Yowza. Not good. The liquid inside that got sprayed about is sulfuric acid, highly corrosive. You need to clean up the area well with a mixture of baking soda and water. It's possible that you had a loose battery terminl connection that arced and exploded the hydrogen gas that is emitted from a battery as part of its normal cycle. Maybe you have a direct short?

You don't need and should NOT buy a Volvo battery. Get an Interstate Megatron MT-47 or MTP-91 battery. The 47 will fit perfectly and the 91 wil be just a bit longer but I believe it will still fit in the tray and clamp down well. Both are better by far than the OEM battery. You may want to have a shop do this instead of yourself in case there is an on-going electrical problem under that hood.