Thin Film Battery Technology

Advantage of Thin Film Batteries

  • Current State of the Art
  • Intrinsically Safe
  • High Temperature Performance
  • Long Cycle Life
  • Discharge Capacities & Profiles
  • Polymer Film Substrate for Thin Flexible Profile
  • Unique Proprietary Passivation Barrier and Packaging Solution
  • High Power & Energy Density, Specific Power & Energy
  • High Rate Capability
  • High Capacity Thin Film Batteries

Thin film solid state batteries are constructed by depositing the components of the battery as thin films (less than 5μm) on a substrate. The typical structure of a thin film solid state battery is illustrated in the schematic cross section shown in Figure 1.


Figure 1. Schematic cross section of a thin film solid-state battery

The cathode and anode current collectors (approximately 0.3μm thick) are deposited by sputtering of the appropriate metal in argon (Ar) atmosphere. Cathode films of LiCoO2or LiMn2O4 are deposited by RF magnetron sputtering of sintered targets of the respective compounds in Ar + O2 while films of V2O5 are deposited by reactive sputtering of V in Ar + O2. A sputtered LiPON electrolyte film covers the cathode and a portion of the substrate up to the anode current collector in order to insulate the substrate from direct contact with the anode.For a thin film lithium battery, a thin layer of lithium metal is thermally evaporated on LiPON as the anode. For a thin film lithium ion battery, a thin layer of Sn3N4 (deposited by sputtering of Sn target in N2 environment) is used as the anode. Finally, the battery is sealed.

Because thin film batteries are manufactured using all solid state materials and an inorganic glass electrolyte, these batteries are intrinsically safe.  None of the risks such as spilling, boiling or gassing associated with traditional batteries are present in solid state batteries.

Most existing rechargeable batteries have significant capacity fade at a temperatures higher than 60º;C. Many of them have safety problems related to degassing, leaking, or even explosion problems at elevated temperatures. Excellatron’s thin film batteries have demonstrated excellent temperature stability. They can operate at temperatures ranging from -40º;C to 150ºC. This unique feature has great potential for many applications, including high temperature sensors for the semiconductor industry, oil drilling and space exploration. The temperature performance of Excellatron’s thin film batteries is shown in Figures 2 to 5. Figures 2 and 3 show the charge/discharge profile of Excellatron’s thin film battery at 25ºC and 150ºC, respectively. Figure 4 demonstrates the excellent cyclability of Excellatron’s thin film battery at high operating temperature (150ºC), where charge and discharge capacity of the battery was plotted as a function of the cycle number. The battery exhibits a Coulombs efficiency of near 100% and has been charged/discharged for more than 200 full depth cycles with only ~20% capacity loss. This is the best performance reported in the literature for rechargeable batteries operated at 150ºC. Figure 5 shows capacity and resistance of Excellatron’s thin film battery as a function of temperature. When the temperature increases from 20ºC to 150ºC, battery resistance decreases to only 5% of its original value. A pulse discharge rate of as high as 1000C has been demonstrated at 150ºC for these cells.

Figure 2: Charge/discharge profile of Excellatron’s thin film battery at 25ºC.

Figure 3: Charge/discharge profile of Excellatron’s thin film battery at 150ºC.

Figure 4: High temperature (150ºC) charge and discharge capacity as a function of cycle number for a thin film battery. Sample was charged at 4.2V and discharged at 10C rate with a duty cycle of 100 ms on, 100 ms off.

Figure 5: Capacity and resistance of Excellatron’s thin film battery as a function of temperature. When the temperature is increased from 20ºC to 150ºC, battery resistance decreases to 5% of its original value.

Figure 6 shows the high rate pulse discharge of Excellatron’s battery (0.1 mAh). It is discharged by a 100 mA Pulse at 80ºC (~ 1,000C Rate). Detail of the pulse discharge is shown in Figure 7.

Figure 6: Excellatron’s battery (0.1 mAh) discharged by a 100 mA pulse at 80ºC.

Figure 7: Details on the high rate pulse discharge of Excellatron’s battery (0.1 mAh). It is discharged by a 100 mA Pulse at 80ºC (~ 1,000C Rate).

 

Unlike any other battery technology, thin film solid state batteries show very high cycle life.  Using very thin cathodes (0.05µm) batteries have been cycled in excess of 45,000 cycles with very limited loss in capacity.  As can be seen from Figure 8, after 45,000 cycles, 95% of the original capacity remained.  When thicker cathodes are used, cycle performance still far exceeds any current battery technology.  Figure 9 shows cycle performance for an Excellatron cell with a 2μm thick cathode.  With a cycle life in excess of 2,000 cycles, it exceeds the best performance of conventional battery cells by over a factor of two.  The best cycle life available from conventional cells is less than 1,000 cycles at 80% capacity loss.

