Lithium-Ion Capacitor Patents — A Middle Ground Between Battery and Capacitor

What’s at Stake: A Lithium-Ion Capacitor Patent That Moves Pre-Doping into the Binder

KR102164921B1 (Korea Institute of Ceramic Engineering and Technology; filed December 29, 2017; granted October 13, 2020) is a patent that seeks to simplify “pre-doping,” the most demanding process in lithium-ion capacitors, by loading lithium into the binder. Its novelty lies less in inventing a new anode material than in changing the route by which lithium is supplied to the anode. Read closely, however, the experimental data in the specification also suggest that this approach lightens the burden of conventional doping rather than replacing it completely.

To start with the industry backdrop: batteries offer high energy density but limited power characteristics, while supercapacitors have far superior power characteristics but low energy density. The lithium-ion capacitor (LIC) is a hybrid device aiming at the middle ground between the two, and related patents continue to be registered in Korea as well. The tension lies in the manufacturing process. The pre-doping process, in which lithium is loaded into the anode in advance during cell manufacturing, has been cited as an obstacle to commercialization because it is difficult.

This piece answers three questions. First, why is pre-doping needed, and what is inconvenient about the conventional methods? Second, what do the claims of KR102164921B1 protect, and how broad is the scope of rights? Third, when the same applicant’s adjacent patent and the prior art are laid side by side, what design-around options and tracking points emerge?

Basic Mechanism: A Warehouse and a Shelf in One Cell

A lithium-ion capacitor combines, in a single cell, an electrode in which lithium ions are stored through oxidation-reduction reactions as in a battery, and an electrode on whose surface ions are physically adsorbed as in a supercapacitor. As an analogy, the battery electrode is a “warehouse” that stacks goods deep inside, while the capacitor electrode is a “display shelf” on which goods are briefly placed on the surface. The warehouse holds a lot but takes time to load and unload; the shelf holds little but can be loaded and unloaded in an instant. Thanks to this combination, an LIC can deliver higher energy density than a supercapacitor while achieving much faster charge-discharge and longer life than an ordinary battery.

Pre-doping is the process of loading lithium into the anode (a carbon material such as graphite) before the cell is put into operation. It is like stocking the warehouse before opening the shop. The stock must already be in place so that the anode potential stays low and the operating voltage window of the whole cell widens. The specification of KR102164921B1 cites, as conventional approaches, bringing lithium metal into direct contact with graphite, the external short-circuit method, and the electrical method, and explains that these involve complex processes, raise stability concerns, and make the doping amount hard to control.

This patent’s solution is closer to bringing the stock in “packed in the delivery box.” The functional groups of the water-based polyacrylate binder used to make the anode are substituted with a lithium source, so that the binder carries lithium in from the moment the electrode is formed. Compared with the conventional method of placing a separate lithium metal foil inside the cell for doping, the design aims to reduce process steps and make doping uniform.

• Anode material: expanded graphite, made by rapidly heating natural graphite to open its interlayers (per the specification: expanded at 600-900°C for 1-5 minutes)
• Binder: lithium polyacrylate whose functional groups are substituted with lithium hydroxide, lithium chloride, lithium nitride, or the like
• Expected effects: the specification states “high power, long life and high energy density,” along with reduced reliance on expensive lithium metal and lower cost and environmental burden by using a water-based binder instead of organic solvents

Comparison: Where the Device Sits, and the Adjacent Patents

First, let us confirm in figures where the LIC stands. The table below shows representative ranges presented in a review paper published in 2021 (Energies 14(4), 979). Because values vary widely with cell design and materials, it is safer to read the table for direction rather than absolute values.

