Nanostructured 3D Lithium Battery Run Time Could Be Measured in Years, Outperforms Conventional Rechargeable Lithium Batteries

Physical Sciences, Inc. (Andover, MA) earned U.S. Patent 7,709,139 for a rechargeable three-dimensional lithium battery that could remain unattended and functional for years.  The cathode is an electrospun mesh of ceramic fibers formed of LiNi_0.7 Co_0.3O₂ fibers The ceramic fibers have a thickness between about 50 nanometers (nm) and 1,000 nanometers. The anode particles comprise carbon nanoparticles.  Poly(phenylenediamine) is exposed to a liquid electrolyte solution after electrodeposition to form the electrolyte. The electrolytic polymer can be coated over the fibers to a thickness of about 5 nm to about 100 nm.  

Fibers and/or a plurality of nanoparticles function as the electrode material of the battery device. A technique for making a battery device has also been developed. The battery device includes a high energy storage capacity relative to its size, and can generate relatively high current using stable single cell potentials. The battery device can be used in small scale distributed devices, such as sensors and robotics, which require a burst of power. The battery device can be effectively micro-scaled and is, therefore, applicable to various size constrained applications. The battery device can be used in an autonomous device with an expected run time measured in years, say inventors Kevin White, Quinn Horn, Edward Salley and John Lennhoff.

The worldwide demand for portable electronic devices in the past decade have had an enormous impact on the development of portable energy storage devices. Batteries in which lithium ions shuttle between a cathode and an anode have emerged as the power source of choice for the high performance rechargeable battery market. The thick metal plates of traditional batteries have given way to lithium ion cells, which are lighter and more compact. Although the materials in today's batteries differ from those of displaced technologies, the basic two-dimensional character and layer-by-layer construction of the cells remain.

The planar two dimensional construction leads to several drawbacks, for example, in terms of energy storage capacity relative to size. Drawbacks include slow transport of ions, particle agglomeration inside the cell, particle to particle contact resistance, and containment of the particles in a binder that prevents the particles from contributing effectively to electron storage capacity. To address these issues, the thickness of the electrodes can be minimized in conventional two-dimensional devices. However, reduction of the electrode thickness results in a lower fraction of electroactive material in a fixed volume, resulting in a lower cell capacity. 

Scaling is perceived as an important feature of a three-dimensional battery. The ability to generate relatively large currents at stable single cell potentials above two volts with volumes less than a cubic centimeter make it especially applicable to small scale distributed devices requiring burst power such as autonomous sensors and robotics. For example, a DARPA/MTO conceptualized autonomous robotic moth requires 40 mW to run actuators for flight.

A three-dimensional battery can have an average discharge potential of 2.5 V requiring a current of 16 mA to satisfy the 40 mW requirement. Based on the maximum gravimetric current allowed by a three-dimensional battery system, the mass of a battery that can generate 16 mA of current, and subsequently the volume, can be 40 mg and 0.027 cm³. Conventional lithium ion batteries are not appropriate because engineering constraints prohibit effective micro-scaling. For this (and potentially many other) size constrained applications, the three-dimensional battery has an advantage.

In concert with a high capacity, low power supply like Radio Isotope Micropower Sources (RIMS) or micro-fuel cells generating off-peak and recharge power, such autonomous devices can have unattended run times measured in years. This becomes especially attractive for covertly monitoring hostile battle space where servicing autonomous devices comes at too high a personnel risk. The unique attributes of high power and small scaling are especially suited to autonomous robotics and sensor devices.

U.S. Patent 7,709,139 FIGS. 8A-8B show SEM images of cathode fibers before and after electrodeposition of PPD. The deposition cycle can be alternated with a resting cycle to obtain a substantially uniform and complete coating of the cathode fibers. The resting cycle typically includes a residence time of several seconds at a suitable resting potential (e.g., 0.0 volts). The electrolyte deposition can include up to 400 cycles, and the thickness of the resulting electrolyte layer can be between about 5 nm and about 1000 nm, although thinner or thicker layers can be applied depending on the application. 

 

FIGS. 9A-9B shows SEM images of an anode material deposited on electrolyte coated cathode fibers. . 

FIG. 14 is a Ragone plot showing the performance of a three-dimensional battery.

 

Physical Sciences Inc is also working on a research contract from the Air Force Research Laboratory, Kirtland, NM, to develop a metal organic framework (MOF) based lithium ion electrolyte.

 

PSI has demonstrated a nano-porous/polymer composite separator for low temperature operation of lithium ion batteries. These continuous nano-porous structures sequester inexpensive liquid lithium ion battery electrolytes depressing both their freezing point and vapor pressure. During the Phase II program PSI will optimize and demonstrate this system in prototype cells. In Phase I, more than an order of magnitude increase in lithium ion conductivity over conventional separator/electrolyte systems was demonstrated at -40°C, resulting in significantly improved battery rate capability.

 

In Phase II, the system performance will be further improved by optimizing the polymer and electrolyte components. Pouch cells will be constructed to demonstrate scale up and cell level performance at low temperatures and over extended cycling. In year 2, larger cylindrical cells will be constructed by an industrial partner and the performance evaluated in order to demonstrate readiness for transition to a commercial or military application.

 

The primary market for this technology is the military, in particular for space applications. The temperature extremes and long cycle life demands of space deployment would benefit from the robust electrolyte. Similarly, the proposed technology would be beneficial in the uniquely harsh environments in which battery powered combat devices operate. The reduced solvent vapor pressure and char forming ability of the nanoporous components could allow the development of a non-flammable electrolyte for use in everyday batteries. This would allow the technology to be extended to commercial devices such as hybrid and electric vehicles, cordless power tools, remote sensing devices, and portable communications such as cell phones and two-way radios.