Filed by Decarbonization Plus Acquisition Corporation III

Pursuant to Rule 425 under the Securities Act of 1933

and deemed filed pursuant to Rule 14a-12

under the Securities Exchange Act of 1934

Subject Company: Decarbonization Plus Acquisition Corporation III

Commission File No.: 001-40284

Date: October 6, 2021

The following press release was issued by Solid Power, Inc. on October 6, 2021.

UPDATE — Solid Power Appoints Former AT&T Senior Executive Vice President and CFO John Stephens to Board of Directors

Stephens adds public company and financial expertise ahead of anticipated SPAC business combination

LOUISVILLE, Colo., October 6, 2021 – Solid Power, Inc., an industry-leading developer of all-solid-state battery cells for electric vehicles, which is in the process of combining with Decarbonization Plus Acquisition Corporation III (“DCRC”) (NASDAQ: DCRC), today announced the appointment of John Stephens to its board of directors. Mr. Stephens is also expected to be nominated to serve on the board of directors of the combined company following completion of the proposed business combination with DCRC and is expected to serve as chairman of the audit committee.

“We welcome John to the current Solid Power board and are pleased that he has agreed to serve both now and following the completion of our pending business combination with DCRC,” said Doug Campbell, Co-Founder and Chief Executive Officer of Solid Power. “We believe John’s executive management experience in the oversight of a large, publicly traded company, as well as his extensive experience with financial and accounting matters, corporate transactions and international business and affairs will enable him to provide valuable perspectives on the operational, financial and strategic matters that lie ahead of us.”

John Stephens joins Solid Power Board of Directors

Mr. Stephens brings important experience that will assist the company as it prepares for its next chapter of growth

Mr. Stephens brings to the Solid Power board more than 35 years of accounting and finance expertise, including experience in matters of financial planning, corporate development, accounting and accounting policy, tax, auditing, treasury, investor relations, corporate real estate, business planning, and financial, operational and regulatory reporting. Prior to his March 2021 retirement, Mr. Stephens served as Senior Executive Vice President and Chief Financial Officer of AT&T, Inc., having previously served in a series of successive positions in AT&T’s finance department. Prior to his tenure at AT&T, Mr. Stephens held a variety of roles in public accounting. He is also a member of the board of directors of Freeport-McMoRan Inc., where he serves as chairman of the audit committee.

“I’m very excited to be joining the Solid Power board during such a critical moment in the company’s journey,” said Mr. Stephens. “Solid Power is at the forefront of battery technology innovation as the world transitions to battery-powered electric vehicles. I look forward to helping the company advance its leadership position during this next stage of growth.”

Mr. Campbell said, “As we prepare to enter the next phase of Solid Power’s evolution, we have set out to assemble a group of highly accomplished individuals that are dedicated to driving forward our strategic vision of powering a cleaner, safer and more cost-effective electric future, while bringing to the board a collective set of expertise and perspectives that will enable us to deliver shareholder value for the long term. Adding John to our board is a key step in achieving that vision.”

Completion of the proposed business combination with DCRC is subject to customary closing conditions and is expected to occur in the fourth quarter of 2021.

Important Information for Investors and Stockholders

This communication is being made in respect of the proposed transaction involving Decarbonization Plus Acquisition Corporation III (“DCRC”) and Solid Power, Inc. (“Solid Power”). A full description of the terms of the transaction is provided in the registration statement on Form S-4 (File No. 333-258681) (the “Registration Statement”) filed with the Securities and Exchange Commission (the “SEC”) by DCRC. The Registration Statement includes a prospectus with respect to the combined company’s securities to be issued in connection with the business combination and a preliminary proxy statement with respect to the stockholder meeting of DCRC to vote on the business combination. Additionally, DCRC will file other relevant materials with the SEC in connection with the business combination. Copies may be obtained free of charge at the SEC’s web site at www.sec.gov. Security holders of DCRC are urged to read the proxy statement/prospectus, including all amendments and supplements thereto, and the other relevant materials when they become available before making any voting decision with respect to the proposed business combination because they will contain important information about the business combination and the parties to the business combination. After the Registration Statement is declared effective, the definitive proxy statement/prospectus included in the Registration Statement will be mailed to stockholders of DCRC as of a record date to be established for voting on the proposed business combination. Once available, stockholders will also be able to obtain a copy of the S-4, including the proxy statement/prospectus, and other documents filed with the SEC without charge, by directing a request to: Decarbonization Plus Acquisition Corporation III, 2744 Sand Hill Road, Suite 100, Menlo Park, California 94025. The information contained on, or that may be accessed through, the websites referenced herein is not incorporated by reference into, and is not a part of, this filing.