Figure 8: Long term cyclability of a thin film solid state battery (cathode thickness ~ 0.05µm).

Figure 9: Long term cyclability of an Excellatron thin film battery (cathode thickness ~ 2µm).

Discharge capacity of thin-film batteries depends on the choice of cathode and anode materials as shown in Figure 10.  LiCoO2 can be used in applications where a high rate, high voltage profile is required.  V2O5 can be used in applications where a low rate, large capacity is preferred.Figure 10: Discharge capacity of several typical cathode materials.

(a) crystalline LiCoO2 , (b) amorphous LiMn2O4; (c) amorphous V2O5.

Excellatron has developed a low temperature deposition process for thin film batteries that enables us to use flexible, polymer foil as the substrate.  This technology largely reduces the production cost of the thin film batteries.  Successful development of a low temperature manufacturing process (<350ºC) opened up the possibility of using a polymer substrate such as Kapton, thereby significantly reducing manufacturing cost, while gaining flexibility and significantly reducing the overall thickness of the cells.

Figure 11: Thin film batteries deposited on a thin polymer substrate.

A unique packaging technology has also been developed by Excellatron, enabling long-term shelf life of thin film batteries under harsh environmental conditions, such as high pressure, high temperature, and high humidity.  A combination of organic and inorganic coatings is used to protect the batteries.  Excellatron has produced more than 10,000 prototype batteries and has provided samples to two major semiconductor manufacturers for evaluation and testing. Many other companies have also requested samples.  The pictures of some of Excellatron’s batteries are shown in Figure 12.

Fig. 5. Rechargeable thin film solid state batteries manufactured by Excellatron.

The total thickness of the battery is only 0.31mm.

Table 1 shows a comparison of battery performance for various rechargeable batteries, including data for thin film batteries using very thin substrates.  Thin film lithium batteries have the potential to reach an energy density as high as 1000 Wh/l. In the future, cell phones and laptops using these thin film batteries will be capable of running up to four times longer than on other lithium ion batteries having the same physical size.

Table 1. Comparison of battery performances

Battery Type

Specific
Energy
(Wh/kg)

Energy
Density
(Wh/l)

Specific
Power
(W/kg)

Cycle
Life

  Nickel Cadmium

40

100

400

400

  Nickel Metal Hydride

90

245

180

600

  Lithium ion (liquid electrolyte)

155

410

300

500

  Lithium Polymer

180

380

360

500

  Thin Film Li-ion

250

1,041

2,500

1,000

  Thin Film Li

300

959

6,000

40,000

The power rate of most conventional batteries is limited by high internal resistance and the danger of over-heating. The discharge and charge rates of batteries are measured on a scale normalized to the amount of current flow required to either fully charge or deplete a battery in one hour. This rate is referred to as the C-rate. For example, charging a 100 mAh battery at 100 mA for one hour is equivalent to a 1C rate. Most conventional batteries are limited to a charge/discharge rate of < 2C rate.

Excellatron’s thin film batteries show remarkable rate capability. They can be discharged at a rate of more than 60C during continuous discharge. A much higher discharge rate (up to 1,000C) has been demonstrated during pulse discharge at elevated temperatures. This characteristic has important implications for the burst power requirements of digital transmitters, implantable heart defibrillators, and many other devices.

Typical characteristics of Excellatron’s batteries are shown in the following table. The nominal capacities of Excellatron’s high performance thin film battery are 0.1 mAh, 0.5 mAh, 1 mAh and 10 mAh (size of the battery increases with increasing capacity).

  Nominal Capacity

1 mAh

  Dimension (T x W x D)

5cm x 3.8 cm x 0.037 cm

  Storage temperature

-40 to 150ºC

  Operating Temperature

-40 to 150ºC

  Discharge rate

> 10C at 20ºC
> 500C at 150ºC

  Cyclability

< 10% capacity loss in 1,000 cycles at 20ºC
< 10% capacity loss in 100 cycles at 150ºC

Figure 12 shows the voltage and current profile of a 10 mAh Excellatron battery. The battery capacity is 10 mAh. It is charged at a constant voltage of 4.2V and discharged at 10 mA. The charge current exceeds 50 mA. 

Figure 12: Performance of an Excellatron thin film lithium battery. The battery capacity is 10 mAh. It is charged at a constant voltage of 4.2 V and discharged at 10 mA. The charge current exceeds 50 mA.


