Accounts receivable, net - Aging of accounts receivable (Details)	Jun. 30, 2026 CNY (¥)	Jun. 30, 2026 USD ($)	Dec. 31, 2025 CNY (¥)
Accounts receivable
Accounts receivable	¥ 8,337,549	$ 1,228,803	¥ 7,146,902
Within 90 days
Accounts receivable
Accounts receivable	2,589,833	381,694	4,016,277
90 - 180 days
Accounts receivable
Accounts receivable	2,688,785	396,279	1,209,825
180 days - 1 year
Accounts receivable
Accounts receivable	1,745,225	257,214	¥ 1,920,800
Over 1 year
Accounts receivable
Accounts receivable	¥ 1,313,706	$ 193,616

Amount, before allowance for credit loss, of right to consideration from customer for product sold and service rendered in normal course of business, classified as current.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481990/310-10-45-2

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(3)(a)(1))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1

Reference 3: http://www.xbrl.org/2003/role/exampleRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483467/210-10-45-1

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant