A bitcoin private key provides 128 bits of entropy and there is no way to increase the security of your private key to more than 128 bits.
Let's say your seed phrase is compromised and the hacker needs to brute-force your passphrase to access your fund.
Whether you use space between the words or not, the entropy provided by your passphrase would be more than 128 bits. Even if the hacker knows that you have used a seed phrase generated by electrum as your passphrase, the entropy would be 132 bits which is still bigger than the entropy provided by a private key.