolution TEM image of the cathode’s CoO2 layer, while the graphite layered structure is shown in Figure 10.
Figure 9: CoO2 cathode layers. (Source: Detailed Structural Analysis of the Apple iPhone 6 Plus Li-ion Polymer Battery, TechInsights)
Figure 10: Graphite anode layers. (Source: TechInsights)
Finding manufacturing cost models (BoM) for mobile Li-ion batteries has proved to be a bit of a challenge. Several papers have been published on the manufacturing costs for electric vehicle (EV) or hybrid electric vehicle (HEV) Li-ion batteries: Argonne National Laboratories (2000 and 2012), Rempel et al. (TIAX presentation 2013), and Wood et al. (J. Power Sciences 2015) to name a few. But we found little in the way of the manufacturing costs for the smaller batteries used in cellphones and laptops. The TIAX presentation provides a $0.47/Wh for PHEV type batteries, and Wood et al. derive a baseline model calculation of $ 0.50/Wh for the complete battery. This last report was published in 2015 and represents the most recent calculation that we found.
Our Teardown business routinely disassembles electronic devices such as watches, smartphones, tables and laptops and derives their BoM using a sum of the parts methodology. These Teardown reports often include the BoM for the complete battery including its electronics, labor and margin. We are interested in the battery maker’s cost so we have subtracted the margin from the Teardown.com BoM’s and have plotted this in Figure 11 for many of the devices used in Figure 3.
Figure 11: Battery Mmaker’s BoM vs. cell capacity. (Source: TechInsights)
The data (red diamonds) shows a BoM trend line of about $0.37/Wh with a fair amount of scatter. The scatter is not too surprising as the batteries often contain different sets of electronics appended to them. The $ 0.37/Wh BoM is less than the $0.50/Wh of Wood and this is perhaps no surprise as cell phones and car batteries use different technologies even if they both use lithium ions as the energy storage medium. The cell phone battery is also a mature technology that would support a lower build cost.
We have also plotted the retail prices for Li-ion batteries that we found on Amazon. We have been a bit selective with these, picking the lowest priced batteries that we found. Our thought here is that the lowest priced batteries are priced with the least margin for the battery maker, the wholesaler and retailer. The retail price is about twice that of estimate our BoM for the battery, and this seems quite reasonable.
Figure 11: Battery Mmaker’s BoM vs. cell capacity. (Source: TechInsights)
I have a predilection for plotting graphs of everything in sight and it gives me a small thrill to find straight lines. It is a physics thing, straight lines fitted to data.
So returning to my question: Is there a simple proxy for the BoM? We think so, as the results shown in Figure 11 suggest that battery capacity (Wh) or even its weight do a pretty good job of it. And this makes sense; the battery cost comprises materials and labor, and we might suggest that both scale with the battery size.
- Kevin Gibb is the product line manager for Process at TechInsights. As PLM, Dr. Gibb is responsible for the technology coverage, manufacturing processes, and pricing strategies for TechInsights’ semiconductor process open market reports covering state-of-the-art semiconductor devices. Dr. Gibb has a broad knowledge of CMOS, bipolar, III-V, and MEMS technologies gained over nearly 25 years of working in semiconductor consulting firms, manufacturing, and government research laboratories. He has written process analysis reports on hundreds of devices over the past decade and half, spanning: CMOS, memory, MEMS and CMOS image sensors.