Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Include electrolyte chemically specified and method
Reexamination Certificate
2000-03-21
2002-07-16
Dunn, Tom (Department: 1725)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Include electrolyte chemically specified and method
C429S126000, C429S144000, C429S304000, C029S623100
Reexamination Certificate
active
06420071
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention relates generally to devices comprising ion insertion materials and methods for manufacturing the same, and more particularly to methods of protecting ion insertion or intercalation materials in electrochemical cells, such as lithium ion batteries or electrochromic devices, to improve durability of such materials.
2. Description of the State of the Art
Electrochemical cells find utility in numerous devices such as lithium rechargeable batteries and electrochromic devices. Small-sized lithium rechargeable (secondary) batteries have been widely used as a power sources for portable electronic equipment in the fields of office automation equipment, household electronic equipment, communication equipment and the like. Electrochromic devices are highly beneficial in a variety of practical applications where light modulation is desirable. These include, for example, alphanumeric displays for clocks, watches, computer monitors, outdoor advertisement and announcement boards, and other types of displays. In addition, an important application for the electrochromic devices of the present invention is light modulation in, for example, mirrors of variable reflectance (as are used in some automotive rearview mirrors), sunglasses, automotive windshields, sunroofs, and building windows. Both rechargeable lithium batteries and electrochromic devices operate on the principle of an electrochemical cell (also referred to as a galvanic cell). An electrochemical cell is a composite structure containing a negative electrode (the cathode), a positive electrode (the anode) and an ion-conducting electrolyte interposed therebetween.
A conventional lithium rechargeable battery has a negative electrode (the cathode) comprising an active material which releases lithium ions when discharging, and intercalates or absorbs lithium ions when the battery is being charged. The negative active materials commonly utilized in lithium ion batteries include niobium pentoxide, carbon, and similar materials capable of intercalating lithium ions. The positive electrode (the anode) of a conventional lithium ion battery contains a substance capable of reacting chemically or interstitially with lithium ions, such as transition metal oxides, including vanadium oxides, cobalt oxides, iron oxides, manganese oxide and the like. In general, the positive active material comprised by the positive electrode will react with lithium ions in the discharging step of the battery, and release lithium ions in the charging step of the battery. Since both the anode and cathode materials of lithium ion batteries can intercalate lithium ions, the anode and cathode materials are often referred to as “ion insertion materials” or “intercalation materials.” The external faces of the anode and cathode lithium ion batteries are usually equipped with some structure or component to collect the charge generated by the battery during discharge and to permit connection to an external power source during recharging. Conventional lithium ion batteries usually comprise a non-aqueous liquid or a solid polymer electrolyte, which has dissolved lithium salt that is capable of dissociating to lithium ion(s) and an anions, such as for example lithium perchlorate, lithium borohexafluoride, and other lithium salts that are soluble in the electrolyte utilized. During discharge, lithium ions from the anode pass through the liquid electrolyte to the electrochemically active material of the cathode, where the ions are taken up or absorbed with the simultaneous release of electrical energy. During charging, the flow of ions is reversed so that lithium ions pass from the electrochemically active cathode material through the electrolyte and are plated back onto the anode.
Another example of an electrochemical cell is an electrochromic device, such as those used on electrochromic windows. Conventional electrochromic windows comprise multi-layered devices, similar to a lithium secondary battery, comprising a pair of transparent electrodes sandwiched between two transparent substrates. A pair of ion-insertion materials, referred to as the electrochromic layer and an ion storage layer, are sandwiched between the pair of electrodes. The electrochromic layer of an electrochromic device is an electrochromic ion insertion material, which reversibly changes its color by the injection or extraction of ions as a result of an application of an electric potential. This reversible color change in a material caused by an applied electric field or current is known as “electrochromism.” The ion storage layer of an electrochromic device is an ion insertion material, which may or may not have electrochromic properties. An ion-conducting material (also known as an electrolyte layer) is disposed between the electrochromic layer and the ion storage layer. Positive ions are induced by the voltage to move through the ion conducting material, i.e., electrolyte, in the direction from the ion storage layer and toward the electrochromic layer. Upon application of a voltage across the electrochromic device, electrons flow through an external circuit in a direction from the electrode adjacent the ion storage layer to the electrode adjacent the electrochromic layer. Simultaneously, a resulting current is conducted by ions, such as lithium ions (Li
+
) or hydrogen ions (H
+
). The positive ions are induced by the voltage to move through the ion conducting layer in the direction from the ion storage layer and toward the electrochromic layer.
An example of an electrochromic material used in an electrochromic device is a tungsten oxide (WO
3
) film. To color the W
0
3
film, a battery is connected between the pair of transparent conductive electrodes. When a negative voltage is applied to one of the electrodes (the negative electrode), electrons from the negative electrode and lithium ions from the lithium electrolyte are injected simultaneously into the WO
3
film. This ion injection process continues until the colorless WO
3
is converted into the blue-colored Li
x
WO
3
. To bleach the blue-colored Li
x
WO
3
film, the polarity is reversed so that the electrons and lithium ions are depleted from the Li
x
WO
3
film. Current flows until the entire film is restored to its original WO
3
(colorless) state. Thus, it is convenient to think of the coloring and bleaching process of an electrochromic device as the charging and discharging of a battery. Typically, for maximum efficiency, electrochromic devices include an electrochromic layer comprising an electrochromic material and an ion storage layer comprising a “complementary” electrochromic material, i.e., an electrochromic layer that becomes colored upon positive ion insertion and an ion storage material that becomes colored upon removal of positive ions. As a result of this type of complementary system, the electrochromic and ion storage layers change color simultaneously as a result of an applied voltage to produces a more highly colored (darker) state.
Electrochemical devices such as lithium secondary batteries and electrochromic devices can use either a solid, liquid, or polymer gel-type electrolyte as the ion conducting layer, and therefore are referred to as either solid-state, liquid or polymer gel (also known as gel-type) devices, respectively. The ion conducting layer must possess high ionic conductivity (i.e., conducts positive ions such as Li
+
or H
+
) and low electronic conductivity (does not conduct electrons).
Solid-state electrochemical devices have solid thin-film electrolytes made of so-called fast-ion conductor materials, in which either lithium or hydrogen ions diffuse readily. Examples of such fast-ion conductor materials include Li
3
N, Li
2
NH, Li
1−x
M
x
Ti
2−x
(PO
4
)
3
, and LiAlF
4
. During the manufacture of solid-state electrochemical devices, the solid electrolyte layer (which is disposed between the cathode and the anode) is deposited in a manner which often results unavoidably in the formation of “pinholes”. Pinholes are defec
Cheong Hyeonsik M.
Lee Se-Hee
Tracy C. Edwin
Dunn Tom
Midwest Research Institute
Pittman Zidia
White Paul J.
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