Category	Energy density (Wh/kg)	Power density (kW/kg)	Cycle life	Operating voltage (V)
Supercapacitor (EDLC)	Up to about 7	Up to about 10	(not stated in review)	About 2.7
Lithium-ion capacitor (LIC)	Reported as 4-5 times EDLC	10 or more	Usually more than 5,000 (10,000-100,000 reported)	1.5-4.5 with organic electrolyte
Lithium-ion battery (LIB)	150 or more (up to about 200)	Below 1	Shorter than LIC	(not stated in review)

What this table says: In power density, the LIC sits in a range more than ten times higher than batteries (below 1 kW/kg), and its energy density is reported at 4-5 times that of EDLCs. The figures show its “middle-ground” position: energy short of a battery, power at capacitor level.

Next is the patent landscape. The prior art cited by KR102164921B1 and an adjacent patent filed two days earlier by the same applicant are laid side by side, checked against their Google Patents bibliographic records.

Patent number	Applicant	Filed / Granted	Status	Gist of claim 1 (restated)
KR101173673B1	Korea Electronics Technology Institute	2011-05-09 / 2012-08-13	Expired (fee-related)	Method of making a carbon-based LIC anode material by heat-treating expandable graphite with at least 5,000 ppm intercalation compounds at 500°C or higher and grinding it to an average particle size of 11 μm or less
KR102057128B1	Korea Institute of Ceramic Engineering and Technology	2017-12-27 / 2020-01-22	Active	LIC anode material of 87 wt% expanded graphite vacuum-impregnated with a lithium source, 5 wt% conductive agent (Ketjen Black), and 8 wt% water-based polyacrylate binder
KR102164921B1	Korea Institute of Ceramic Engineering and Technology	2017-12-29 / 2020-10-13	Active	LIC with 87 wt% expanded graphite, 5 wt% Ketjen Black, and 8 wt% lithium polyacrylate binder whose functional groups are substituted with a lithium source

What this table says: The idea of using expanded graphite for an LIC anode was already disclosed in a 2011 filing (KR101173673B1). The two 2017 patents share the same 87:5:8 composition and each secures rights by splitting the lithium supply route into “impregnating the anode material” versus “substituting into the binder.”

Patent Perspective: Narrow Claims, a Portfolio That Covers Routes

Claim 1 of KR102164921B1 (application number KR10-2017-0184537; applicant Korea Institute of Ceramic Engineering and Technology; inventors Ji Mi-jeong, Choi Byung-hyun, Lee Seo-hwan, Gu Ja-bin, Seol Gwang-hui) bundles three elements together with figures: 87 wt% expanded graphite as the anode material, 5 wt% Ketjen Black as the conductive agent, and 8 wt% lithium polyacrylate as the binder, with its functional groups substituted by a lithium source such as lithium hydroxide, lithium chloride, or lithium nitride. According to Google Patents, its legal status is Active, and its anticipated expiration is shown as December 29, 2037, 20 years from filing. KR102835360B1 of Korea University of Technology and Education (published 2025) is identified as a later patent citing it.

From the standpoint of reading the scope of rights, the most notable point is that claim 1 is written with fixed values (87, 5, and 8 wt%) rather than ranges. Under the all-elements rule, infringement requires practicing every element of the claim, so on a literal reading, changing the composition ratio even slightly may lower the risk of literal infringement. Conversely, the right holder retains room to argue infringement under the doctrine of equivalents on the grounds that the numerical difference is insubstantial, so it is hard to conclude that changing the ratio alone secures FTO (freedom to operate).

Design-around scenarios (including counterarguments) can be summarized as follows.

• Route avoidance: supplying lithium by a route other than the binder. However, the route of impregnating lithium into the anode material is covered by the same applicant’s KR102057128B1 with the same 87:5:8 composition, so avoiding one patent may run into the adjacent one.
• Binder-chemistry avoidance: loading lithium into a polymer binder other than polyacrylate. Because the effect emphasized by the specification lies in the “lithium substitution of functional groups,” however, a binder with similar functional groups could raise a doctrine-of-equivalents issue.
• Sacrificial cathode additive route: using, on the cathode side rather than the anode, an additive that releases lithium on the first charge (such as Li₅FeO₄ or Li₆CoO₄, introduced in the review paper). This leaves ample room to differ from the binder configuration of this claim, but separate FTO on patents in that additive field is required.