Pilot Production Line

Excellatron has set up a pilot line for prodution of thin film batteries.  The multiple in-line deposition systems are capable of producing 10,000 cells/month in the current configuration.  It also possesses a large scale web coating system with a web width of ~ 40″ for continuous deposition.  The combination of the inline system and continuous web coating system will enable Excellatron to produce more than 100,000 cells/month.


High Rate Deposition Process

High Rate Deposition Process (Plasma Enhanced Chemical Vapor Deposition)
Excellatron has made significant progress in the development of high rate, PECVD deposition of thin film batteries. This project is supported by a $1.4 million, three-year research grant from the U. S. Department of Commerce (NIST, Advanced Technology Program or ATP). The advantage of this technology is that it can be several times (three to ten times) faster than conventional sputtering technology. With the development of this novel technology, Excellatron can produce thin film batteries at a much faster rate and at a much lower cost than with other technologies. Three patents have been filed on the PECVD deposition technology for thin film batteries. Operational thin film batteries deposited by the PECVD process have been successfully prepared.

The primary achievements of this project include:

  • Successful deposition of solid state electrolyte by the PECVD process with a high deposition rate (4 times faster than sputter deposition). The electrolyte has an ionic conductivity of 5.8*10-6 S/cm (three times higher than sputtered LiPON electrolyte).
  • Successful deposition of high capacity anode films (2,250 mAh/g, which is 6 times as large as graphite anode)
  • Preparation of both V2O5 and LiCoO2 cathodes by the PECVD process.
  • Three patent applications have been filed under the ATP project.

Intellectual Properties

Thin film batteries (TFB) have the potential to become the next generation of lithium batteries for portable electronic applications; however, there is a large gap between the results obtained in the laboratory and the commercial products.For example, until now, most TFBs have only a very limited shelf life outside the glove box. These batteries also needed to be annealed at high temperature (~ 700ºC), a process not compatible with many realistic substrate materials such as polymers or integrated circuit boards. Excellatron has overcome these barriers and is today able to produce commercial products. To date, Excellatron has filed 20 patent applications, with ten patents issued or allowed in the field of thin film batteries, and has accumulated a wealth of production know-how and trade secrets in the manufacturing of thin film batteries.

Excellatron’s first commercial product was designed for smart cards and other flexible electronic devices. This product is protected by several key Excellatron patents. One patent describes the materials and process to produce TFBs on polymer (such as Kapton) substrate. It includes a low temperature manufacturing process (<350ºC) which allows the use of a polymer substrate such as Kapton, thereby significantly reducing manufacturing cost while gaining flexibility and significantly reducing the overall thickness of the battery cells. Another Excellatron patent describes a unique packaging solution for flexible batteries. The passivated cells are sandwiched between the packaging foils, the whole cell assembly (instead of only the edge of the cell assembly as reported by prior art) is passed through a roller or platen laminator to form a monolithic battery structure.A unique packaging foil was selected so that both the cell and packaging foil are not damaged during the high temperature (130ºC) and high pressure (200N/cm²) lamination process. This novel packaging solution, in combination with Excellatron’s invention to deposit thin film batteries on Kapton substrate, can also be used in the development of high capacity batteries for cellular phone applications.

Excellatron also holds patents in several other key areas of the development and production of TFBs. These include three issued patents on a method to produce high capacity TFBs on both sides of a very thin aluminum substrate. Two patents are pending on production of thin film batteries by using atmospheric pressure chemical vapor deposition which can reduce the production cost of electrolyte and cathode by an order of magnitude. Two patents are pending on plasma enhanced chemical vapor deposition of LiPON and cathode materials which can increase the deposition rate from 3 to 10 times compared to sputtering. Three patents are pending on high temperature packaging methods for TFBs which allow packaged batteries to endure temperatures up to 260ºC (necessary for the solder reflow process utilized in the semiconductor industry).

Excellatron has not only developed TFB production technology, but has also made advances on new materials for TFBs. For example, Excellatron invented a high capacity anode which has a capacity of 2,250mAh/g, far exceeding other lithium ion intercalation compounds reported to date (patent pending). Two other patents issued to Excellatron describe methods for making an Sn:Li3N anode and a Li:metal alloy based anode. Excellatron also has a pending patent that describes a method to reduce switching noise in an integrated circuit by adopting thin film batteries as distributed power sources.

Excellatron’s unique technologies covering the substrate, cathode deposition, passivation and packaging have enabled us to produce revolutionary new batteries that can be used in many processes and applications that were not possible before. These batteries are ideally suited for applications that require a high temperature compatible, compact, safe, and high power rate battery. They are ideally suited for applications such as smart cards, cellular phones, and other portable electronics.

Excellatron

A U.S. based technology company, is introducing innovative and enabling energy storage technology.


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