Participants in the Solicitation

DCRC and Solid Power and their respective directors and officers may be deemed participants in the solicitation of proxies of DCRC’s stockholders in connection with the proposed business combination. Security holders may obtain more detailed information regarding the names, affiliations and interests of certain of DCRC’s executive officers and directors in the solicitation by reading DCRC’s definitive proxy statement/prospectus, which will become available after the Registration Statement has been declared effective by the SEC, DCRC’s final prospectus for its initial public offering filed with the SEC on March 25, 2021, and other relevant materials filed with the SEC in connection with the business combination when they become available. Information concerning the interests of DCRC’s participants in the solicitation, which may, in some cases, be different than those of DCRC’s stockholders generally, is set forth in the preliminary proxy statement/prospectus relating to the proposed business combination.

No Offer or Solicitation

This communication does not constitute an offer to sell or the solicitation of an offer to buy any securities or constitute a solicitation of any vote or approval in respect of the potential transaction and shall not constitute an offer to sell or a solicitation of an offer to buy the securities of DCRC, Solid Power or the combined company, nor shall there be any sale of any such securities in any state or jurisdiction in which such offer, solicitation, or sale would be unlawful prior to registration or qualification under the securities laws of such state or jurisdiction. No offer of securities shall be made except by means of a prospectus meeting the requirements of the Securities Act.

Forward Looking Statements

The information herein includes “forward-looking statements” within the meaning of Section 27A of the Securities Act of 1933, as amended, and Section 21E of the Securities Exchange Act of 1934, as amended, including DCRC’s or Solid Power’s or their management teams’ expectations, hopes, beliefs, intentions or strategies regarding the future. All statements, other than statements of present or historical fact included herein, regarding DCRC’s proposed acquisition of Solid Power, DCRC’s ability to consummate the transaction, the benefits of the transaction and the combined company’s future financial performance, as well as the combined company’s strategy, future operations, estimated financial position, estimated revenues and losses, projected costs, prospects, plans and objectives of management are forward-looking statements. When used herein, the words “could,” “should,” “will,” “may,” “believe,” “anticipate,” “intend,” “estimate,” “expect,” “project,” the negative of such terms and other similar expressions are intended to identify forward-looking statements, although not all forward-looking statements contain such identifying words. These forward-looking statements are based on management’s current expectations and assumptions about future events and are based on currently available information as to the outcome and timing of future events. Except as otherwise required by applicable law, DCRC and Solid Power disclaim any duty to update any forward-looking statements, all of which are expressly qualified by the statements in this section, to reflect events or circumstances after the date hereof. DCRC and Solid Power caution you that these forward-looking statements are subject to numerous risks