To add one interpretation of our own: this patent’s defensive strength comes not from the breadth of any single claim but from a portfolio structure that bundles multiple “lithium supply routes.” The same applicant filing the anode-impregnation type and the binder-substitution type separately two days apart reads as a strategy of blocking several routes in exchange for narrow claims. A competitor’s FTO review therefore leaves fewer gaps when it treats the two patents as a pair rather than KR102164921B1 alone.

The experimental data in the specification also help gauge the value of the rights. The specification states that at 0.1C, the charge capacity was 339.1 mAh/g and the discharge capacity 339.0 mAh/g, with no loss of initial efficiency, and that a capacity of about 175 mAh/g was maintained after 30 cycles. It also records that the lithium source in the binder contributes about 7-13.7% to lithium doping compared with the conventional approach. Read as stated, these figures are more accurately understood as a “reduction” effect that cuts part of the lithium metal required, rather than the binder replacing pre-doping entirely.

Limits and Outlook: Replacement or Reduction?

Lithium-ion capacitors still have lower energy density than ordinary lithium-ion batteries, so rather than becoming the main power source of electric vehicles, they are first establishing themselves in regenerative-braking energy recovery and industrial equipment that needs momentary high power. How simple and inexpensive the pre-doping process can be made is cited as the next gate that will decide whether this device reaches wide adoption.

Optimistically, if the approach of loading lithium into a water-based binder settles into mass production, it could lower LIC manufacturing costs by reducing lithium-metal handling equipment and organic-solvent use. The counter-scenario is clear too. If the doping contribution stated in the specification stays at about 7-13.7% relative to the conventional approach, manufacturers may ultimately have to keep their existing pre-doping equipment, and the process-simplification effect may be limited. Managing moisture and residual ions in a binder substituted with lithium salts may also remain an additional verification task.

The strategic alternative is a design that treats binder substitution not as a standalone solution but as an “auxiliary route,” combining it with sacrificial cathode additives or conventional electrical doping to reduce total lithium-metal use step by step. Because different rights attach to each route, it is sensible from a risk-management standpoint to draw a route-by-route FTO map from the combination-design stage onward.

Practical action: Planning/IP staff developing LIC anodes or binders are advised to look up, on KIPRIS, the annuity-payment status and the existence of overseas family members for both KR102164921B1 and KR102057128B1, and to prepare a one-page comparison of how far their own electrode composition lies from the 87:5:8 composition from a doctrine-of-equivalents perspective.

Items requiring verification

• Grant status, current right holder, and legal status of the Korean prior documents cited in the specification’s background (10-2011-0043457 “Cathode active material for lithium-ion capacitor,” 10-2014-0062807, and others)
• Exact registration numbers of the patents mentioned in the original article on a “carbon nanotube-lithium metal oxide composite cathode,” a “hard-carbon-coated graphite anode material,” and “adding lithium composite metal oxide to the cathode”
• Whether KR102164921B1 and KR102057128B1 have overseas family filings (US, China, Japan)
• Measurement current conditions for the 30-cycle capacity data in the specification, and the figures relative to the comparative example

Sources

1. Google Patents, KR102164921B1 “Lithium ion capacitor” (Korea Institute of Ceramic Engineering and Technology), bibliographic data, claims, and specification
2. Google Patents, KR102057128B1 “Expanded graphite anode material for lithium-ion capacitor with lithium impregnated in expanded graphite” (Korea Institute of Ceramic Engineering and Technology)
3. Google Patents, KR101173673B1 “Carbon based anode materials for lithium ion capacitor and preparation method thereof” (Korea Electronics Technology Institute)
4. J. J. Lamb, O. S. Burheim, “Lithium-Ion Capacitors: A Review of Design and Active Materials,” Energies 14(4), 979, 2021