You can not solve your issue by adding MySQLi to php.ini, here you have install real mysqli extension on server that can be done Easyapache by enabling MySQL Improved extension , and it can be done by root user only. if you have than check below link.
如何在PHP7上启用MySQLi扩展（LAMP / CPANEL）？
My server upgraded to PHP7 and now I am getting an error which reads "Your PHP installation appears to be missing the MySQL extension which is required by WordPress."
I have tried adding
extension=php_mysqli.so to my PHP INI but that doesn't seem to help. I am on a LAMP with CentOS and Apache 2.4 with MariaDB 10.0... All was working before the update. \
php -m shows:
[PHP Modules] bcmath bz2 calendar Core ctype curl date dba dom enchant ereg exif fileinfo filter ftp gd gettext gmp hash iconv imap intl ionCube Loader json ldap libxml mbstring mcrypt mhash mysql mysqli mysqlnd odbc openssl pcntl pcre PDO pdo_mysql PDO_ODBC pdo_pgsql pdo_sqlite pgsql Phar posix pspell readline Reflection session shmop SimpleXML snmp soap sockets SourceGuardian SPL sqlite3 standard sysvmsg sysvsem sysvshm tidy tokenizer wddx xml xmlreader xmlrpc xmlwriter xsl Zend Guard Loader Zend OPcache zip zlib [Zend Modules] Zend Guard Loader Zend OPcache the ionCube PHP Loader