and uncertainties, most of which are difficult to predict and many of which are beyond the control of either DCRC or Solid Power. In addition, DCRC cautions you that the forward-looking statements contained herein are subject to the following factors: (i) the occurrence of any event, change or other circumstances that could delay the business combination or give rise to the termination of the agreements related thereto; (ii) the outcome of any legal proceedings that may be instituted against DCRC or Solid Power following announcement of the transactions; (iii) the inability to complete the business combination due to the failure to obtain approval of the stockholders of DCRC, or other conditions to closing in the transaction agreement; (iv) the risk that the proposed business combination disrupts DCRC’s or Solid Power’s current plans and operations as a result of the announcement of the transactions; (v) Solid Power’s ability to realize the anticipated benefits of the business combination, which may be affected by, among other things, competition and the ability of Solid Power to grow and manage growth profitably following the business combination; (vi) costs related to the business combination; (vii) changes in applicable laws or regulations; (viii) rollout of Solid Power’s business plan and the timing of expected business milestones, (ix) the effects of competition on Solid Power’s business, (x) supply shortages in the materials necessary for the production of Solid Power’s products, (xi) risks related to original equipment manufacturers and other partners being unable or unwilling to initiate or continue business partnerships on favorable terms, (xii) the termination or reduction of government clean energy and electric vehicle incentives, (xiii) delays in the construction and operation of production facilities, (xiv) the amount of redemption requests made by DCRC’s public stockholders, (xv) changes in domestic and foreign business, market, financial, political and legal conditions, and (xvi) the possibility that Solid Power may be adversely affected by other economic, business, and/or competitive factors. Should one or more of the risks or uncertainties described herein, or should underlying assumptions prove incorrect, actual results and plans could differ materially from those expressed in any forward-looking statements. Additional information concerning these and other factors that may impact the operations and projections discussed herein can be found in DCRC’s periodic filings with the SEC, including DCRC’s final prospectus for its initial public offering filed with the SEC on March 25, 2021, and the Registration Statement filed in connection with the business combination. DCRC’s SEC filings are available publicly on the SEC’s website at www.sec.gov.

About Solid Power

Solid Power is an industry-leading developer of all-solid-state rechargeable battery cells for electric vehicles and mobile power markets. Solid Power replaces the flammable liquid electrolyte in a conventional lithium-ion battery with a proprietary sulfide-based solid electrolyte. As a result, Solid Power’s all-solid-state battery cells are expected to be safer and more stable across a broad temperature range, provide an increase in energy density compared to the best available rechargeable battery cells, enable less expensive, more energy-dense battery pack designs and be compatible with traditional lithium-ion manufacturing processes. For more information, visit http://www.solidpowerbattery.com/.

Contact Information

For Media:

Will McKenna

Marketing Communications Director

(720) 598-2877

press@solidpowerbattery.com

For Investors:

investors@solidpowerbattery.com

Website: www.solidpowerbattery.com

Twitter: https://twitter.com/SolidPowerInc

LinkedIn: https://www.linkedin.com/company/solid-power

Important Information for Investors and Stockholders

This communication is being made in respect of the proposed transaction involving Decarbonization Plus Acquisition Corporation III (“DCRC”) and Solid Power, Inc. (“Solid Power”). A full description of the terms of the transaction is provided in the registration statement on Form S-4 (File No. 333-258681) (the “Registration Statement”) filed with the Securities and Exchange Commission (the “SEC”) by DCRC. The Registration Statement includes a prospectus with respect to the combined company’s securities to be issued in connection with the business combination and a preliminary proxy statement with respect to the stockholder meeting of DCRC to vote on the business combination. Additionally, DCRC will file other relevant materials with the SEC in connection with the business combination. Copies may be obtained free of charge at the SEC’s web site at www.sec.gov. Security holders of DCRC are urged to read the proxy statement/prospectus, including all amendments and supplements thereto, and the other relevant materials when they become available before making any voting decision with respect to the proposed business combination because they will contain important information about the business combination and the parties to the business combination. After the Registration Statement is declared effective, the definitive proxy statement/prospectus included in the Registration Statement will be mailed to stockholders of DCRC as of a record date to be established for voting on the proposed business combination. Once available, stockholders will also be able to obtain a copy of the S-4, including the proxy statement/prospectus, and other documents filed with the SEC without charge, by directing a request to: Decarbonization Plus Acquisition Corporation III, 2744 Sand Hill Road, Suite 100, Menlo Park, California 94025. The information contained on, or that may be accessed through, the websites referenced herein is not incorporated by reference into, and is not a part of, this filing.

Participants in the Solicitation

DCRC and Solid Power and their respective directors and officers may be deemed participants in the solicitation of proxies of DCRC’s stockholders in connection with the proposed business combination. Security holders may obtain more detailed information regarding the names, affiliations and interests of certain of DCRC’s executive officers and directors in the solicitation by reading DCRC’s definitive proxy statement/prospectus, which will become available after the Registration Statement has been declared effective by the SEC, DCRC’s final prospectus for its initial public offering filed with the SEC on March 25, 2021, and other relevant materials filed with the SEC in connection with the business combination when they become available. Information concerning the interests of DCRC’s participants in the solicitation, which may, in some cases, be different than those of DCRC’s stockholders generally, is set forth in the preliminary proxy statement/prospectus relating to the proposed business combination.

No Offer or Solicitation

This communication does not constitute an offer to sell or the solicitation of an offer to buy any securities or constitute a solicitation of any vote or approval in respect of the potential transaction and shall not constitute an offer to sell or a solicitation of an offer to buy the securities of DCRC, Solid Power or the combined company, nor shall there be any sale of any such securities in any state or jurisdiction in which such offer, solicitation, or sale would be unlawful prior to registration or qualification under the securities laws of such state or jurisdiction. No offer of securities shall be made except by means of a prospectus meeting the requirements of the Securities Act.

Forward Looking Statements

The information herein includes “forward-looking statements” within the meaning of Section 27A of the Securities Act of 1933, as amended, and Section 21E of the Securities Exchange Act of 1934, as amended, including DCRC’s or Solid Power’s or their management teams’ expectations, hopes, beliefs, intentions or strategies regarding the future. All statements, other than statements of present or historical fact included herein, regarding DCRC’s proposed acquisition of Solid Power, DCRC’s ability to consummate the transaction, the benefits of the transaction and the combined company’s future financial performance, as well as the combined company’s strategy, future operations, estimated financial position, estimated revenues and losses, projected costs, prospects, plans and objectives of management are forward-looking statements. When used herein, the words “could,” “should,” “will,” “may,” “believe,” “anticipate,” “intend,” “estimate,” “expect,” “project,” the negative of such terms and other similar expressions are intended to identify forward-looking statements, although not all forward-looking statements contain such identifying words. These forward-looking statements are based on management’s current expectations and assumptions about future events and are based on currently available information as to the outcome and timing of future events. Except as otherwise required by applicable law, DCRC and Solid Power disclaim any duty to update any forward-looking statements, all of which are expressly qualified by the statements in this section, to reflect events or circumstances after the date hereof. DCRC and Solid Power caution you that these forward-looking statements are subject to numerous risks and uncertainties, most of which are difficult to predict and many of which are beyond the control of either DCRC or Solid Power. In addition, DCRC cautions you that the forward-looking statements contained herein are subject to the following factors: (i) the occurrence of any event, change or other circumstances that could delay the business combination or give rise to the termination of the agreements related thereto; (ii) the outcome of any legal proceedings that may be instituted against DCRC or Solid Power following announcement of the transactions; (iii) the inability to complete the business combination due to the failure to obtain approval of the stockholders of DCRC, or other conditions to closing in the transaction agreement; (iv) the risk that the proposed business combination disrupts DCRC’s or Solid Power’s current plans and operations as a result of the announcement of the transactions; (v) Solid Power’s ability to realize the anticipated benefits of the business combination, which may be affected by, among other things, competition and the ability of Solid Power to grow and manage growth profitably following the business combination; (vi) costs related to the business combination; (vii) changes in applicable laws or regulations; (viii) rollout of Solid Power’s business plan and the timing of expected business milestones, (ix) the effects of competition on Solid Power’s business, (x) supply shortages in the materials necessary for the production of Solid Power’s products, (xi) risks related to original equipment manufacturers and other partners being unable or unwilling to initiate or continue business partnerships on favorable terms, (xii) the termination or reduction of government clean energy and electric vehicle incentives, (xiii) delays in the construction and operation of production facilities, (xiv) the amount of redemption requests made by DCRC’s public stockholders, (xv) changes in domestic and foreign business, market, financial, political and legal conditions, and (xvi) the possibility that Solid Power may be adversely affected by other economic, business, and/or competitive factors. Should one or more of the risks or uncertainties described herein, or should underlying assumptions prove incorrect, actual results and plans could differ materially from those expressed in any forward-looking statements. Additional information concerning these and other factors that may impact the operations and projections discussed herein can be found in DCRC’s periodic filings with the SEC, including DCRC’s final prospectus for its initial public offering filed with the SEC on March 25, 2021, and the Registration Statement filed in connection with the business combination. DCRC’s SEC filings are available publicly on the SEC’s website at www.sec.gov.